Experimental study on the plowing effect of ripper tooth and its influence on scraper wear during shield TBM tunneling in abrasive sandy ground

Experimental study on the plowing effect of ripper tooth and its influence on scraper wear during shield TBM tunneling in abrasive sandy ground | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Experimental study on the plowing effect of ripper tooth and its influence on scraper wear during shield TBM tunneling in abrasive sandy ground Shao-Hui Tang, Quan-Sheng Liu, Qi Zhang, Wei-Qiang Xie, Wei Sun, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6424309/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract When shield TBM tunnelling in dense sandy ground, the installation height of the ripper tooth is higher than that of the scraper. The ripper tooth plows the excavation surface, followed by the scraper cutting the loose sand. The plowing effect refers to the mitigation of scraper wear by the ripper tooth, which loosens the dense sand on the tunnel surface. Although it has been analyzed qualitatively over the past few decades, there is still a lack of reliable parameters for quantitative evaluation. The influence of cutter height difference, sand density and particle size on plowing effect is unclear. In the present study, the plowing coefficient has been proposed to quantify the plowing effect. The variation in plowing coefficient with cutter height difference, sand density and particle size has been studied using the newly developed WHU-SAT tester. The plowing mechanism of ripper tooth has been revealed based on excavation process analysis. The cutter height difference between ripper tooth and scraper has been optimized for dense sandy ground tunnelling. The results indicate that as cutter height difference increases, the loosening depth of ripper tooth on tunnel face increases. The density of sand samples cut by the scraper decreases first and then stabilizes, leading to a similar trend in the plowing coefficient. When the sand density is ρ = 1.7 g/cm 3 and and the average particle size is D 50 = 0.425 mm, the optimal height difference between ripper tooth and scraper is ΔH = 22.5 mm. As sand density increases, the loosing depth corresponding to the stable plowing coefficient increases first and then stabilizes, resulting in a similar pattern for the optimal height difference. When the sand density is ρ = 1.9 g/cm 3 , the optimal height difference reaches a maximum value ΔH = 37.5 mm. As the average particle size increases, the loosing depth corresponding to the stable plowing coefficient increases, leading to an increase in the optimal height difference. When the average particle size increases to D 50 = 0.710 mm, the optimal height difference increases to ΔH = 45 mm. The present study provides a reference for optimizing cutter height difference and enhancing cutterhead adaptability in dense sandy ground tunnelling. Ripper tooth Plowing coefficient Cutter height difference Sand density Particle size Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Article Highlights The newly developed WHU-SAT test apparatus is used to study the plowing effect of ripper tooth. The plowing coefficient is proposed to quantify the influence of plowing effect on scraper wear. The influence mechanism of plowing coefficient is revealed based on excavation process analysis. The height difference between ripper tooth and scraper is optimized for sandy ground tunneling. 1 Introduction During shield TBM tunnelling in dense sandy ground, the cutterhead is mainly equipped with ripper teeth and scrapers for tunnel excavation (Wei et al., 2020 ; Li et al., 2021 ; Zhang et al., 2021a , Tang et al., 2020 , 2021a , b , 2023 ). The installation height of the ripper teeth is typically 20 mm to 60 mm higher than that of the scrapers, depending on the physical and mechanical properties of the sandy ground (Fig. 1 ) (Huang, 2010 ; Guo and Dai, 2013 ; Chen and Huang, 2015 ; Huang et al., 2018 ; Tang et al., 2020 ; Zhang et al., 2023 ). When there is a height difference between two cutters, the ripper teeth plow excavation surface to loosen dense sand, followed by the scrapers cutting the loose sand for tunnel excavation (Zhang et al., 2021a , b ; Jiang et al., 2021a , 2022 ; Tang et al., 2023 ). Compared with cutting dense sand directly, the wear of the scrapers is significantly reduced when cutting loose sand plowed by ripper teeth (Huang, 2010 ; Guo and Dai, 2013 ; Li et al., 2017 ; Zhang et al., 2022a ; Wei et al., 2023 ). The plowing effect is the protection of ripper teeth on scraper wear by loosing the excavation surface. It is related to the cutter height difference, sand density and particle size (Xia et al., 2019 ; Tang et al., 2020 ; Jiang et al., 2021b ; Li et al., 2021 ). A rational evaluation of plowing effect is crucial for optimizing the cutter height difference and enhancing cutterhead excavation capacity (Guo and Dai, 2013 ; Tang et al., 2022 , 2023 ). A preliminary literature review indicates that the plowing effect has been assessed by comparing cutting efficiency or scraper wear with and without ripper teeth (Peng, 2013 ; Tang et al., 2020 ; Jiang et al., 2021a , b ). For instance, Guo and Dai ( 2013 ) compared the scraper wear coefficient before and after the failure of ripper teeth, and concluded that it increased by approximately two times following the failure. However, the in-situ tests were conducted under conditions where multiple parameters changed simultaneously. Variations in geological conditions and tunnelling parameters significantly interfered with the test results. Tang et al. ( 2020 ) proposed a synergistic coefficient to quantify the protection provided by ripper teeth against scraper wear, and found that the synergistic coefficient in fine silty sand is approximately 0.496. Since the sand density remained stable during the tests, the variation in synergistic coefficient with sand density has not been discussed. Li et al. ( 2021 ) studied the cutting efficiency under varying cutter height differences, and optimized ripper teeth height for EPB-TBM cutting the reinforced concrete piles. Since the in-situ test only examined two cutter height differences, the variation in plowing coefficient with cutter height difference remains unclear. Zhang et al. ( 2021a ) proposed a multi-dimensional gradient configuration method for ripper teeth, and concluded that scraper wear coefficient could be reduced by arranging ripper teeth at different installation heights. However, this installation height only applies to coarse sandy gravel, and its variation with particle size remains to be discussed. Jiang et al. ( 2021b , 2022 ) simulated the cutting performance of ripper teeth using discrete element method, and found that the tunnelling efficiency increased when the cutter height difference was 70 mm. Since cutterhead torque rather than wear coefficient was considered for evaluating cutting performance, the variation in scraper wear with cutter height difference has not been analyzed. The studies on the influence of the plowing effect on scraper wear are based on either in-situ tests or numerical simulations. The simultaneous variation of multiple parameters significantly interfered with the results of in-situ tests, while unrealistic simulation of cutter wear lead to unacceptable errors in plowing coefficients. Hence, laboratory tests with controllable parameters have been considered as a viable method to analyze the plowing effect and its influence on scraper wear. Several test apparatuses have been developed by institutions worldwide. However, the initial test apparatuses (such as SAT™, LCPC and DTWA) were derived from rock abrasion testers (Alavi Gharahbagh et al., 2011 ; Drucker et al., 2011; Rostami et al., 2012 ). Their cutterhead structure and cutter shape are too simplistic to match the interaction between tunnel face and cutting tool. Improved test apparatus (such as RUB, CUGB and BJTU) were designed to accommodate one type of cutting tool (Küpferle et al., 2018 ; Wei et al., 2018 , 2019 , 2020 ; Wu, 2020 ). These apparatuses can only evaluate the plowing effect of ripper teeth on the excavation face, without assessing their protective role in reducing scraper wear. To the best of our knowledge, there is still a lack of a reliable test apparatus that can accommodate two or more types of cutting tools to reveal the internaction between the ripper teeth and the scrape. In the present study, the newly developed WHU-SAT test apparatus that can be equipped with two types of cutting tools has been utilized for analyzing the plowing effect of ripper tooth and its influence on scraper wear. The plowing coefficient defined as the ratio of scraper wear with and without the protection of ripper tooth has been prosed to quantify the plowing effect. The influence of cutter height difference, sand density and particle size on plowing coefficient has been studied using the WHU-SAT tests. The plowing mechanism has been revealed by analyzing the loosing process of the ripper tooth on excavation face. The cutter height difference between the ripper tooth and scraper has been optimized for dense sandy ground tunnelling. 2 Test method and evaluation parameter 2.1 The WHU-SAT test method The newly developed WHU-SAT test apparatus consists of XK7130 CNC milling machine, modelled cutterhead, modelled cutting tool, soil chamber, monitoring system, and control terminal (Fig. 2 ). The XK7130 CNC milling machine with 2200 mm in length, 1900 mm in width and 2300 mm in height serves as the basic platform for the WHU-SAT test apparatus. The modelled cutterhead mounted at the shaft of XK7130 CNC milling machine consists of five spokes. The tool mounting radii are arranged according to the Archimedes spiral pattern. Each cutterhead spoke has three mounting radii, and each mounting radius has three holes for mounting the modelled cutting tools. The side mounting holes are fitted with scrapers, while the middle hole is fitted with a ripper tooth. The structure of the modelled cutterhead and the distribution of mounting hole in the WHU-SAT test apparatus are generally comparable to those of the shield TBM. The cylindrical chamber can be filled with soil samples with grain sizes corresponding to clay, silt, sand and gravel with grain sizes less than 30 mm. When the test apparatus is in operation mode, the modelled cutterhead excavates soil samples in the cylindrical chamber at a rotation speed of 0 to 500 rpm and a tunnelling speed of 0 to 50 mm/min. During the WHU-SAT soil abrasion test, the tunneling parameters (such as rotation speed, tunneling speed, tunneling depth and test time) of the modelled cutterhead can be inputted on the control terminal and detected by the monitoring software. The modelled cutting tools (including the ripper tooth and scraper) consist of a cutter edge, cutter body and connecting bolt with lengths of 10 mm, 10 mm and 40 mm, respectively. The cross sections of the cutter edges of scraper and ripper tooth are rectangular with lengths of 15 mm and 12 mm, respectively (Fig. 2 ). Since the lengths of the welded scraper and ripper tooth in a shield TBM are usually 225 and 180 mm, the reduced scale of the WHU-SAT test is approximately 1:15. When the modelled cutting tools are mounted on the cutterhead spokes, there is no initial height difference between the ripper tooth and the scraper. The height difference is adjusted by turning the screws. For each rotation of the screws, the height difference between the ripper tooth and the scraper increases by 1 mm. The bolted connection is beneficial not only for the precise control of the height difference, but also for the timely replacement of cutting tools (Tang et al., 2022 ). With the protection of the newly replaced cutting tools, the maintenance frequency of the modelled cutterhead can be minimized. When the start button on the instruction module of control terminal is pressed, the modelled cutterhead excavates soil according to the preset tunneling parameters. Once the tunneling depth reaches the target value, the modelled cutterhead stops tunneling and continues to rotate until the test time is exhausted. Then, the modelled cutterhead stops and returns to its initial position according to the preset program. After removing the muck adhering to the metal surface, the modelled cutterhead and cutting tools are disassembled by loosening the corresponding bolts. The cutting tools are cleaned and dried to eliminate the residual moisture. Next, they are weighed three times using a high-precision electronic balance (0.001 g) to evaluate the value of worn. Cutting tool wear is quantified by calculating the average weight loss of cutting tool before and after the soil abrasion test. Compared to existing soil abrasion test methods, the advantages of the WHU-SAT test apparatus and test method are as follows: (1) Rational simulation of cutterhead structure and cutter arrangement. The cutterhead structures of initial tests (such as SAT™, LCPC and DTWA) are block, disc or rectangle, while those of subsequent tests (such as RUB, CUGB and BJTU) are propeller, tube, cross, bolt or star. These designs This do not allow for the simultaneous installation of modelled scraper and ripper tooth. Hence, the existing test apparatus cannot reveal the influence mechanism of plowing effect on scraper wear. Since the Archimedes spiral pattern principle is used to arrange the mounting holes and each mounting radius has three holes for mounting two modelled scpraera and one ripper tooth simultaneously, the modelled cutterhead structure and cutter arrangemen of the WHU-SAT test simulates those of the shield TBM. (2) Reasonable design of cutter geometry. The modelled cutting tools simplify the local characteristics (such as welding procedure, surface treatment and cutter chamfer), while retaining the morphological characteristics (such as front angle, back angle and edge angle) of shield cutting tools. This design not only reduces the production cycle and manufacturing cost, but also facilitates the exploration of the influence of cutter geometry on tool wear. For instance, the modelled scraper simulates the wedge-shaped characteristics of the shield scraper by retaining cutting angles. Consequently, cutting process and wear mechanism can be well reproduced. (3) Precise monitoring and control of tunneling parameters. The accuracy of position coordinates is 0.001, while the accuracies of rotation speed, tunneling speed, cutterhead torque, and motor power are 0.01. The high-precision monitoring and control system increases the accuracy of tunneling parameters and promotes a more rigorous test procedure. Moreover, the emergency protection function of the automatic control system is fully developed. Once abnormal conditions occurs, a warning signal will appear on the control terminal, and the the modelled cutterhead stops running and the returns to the initial position to ensure security. 2.2 The evaluation parameter The preset tunnelling parameters for the modelled cutterhead are the rotation speed N = 150 rpm, the tunnelling speed V = 20 mm/min, the tunnelling depth h = 140 mm and the test time T = 60 min. As the modelled cutterhead excavates soil samples, the higher ripper teeth plow the dense soils, followed by the lower scrapers cut the loosened soils. Compared to directly cutting dense soil samples, scraper wear is significantly reduced when cutting loose soil plowed by ripper teeth. The plowing effect involves the protection of the scrapers from wear due to the loosing of the excavation face by the ripper teeth. To quantify the plowing effect, the ratio of scraper wear with and without the protection of ripper teeth is defined as the plowing coefficient. This can be expressed as: Where, ξ is the plowing coefficient of ripper tooth; δ rn is the scraper wear with the protection of ripper tooth; δ rf is the scraper wear without the protection of ripper tooth. Engineering experience suggests that the plowing coefficient is related to the cutter height difference, sand density and particle size (Guo and Dai, 2013 ; Mu, 2016 ; Jiang et al., 2021c ; Zhang et al., 2022b ). When shield TBM tunnelling in silty clay or fine sand with lower density, the scraper wear and plowing coefficient are insensitive to the variation in cutter height difference. However, when shield TBM tunnelling in coarse sand or sandy gravel with high density, an appropriate increase in cutter height difference significantly decrease scraper wear and plowing coefficient. It is essential to analyze the plowing coefficient of the ripper teeth and its influence on scraper wear, and propose the optimal cutter height difference for various geological conditions to reduce tool wear and maintenance frequency. 3 The influence of cutter height difference on plowing coefficient 3.1 The preparation of sand samples for the WHU-SAT test The nature sand samples and quartz sand samples were used for the WHU-SAT test. These samples were pretreated to align with the physical and mechanical parameters. For nature sand samples, they were dried and sieved into sand particles with sizes of 0.125–0.212, 0.212–0.425, 0.425–0.710, 0.710–1.180, 1.180–2.360, 2.360–3.350 and 3.350–4.750 mm. For quartz sand samples, they were obtained by crushing the dry quartz with a purity of 99.75% into sand particles of the aforementioned seven sizes. As shown in Fig. 3 , the target sand samples were obtained by uniformly mixing sand samples of the aforementioned seven sizes in the mass ratio of 6: 6: 4: 4: 4: 2: 1. Subsequently, they were mixed with an appropriate water to prepare sand samples with a water content of ω = 15%. The aqueous sand samples were filled into a cylindrical chamber with a density of ρ = 1.80 g/cm 3 . 3.2 The variation in plowing coefficient with cutter height difference The metal materials 06Cr19Ni10 and 45# have been extensively used as cutter materials in existing tests such as SGAT, RUB, BJTU and CUGB (Jakobsen et al., 2013 ; Küpferle et al., 2018 ; Wei, 2019; Wu, 2020 ). To facilitate comparison with existing test results, the present study employed the same materials. As illustrated in Fig. 2 (b), five tool mounting holes were designated for the installation of cutting tools. The corresponding mounting radii were 52.5 mm, 61.0 mm, 69.5 mm, 78.0 mm and 86.5 mm, respectively. For each radius, the center mounting hole was fitted with a ripper tooth made of 06Cr19Ni10, while the left and right holes were fitted with scrapers made of 06Cr19Ni10 and 45#, respectively. The modelled cutting tools were secured in the mounting holes using M8 screws. Each full revolution of the screw increases the cutter height difference by 1 mm; the corresponding height difference for the shield TBM is 15 mm. As shown in Fig. 4 , seven experimental tests were conducted to examine the variation of plowing coefficient with cutter height difference in both natural sand samples and quartz sand samples. The corresponding cutter height differences between the actual ripper tooth and scraper were ΔH = 0, 7.5, 15.0, 22.5, 30.0, 37.5, 45.0 mm. The results indicate that the plowing coefficient decreases first and then stabilizes with increasing cutter height difference. When the cutter height difference is ΔH = 0 mm, the ripper teeth are unable to loosen dense sand samples before the scrapers cut the excavation surface. Without the protection of ripper teeth, scraper wear is most serious, resulting in a plowing coefficient of ξ = 1.00. As the cutter height difference increases, the plowing depth of the ripper teeth increases, while the sand density on the excavation surface decreases. When scrapers cut looser sand samples, the plowing coefficient of the ripper teeth decreases. When the cutter height difference is ΔH = 30.0 mm, the plowing coefficients for scraper made of 06Cr19Ni10 and 45# in nature sand samples (or quartz sand samples) are ξ = 0.64 (or ξ = 0.68) and ξ = 0.69 (or ξ = 0.70), respectively. As the cutter height difference continues to increase, the sand density on the excavation surface remains at a low level. Consequently, the plowing coefficient stabilizes with increasing cutter height difference. In addition to the plowing coefficient, the ripper teeth wear in seven tests has been weighed using a high-precision scale (0.001 g). As shown in Fig. 5 , the results indicate that the ripper teeth wear increases slowly first and then rapidly with an increasing cutter height difference. This trend is related to variations in the plowing depth of the ripper teeth. When the cutter height difference is ΔH = 0 mm, the ripper teeth and scrapers cut dense sand samples on the excavation surface simultaneously. The synergistic cutting of the modelled scrapers keeps the ripper teeth wear at a low level. With the cutter height difference increases to ΔH = 30 mm, the ripper teeth begin to plow dense sand on the excavation surface. Because the frictional resistance of shallow sand samples is low, the ripper teeth wear increases slowly with increasing the cutter height difference. As the cutter height difference continues to increase to ΔH = 45 mm, the ripper teeth plow the dense sand in front of excavation face. The frictional resistance of deep sand samples increases significantly. As extrusion and friction between the cutter edge and sand particles increase, the ripper teeth wear increases rapidly with an increasing cutter height difference. The cutterhead torque has been monitored during the WHU-SAT tests. As shown in Fig. 6 , the results indicate that the average torque in the stable phase (after the tunneling depth reaches h = 140 mm) decreases first and then decreases with an increasing cutter height difference. This trend is related to the variation in cutting resistance and friction resistance. When the cutter height difference is ΔH = 0 mm, the ripper teeth and scrapers simultaneously contact the excavation face. Because the dense sand samples have not been loosened, the cutting resistance and friction resistance remain at a high level. As the cutter height difference increases to ΔH = 30 mm, the cutting resistance and friction resistance of the ripper teeth increase slowly when plowing shallow excavation face, while those of scrapers decrease rapidly when cutting looser sand samples. Because the number of ripper teeth is much smaller than that of the modelled scrapers, the increase in cutting resistance and friction resistance is smaller than the decrease. Hence, the cutterhead torque decreases with increasing the cutter height differenc. As the cutter height difference continues to increase to ΔH = 45 mm, the cutting resistance and friction resistance of ripper teeth increases rapidly when plowing the deep excavation face, while those of the scrapers remain stable because the surface sand samples are sufficiently loose. Hence, the cutterhead torque increases with increasing the cutter height difference. 3.3 The optimal cutter height difference for dense sand samples As shown in Fig. 4 and Fig. 6 , the experiment results indicate that when the cutter height difference between the ripper teeth and scrapers is ΔH = 30 mm, the plowing coefficient of the ripper teeth has stabilized, and the cutterhead torque in the stable phase has been minimized. The modelled cutterhead of the WHU-SAT test apparatus has reached a relatively minimum load state. In this case, the plowing effect of the ripper teeth on the excavation surface has been maximized, while the bulk density of sand samples cut by the scrapers has been minimized. Since the protection of the ripper teeth against scraper wear has been maximized, the optimal cutter height difference for shield TBMs tunnelling in the tested sand samples is ΔH = 30 mm. The optimal cutter height difference was compared with the actual cutter height difference of shield TBMs under similar geological conditions. As shown in Table 1 , the results indicate that the optimal cutter height difference ( ΔH = 30 mm) is greater than the actual cutter height difference ( ΔH = 20 mm) of the Yellow River Jiluo Road Tunnel, but smaller than that ( ΔH = 40 mm) of the Sutong GIL Yangtze River Crossing Cable Tunnel. This discrepancy is related to the differences in sand density and particle size. Generally, the optimal cutter height difference is positively correlated with sand density and particle size. The in-situ density and average particle size of the silty sand at the Yellow River Jiluo Road Tunnel are ρ = 1.78 g/cm 3 and D 50 = 0.208 mm, while those of the medium coarse sand at the Sutong GIL Yangtze River Crossing Cable Tunnel are ρ = 2.06 g/cm 3 and D 50 = 0.554 mm. The parameter values of the two types of sand are smaller and larger than those the tested sand samples in the present study. Hence, the actual cutter height difference of shield TBMs are smaller and larger than the optimal cutter height difference observed in the WHU-SAT test. Table 1 Comparisons between the optimal cutter height difference of WHU-SAT test and the actual cutter height difference of shield TBMs under similar sand density conditions. Sand density ρ (g/cm 3 ) Average particle size D 50 (mm) Cutter height difference ΔH (mm) The WHU-SAT test 1.80 0.425 30 The Yellow River Jiluo Road Tunnel 1.78 0.208 20 The Sutong GIL Yangtze River Crossing Cable Tunnel 2.06 0.554 40 4 The influence of sand density on plowing effect The preparation of sand samples to analyze the influence of sand density on the plowing coefficient is similar to the method described in Section 3.1 . The mixed sand samples with a water content of ω = 15% were filled into the cylindrical chamber at a bulk densities of ρ = 1.70, 1.80, 1.90, 2.00 g/cm 3 . The modelled scrapers used in the experimental studies were made of 06Cr19Ni10. The WHU-SAT test was conducted to obtain the plowing coefficient under various sand density conditions. The variation in the plowing coefficient of ripper teeth with cutter height difference in nature sand and quartz sand has been shown in Fig. 7 and Fig. 8 . The results indicate that the plowing coefficient decreases first and then stabilizes with increasing cutter height difference, remaining unaffected by sand density. 4.1 The variation in the optimal cutter height difference with sand density Although the variation tendencies in the plowing coefficient with cutter height difference are comparable across various sand densities, the optimal cutter height differences are significantly different. As shown in Fig. 9 , the variation in the optimal cutter height difference with sand density has been depicted. The results indicate that when the sand density is ρ = 1.70 g/cm 3 , the minimum optimal cutter height difference is ΔH = 22.5 mm. With the sand density increases to ρ = 1.90 g/cm 3 , the optimal cutter height difference increases to the maximum value ΔH = 37.5 mm. As the sand density continues to increase to ρ = 2.00 g/cm 3 , the optimal cutter height difference remains relatively stable. The optimal cutter height difference from the WHU-SAT test has been compared with the actual cutter height differences of the shield TBMs (Tang et al., 2020 , 2023 ; Zhang et al., 2022a ). The results indicate that when the bulk density of the tested sand ( ρ = 2.00 g/cm 3 ) closely matches that of the in-situ sand ( ρ = 2.06 g/cm 3 ), the optimal cutter height difference ( ΔH = 37.5 mm) is comparable to the actual cutter height difference ( ΔH = 40.0 mm). The optimal cutter height difference varies with sand density, which is related to the plowing depth of the loosest sand samples on the excavation surface. When the sand density is ρ = 1.70 g/cm 3 , the plowing depth of the loosest sand samples is at its minimum value ΔH = 22.5 mm. With the sand density increases, the plowing depth of the loosest sand samples increases. This indicates that the extrusion and friction between the modelled scraper and the excavation surface reach their lowest level only when the plowing depth is greater. Hence, the optimal cutter height difference increases with increasing sand density. When the sand density increases to ρ = 1.90 g/cm 3 , the plowing depth of the loosest sand samples reaches the maximum value ΔH = 37.5 mm. As the sand density continues to increase to ρ = 2.00 g/cm 3 , the plowing depth of the loosest sand samples stabilizes. The maximum influence depth of the ripper teeth on the excavation surface is ΔH = 37.5 mm. Consequently, the optimal cutter height difference remains stable with increasing sand density. 4.2 The variation in the stable plowing coefficient with sand density The optimal cutter height difference between the ripper tooth and the scraper, as well as the stable plowing coefficient (the average plowing coefficient corresponding to this cutter height difference) varies with different sand densities. As shown in Fig. 10 , the variation in the stable plowing coefficient with sand density has been depicted. The results indicate that when the sand density is ρ = 1.70 g/cm 3 , the stable plowing coefficients for natural sand and quartz sand are ξ = 0.77 and ξ = 0.79, respectively. With the sand density increases to ρ = 2.00 g/cm 3 , the stable plowing coefficients for natural sand and quartz sand decrease to ξ = 0.54 and ξ = 0.56, respectively. The stable plowing coefficient from the WHU-SAT test has been compared with the actual plowing coefficient of shield TBMs (Tang et al., 2020 ; Zhang et al., 2022a ). The results indicate that when the bulk density of the nature sand ( ρ = 2.00 g/cm 3 ) closely matches that of the in-situ sand ( ρ = 2.06 g/cm 3 ), the stable plowing coefficient ( ξ = 0.54) for the nature sand is comparable to the actual plowing coefficient ( ξ = 0.50) in the in-situ sand. The decrease in the stable plowing coefficient is associated with a reduction in sand density. The greater the reduction in sand density is, the greater the decrement of extrusion and friction between the modelled scrapers and sand particles will be. Consequently, the greater the decrement of scraper wear and the smaller the stable plowing coefficient will be. After the ripper teeth have plowed the excavation surface, the densities of the loose sand samples cut by the modelled scrapers become comparable. This indicates that the greater the filled sand density is, the greater the reduction in sand density and the smaller the stable plowing coefficient will be. Hence, with the sand density increases from ρ = 1.70 g/cm 3 to ρ = 2.00 g/cm 3 , the stable plowing coefficient for natural sand (or quartz sand) decrease from ξ = 0.77 (or 0.79) to ξ = 0.54 (or 0.56). Comparisons indicate that the stable plowing coefficient for natural sand is lower than that for quartz sand. This difference is attributed to the difference in particle shape between the two sand samples. Images analysis via a Digital Microscope reveals that the roundness of natural sand is C = 0.79, which is greater than that of quartz sand C = 0.60 (Tang et al., 2022 ). This indicates that the particle surface of natural sand is smoother than that of quartz sand. When the ripper teeth plow the tunnel face, the natural sand with smooth surface is looser due to particle rearrangement. The stable plowing coefficient is lower when scrapers cut looser sand. Conversely, the quartz sand with a rough surface is relatively denser due to particle occlusion. The stable plowing coefficient is higher when scrapers cut denser sand. 4.3 The variation in the minimum cutterhead torque with sand density The cutterhead torque during the stable phase has been monitored during the WHU-SAT test. The results indicate that the cutterhead torque at the optimal cutter height difference (the minimum cutterhead torque) is the lowest, which does not change with the increase of sand density. As shown in Fig. 11 , the variation in the minimum cutterhead torque with sand density has been depicted. When the sand density is ρ = 1.70 g/cm 3 , the minimum cutterhead torque in natural sand and quartz sand is T = 4.97 N*m and T = 10.78 N*m, respectively. With the sand density increases to ρ = 1.90 g/cm 3 , the minimum cutterhead torque for natural sand and quartz sand increases rapidly to T = 10.53 N*m and T = 18.84 N*m, respectively. As the sand density increases to ρ = 2.00 g/cm 3 , the minimum cutterhead torque for natural sand and quartz sand increases slowly to T = 11.74 N*m and T = 20.37 N*m, respectively. The minimum cutterhead torque varies with sand density due to the plowing resistance and friction resistance of ripper teeth. As shown in Fig. 9 , when the sand density increases from ρ = 1.70 g/cm 3 to ρ = 1.90 g/cm 3 , the optimal cutter height difference between ripper teeth and scrapers increases. The larger the optimal cutter height difference is, the greater the plowing depth will be. When plowing deeper and denser sand samples, both the plowing resistance and friction resistance of ripper teeth increase. Since the bulk densities of sand samples plowed by ripper teeth are similar, the cutting resistance and friction resistance of the scrapers are comparable. The total resistance of ripper teeth and scrapers increases rapidly. There is a positive correlation between driving torque and total resistance. Hence, the minimum cutterhead torque increases rapidly with increasing sand density. With the sand density increases from ρ = 1.90 g/cm 3 to ρ = 2.00 g/cm 3 , the optimal cutter height difference and plowing resistance remain relatively stable. Under the condition that only the friction resistance of ripper teeth increases due to plowing denser sand samples, the growth rate of the total resistance decreases. Consequently, the minimum cutterhead torque increases slowly with increasing sand density. 5 The influence of particle size on plowing effect The influence of particle size on the plowing effect has been studied using the WHU-SAT test. The average particle sizes of sand samples were D 50 = 0.212, 0.319, 0.425, 0.710 mm (Fig. 12 ), corresponding to the fine sand, medium sand, medium sand, coarse sand, respectively. The preparation method for the sand samples followed the procedures outlined in Section 3.1 . The sand samples were placed in a cylindrical chamber with a water content of ω = 15%. The modelled scrapers used in this test were made of 06Cr19Ni10. The variation in the plowing coefficient with cutter height difference for nature sand and quartz sand has been shown in Fig. 13 and Fig. 14 . The results indicate that the plowing coefficient decreases first and then stabilizes with increasing cutter height difference, remaining unaffected by the average particle size. 5.1 The variation in the optimal cutter height difference with average particle size The variation in the optimal cutter height difference with the average particle size has been depicted. As shown in Fig. 15 , the results indicate that when the average particle size is D 50 = 0.212 mm, the optimal cutter height difference is ΔH = 22.5 mm. With the average particle size increases to D 50 = 0.319 mm (or D 50 = 0.425 mm), the optimal cutter height difference increases to ΔH = 30.0 mm (or ΔH = 37.5 mm), respectively. When the average particle size continues to increase to D 50 = 0.710 mm, the optimal cutter height difference increases to ΔH = 45.0 mm. The variation in the optimal cutter height difference with average particle size is linked to the occlusion effect of sand particles on the excavation surface. Generally, the larger the particle size of sand samples is, the greater the occlusion depth of surface particles will be. This implies that the plowing depth at which the sand samples on the excavation surface reach their loosest state will be greater. Hence, the optimal cutter height difference increases with increasing average particle size. The optimal cutter height differences from the WHU-SAT tests have been compared with those of shield TBMs under similar average particle size conditions. As shown in Table 2 , the results indicate that when the average particle size is D 50 = 0.208 mm, the actual cutter height difference for the Yellow River Jiluo Road Tunnel is ΔH = 20.0 mm. With the average particle size increases D 50 = 0.447 mm, the actual cutter height difference for the Sanyang Road Yangtze River Tunnel increases to ΔH = 40.0 mm (Huang et al., 2018 ; Li and Bao, 2019 ). When the average particle size continues to increase to D 50 = 0.854 mm, the actual cutter height difference for the Nanjing Yangtze River Tunnel increases to ΔH = 50.0 mm (Huang, 2010 ; Guo and Dai, 2013 ). The larger the average particle size is, the greater the actual cutter height difference will be. The variation in the actual cutter height difference of shield TBMs closely aligns with the optimal cutter height difference from the WHU-SAT test. Table 2 Comparisons between the optimal cutter height difference of WHU-SAT test and the actual cutter height difference under similar particle size conditions. Average particle size D 50 (mm) Sand density ρ (g/cm 3 ) Cutter height difference ΔH (mm) The Yellow River Jiluo Road Tunnel 0.208 1.78 20 The Sanyang Road Yangtze River Tunnel (Huang et al., 2018 ; Li and Bao, 2019 ) 0.447 1.93 40 The Nanjing Yangtze River Tunnel (Huang, 2010 ; Guo and Dai, 2013 ) 0.854 2.68 50 5.2 The variation in the stable plowing coefficient with average particle size As shown in Fig. 16 , the variation in the stable plowing coefficient with the average particle size has been depicted. The results indicate that when the average particle size is D 50 = 0.212 mm, the stable plowing coefficients for natural sand and quartz sand are ξ = 0.76 and ξ = 0.82, respectively. With the average particle size increases to D 50 = 0.710 mm, the stable plowing coefficients for natural sand and quartz sand decrease to ξ = 0.61 and ξ = 0.62, respectively. The stable plowing coefficient for natural sand is lower than that for quartz sand. This is because the particle surfaces of natural sand are smoother than those of quartz sand, and nature sand is looser than quartz sand after being plowed by the ripper teeth. The decrease of the stable plowing coefficient with increasing the average particle size is related to the occlusion and cohesion among sand particles. After being plowed by the ripper teeth, the sand particles rearrange into a loose state. For coarse particles, their contact mode in the loose state is mainly “point to point”. The occlusion among coarse particles are significantly weakened. When they are cut by the modelled scrapers, the decrement of wear extent is significant. For fine particles, they are bonded together by a water film on their surface (Chen and Ye, 2004 ). Generally, the smaller the sand particles are, the stronger the cohesion effect will be (Li, 2016 ). When they are cut by the modelled scrapers, the decrement of wear extent is limited. As the average particle size increases from D 50 = 0.212 mm to D 50 = 0.710 mm, the proportion of coarse particles in sand sampels increases. Under the conditions of increased scraper wear, the stable plowing coefficient decreases. 5.3 The variation in the minimum cutterhead torque with average particle size Monitoring results indicate that the cutterhead torque decreases first and then increases with increasing cutter height difference, which does not change with the increase of average particle size. When the cutter height difference is at its optimal level, the cutter head torque is minimized. As shown in Fig. 17 , the variation in the minimum cutterhead torque with average particle size has been depicted. When the average particle size is D 50 = 0.212 mm, the minimum cutterhead torque for natural sand and quartz sand is T = 3.87 N*m and T = 8.03 N*m, respectively. As the average particle size increases to D 50 = 0.710 mm, the minimum cutterhead torque for natural sand and quartz sand increases to T = 11.02 N*m and T = 21.34 N*m, respectively. The minimum cutterhead torque in nature sand is lower than that in quartz sand. This is due to the fact that the particle surfaces of nature sand are smoother than those of quartz sand. When they are cut by the cutterhead, natural sand exhibits lower occlusion and friction compared to quartz sand. The increase in the minimum cutterhead torque with increasing the average particle size is attributed to the plowing resistance and friction resistance. As shown in Fig. 15 , the optimal cutter height difference increases with increasing the average particle size. The greater the optimal cutter height difference is, the greater the plowing depth of ripper teeth will be. Under the conditions of plowing deeper sand samples, the plowing resistance and friction resistance of ripper teeth will be larger. Moreover, with the increase of the average particle size, the occlusion between sand particles will increase. When the coarser sand particles are cut by the modelled scrapers, the cutting resistance and frictional resistance will increase. Under the condition that the resistance of ripper teeth and scrapers increases, the minimum cutterhead torque increases with increasing the average particle size. 6 Conclusions In the present study, the plowing effect of ripper teeth has been evaluated using the plowing coefficient. The influence of cutter height difference, sand density and particle size on the plowing coefficient has been studied using the WHU-SAT test. The plowing mechanism has been revealed by analyzing the loosening process of ripper teeth on the excavation face. The cutter height difference has been optimized for dense sandy ground tunnelling. The present study provides a reference for mitigating cutting tool wear and enhancing cutterhead tunnelling efficiency. From the present study, the following conclusions can be drawn: (1) With the increase of cutter height difference, the plowing coefficient of the ripper teeth decreases first and then stabilizes, remaining unaffected by increases in sand density and average particle size. Since the denser and coarser sand samples exhibit a greater decrement in soil abrasivity after plowing, the stable plowing coefficient decreases with increasing the sand density and average particle size. (2) When the plowing coefficient of the ripper teeth transitions from a reduced state to a stable state, the corresponding cutter height difference is considered as the optimal cutter height difference. There are differences in the optimal cutter height difference among different sand samples. It increases first and then stable with increasing sand density, and increases with increasing average particle size. (3) With the increase of cutter height difference, the cutterhead torque decreases first and then increase, remaining unaffected by increases in sand density and average particle size. When the cutter height difference is optimal, the corresponding cutterhead torque is at its minimum. Since the plow depth and cutter resistance are greater when cutting denser and coarser sand samples, the minimum cutterhead torque increases with increasing sand density and average particle size. Abbreviations SAT™ Soil Abrasion Tester LCPC Laboratoire central des ponts et chaussées tester DTWA Das TU Wien Abrasimeter SGAT Soft Ground Abrasion Tester RUB Ruhr-University Bochum Tester CUGB China University of Geosciences (Beijing) Tester BJTU Beijing Jiaotong University Tester WHU-SAT Soil Abrasion Tester developed by Wuhan University EPB-TBM Earth Pressure Balance Tunnel Boring Machine Declarations Acknowledgments None. Author contributions Shao-Hui Tang contributed to investigation, methodology and writing-original draft. Quan-Sheng Liu contributed to project administration and resources. Qi Zhang contributed to writing-review & editing, formal analysis and funding acquisition. Wei-Qiang Xie contributed to conceptualization and validation. Wei Sun contributed to visualization and data curation. Hao-Jie Wang contributed to supervision and validation. Xin-Fang Li contributed to software and visualization. Funding The support provided by National Natural Science Foundation of China (Grant Nos. 52308415, 52108382, 52378409) is gratefully acknowledged. Data availability Data will be made available on request. Conflicts of interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 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China Architecture and Building Press, Beijing (in Chinese) Zhang JX, Yin ML, Jiang YS, Jiang H, Zhou LG, Sun ZY (2022b) Mechanical behavior of sandy gravel strata cut by wedge-shaped cutter on earth pressure balance shield. Tunn. Constr. 42(09):1501–1513. (in Chinese) Zhang XP, Tang SH, Liu QS, Wang HJ, Li XF, Chen P, Liu H (2023) Key technology for the construction and inspection of long-distance underwater tunnel for 1000 kV gas-insulated transmission line. Bull. Eng. Geol. Environ 82(1), 7 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6424309","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":472342688,"identity":"d168e4a0-01ef-4143-8ce2-e28b8ce48761","order_by":0,"name":"Shao-Hui Tang","email":"","orcid":"","institution":"Guangxi University","correspondingAuthor":false,"prefix":"","firstName":"Shao-Hui","middleName":"","lastName":"Tang","suffix":""},{"id":472342691,"identity":"cd217884-80c4-4673-a5bc-48daf3deb009","order_by":1,"name":"Quan-Sheng Liu","email":"","orcid":"","institution":"Wuhan 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03:23:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6424309/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6424309/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":84915865,"identity":"d9781ec5-5ec0-4698-9aca-abd245145576","added_by":"auto","created_at":"2025-06-18 18:19:02","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":343413,"visible":true,"origin":"","legend":"\u003cp\u003eArrangement of cutting tools (Jiang et al., 2022): (a) distribution of cutting tools on the cutterhead; (b) installation heights of the cutting tools; (c) height differences between cutters.\u003c/p\u003e","description":"","filename":"image1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6424309/v1/a69833ad0c3f92445df7e4c9.jpeg"},{"id":84915724,"identity":"41f9dd61-4944-4775-af9b-916772ad436c","added_by":"auto","created_at":"2025-06-18 18:11:02","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":325254,"visible":true,"origin":"","legend":"\u003cp\u003eThe newly developed WHU-SAT test system: (a) The WHU-SAT test apparatus; (b) Modelled cutterhead; (c) Modelled cutting tool; (d) Control system; (e) Monitoring system.\u003c/p\u003e","description":"","filename":"image2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6424309/v1/ab18af9a4e2aad0ea5b23752.jpeg"},{"id":84915723,"identity":"0ebe51a6-37d6-4966-b221-ce144a9af174","added_by":"auto","created_at":"2025-06-18 18:11:02","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":73594,"visible":true,"origin":"","legend":"\u003cp\u003eParticle gradation of sand samples for analyzing the influence of cutter height difference on plowing 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18:11:03","extension":"jpeg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":67933,"visible":true,"origin":"","legend":"\u003cp\u003eThe variation in the minimum cutterhead torque with sand density.\u003c/p\u003e","description":"","filename":"image12.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6424309/v1/4b14fecaf5f4fb4bf04d6d6e.jpeg"},{"id":84916398,"identity":"7dbe805c-f079-42f6-8829-e9f34d4ec336","added_by":"auto","created_at":"2025-06-18 18:27:03","extension":"jpeg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":167488,"visible":true,"origin":"","legend":"\u003cp\u003eThe particle gradation of sand samples for analyzing the influence of particle size on plowing coefficient.\u003c/p\u003e","description":"","filename":"image13.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6424309/v1/026b0e156278a84dfc2d7025.jpeg"},{"id":84915742,"identity":"a132cf0b-51e9-4086-88e6-e6848cc9c3e7","added_by":"auto","created_at":"2025-06-18 18:11:02","extension":"jpeg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":327423,"visible":true,"origin":"","legend":"\u003cp\u003eThe variation in plowing coefficient with cutter height difference in various average particle sizes of nature sand.\u003c/p\u003e","description":"","filename":"image14.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6424309/v1/5dcaa949afd1327231c25f31.jpeg"},{"id":84915759,"identity":"7712945a-4793-431f-a268-05577c7abfa5","added_by":"auto","created_at":"2025-06-18 18:11:03","extension":"jpeg","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":294416,"visible":true,"origin":"","legend":"\u003cp\u003eThe variation in plowing coefficient with cutter height difference in various average particle sizes of quartz sand.\u003c/p\u003e","description":"","filename":"image15.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6424309/v1/a10f17082134c1c576f6c62d.jpeg"},{"id":84915752,"identity":"3aa6c7e6-88fd-4513-9587-edfbc16cb460","added_by":"auto","created_at":"2025-06-18 18:11:03","extension":"jpeg","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":85652,"visible":true,"origin":"","legend":"\u003cp\u003eThe variation in the optimal cutter height difference with the average particle size.\u003c/p\u003e","description":"","filename":"image16.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6424309/v1/6bf6f0df60849f0371ca3918.jpeg"},{"id":84915743,"identity":"75fa315a-d003-4dcc-b02d-cb2f2a6b5d52","added_by":"auto","created_at":"2025-06-18 18:11:02","extension":"jpeg","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":87704,"visible":true,"origin":"","legend":"\u003cp\u003eThe variation in the stable plowing coefficient with the average particle size.\u003c/p\u003e","description":"","filename":"image17.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6424309/v1/f07b4b0ee0da1b72bedc37ba.jpeg"},{"id":84915731,"identity":"4a80e9ab-5fad-4759-8282-18a737b4eda0","added_by":"auto","created_at":"2025-06-18 18:11:02","extension":"jpeg","order_by":17,"title":"Figure 17","display":"","copyAsset":false,"role":"figure","size":83708,"visible":true,"origin":"","legend":"\u003cp\u003eThe variation in the minimum cutterhead torque with the average particle size.\u003c/p\u003e","description":"","filename":"image18.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6424309/v1/2762845f7fef9aee97d72a8b.jpeg"},{"id":87996671,"identity":"75f6aa88-e82f-46bc-a729-4ea15f2268cf","added_by":"auto","created_at":"2025-07-31 09:32:27","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4333894,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6424309/v1/810a6cc7-b68f-419d-8ed3-20d5f987ecb1.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Experimental study on the plowing effect of ripper tooth and its influence on scraper wear during shield TBM tunneling in abrasive sandy ground","fulltext":[{"header":"Article Highlights","content":"\u003cul\u003e\n \u003cli\u003eThe newly developed WHU-SAT test apparatus is used to study the plowing effect of ripper tooth.\u003c/li\u003e\n \u003cli\u003eThe plowing coefficient is proposed to quantify the influence of plowing effect on scraper wear.\u003c/li\u003e\n \u003cli\u003eThe influence mechanism of plowing coefficient is revealed based on excavation process analysis.\u003c/li\u003e\n \u003cli\u003eThe height difference between ripper tooth and scraper is optimized for sandy ground tunneling.\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"1 Introduction","content":"\u003cp\u003eDuring shield TBM tunnelling in dense sandy ground, the cutterhead is mainly equipped with ripper teeth and scrapers for tunnel excavation (Wei et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2021a\u003c/span\u003e, Tang et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2021a\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003eb\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The installation height of the ripper teeth is typically 20 mm to 60 mm higher than that of the scrapers, depending on the physical and mechanical properties of the sandy ground (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) (Huang, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Guo and Dai, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Chen and Huang, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Huang et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Tang et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). When there is a height difference between two cutters, the ripper teeth plow excavation surface to loosen dense sand, followed by the scrapers cutting the loose sand for tunnel excavation (Zhang et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2021a\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003eb\u003c/span\u003e; Jiang et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2021a\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Tang et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Compared with cutting dense sand directly, the wear of the scrapers is significantly reduced when cutting loose sand plowed by ripper teeth (Huang, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Guo and Dai, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2022a\u003c/span\u003e; Wei et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The plowing effect is the protection of ripper teeth on scraper wear by loosing the excavation surface. It is related to the cutter height difference, sand density and particle size (Xia et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Tang et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Jiang et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2021b\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA rational evaluation of plowing effect is crucial for optimizing the cutter height difference and enhancing cutterhead excavation capacity (Guo and Dai, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Tang et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2022\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). A preliminary literature review indicates that the plowing effect has been assessed by comparing cutting efficiency or scraper wear with and without ripper teeth (Peng, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Tang et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Jiang et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2021a\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003eb\u003c/span\u003e). For instance, Guo and Dai (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) compared the scraper wear coefficient before and after the failure of ripper teeth, and concluded that it increased by approximately two times following the failure. However, the in-situ tests were conducted under conditions where multiple parameters changed simultaneously. Variations in geological conditions and tunnelling parameters significantly interfered with the test results. Tang et al. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) proposed a synergistic coefficient to quantify the protection provided by ripper teeth against scraper wear, and found that the synergistic coefficient in fine silty sand is approximately 0.496. Since the sand density remained stable during the tests, the variation in synergistic coefficient with sand density has not been discussed. Li et al. (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) studied the cutting efficiency under varying cutter height differences, and optimized ripper teeth height for EPB-TBM cutting the reinforced concrete piles. Since the in-situ test only examined two cutter height differences, the variation in plowing coefficient with cutter height difference remains unclear. Zhang et al. (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2021a\u003c/span\u003e) proposed a multi-dimensional gradient configuration method for ripper teeth, and concluded that scraper wear coefficient could be reduced by arranging ripper teeth at different installation heights. However, this installation height only applies to coarse sandy gravel, and its variation with particle size remains to be discussed. Jiang et al. (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2021b\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) simulated the cutting performance of ripper teeth using discrete element method, and found that the tunnelling efficiency increased when the cutter height difference was 70 mm. Since cutterhead torque rather than wear coefficient was considered for evaluating cutting performance, the variation in scraper wear with cutter height difference has not been analyzed.\u003c/p\u003e \u003cp\u003eThe studies on the influence of the plowing effect on scraper wear are based on either in-situ tests or numerical simulations. The simultaneous variation of multiple parameters significantly interfered with the results of in-situ tests, while unrealistic simulation of cutter wear lead to unacceptable errors in plowing coefficients. Hence, laboratory tests with controllable parameters have been considered as a viable method to analyze the plowing effect and its influence on scraper wear. Several test apparatuses have been developed by institutions worldwide. However, the initial test apparatuses (such as SAT\u0026trade;, LCPC and DTWA) were derived from rock abrasion testers (Alavi Gharahbagh et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Drucker et al., 2011; Rostami et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Their cutterhead structure and cutter shape are too simplistic to match the interaction between tunnel face and cutting tool. Improved test apparatus (such as RUB, CUGB and BJTU) were designed to accommodate one type of cutting tool (K\u0026uuml;pferle et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Wei et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2018\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2019\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Wu, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). These apparatuses can only evaluate the plowing effect of ripper teeth on the excavation face, without assessing their protective role in reducing scraper wear. To the best of our knowledge, there is still a lack of a reliable test apparatus that can accommodate two or more types of cutting tools to reveal the internaction between the ripper teeth and the scrape.\u003c/p\u003e \u003cp\u003eIn the present study, the newly developed WHU-SAT test apparatus that can be equipped with two types of cutting tools has been utilized for analyzing the plowing effect of ripper tooth and its influence on scraper wear. The plowing coefficient defined as the ratio of scraper wear with and without the protection of ripper tooth has been prosed to quantify the plowing effect. The influence of cutter height difference, sand density and particle size on plowing coefficient has been studied using the WHU-SAT tests. The plowing mechanism has been revealed by analyzing the loosing process of the ripper tooth on excavation face. The cutter height difference between the ripper tooth and scraper has been optimized for dense sandy ground tunnelling.\u003c/p\u003e"},{"header":"2 Test method and evaluation parameter","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 The WHU-SAT test method\u003c/h2\u003e \u003cp\u003eThe newly developed WHU-SAT test apparatus consists of XK7130 CNC milling machine, modelled cutterhead, modelled cutting tool, soil chamber, monitoring system, and control terminal (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The XK7130 CNC milling machine with 2200 mm in length, 1900 mm in width and 2300 mm in height serves as the basic platform for the WHU-SAT test apparatus. The modelled cutterhead mounted at the shaft of XK7130 CNC milling machine consists of five spokes. The tool mounting radii are arranged according to the Archimedes spiral pattern. Each cutterhead spoke has three mounting radii, and each mounting radius has three holes for mounting the modelled cutting tools. The side mounting holes are fitted with scrapers, while the middle hole is fitted with a ripper tooth. The structure of the modelled cutterhead and the distribution of mounting hole in the WHU-SAT test apparatus are generally comparable to those of the shield TBM. The cylindrical chamber can be filled with soil samples with grain sizes corresponding to clay, silt, sand and gravel with grain sizes less than 30 mm. When the test apparatus is in operation mode, the modelled cutterhead excavates soil samples in the cylindrical chamber at a rotation speed of 0 to 500 rpm and a tunnelling speed of 0 to 50 mm/min. During the WHU-SAT soil abrasion test, the tunneling parameters (such as rotation speed, tunneling speed, tunneling depth and test time) of the modelled cutterhead can be inputted on the control terminal and detected by the monitoring software.\u003c/p\u003e\u003cp\u003eThe modelled cutting tools (including the ripper tooth and scraper) consist of a cutter edge, cutter body and connecting bolt with lengths of 10 mm, 10 mm and 40 mm, respectively. The cross sections of the cutter edges of scraper and ripper tooth are rectangular with lengths of 15 mm and 12 mm, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Since the lengths of the welded scraper and ripper tooth in a shield TBM are usually 225 and 180 mm, the reduced scale of the WHU-SAT test is approximately 1:15. When the modelled cutting tools are mounted on the cutterhead spokes, there is no initial height difference between the ripper tooth and the scraper. The height difference is adjusted by turning the screws. For each rotation of the screws, the height difference between the ripper tooth and the scraper increases by 1 mm. The bolted connection is beneficial not only for the precise control of the height difference, but also for the timely replacement of cutting tools (Tang et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). With the protection of the newly replaced cutting tools, the maintenance frequency of the modelled cutterhead can be minimized.\u003c/p\u003e \u003cp\u003eWhen the start button on the instruction module of control terminal is pressed, the modelled cutterhead excavates soil according to the preset tunneling parameters. Once the tunneling depth reaches the target value, the modelled cutterhead stops tunneling and continues to rotate until the test time is exhausted. Then, the modelled cutterhead stops and returns to its initial position according to the preset program. After removing the muck adhering to the metal surface, the modelled cutterhead and cutting tools are disassembled by loosening the corresponding bolts. The cutting tools are cleaned and dried to eliminate the residual moisture. Next, they are weighed three times using a high-precision electronic balance (0.001 g) to evaluate the value of worn. Cutting tool wear is quantified by calculating the average weight loss of cutting tool before and after the soil abrasion test. Compared to existing soil abrasion test methods, the advantages of the WHU-SAT test apparatus and test method are as follows:\u003c/p\u003e\u003cp\u003e(1) Rational simulation of cutterhead structure and cutter arrangement. The cutterhead structures of initial tests (such as SAT\u0026trade;, LCPC and DTWA) are block, disc or rectangle, while those of subsequent tests (such as RUB, CUGB and BJTU) are propeller, tube, cross, bolt or star. These designs This do not allow for the simultaneous installation of modelled scraper and ripper tooth. Hence, the existing test apparatus cannot reveal the influence mechanism of plowing effect on scraper wear. Since the Archimedes spiral pattern principle is used to arrange the mounting holes and each mounting radius has three holes for mounting two modelled scpraera and one ripper tooth simultaneously, the modelled cutterhead structure and cutter arrangemen of the WHU-SAT test simulates those of the shield TBM.\u003c/p\u003e \u003cp\u003e(2) Reasonable design of cutter geometry. The modelled cutting tools simplify the local characteristics (such as welding procedure, surface treatment and cutter chamfer), while retaining the morphological characteristics (such as front angle, back angle and edge angle) of shield cutting tools. This design not only reduces the production cycle and manufacturing cost, but also facilitates the exploration of the influence of cutter geometry on tool wear. For instance, the modelled scraper simulates the wedge-shaped characteristics of the shield scraper by retaining cutting angles. Consequently, cutting process and wear mechanism can be well reproduced.\u003c/p\u003e \u003cp\u003e(3) Precise monitoring and control of tunneling parameters. The accuracy of position coordinates is 0.001, while the accuracies of rotation speed, tunneling speed, cutterhead torque, and motor power are 0.01. The high-precision monitoring and control system increases the accuracy of tunneling parameters and promotes a more rigorous test procedure. Moreover, the emergency protection function of the automatic control system is fully developed. Once abnormal conditions occurs, a warning signal will appear on the control terminal, and the the modelled cutterhead stops running and the returns to the initial position to ensure security.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 The evaluation parameter\u003c/h2\u003e \u003cp\u003eThe preset tunnelling parameters for the modelled cutterhead are the rotation speed \u003cem\u003eN\u003c/em\u003e\u0026thinsp;=\u0026thinsp;150 rpm, the tunnelling speed \u003cem\u003eV\u003c/em\u003e\u0026thinsp;=\u0026thinsp;20 mm/min, the tunnelling depth \u003cem\u003eh\u003c/em\u003e\u0026thinsp;=\u0026thinsp;140 mm and the test time \u003cem\u003eT\u003c/em\u003e\u0026thinsp;=\u0026thinsp;60 min. As the modelled cutterhead excavates soil samples, the higher ripper teeth plow the dense soils, followed by the lower scrapers cut the loosened soils. Compared to directly cutting dense soil samples, scraper wear is significantly reduced when cutting loose soil plowed by ripper teeth. The plowing effect involves the protection of the scrapers from wear due to the loosing of the excavation face by the ripper teeth. To quantify the plowing effect, the ratio of scraper wear with and without the protection of ripper teeth is defined as the plowing coefficient. This can be expressed as:\u003c/p\u003e\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" height=\"48\" width=\"304\"\u003e\u003c/p\u003e \u003cp\u003eWhere,\u003c/p\u003e \u003cp\u003e \u003cem\u003eξ\u003c/em\u003e is the plowing coefficient of ripper tooth;\u003c/p\u003e \u003cp\u003e \u003cem\u003eδ\u003c/em\u003e \u003csub\u003e \u003cem\u003ern\u003c/em\u003e \u003c/sub\u003e is the scraper wear with the protection of ripper tooth;\u003c/p\u003e \u003cp\u003e \u003cem\u003eδ\u003c/em\u003e \u003csub\u003e \u003cem\u003erf\u003c/em\u003e \u003c/sub\u003e is the scraper wear without the protection of ripper tooth.\u003c/p\u003e \u003cp\u003eEngineering experience suggests that the plowing coefficient is related to the cutter height difference, sand density and particle size (Guo and Dai, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Mu, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Jiang et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021c\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022b\u003c/span\u003e). When shield TBM tunnelling in silty clay or fine sand with lower density, the scraper wear and plowing coefficient are insensitive to the variation in cutter height difference. However, when shield TBM tunnelling in coarse sand or sandy gravel with high density, an appropriate increase in cutter height difference significantly decrease scraper wear and plowing coefficient. It is essential to analyze the plowing coefficient of the ripper teeth and its influence on scraper wear, and propose the optimal cutter height difference for various geological conditions to reduce tool wear and maintenance frequency.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 The influence of cutter height difference on plowing coefficient","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1 The preparation of sand samples for the WHU-SAT test\u003c/h2\u003e \u003cp\u003eThe nature sand samples and quartz sand samples were used for the WHU-SAT test. These samples were pretreated to align with the physical and mechanical parameters. For nature sand samples, they were dried and sieved into sand particles with sizes of 0.125\u0026ndash;0.212, 0.212\u0026ndash;0.425, 0.425\u0026ndash;0.710, 0.710\u0026ndash;1.180, 1.180\u0026ndash;2.360, 2.360\u0026ndash;3.350 and 3.350\u0026ndash;4.750 mm. For quartz sand samples, they were obtained by crushing the dry quartz with a purity of 99.75% into sand particles of the aforementioned seven sizes. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the target sand samples were obtained by uniformly mixing sand samples of the aforementioned seven sizes in the mass ratio of 6: 6: 4: 4: 4: 2: 1. Subsequently, they were mixed with an appropriate water to prepare sand samples with a water content of \u003cem\u003eω\u003c/em\u003e\u0026thinsp;=\u0026thinsp;15%. The aqueous sand samples were filled into a cylindrical chamber with a density of \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.80 g/cm\u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2 The variation in plowing coefficient with cutter height difference\u003c/h2\u003e \u003cp\u003eThe metal materials 06Cr19Ni10 and 45# have been extensively used as cutter materials in existing tests such as SGAT, RUB, BJTU and CUGB (Jakobsen et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; K\u0026uuml;pferle et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Wei, 2019; Wu, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). To facilitate comparison with existing test results, the present study employed the same materials. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b), five tool mounting holes were designated for the installation of cutting tools. The corresponding mounting radii were 52.5 mm, 61.0 mm, 69.5 mm, 78.0 mm and 86.5 mm, respectively. For each radius, the center mounting hole was fitted with a ripper tooth made of 06Cr19Ni10, while the left and right holes were fitted with scrapers made of 06Cr19Ni10 and 45#, respectively. The modelled cutting tools were secured in the mounting holes using M8 screws. Each full revolution of the screw increases the cutter height difference by 1 mm; the corresponding height difference for the shield TBM is 15 mm.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, seven experimental tests were conducted to examine the variation of plowing coefficient with cutter height difference in both natural sand samples and quartz sand samples. The corresponding cutter height differences between the actual ripper tooth and scraper were \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0, 7.5, 15.0, 22.5, 30.0, 37.5, 45.0 mm. The results indicate that the plowing coefficient decreases first and then stabilizes with increasing cutter height difference. When the cutter height difference is \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0 mm, the ripper teeth are unable to loosen dense sand samples before the scrapers cut the excavation surface. Without the protection of ripper teeth, scraper wear is most serious, resulting in a plowing coefficient of \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.00. As the cutter height difference increases, the plowing depth of the ripper teeth increases, while the sand density on the excavation surface decreases. When scrapers cut looser sand samples, the plowing coefficient of the ripper teeth decreases. When the cutter height difference is \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;30.0 mm, the plowing coefficients for scraper made of 06Cr19Ni10 and 45# in nature sand samples (or quartz sand samples) are \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.64 (or \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.68) and \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.69 (or \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.70), respectively. As the cutter height difference continues to increase, the sand density on the excavation surface remains at a low level. Consequently, the plowing coefficient stabilizes with increasing cutter height difference.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn addition to the plowing coefficient, the ripper teeth wear in seven tests has been weighed using a high-precision scale (0.001 g). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, the results indicate that the ripper teeth wear increases slowly first and then rapidly with an increasing cutter height difference. This trend is related to variations in the plowing depth of the ripper teeth. When the cutter height difference is \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0 mm, the ripper teeth and scrapers cut dense sand samples on the excavation surface simultaneously. The synergistic cutting of the modelled scrapers keeps the ripper teeth wear at a low level. With the cutter height difference increases to \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;30 mm, the ripper teeth begin to plow dense sand on the excavation surface. Because the frictional resistance of shallow sand samples is low, the ripper teeth wear increases slowly with increasing the cutter height difference. As the cutter height difference continues to increase to \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;45 mm, the ripper teeth plow the dense sand in front of excavation face. The frictional resistance of deep sand samples increases significantly. As extrusion and friction between the cutter edge and sand particles increase, the ripper teeth wear increases rapidly with an increasing cutter height difference.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe cutterhead torque has been monitored during the WHU-SAT tests. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, the results indicate that the average torque in the stable phase (after the tunneling depth reaches \u003cem\u003eh\u003c/em\u003e\u0026thinsp;=\u0026thinsp;140 mm) decreases first and then decreases with an increasing cutter height difference. This trend is related to the variation in cutting resistance and friction resistance. When the cutter height difference is \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0 mm, the ripper teeth and scrapers simultaneously contact the excavation face. Because the dense sand samples have not been loosened, the cutting resistance and friction resistance remain at a high level. As the cutter height difference increases to \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;30 mm, the cutting resistance and friction resistance of the ripper teeth increase slowly when plowing shallow excavation face, while those of scrapers decrease rapidly when cutting looser sand samples. Because the number of ripper teeth is much smaller than that of the modelled scrapers, the increase in cutting resistance and friction resistance is smaller than the decrease. Hence, the cutterhead torque decreases with increasing the cutter height differenc. As the cutter height difference continues to increase to \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;45 mm, the cutting resistance and friction resistance of ripper teeth increases rapidly when plowing the deep excavation face, while those of the scrapers remain stable because the surface sand samples are sufficiently loose. Hence, the cutterhead torque increases with increasing the cutter height difference.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.3 The optimal cutter height difference for dense sand samples\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, the experiment results indicate that when the cutter height difference between the ripper teeth and scrapers is \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;30 mm, the plowing coefficient of the ripper teeth has stabilized, and the cutterhead torque in the stable phase has been minimized. The modelled cutterhead of the WHU-SAT test apparatus has reached a relatively minimum load state. In this case, the plowing effect of the ripper teeth on the excavation surface has been maximized, while the bulk density of sand samples cut by the scrapers has been minimized. Since the protection of the ripper teeth against scraper wear has been maximized, the optimal cutter height difference for shield TBMs tunnelling in the tested sand samples is \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;30 mm.\u003c/p\u003e \u003cp\u003eThe optimal cutter height difference was compared with the actual cutter height difference of shield TBMs under similar geological conditions. As shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the results indicate that the optimal cutter height difference (\u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;30 mm) is greater than the actual cutter height difference (\u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;20 mm) of the Yellow River Jiluo Road Tunnel, but smaller than that (\u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;40 mm) of the Sutong GIL Yangtze River Crossing Cable Tunnel. This discrepancy is related to the differences in sand density and particle size. Generally, the optimal cutter height difference is positively correlated with sand density and particle size. The in-situ density and average particle size of the silty sand at the Yellow River Jiluo Road Tunnel are \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.78 g/cm\u003csup\u003e3\u003c/sup\u003e and \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.208 mm, while those of the medium coarse sand at the Sutong GIL Yangtze River Crossing Cable Tunnel are \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.06 g/cm\u003csup\u003e3\u003c/sup\u003e and \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.554 mm. The parameter values of the two types of sand are smaller and larger than those the tested sand samples in the present study. Hence, the actual cutter height difference of shield TBMs are smaller and larger than the optimal cutter height difference observed in the WHU-SAT test.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparisons between the optimal cutter height difference of WHU-SAT test and the actual cutter height difference of shield TBMs under similar sand density conditions.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSand density\u003c/p\u003e \u003cp\u003e\u003cem\u003eρ\u003c/em\u003e (g/cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAverage particle size \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCutter height difference \u003cem\u003eΔH\u003c/em\u003e (mm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThe WHU-SAT test\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.425\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThe Yellow River Jiluo Road Tunnel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.208\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThe Sutong GIL Yangtze River Crossing Cable Tunnel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.554\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4 The influence of sand density on plowing effect","content":"\u003cp\u003eThe preparation of sand samples to analyze the influence of sand density on the plowing coefficient is similar to the method described in Section \u003cspan refid=\"Sec6\" class=\"InternalRef\"\u003e3.1\u003c/span\u003e. The mixed sand samples with a water content of \u003cem\u003eω\u003c/em\u003e\u0026thinsp;=\u0026thinsp;15% were filled into the cylindrical chamber at a bulk densities of \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.70, 1.80, 1.90, 2.00 g/cm\u003csup\u003e3\u003c/sup\u003e. The modelled scrapers used in the experimental studies were made of 06Cr19Ni10. The WHU-SAT test was conducted to obtain the plowing coefficient under various sand density conditions. The variation in the plowing coefficient of ripper teeth with cutter height difference in nature sand and quartz sand has been shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. The results indicate that the plowing coefficient decreases first and then stabilizes with increasing cutter height difference, remaining unaffected by sand density.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e4.1 The variation in the optimal cutter height difference with sand density\u003c/h2\u003e \u003cp\u003eAlthough the variation tendencies in the plowing coefficient with cutter height difference are comparable across various sand densities, the optimal cutter height differences are significantly different. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, the variation in the optimal cutter height difference with sand density has been depicted. The results indicate that when the sand density is \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.70 g/cm\u003csup\u003e3\u003c/sup\u003e, the minimum optimal cutter height difference is \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;22.5 mm. With the sand density increases to \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.90 g/cm\u003csup\u003e3\u003c/sup\u003e, the optimal cutter height difference increases to the maximum value \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;37.5 mm. As the sand density continues to increase to \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.00 g/cm\u003csup\u003e3\u003c/sup\u003e, the optimal cutter height difference remains relatively stable. The optimal cutter height difference from the WHU-SAT test has been compared with the actual cutter height differences of the shield TBMs (Tang et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2022a\u003c/span\u003e). The results indicate that when the bulk density of the tested sand (\u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.00 g/cm\u003csup\u003e3\u003c/sup\u003e) closely matches that of the in-situ sand (\u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.06 g/cm\u003csup\u003e3\u003c/sup\u003e), the optimal cutter height difference (\u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;37.5 mm) is comparable to the actual cutter height difference (\u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;40.0 mm).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe optimal cutter height difference varies with sand density, which is related to the plowing depth of the loosest sand samples on the excavation surface. When the sand density is \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.70 g/cm\u003csup\u003e3\u003c/sup\u003e, the plowing depth of the loosest sand samples is at its minimum value \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;22.5 mm. With the sand density increases, the plowing depth of the loosest sand samples increases. This indicates that the extrusion and friction between the modelled scraper and the excavation surface reach their lowest level only when the plowing depth is greater. Hence, the optimal cutter height difference increases with increasing sand density. When the sand density increases to \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.90 g/cm\u003csup\u003e3\u003c/sup\u003e, the plowing depth of the loosest sand samples reaches the maximum value \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;37.5 mm. As the sand density continues to increase to \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.00 g/cm\u003csup\u003e3\u003c/sup\u003e, the plowing depth of the loosest sand samples stabilizes. The maximum influence depth of the ripper teeth on the excavation surface is \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;37.5 mm. Consequently, the optimal cutter height difference remains stable with increasing sand density.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e4.2 The variation in the stable plowing coefficient with sand density\u003c/h2\u003e \u003cp\u003eThe optimal cutter height difference between the ripper tooth and the scraper, as well as the stable plowing coefficient (the average plowing coefficient corresponding to this cutter height difference) varies with different sand densities. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, the variation in the stable plowing coefficient with sand density has been depicted. The results indicate that when the sand density is \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.70 g/cm\u003csup\u003e3\u003c/sup\u003e, the stable plowing coefficients for natural sand and quartz sand are \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.77 and \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.79, respectively. With the sand density increases to \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.00 g/cm\u003csup\u003e3\u003c/sup\u003e, the stable plowing coefficients for natural sand and quartz sand decrease to \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.54 and \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.56, respectively. The stable plowing coefficient from the WHU-SAT test has been compared with the actual plowing coefficient of shield TBMs (Tang et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2022a\u003c/span\u003e). The results indicate that when the bulk density of the nature sand (\u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.00 g/cm\u003csup\u003e3\u003c/sup\u003e) closely matches that of the in-situ sand (\u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.06 g/cm\u003csup\u003e3\u003c/sup\u003e), the stable plowing coefficient (\u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.54) for the nature sand is comparable to the actual plowing coefficient (\u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.50) in the in-situ sand.\u003c/p\u003e \u003cp\u003eThe decrease in the stable plowing coefficient is associated with a reduction in sand density. The greater the reduction in sand density is, the greater the decrement of extrusion and friction between the modelled scrapers and sand particles will be. Consequently, the greater the decrement of scraper wear and the smaller the stable plowing coefficient will be. After the ripper teeth have plowed the excavation surface, the densities of the loose sand samples cut by the modelled scrapers become comparable. This indicates that the greater the filled sand density is, the greater the reduction in sand density and the smaller the stable plowing coefficient will be. Hence, with the sand density increases from \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.70 g/cm\u003csup\u003e3\u003c/sup\u003e to \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.00 g/cm\u003csup\u003e3\u003c/sup\u003e, the stable plowing coefficient for natural sand (or quartz sand) decrease from \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.77 (or 0.79) to \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.54 (or 0.56).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eComparisons indicate that the stable plowing coefficient for natural sand is lower than that for quartz sand. This difference is attributed to the difference in particle shape between the two sand samples. Images analysis via a Digital Microscope reveals that the roundness of natural sand is \u003cem\u003eC\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.79, which is greater than that of quartz sand \u003cem\u003eC\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.60 (Tang et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This indicates that the particle surface of natural sand is smoother than that of quartz sand. When the ripper teeth plow the tunnel face, the natural sand with smooth surface is looser due to particle rearrangement. The stable plowing coefficient is lower when scrapers cut looser sand. Conversely, the quartz sand with a rough surface is relatively denser due to particle occlusion. The stable plowing coefficient is higher when scrapers cut denser sand.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e4.3 The variation in the minimum cutterhead torque with sand density\u003c/h2\u003e \u003cp\u003eThe cutterhead torque during the stable phase has been monitored during the WHU-SAT test. The results indicate that the cutterhead torque at the optimal cutter height difference (the minimum cutterhead torque) is the lowest, which does not change with the increase of sand density. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, the variation in the minimum cutterhead torque with sand density has been depicted. When the sand density is \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.70 g/cm\u003csup\u003e3\u003c/sup\u003e, the minimum cutterhead torque in natural sand and quartz sand is \u003cem\u003eT\u003c/em\u003e\u0026thinsp;=\u0026thinsp;4.97 N*m and \u003cem\u003eT\u003c/em\u003e\u0026thinsp;=\u0026thinsp;10.78 N*m, respectively. With the sand density increases to \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.90 g/cm\u003csup\u003e3\u003c/sup\u003e, the minimum cutterhead torque for natural sand and quartz sand increases rapidly to \u003cem\u003eT\u003c/em\u003e\u0026thinsp;=\u0026thinsp;10.53 N*m and \u003cem\u003eT\u003c/em\u003e\u0026thinsp;=\u0026thinsp;18.84 N*m, respectively. As the sand density increases to \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.00 g/cm\u003csup\u003e3\u003c/sup\u003e, the minimum cutterhead torque for natural sand and quartz sand increases slowly to \u003cem\u003eT\u003c/em\u003e\u0026thinsp;=\u0026thinsp;11.74 N*m and \u003cem\u003eT\u003c/em\u003e\u0026thinsp;=\u0026thinsp;20.37 N*m, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe minimum cutterhead torque varies with sand density due to the plowing resistance and friction resistance of ripper teeth. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, when the sand density increases from \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.70 g/cm\u003csup\u003e3\u003c/sup\u003e to \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.90 g/cm\u003csup\u003e3\u003c/sup\u003e, the optimal cutter height difference between ripper teeth and scrapers increases. The larger the optimal cutter height difference is, the greater the plowing depth will be. When plowing deeper and denser sand samples, both the plowing resistance and friction resistance of ripper teeth increase. Since the bulk densities of sand samples plowed by ripper teeth are similar, the cutting resistance and friction resistance of the scrapers are comparable. The total resistance of ripper teeth and scrapers increases rapidly. There is a positive correlation between driving torque and total resistance. Hence, the minimum cutterhead torque increases rapidly with increasing sand density. With the sand density increases from \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.90 g/cm\u003csup\u003e3\u003c/sup\u003e to \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.00 g/cm\u003csup\u003e3\u003c/sup\u003e, the optimal cutter height difference and plowing resistance remain relatively stable. Under the condition that only the friction resistance of ripper teeth increases due to plowing denser sand samples, the growth rate of the total resistance decreases. Consequently, the minimum cutterhead torque increases slowly with increasing sand density.\u003c/p\u003e \u003c/div\u003e"},{"header":"5 The influence of particle size on plowing effect","content":"\u003cp\u003eThe influence of particle size on the plowing effect has been studied using the WHU-SAT test. The average particle sizes of sand samples were \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.212, 0.319, 0.425, 0.710 mm (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e), corresponding to the fine sand, medium sand, medium sand, coarse sand, respectively. The preparation method for the sand samples followed the procedures outlined in Section \u003cspan refid=\"Sec6\" class=\"InternalRef\"\u003e3.1\u003c/span\u003e. The sand samples were placed in a cylindrical chamber with a water content of \u003cem\u003eω\u003c/em\u003e\u0026thinsp;=\u0026thinsp;15%. The modelled scrapers used in this test were made of 06Cr19Ni10. The variation in the plowing coefficient with cutter height difference for nature sand and quartz sand has been shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e. The results indicate that the plowing coefficient decreases first and then stabilizes with increasing cutter height difference, remaining unaffected by the average particle size.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e5.1 The variation in the optimal cutter height difference with average particle size\u003c/h2\u003e \u003cp\u003eThe variation in the optimal cutter height difference with the average particle size has been depicted. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003e, the results indicate that when the average particle size is \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.212 mm, the optimal cutter height difference is \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;22.5 mm. With the average particle size increases to \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.319 mm (or \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.425 mm), the optimal cutter height difference increases to \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;30.0 mm (or \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;37.5 mm), respectively. When the average particle size continues to increase to \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.710 mm, the optimal cutter height difference increases to \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;45.0 mm. The variation in the optimal cutter height difference with average particle size is linked to the occlusion effect of sand particles on the excavation surface. Generally, the larger the particle size of sand samples is, the greater the occlusion depth of surface particles will be. This implies that the plowing depth at which the sand samples on the excavation surface reach their loosest state will be greater. Hence, the optimal cutter height difference increases with increasing average particle size.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe optimal cutter height differences from the WHU-SAT tests have been compared with those of shield TBMs under similar average particle size conditions. As shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the results indicate that when the average particle size is \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.208 mm, the actual cutter height difference for the Yellow River Jiluo Road Tunnel is \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;20.0 mm. With the average particle size increases \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.447 mm, the actual cutter height difference for the Sanyang Road Yangtze River Tunnel increases to \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;40.0 mm (Huang et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Li and Bao, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). When the average particle size continues to increase to \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.854 mm, the actual cutter height difference for the Nanjing Yangtze River Tunnel increases to \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;50.0 mm (Huang, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Guo and Dai, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). The larger the average particle size is, the greater the actual cutter height difference will be. The variation in the actual cutter height difference of shield TBMs closely aligns with the optimal cutter height difference from the WHU-SAT test.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparisons between the optimal cutter height difference of WHU-SAT test and the actual cutter height difference under similar particle size conditions.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAverage particle size \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSand density\u003c/p\u003e \u003cp\u003e\u003cem\u003eρ\u003c/em\u003e (g/cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCutter height difference \u003cem\u003eΔH\u003c/em\u003e (mm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThe Yellow River Jiluo Road Tunnel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.208\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThe Sanyang Road Yangtze River Tunnel (Huang et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Li and Bao, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.447\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThe Nanjing Yangtze River Tunnel (Huang, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Guo and Dai, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2013\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.854\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e5.2 The variation in the stable plowing coefficient with average particle size\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e16\u003c/span\u003e, the variation in the stable plowing coefficient with the average particle size has been depicted. The results indicate that when the average particle size is \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.212 mm, the stable plowing coefficients for natural sand and quartz sand are \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.76 and \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.82, respectively. With the average particle size increases to \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.710 mm, the stable plowing coefficients for natural sand and quartz sand decrease to \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.61 and \u003cem\u003eξ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.62, respectively. The stable plowing coefficient for natural sand is lower than that for quartz sand. This is because the particle surfaces of natural sand are smoother than those of quartz sand, and nature sand is looser than quartz sand after being plowed by the ripper teeth.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe decrease of the stable plowing coefficient with increasing the average particle size is related to the occlusion and cohesion among sand particles. After being plowed by the ripper teeth, the sand particles rearrange into a loose state. For coarse particles, their contact mode in the loose state is mainly \u0026ldquo;point to point\u0026rdquo;. The occlusion among coarse particles are significantly weakened. When they are cut by the modelled scrapers, the decrement of wear extent is significant. For fine particles, they are bonded together by a water film on their surface (Chen and Ye, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Generally, the smaller the sand particles are, the stronger the cohesion effect will be (Li, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). When they are cut by the modelled scrapers, the decrement of wear extent is limited. As the average particle size increases from \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.212 mm to \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.710 mm, the proportion of coarse particles in sand sampels increases. Under the conditions of increased scraper wear, the stable plowing coefficient decreases.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e5.3 The variation in the minimum cutterhead torque with average particle size\u003c/h2\u003e \u003cp\u003eMonitoring results indicate that the cutterhead torque decreases first and then increases with increasing cutter height difference, which does not change with the increase of average particle size. When the cutter height difference is at its optimal level, the cutter head torque is minimized. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e17\u003c/span\u003e, the variation in the minimum cutterhead torque with average particle size has been depicted. When the average particle size is \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.212 mm, the minimum cutterhead torque for natural sand and quartz sand is \u003cem\u003eT\u003c/em\u003e\u0026thinsp;=\u0026thinsp;3.87 N*m and \u003cem\u003eT\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.03 N*m, respectively. As the average particle size increases to \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.710 mm, the minimum cutterhead torque for natural sand and quartz sand increases to \u003cem\u003eT\u003c/em\u003e\u0026thinsp;=\u0026thinsp;11.02 N*m and \u003cem\u003eT\u003c/em\u003e\u0026thinsp;=\u0026thinsp;21.34 N*m, respectively. The minimum cutterhead torque in nature sand is lower than that in quartz sand. This is due to the fact that the particle surfaces of nature sand are smoother than those of quartz sand. When they are cut by the cutterhead, natural sand exhibits lower occlusion and friction compared to quartz sand.\u003c/p\u003e \u003cp\u003eThe increase in the minimum cutterhead torque with increasing the average particle size is attributed to the plowing resistance and friction resistance. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003e, the optimal cutter height difference increases with increasing the average particle size. The greater the optimal cutter height difference is, the greater the plowing depth of ripper teeth will be. Under the conditions of plowing deeper sand samples, the plowing resistance and friction resistance of ripper teeth will be larger. Moreover, with the increase of the average particle size, the occlusion between sand particles will increase. When the coarser sand particles are cut by the modelled scrapers, the cutting resistance and frictional resistance will increase. Under the condition that the resistance of ripper teeth and scrapers increases, the minimum cutterhead torque increases with increasing the average particle size.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"6 Conclusions","content":"\u003cp\u003eIn the present study, the plowing effect of ripper teeth has been evaluated using the plowing coefficient. The influence of cutter height difference, sand density and particle size on the plowing coefficient has been studied using the WHU-SAT test. The plowing mechanism has been revealed by analyzing the loosening process of ripper teeth on the excavation face. The cutter height difference has been optimized for dense sandy ground tunnelling. The present study provides a reference for mitigating cutting tool wear and enhancing cutterhead tunnelling efficiency. From the present study, the following conclusions can be drawn:\u003c/p\u003e \u003cp\u003e(1) With the increase of cutter height difference, the plowing coefficient of the ripper teeth decreases first and then stabilizes, remaining unaffected by increases in sand density and average particle size. Since the denser and coarser sand samples exhibit a greater decrement in soil abrasivity after plowing, the stable plowing coefficient decreases with increasing the sand density and average particle size.\u003c/p\u003e\u003cp\u003e(2) When the plowing coefficient of the ripper teeth transitions from a reduced state to a stable state, the corresponding cutter height difference is considered as the optimal cutter height difference. There are differences in the optimal cutter height difference among different sand samples. It increases first and then stable with increasing sand density, and increases with increasing average particle size.\u003c/p\u003e\u003cp\u003e(3) With the increase of cutter height difference, the cutterhead torque decreases first and then increase, remaining unaffected by increases in sand density and average particle size. When the cutter height difference is optimal, the corresponding cutterhead torque is at its minimum. Since the plow depth and cutter resistance are greater when cutting denser and coarser sand samples, the minimum cutterhead torque increases with increasing sand density and average particle size.\u003c/p\u003e "},{"header":"Abbreviations","content":" \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cdiv class=\"SimplePara\"\u003eSAT\u0026trade;\u003c/div\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cdiv class=\"SimplePara\"\u003eSoil Abrasion Tester\u003c/div\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cdiv class=\"SimplePara\"\u003eLCPC\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cdiv class=\"SimplePara\"\u003eLaboratoire central des ponts et chauss\u0026eacute;es tester\u003c/div\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cdiv class=\"SimplePara\"\u003eDTWA\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cdiv class=\"SimplePara\"\u003eDas TU Wien Abrasimeter\u003c/div\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cdiv class=\"SimplePara\"\u003eSGAT\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cdiv class=\"SimplePara\"\u003eSoft Ground Abrasion Tester\u003c/div\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cdiv class=\"SimplePara\"\u003eRUB\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cdiv class=\"SimplePara\"\u003eRuhr-University Bochum Tester\u003c/div\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cdiv class=\"SimplePara\"\u003eCUGB\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cdiv class=\"SimplePara\"\u003eChina University of Geosciences (Beijing) Tester\u003c/div\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cdiv class=\"SimplePara\"\u003eBJTU\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cdiv class=\"SimplePara\"\u003eBeijing Jiaotong University Tester\u003c/div\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cdiv class=\"SimplePara\"\u003eWHU-SAT\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cdiv class=\"SimplePara\"\u003eSoil Abrasion Tester developed by Wuhan University\u003c/div\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cdiv class=\"SimplePara\"\u003eEPB-TBM\u003c/div\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cdiv class=\"SimplePara\"\u003eEarth Pressure Balance Tunnel Boring Machine\u003c/div\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003cbr/\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNone.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eShao-Hui Tang\u003c/strong\u003e contributed to investigation, methodology and writing-original draft. \u003cstrong\u003eQuan-Sheng Liu\u003c/strong\u003e contributed to project administration and resources. \u003cstrong\u003eQi Zhang\u003c/strong\u003e contributed to writing-review \u0026amp; editing, formal analysis and funding acquisition. \u003cstrong\u003eWei-Qiang Xie\u003c/strong\u003e contributed to conceptualization and validation. \u003cstrong\u003eWei Sun\u003c/strong\u003e contributed to visualization and data curation. \u003cstrong\u003eHao-Jie Wang\u003c/strong\u003e contributed to supervision and validation. \u003cstrong\u003eXin-Fang Li\u003c/strong\u003e contributed to software and visualization.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe support provided by National Natural Science Foundation\u0026nbsp;of China (Grant Nos. 52308415,\u0026nbsp;52108382,\u0026nbsp;52378409)\u0026nbsp;is gratefully acknowledged.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData will be made available on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of interest \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAlavi Gharahbagh E, Rostami J, Palomino AM (2011) New soil abrasion testing method for soft ground tunneling applications. 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China Architecture and Building Press, Beijing (in Chinese)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang JX, Yin ML, Jiang YS, Jiang H, Zhou LG, Sun ZY (2022b) Mechanical behavior of sandy gravel strata cut by wedge-shaped cutter on earth pressure balance shield. Tunn. Constr. 42(09):1501\u0026ndash;1513. (in Chinese)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang XP, Tang SH, Liu QS, Wang HJ, Li XF, Chen P, Liu H (2023) Key technology for the construction and inspection of long-distance underwater tunnel for 1000 kV gas-insulated transmission line. Bull. Eng. Geol. Environ 82(1), 7\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Ripper tooth, Plowing coefficient, Cutter height difference, Sand density, Particle size","lastPublishedDoi":"10.21203/rs.3.rs-6424309/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6424309/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWhen shield TBM tunnelling in dense sandy ground, the installation height of the ripper tooth is higher than that of the scraper. The ripper tooth plows the excavation surface, followed by the scraper cutting the loose sand. The plowing effect refers to the mitigation of scraper wear by the ripper tooth, which loosens the dense sand on the tunnel surface. Although it has been analyzed qualitatively over the past few decades, there is still a lack of reliable parameters for quantitative evaluation. The influence of cutter height difference, sand density and particle size on plowing effect is unclear. In the present study, the plowing coefficient has been proposed to quantify the plowing effect. The variation in plowing coefficient with cutter height difference, sand density and particle size has been studied using the newly developed WHU-SAT tester. The plowing mechanism of ripper tooth has been revealed based on excavation process analysis. The cutter height difference between ripper tooth and scraper has been optimized for dense sandy ground tunnelling. The results indicate that as cutter height difference increases, the loosening depth of ripper tooth on tunnel face increases. The density of sand samples cut by the scraper decreases first and then stabilizes, leading to a similar trend in the plowing coefficient. When the sand density is \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.7 g/cm\u003csup\u003e3\u003c/sup\u003e and and the average particle size is \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.425 mm, the optimal height difference between ripper tooth and scraper is \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;22.5 mm. As sand density increases, the loosing depth corresponding to the stable plowing coefficient increases first and then stabilizes, resulting in a similar pattern for the optimal height difference. When the sand density is \u003cem\u003eρ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.9 g/cm\u003csup\u003e3\u003c/sup\u003e, the optimal height difference reaches a maximum value \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;37.5 mm. As the average particle size increases, the loosing depth corresponding to the stable plowing coefficient increases, leading to an increase in the optimal height difference. When the average particle size increases to \u003cem\u003eD\u003c/em\u003e\u003csub\u003e50\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.710 mm, the optimal height difference increases to \u003cem\u003eΔH\u003c/em\u003e\u0026thinsp;=\u0026thinsp;45 mm. The present study provides a reference for optimizing cutter height difference and enhancing cutterhead adaptability in dense sandy ground tunnelling.\u003c/p\u003e","manuscriptTitle":"Experimental study on the plowing effect of ripper tooth and its influence on scraper wear during shield TBM tunneling in abrasive sandy ground","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-18 18:10:57","doi":"10.21203/rs.3.rs-6424309/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"b19d3f8c-be45-478e-9da1-4efafbac1abd","owner":[],"postedDate":"June 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-07-31T09:24:05+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-18 18:10:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6424309","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6424309","identity":"rs-6424309","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}