Soil Slaking under the effect of dispersants: characteristics and mechanism

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Dispersants are widely used to disintegrate clay adhering to metal surfaces, but their conditioning characteristics and working mechanisms remain elusive. This study investigates the effect of organic and inorganic dispersants on clay plasticity and slaking characteristics through Atterberg limit and slaking tests, complemented by Zeta potential and swelling tests to explore underlying mechanisms. The results demonstrate that increasing the content of inorganic and organic dispersants reduces soil plasticity and enhances the slaking rate during the rapid development period in pure water. Dispersion slaking occurs in soil blocks treated with inorganic dispersant in pure water, while soil blocks treated with organic dispersant primarily undergo surface slaking. A higher organic dispersant concentration significantly intensified the slaking rate. In contrast, inorganic dispersant solutions inhibit soil slaking. Inorganic dispersant solutions impede soil expansion and slaking due to reduced electrostatic repulsion and increasing difficulty in water infiltration. Conversely, organic dispersant solutions accelerate soil slaking by promoting soil expansion and solution infiltration, reducing surface tension, and increasing pore air pressure. The results may suggest injecting organic dispersant for removal of existing soil clogging in shield tunneling, but both inorganic and organic dispersants can serve to prevent the occurrence of soil clogging for shield tunnelling. Clay Slaking characteristics Organic dispersant Inorganic dispersant Atterberg limits Influence mechanism 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 Introduction When shield tunnelling through cohesive soils, clayey muck easily adheres to the metal surfaces such as the cutterhead and cutters, leading to shield clogging and a decrease in the cutting efficiency of the cutters(Wang et al. 2023 ). Therefore, it is necessary to consider muck conditioning to prevent shield clogging(Djeran-Maigre et al. 2018 ). This can be achieved by injecting dispersants into the muck before the cutterhead, in the excavation chamber and screw conveyor, and then mixing the conditioner with the muck through the rotation of the cutterhead and the stirring rods. This procedure effectively disintegrates and disperses the cohesive soils, enhancing their flowability and preventing the formation of mud cakes in the shield machine(Du et al. 2022 ; Fang et al. 2022 ). Additionally, when the shield is clogged, the dispersant is usually injected into the excavation face and soil chamber to soak the mud cakes, causing them to slake and separate from the metal surfaces of the cutterhead. This method has been adopted in tunnel projects such as the Wangjiang Road Cross-River Tunnel(Fu et al. 2021 ), the Yellow River Jiluo Road Tunnel in Jinan(Du et al. 2022 ), and Changchun Metro Line 2(Wan et al. 2021 ; Zhao et al. 2021 ). It is evident that dispersants play a crucial role in the effective dispersion and slaking of clay cake. Some scholars have researched the effects of dispersants in preventing and treating muck clogging for shield tunnelling. Wang et al.(2020), Liu et al.(2019), and Oliveira et al.(2019) have pointed out that dispersants can improve soil flowability and decrease its adhesive strength by reducing the liquid limit and consistency index of clay. The variation in Atterberg limits of clay conditioned can be observed to evaluate the effectiveness of dispersants in preventing shield clogging(Thewes and Hollmann 2016 ; Khabbazi Basmenj et al. 2017 ). Typical dispersants include anti-clogging polymers(Langmaack and Feng 2005 ; Langmaack and Lee 2016 ) and phosphate dispersants such as sodium hexametaphosphate(Wang et al. 2020 ; Fang et al. 2023 ). Sodium hexametaphosphate is an inorganic dispersant, while the anti-clay polymers (with organic compounds as the main active ingredient) are organic dispersants. Under the action of organic and inorganic dispersants, clay blocks may exhibit radically different slaking characteristics. Moriwaki and Mitchell(1997) conducted slaking tests on kaolin, illite, and montmorillonite and identified four modes of soil slaking, including swelling slaking, dispersion slaking, surface slaking, and body slaking. Swelling slaking is characterised by excessive expansion, leading to loose clay structure and slaking. Dispersion slaking is manifested as the dispersion of clay particles without macroscopic cracking. Surface slaking is displayed as the continuous falling of clay surface debris. Body slaking is manifested as the overall fracture of clay blocks. However, the slaking characteristics of clay under the influence of organic and inorganic dispersants are still unclear. Therefore, it is necessary to investigate the effects of different dispersants on the slaking characteristics and plasticity of clay and compare their various roles in treating muck clogging for shield tunnelling. Various forces affect the clay slaking, including electrostatic repulsion, expansion repulsion, pore air pressure, and mechanical disturbance(Bissonnais 1996 ; Große et al. 2015 ; Liao et al. 2016 ). These forces can disrupt the interparticle connections, leading to clay slaking. Organic and inorganic dispersants may exhibit distinct mechanisms in the clay slaking. Surfactants are the main components of organic dispersants. Liao et al.(2016), Letey(1975), and Monteiro et al.(2018) have pointed out that surfactants can promote clay swelling and reduce solution surface tension, leading to soil slaking. Inorganic dispersants typically exist as ions in solutions. Le Bissonnais(1996), Rengasamy et al.(2016), and Hu et al.(2018) have demonstrated that the total electrolyte concentration (TEC) in the solution and the concentration of exchangeable cations in the soil have an impact on soil dispersion. The lower the TEC in the solution and the higher the exchangeable sodium concentration in the soil, the more prone clay is to disperse and slake. Inorganic dispersants have the potential to affect clay dispersion and slaking by changing the TEC in the solution and the concentration of exchangeable cations in the soil. It is evident that organic and inorganic dispersants may operate through distinct mechanisms. Further study on the mechanisms of dispersants will enhance our comprehension of their role in mitigating muck clogging. This paper investigates the slaking characteristics of clay and the underlying microscopic mechanisms under the effect of organic and inorganic dispersants. The impact of these dispersants on the Atterberg limits is examined. Additionally, the distinct roles for organic and inorganic dispersants in muck clogging treatment are explored by studying the variations in Zeta potential and swelling characteristics. These laboratory experiments-based insights for selecting suitable dispersants in muck clogging treatment during shield tunnelling projects are summarised in detail. Experimental program Testing materials A mixed soil consisting of 10% montmorillonite and 90% kaolinite was selected as the tested soil. It has a liquid limit of 54.4%, a plastic limit of 27.5%, and a plasticity index of 26.9, classified as a high liquid limit clay (CH)(ASTM D2487-17). The mineral composition of the mixed soil is shown in Table 1 . Organic and inorganic dispersants were used to investigate the effects of different dispersant types on treating soil clogging. The inorganic dispersant used was sodium hexametaphosphate with analytical purity, while the organic dispersant was a commercial dispersant previously used in shield tunnelling (Liu et al. 2018 ; Du et al. 2022 ). The chemical composition analysis was conducted to identify the organic dispersant's main components, and the results are shown in Table 2 . The primary component of the organic dispersant is sodium alkane sulfonate, combined with dodecyl trimethyl ammonium chloride, polyethylene glycol (PEG500), and Lauryl Alkaline-8. Table 1 Mineral composition of the mixed soil Mineral name Chemical formula Mass percentage/% Kaolinite Al 2 (Si 2 O 5 )(OH) 4 75.33 Muscovite KAl 2.2 (Si 3 Al) 0.975 O 10 ((OH) 1.72 O 0.28 ) 12.6 Na-montmorillonite Na 0.3 (Al,Mg) 2 Si 4 O 10 (OH) 2 4.88 Soda feldspar NaAlSi 3 O 8 2.83 Quartz SiO 2 2.32 Ca-montmorillonite Ca 0.2 (Al,Mg) 2 Si 4 O 10 (OH) 2 1.41 Microcline (K 0.95 Na 0.05 )(AlSi 3 O 8 ) 0.55 Calcite CaCO 3 0.08 Table 2 Chemical components of the organic dispersant Component Category Mass percentage/% Dodecyl trimethyl ammonium chloride Cationic surfactant 1.5 Polyethylene glycol Nonionic surfactant 1.5 Lauryl Alkaline-8 Nonionic surfactant 0.5 Sodium alkane sulfonate Anionic surfactant 4.5 Water Solvent 92.0 Testing approach Atterberg limit tests Dispersants can reduce the liquid limit of clay to increase its flowability and decrease adhesion strength, thereby reducing the risk of muck clogging during shield tunnelling(Liu et al. 2018 ). Therefore, the Atterberg limit test was conducted to compare the effects of the organic and inorganic dispersants. Firstly, dispersants and pure water were mixed according to a certain dispersant content (the dispersant content was defined as the mass ratio of dispersant to dry clay) and water content, and then the conditioned soil was placed in a sealed chamber for 24 hours. The Atterberg limits were then determined using the fall cone. The testing conditions are listed in Table 3 . Table 3 The Atterberg limit testing conditions The reagent mixed with soil Dispersant content /% Inorganic dispersant 0.0, 0.5, 1.0, 2.0, 3.0, 5.0, 7.0 Organic dispersant Slaking tests Slaking tests are commonly used to assess the slaking characteristics of clays because they allow visualization of the slaking process of clay blocks and obtain the time-varying parameters of slaking (Moriwaki and Mitchell 1997 ; Du et al. 2022 ; Huang et al. 2022 ). As shown in Fig. 1 , the slaking apparatus mainly consists of an organic cylinder, a high-precision buoyancy scale (with an accuracy of 0.001g and a weighing range of 500g), and a mesh plate. The square mesh size is the main parameter determining whether the soil pieces will fall off after slaking. Preliminary tests have shown that the soil pieces were usually smaller than 5 mm after slaking. Thus, the square mesh size was set to 10 mm to prevent soil pieces from blocking the mesh(GB/T 50123 − 2019). The slaking percentage of the clay block can be obtained using Eq. ( 1 ), which represents the ratio of the volume of the slaked part (from the soil block) to that of the initial soil block(Große et al. 2015 ). $${A_t}=\frac{{{R_{\text{0}}} - {R_t}}}{{{R_{\text{0}}}-{R_{\text{z}}}}} \times 100\%$$ 1 where At is the slaking percentage (%) of the clay block at time t; R0 is the initial reading on the buoyancy scale when the soil block starts to slake; Rt is the buoyancy scale reading at time t; Rz is the buoyancy scale reading when the soil block is completely slaked. If the soil block is a polygon with corners, the soil in the corner will slake first, causing the soil block to become more circular(Wang et al. 2019 ). To reduce the influence of the shape changes during clay slaking, cylindrical soil blocks with a radius (R) of 25 mm and a height (H) of 35 mm were prepared for the slaking test. The consistency index of the tested soil was designed to be 0.5 in the tests (with a water content of 40.95%). Since the mud cake became compact under the thrust of the shield machine in practice, all clay specimens were fully compacted with a dry density of 1.347 g/cm3, a void ratio of 1.089, and a saturation of 100%. Each slaking test was conducted with the following main procedures: (a) To achieve a specified water or dispersant content, a certain amount of dry clay is mixed with water or dispersant and stirred thoroughly. The mixture is then sealed in a chamber for 24 hours, allowing uniform distribution of water or dispersant in the soil blocks. (b) The soil for each specimen was divided into four parts of equal mass. After each part was dumped into the compaction mould, the soil was compacted by dropping a 482.5 g hammer from a height of 26.5 cm 10 times. The top layer was roughened before adding the soil of the next layer to ensure a strong bond between adjacent layers. (c) Clean water or the prepared dispersant solution was dumped into a transparent cylinder to the predetermined water level. The soil block was placed in the center of the mesh plate. The mesh plate was hung under the buoyancy scale and quickly immersed in the solution, ensuring the soil block was positioned approximately 3 cm below the water level. Some photographs were taken at intervals of one minute or less to record readings of the buoyancy scale The slaking test conditions are shown in Table 4 , and each condition was tested three times. Table 4 The slaking test conditions The reagent mixed with soil Dispersant content /% Slaking solution Slaking solution concentration (%) Pure water / Inorganic dispersant 0, 2, 4, 6, 8 Pure water / Organic dispersant 0, 2, 4, 6, 8 Inorganic dispersant 0.0, 0.5, 1.0, 2.0, 3.0, 5.0, 7.0 Pure water / Organic dispersant 0.0, 0.5, 1.0, 2.0, 3.0, 5.0, 7.0 Pure water / Zeta potential tests The change in Zeta potential can quantify electrostatic repulsion between clay particles, and therefore be used to indicate the microscopic origin for the cohesion of clay. It is natural to use Zeta potential to examine the dispersion capacity of clay under the action of dispersants (Liu et al. 2018 ). Here, Zeta potential tests (Fig. 2 ) were carried out to explore the electrochemical mechanisms of dispersants. The ZetaProbe device based on the multifrequency electroacoustic measurement technique was used to measure the Zeta potential of clay. A certain amount of dispersant was thoroughly mixed with 22 g dry clay and 220 g deionised water for each test, and the mixture was placed to the ZetaProbe equipment to measure the Zeta potential. The solid-liquid ratio of the experiment is 1:10, with a rotation speed of 300 rpm. The other testing conditions are the same as the Atterberg limits test (see Table 3 ). Swelling tests The effects of organic and inorganic dispersants on the swelling characteristics of the mixed soil were determined to investigate the action mechanism of dispersants. Following the standard for geotechnical testing methods(GB/T 50123 − 2019), specimens were first prepared with a ring knife. Their water content and dry density were consistent with the blocks in the slaking tests. Subsequently, the filter paper and porous plate were arranged on the upper and lower surfaces of the specimens, respectively, and the specimens were placed in the swelling tester. After installing the cover plate and the dial indicators, pure water or dispersant solution was dumped to ensure the water level was 5 mm higher than the specimens. It is noted that two different dispersant solutions were prepared with a concentration of 6%, respectively for the sodium hexametaphosphate and the commercial dispersant. The dial indicator readings were recorded every minute. Analysis of test results Variations of atterberg limits under different dispersants Figure 3 shows variations of the Atterberg limits of the soil with the dispersant content. As the content of the inorganic and organic dispersant increased, the liquid limit of the mixed soil reduced, and this reduction rate decreased. Compared with the liquid limit, the plastic limit of the soil did not change significantly due to a poorer effect of dispersant in the clay state of lower free water content. Thus, the plasticity index, which is the difference between the liquid and plastic limits, showed a similar trend as the liquid limit. The experimental results indicated that both organic and inorganic dispersants decreased the soil plasticity, reducing the risk of clay clogging. Slaking characteristics of dispersant-treated soil blocks immersed in pure water Slaking process of the soil blocks As indicated in Atterberg limits tests, the soil plasticity was reduced under the addition of inorganic and organic dispersants. Thus, to further explore the effect of dispersant on the soil conditioning for treating muck clogging, the slaking characteristics of the blocks of soil mixed with dispersant were investigated when they were placed in pure water. As shown in Fig. 4 , when the soil blocks with 2% inorganic dispersant content were immersed in pure water, the solution quickly became turbid, indicating that the clay particles dispersed rapidly into the solution and the dispersion slaking became significant. However, surface slaking was observed for the soil blocks with a 2% organic dispersant content in pure water(Fig. 5 ), and regardless of whether inorganic or organic dispersants were mixed with soil, the soil slaking was accelerating. When mixed with other inorganic and organic dispersant, the soil blocks also showed similar slaking phenomena in pure water. Variation of equivalent slaking thickness During the slaking process, the volume and surface area of the soil block decreased, reducing the solution-soil interaction area. The clay slaking rate slows down as the solution-soil interaction area decreases. Eq. ( 2 ) defines the equivalent slaking thickness (dt) as the ratio of the slaking volume to its surface area for a better understanding of the slaking characteristics. The equivalent slaking thickness can eliminate the effect of surface area when evaluating slaking characteristics. Therefore, as shown in Fig. 6 , the ratio of the volume of the soil block without slaking to the original volume is equivalent to the unslaked percentage and this index is utilised to establish Eq. ( 3 ) by assuming a uniform slaking rate across all positions of the soil block, based on the equivalent slaking thickness. The slaking percentage At is then converted into the equivalent slaking thickness dt of the soil block, representing the cumulative decrease in size during the slaking process. $${d_t}=\frac{{{V_t}}}{{{S_t}}}$$ 2 where dt is the equivalent slaking thickness of the soil block at time t; Vt is the slaking volume of the soil block at time t; St is the surface area of the soil block at time t. $$\frac{{(H - 2 \times {d_t}) \times {{(R - {d_t})}^2} \times \pi }}{{H \times {R^2} \times \pi }}=1 - {A_t}$$ 3 where At is the slaking percentage at time t; H is the initial soil block height, with a value of 35 mm in this study; R is the original radius of the soil block, with a value of 25 mm in this study. Figure 7 shows the variation of equivalent slaking thickness of the soil blocks with inorganic dispersant content when placed in pure water. Due to the dense data points recorded, a continuous smooth curve was plotted. The slaking process of the soil block without dispersant added (dispersant content = 0.0%) can be generally divided into the initial stable and rapid development periods, as shown in Fig. 8 . The water infiltrated the clay's pores during the initial stable period, weakening the interparticle bonding forces. However, it can be observed that the initial stable period of the mixed soil completely disappeared under the action of inorganic dispersant in the soil. This is because the soil mixed with inorganic dispersant immediately underwent dispersion slaking upon immersion in pure water (see Fig. 4 ). In Fig. 7 , as the content of inorganic dispersant increased, the slaking rate of the rapid development period gradually increased and reached its maximum when the dispersant content was 2%. With higher dispersant content, the slaking rate during the rapid development period almost remained constant. Similar variations of equivalent slaking thickness were found with organic dispersant content in the soil blocks when immersed in pure water. As the content of organic dispersant increased, the slaking rate of the rapid development period gradually increased. However, it did not reach its maximum even when the dispersant content was as high as 7%. Thus, it is indicated that both inorganic and organic dispersants can be injected into the shield muck to facilitate the dispersion of clay blocks and to prevent soil clogging during shield tunnelling. However, the prerequisite is that dispersants are sufficiently mixed with the clayed muck. Slaking characteristics of soil blocks without dispersant when placed in dispersant solution Slaking process of the soil blocks When the clayey muck is not properly conditioned during shield tunnelling, muck clogging easily happens. To treat the muck clogging, dispersants are commonly injected into the excavation chamber to remove the soil clogging on the cutterhead and cutters. Thus, the slaking characteristics of the soil blocks without dispersants were investigated when they were present in dispersant solutions. Figure 10 shows the slaking process of the soil block when placed in a 6% concentration organic dispersant solution. It is evident that among the four slaking modes described by Moriwaki and Mitchell(1997), namely swelling slaking, dispersion slaking, surface slaking, and body slaking, the mixed soil mainly underwent surface slaking, with the surface debris of the soil block continuously peeled off, although it exhibited slight dispersion slaking since the solution became slightly turbid. Similar slaking phenomena were also observed under the actions of other concentration organic dispersant solutions. However, when the soil blocks were placed in the inorganic dispersant solution, no slaking was observed even as long as 10 hours, indicating that the inorganic dispersant ions in the solution inhibited the soil slaking. Therefore, no relevant photos and curves for the soil slaking were obtained for those cases. Variation of equivalent slaking thickness Figure 11 shows the variation of equivalent slaking thickness of the soil blocks in organic dispersant solution with different concentrations. The change rate in the equivalent slaking thickness gradually increased until it reached the maximum, which marks the transition into the rapid development period. Afterwards, the change rate in the equivalent slaking thickness of the clay remained relatively constant. Furthermore, due to an initial height of 35 mm for the soil block, soil block slaking was completed when the equivalent slaking thickness d equalling 17.5 mm. Additionally, when the size of the soil block was smaller than the mesh aperture, the overall fall of the soil block from the mesh plate caused a sudden change at the final moment of the slaking curve, manifesting as the vertical part at the end of the curve for each test. Furthermore, with an increase in organic dispersant concentration, the initial stable period of the mixed soil was significantly shortened, the slaking rate during the rapid development period gradually increased, and the total slaking time decreased. The findings suggest that the injection of organic dispersants can effectively alleviate soil clogging on the shield cutterhead and cutters during shield tunnelling. On the other hand, the use of inorganic dispersants does not provide significant assistance in this regard. Mechanisms of clay slaking The Zeta potential of the soil under the influence of different dispersants was determined to investigate the electrochemical mechanism of dispersants. Figure 12 shows the variation of the Zeta potential of the soil with dispersant content. With an increase in the inorganic dispersant content, the absolute value of the Zeta potential increased, but the increasing rate reduced gradually. After the content exceeds 2%, the Zeta potential almost remained constant. According to the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, the maximum repulsive energy between clay particles increases with increasing absolute value of the Zeta potential, weakening particle connections(Luckham and Rossi 1999 ). Therefore, when the inorganic dispersant content increases, the dispersibility of the soil particles is enhanced, and the soil plasticity is reduced. However, the Zeta potential did not change notably under the effect of organic dispersants, indicating that organic dispersant has little impact on the dispersibility of soil particles. Thus, the change in clay's dispersibility is not the reason for the decrease in soil plasticity under the influence of organic dispersants. To explore the reason why the soil plasticity decreased under the effect of the organic dispersant, swelling tests were conducted, as stated previously. Figure 13 shows the effect of organic and inorganic dispersants on the soil's swelling capacity (Sc). Compared with pure water, the inorganic dispersant solution inhibited the swelling of the mixed soil. In contrast, the organic dispersant solution promoted expansion. Thus, the soil structure was loosened under organic dispersant, reducing its shear strength and plasticity. The clay slaking depends on the relationship between the connecting and repulsive forces between particles. Assuming that the connecting force between clay particles remains constant, the solution infiltrates into the clay pores, and subsequently, the electrostatic repulsion, expansion (hydration) repulsion, and pore air pressure between particles continue to develop under the interaction between water and soil (Große et al. 2015 ; Hu et al. 2018 ). Eventually, the repulsion between particles surpasses the connecting forces, leading to the clay slaking. However, liquid infiltration into the soil blocks is a prerequisite for initiating the slaking under the dispersant solution as shown in Fig. 14 . The electrostatic repulsion between particles is not affected by organic dispersants (Zeta potential remains unchanged), but the organic dispersant promotes the expansion of the soil. Furthermore, the presence of surfactants in organic dispersants reduces the solution's surface tension, as reported in previous studies (Letey 1975 ; Monteiro et al. 2018 ).. This decrease in surface tension facilitates the rapid infiltration of the solution into the clay through its pores, consequently causing an increase in pore air pressure. As a result, the slaking of clay was accelerated when organic dispersants were employed in the previous tests. However, the inorganic dispersant in the soil and solution have different effects on the dispersion and slaking of the soils as shown in Fig. 15 . With an increase in the inorganic dispersant content, the absolute value of the mixed soil's Zeta potential increases, leading to enhanced soil dispersion. Consequently, the dispersion slaking becomes more significant, and the dispersion of soils destroys the clay structure and promotes soil slaking. As shown in Fig. 13 , the swelling of clay was limited when it was immersed in inorganic dispersant. Meanwhile, the total electrolyte concentration in the solution increases with the inorganic dispersant solution concentration, resulting in a decrease in the electric-double-layer thickness on the surface of clay particles and a reduction in the electrostatic repulsion between particles(Bissonnais 1996 ). Under the influence of osmotic pressure, water molecules in the solution are more difficult to infiltrate into the clay, thus inhibiting the solution infiltration and further suppressing the soil dispersion and slaking. Conclusions This study investigates the effect of dispersants on slaking characteristics of the clayey soil through Atterberg limits tests and slaking tests, and explores the mechanisms of dispersants through the Zeta potential and swelling characteristics. The main conclusions are drawn as follows: (1)As the content of inorganic and organic dispersants in the soil increased, the soil plasticity decreased, indicating that both organic and inorganic dispersants can enhance the dispersity of the clay. (2) Upon the inclusion of inorganic and organic dispersants in the preparation of the soil blocks, the slaking process in pure water was accelerated, and the initial stable period was eliminated. As the content of both inorganic and organic dispersants increased, the slaking rate during the rapid development period gradually intensified. However, the slaking rate reached its maximum at a 2% inorganic dispersant content and remained constant at higher concentrations. Consequently, both inorganic and organic dispersants can prevent soil clogging during shield tunnelling, provided that they are thoroughly mixed with the clayey muck. (3) Increasing the concentration of organic dispersant significantly reduced the initial stable period and increased the slaking rate during the rapid development period. Conversely, it was found that the inorganic dispersions in the solution inhibited the soil slaking. Thus, organic dispersants are effective in removing soil clogging during shield tunnelling, while inorganic dispersants are not beneficial for this purpose. (4) With an increase in the inorganic dispersant content, the absolute value of the Zeta potential increased, and clay plasticity reduced. The inorganic dispersant solution inhibited soil expansion by reducing electrostatic repulsion and impeding water infiltration due to osmotic pressure. Conversely, the Zeta potential remained unchanged with organic dispersant, but it promoted expansion and reduced the plasticity. Moreover, surfactants in the organic dispersants decreased solution surface tension, facilitating rapid infiltration through clay pores and increasing pore air pressure, accelerating soil slaking. Declarations Conflict 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. Funding This research is financially supported by the National Natural Science Foundation of China (No. 51778637, 52022112), the China Postdoctoral Science Foundation (No. 2022M723536) and the Fundamental Research Funds for the Central Universities of the Central South University (No. 2022ZZTS0689) Author Contribution SW: conceptualization, writing —original draft, methodology. HZ: lab experiments, investigation, methodology, writing—review and editing.PL: supervision, writing (review and editing), methodology. 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Dispersive Clays, Related Piping, and Erosion in Geotechnical Projects 623:287–302. https://doi.org/10.1520/stp26994s Oliveira DGG de, Thewes M, Diederichs MS (2019) Clogging and flow assessment of cohesive soils for EPB tunnelling: Proposed laboratory tests for soil characterisation. Tunnelling Underground Space Technol 94:103110. https://doi.org/10.1016/j.tust.2019.103110 Rengasamy P, Tavakkoli E, McDonald GK (2016) Exchangeable cations and clay dispersion: net dispersive charge, a new concept for dispersive soil: Net dispersive charge in soil. Eur J Soil Sci 67:659–665. https://doi.org/10.1111/ejss.12369 Thewes M, Hollmann F (2016) Assessment of clay soils and clay-rich rock for clogging of TBMs. Tunnelling Underground Space Technol 57:122–128. https://doi.org/10.1016/j.tust.2016.01.010 Wan Z, Li S, Yuan C, et al (2021) Soil Conditioning for EPB Shield Tunneling in Silty Clay and Weathered Mudstone. Int J Geomech 21:06021020. https://doi.org/10.1061/(asce)gm.1943-5622.0002119 Wang J, Gu T, Zhang M, et al (2019) Experimental study of loess disintegration characteristics. Earth Surf Processes Landf 44:1317–1329. https://doi.org/10/ghmbw3 Wang S, Liu P, Hu Q, Zhong J (2020) Effect of dispersant on the tangential adhesion strength between clay and metal for EPB shield tunnelling. Tunnelling Underground Space Technol 95:103144. https://doi.org/10.1016/j.tust.2019.103144 Wang S, Zhou Z, Liu P, et al (2023) On the critical particle size of soil with clogging potential in shield tunneling. Journal of Rock Mechanics and Geotechnical Engineering 15:477–485. https://doi.org/10.1016/j.jrmge.2022.05.010 Zhao S, Li S, Wan Z, et al (2021) Effects of anti-clay agents on bubble size distribution and stability of aqueous foam under pressure for earth pressure balance shield tunneling. Colloids Interface Sci Commun 42:100424. https://doi.org/10.1016/j.colcom.2021.100424 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 17 Jun, 2024 Read the published version in Environmental Earth Sciences → Version 1 posted Editorial decision: Revision requested 17 Feb, 2024 Reviews received at journal 16 Feb, 2024 Reviewers agreed at journal 15 Jan, 2024 Reviewers invited by journal 15 Jan, 2024 Submission checks completed at journal 29 Dec, 2023 Editor assigned by journal 29 Dec, 2023 First submitted to journal 22 Dec, 2023 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-3792474","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":264228000,"identity":"c01dd48e-0a53-4eef-8b9f-89cff9787d50","order_by":0,"name":"Shuying Wang","email":"","orcid":"","institution":"Central South University","correspondingAuthor":false,"prefix":"","firstName":"Shuying","middleName":"","lastName":"Wang","suffix":""},{"id":264228001,"identity":"3e17d0de-eff9-4ca7-a128-a5af78ea2f56","order_by":1,"name":"Hanbiao Zhu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5klEQVRIiWNgGAWjYDACCQY2IHmAh4GB+QBE5ADxWtgSSNMCxDwGxGmRn91j9uDnjjsy/O09Hz/+bGOQ47uRwPi5AI8WxjlnzA17zzzjkThzdrM0bxuDseSNBGbpGXi0MEvkmEnwth3mYbiRu42ZsY0hccONBDZmHjxa2IBaJP8CtcjfyHnGCHRYPUEtPEAt0iBbDG7ksDEAHZZgQEiLhERambRs2zMewzPHjKV5zkkYzjzzsFkanxb5GcnbJN+23bGXO9788OOPMht5vuPJBz/j04JhKxAzNpCgYRSMglEwCkYBNgAAfCBIso/2DqwAAAAASUVORK5CYII=","orcid":"","institution":"Central South University","correspondingAuthor":true,"prefix":"","firstName":"Hanbiao","middleName":"","lastName":"Zhu","suffix":""},{"id":264228002,"identity":"b9986a19-1a46-4ee8-bdbd-0ea1b1ac2620","order_by":2,"name":"Pengfei Liu","email":"","orcid":"","institution":"CCCC Second Harbor Engineering Company Ltd","correspondingAuthor":false,"prefix":"","firstName":"Pengfei","middleName":"","lastName":"Liu","suffix":""},{"id":264228003,"identity":"305767f3-4db7-4f89-9fbe-4acf4029cb78","order_by":3,"name":"Tongming Qu","email":"","orcid":"","institution":"Hong Kong University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Tongming","middleName":"","lastName":"Qu","suffix":""}],"badges":[],"createdAt":"2023-12-22 14:15:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3792474/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3792474/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s12665-024-11708-w","type":"published","date":"2024-06-17T15:16:59+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":49028781,"identity":"c3bf6e2f-94b1-4a06-b1a9-fb11d6c08138","added_by":"auto","created_at":"2024-01-01 15:37:15","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":277282,"visible":true,"origin":"","legend":"\u003cp\u003eThe slaking apparatus\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/a190ffba1141fc4bcbda7396.png"},{"id":49028662,"identity":"a837257d-0854-4777-9198-ed14c9bc1478","added_by":"auto","created_at":"2024-01-01 15:29:15","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":753627,"visible":true,"origin":"","legend":"\u003cp\u003eThe ZetaProbe device used in this study\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/717fb5cf54243b47770085bb.png"},{"id":49028631,"identity":"5e9ddfd4-9fb5-40c0-af30-ffb122ad303c","added_by":"auto","created_at":"2024-01-01 15:21:15","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":34516,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of the Atterberg limits under different dispersants (PL - plastic limit, LL - liquid limit, PI - plasticity index, ID - Inorganic dispersant, OD - Organic dispersant)\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/afaeb49cd4e6b39b566f0c79.png"},{"id":49028644,"identity":"7b471406-7408-4adf-af19-6c10bde85e15","added_by":"auto","created_at":"2024-01-01 15:21:15","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":769473,"visible":true,"origin":"","legend":"\u003cp\u003eSlaking process of the soil block with 2% inorganic dispersant content when placed in pure water\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/6924f32c3a6b67644583120a.png"},{"id":49028784,"identity":"7b91595c-ed89-4579-8180-0d923ca9e45a","added_by":"auto","created_at":"2024-01-01 15:37:15","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":863152,"visible":true,"origin":"","legend":"\u003cp\u003eSlaking process of the soil block with 2% organic dispersant content when placed in pure water\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/c7acf66ed29d279828722111.png"},{"id":49028632,"identity":"d66250e8-c4da-46c7-bb04-c61f2573a61e","added_by":"auto","created_at":"2024-01-01 15:21:15","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":120049,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the axial cross-section of soil blocks\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/76cfc3e8dcd6e83b6abb77ea.png"},{"id":49028667,"identity":"603d0ded-9110-42ef-adba-e42352f22451","added_by":"auto","created_at":"2024-01-01 15:29:15","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":53772,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of the equivalent slaking thickness of the soil blocks with different inorganic dispersant contents\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/028d6a15104879968457be73.png"},{"id":49028782,"identity":"69149ab0-377f-4791-b3b1-64029da4eb46","added_by":"auto","created_at":"2024-01-01 15:37:15","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":21896,"visible":true,"origin":"","legend":"\u003cp\u003eFeatured variation curve of equivalent slaking thickness of soil block\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/35c195746c7d7e721f50501d.png"},{"id":49028638,"identity":"bae10778-ac2d-4fc1-896d-edb348ef9b71","added_by":"auto","created_at":"2024-01-01 15:21:15","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":53894,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of equivalent slaking thickness of the soil blocks with different organic dispersant contents when placed in pure water\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/297670022fe60ae348b14be6.png"},{"id":49028670,"identity":"615f5362-0fcb-4012-92d2-172900be6522","added_by":"auto","created_at":"2024-01-01 15:29:15","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":1227412,"visible":true,"origin":"","legend":"\u003cp\u003eSlaking process of the soil block when placed in the organic dispersant solution\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/f5c892e5aff6357826dd2b39.png"},{"id":49028664,"identity":"e465357b-dec5-4086-83b6-8b302ada023c","added_by":"auto","created_at":"2024-01-01 15:29:15","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":36175,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of the equivalent slaking thickness of the soil blocks when placed in organic dispersant solution with different concentrations\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/347fc144894cfd3eb38329ba.png"},{"id":49028635,"identity":"18fdb35a-5716-47e6-9f17-e2a1fdc62994","added_by":"auto","created_at":"2024-01-01 15:21:15","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":21135,"visible":true,"origin":"","legend":"\u003cp\u003eInfluence of organic and inorganic dispersants on the zeta potential of the soil\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/b1cb0b06a8fdf06aadec689e.png"},{"id":49028924,"identity":"42c27cc5-c518-4452-be2d-75e93833342d","added_by":"auto","created_at":"2024-01-01 15:45:15","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":26471,"visible":true,"origin":"","legend":"\u003cp\u003eThe swelling capacity of the soil in organic and inorganic dispersant solutions\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/f17e41cbb6f3f81da495e753.png"},{"id":49028642,"identity":"ca94011c-d1d5-427c-b67a-35a7dd8f92a0","added_by":"auto","created_at":"2024-01-01 15:21:15","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":57411,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of organic dispersants action mechanism\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/bc8e6a342d9aa82fab3e09f8.png"},{"id":49028645,"identity":"6242c42a-222c-4f35-b543-3c180c7b67b1","added_by":"auto","created_at":"2024-01-01 15:21:15","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":63498,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of inorganic dispersants action mechanism\u003c/p\u003e","description":"","filename":"15.png","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/45c1101f50769f99bb8ab6b9.png"},{"id":58823070,"identity":"30688caa-ddef-4035-b2a8-8f694b88c886","added_by":"auto","created_at":"2024-06-21 16:52:06","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4710086,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3792474/v1/0421ea45-5b07-4dbc-88ae-454106ed2026.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Soil Slaking under the effect of dispersants: characteristics and mechanism","fulltext":[{"header":"Introduction","content":"\u003cp\u003eWhen shield tunnelling through cohesive soils, clayey muck easily adheres to the metal surfaces such as the cutterhead and cutters, leading to shield clogging and a decrease in the cutting efficiency of the cutters(Wang et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Therefore, it is necessary to consider muck conditioning to prevent shield clogging(Djeran-Maigre et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). This can be achieved by injecting dispersants into the muck before the cutterhead, in the excavation chamber and screw conveyor, and then mixing the conditioner with the muck through the rotation of the cutterhead and the stirring rods. This procedure effectively disintegrates and disperses the cohesive soils, enhancing their flowability and preventing the formation of mud cakes in the shield machine(Du et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Fang et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Additionally, when the shield is clogged, the dispersant is usually injected into the excavation face and soil chamber to soak the mud cakes, causing them to slake and separate from the metal surfaces of the cutterhead. This method has been adopted in tunnel projects such as the Wangjiang Road Cross-River Tunnel(Fu et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), the Yellow River Jiluo Road Tunnel in Jinan(Du et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), and Changchun Metro Line 2(Wan et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Zhao et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). It is evident that dispersants play a crucial role in the effective dispersion and slaking of clay cake.\u003c/p\u003e \u003cp\u003eSome scholars have researched the effects of dispersants in preventing and treating muck clogging for shield tunnelling. Wang et al.(2020), Liu et al.(2019), and Oliveira et al.(2019) have pointed out that dispersants can improve soil flowability and decrease its adhesive strength by reducing the liquid limit and consistency index of clay. The variation in Atterberg limits of clay conditioned can be observed to evaluate the effectiveness of dispersants in preventing shield clogging(Thewes and Hollmann \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Khabbazi Basmenj et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Typical dispersants include anti-clogging polymers(Langmaack and Feng \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Langmaack and Lee \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) and phosphate dispersants such as sodium hexametaphosphate(Wang et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Fang et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Sodium hexametaphosphate is an inorganic dispersant, while the anti-clay polymers (with organic compounds as the main active ingredient) are organic dispersants. Under the action of organic and inorganic dispersants, clay blocks may exhibit radically different slaking characteristics. Moriwaki and Mitchell(1997) conducted slaking tests on kaolin, illite, and montmorillonite and identified four modes of soil slaking, including swelling slaking, dispersion slaking, surface slaking, and body slaking. Swelling slaking is characterised by excessive expansion, leading to loose clay structure and slaking. Dispersion slaking is manifested as the dispersion of clay particles without macroscopic cracking. Surface slaking is displayed as the continuous falling of clay surface debris. Body slaking is manifested as the overall fracture of clay blocks. However, the slaking characteristics of clay under the influence of organic and inorganic dispersants are still unclear. Therefore, it is necessary to investigate the effects of different dispersants on the slaking characteristics and plasticity of clay and compare their various roles in treating muck clogging for shield tunnelling.\u003c/p\u003e \u003cp\u003eVarious forces affect the clay slaking, including electrostatic repulsion, expansion repulsion, pore air pressure, and mechanical disturbance(Bissonnais \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1996\u003c/span\u003e; Gro\u0026szlig;e et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Liao et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). These forces can disrupt the interparticle connections, leading to clay slaking. Organic and inorganic dispersants may exhibit distinct mechanisms in the clay slaking. Surfactants are the main components of organic dispersants. Liao et al.(2016), Letey(1975), and Monteiro et al.(2018) have pointed out that surfactants can promote clay swelling and reduce solution surface tension, leading to soil slaking. Inorganic dispersants typically exist as ions in solutions. Le Bissonnais(1996), Rengasamy et al.(2016), and Hu et al.(2018) have demonstrated that the total electrolyte concentration (TEC) in the solution and the concentration of exchangeable cations in the soil have an impact on soil dispersion. The lower the TEC in the solution and the higher the exchangeable sodium concentration in the soil, the more prone clay is to disperse and slake. Inorganic dispersants have the potential to affect clay dispersion and slaking by changing the TEC in the solution and the concentration of exchangeable cations in the soil. It is evident that organic and inorganic dispersants may operate through distinct mechanisms. Further study on the mechanisms of dispersants will enhance our comprehension of their role in mitigating muck clogging.\u003c/p\u003e \u003cp\u003eThis paper investigates the slaking characteristics of clay and the underlying microscopic mechanisms under the effect of organic and inorganic dispersants. The impact of these dispersants on the Atterberg limits is examined. Additionally, the distinct roles for organic and inorganic dispersants in muck clogging treatment are explored by studying the variations in Zeta potential and swelling characteristics. These laboratory experiments-based insights for selecting suitable dispersants in muck clogging treatment during shield tunnelling projects are summarised in detail.\u003c/p\u003e"},{"header":"Experimental program","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eTesting materials\u003c/h2\u003e \u003cp\u003eA mixed soil consisting of 10% montmorillonite and 90% kaolinite was selected as the tested soil. It has a liquid limit of 54.4%, a plastic limit of 27.5%, and a plasticity index of 26.9, classified as a high liquid limit clay (CH)(ASTM D2487-17). The mineral composition of the mixed soil is shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Organic and inorganic dispersants were used to investigate the effects of different dispersant types on treating soil clogging. The inorganic dispersant used was sodium hexametaphosphate with analytical purity, while the organic dispersant was a commercial dispersant previously used in shield tunnelling (Liu et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Du et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The chemical composition analysis was conducted to identify the organic dispersant's main components, and the results are shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The primary component of the organic dispersant is sodium alkane sulfonate, combined with dodecyl trimethyl ammonium chloride, polyethylene glycol (PEG500), and Lauryl Alkaline-8.\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\u003eMineral composition of the mixed soil\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\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 \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMineral name\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eChemical formula\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMass percentage/%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKaolinite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003e(Si\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e)(OH)\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e75.33\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMuscovite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eKAl\u003csub\u003e2.2\u003c/sub\u003e(Si\u003csub\u003e3\u003c/sub\u003eAl)\u003csub\u003e0.975\u003c/sub\u003eO\u003csub\u003e10\u003c/sub\u003e((OH)\u003csub\u003e1.72\u003c/sub\u003eO\u003csub\u003e0.28\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e12.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNa-montmorillonite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNa\u003csub\u003e0.3\u003c/sub\u003e(Al,Mg)\u003csub\u003e2\u003c/sub\u003eSi\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e10\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.88\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSoda feldspar\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNaAlSi\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.83\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQuartz\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.32\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCa-montmorillonite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCa\u003csub\u003e0.2\u003c/sub\u003e(Al,Mg)\u003csub\u003e2\u003c/sub\u003eSi\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e10\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.41\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMicrocline\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(K\u003csub\u003e0.95\u003c/sub\u003eNa\u003csub\u003e0.05\u003c/sub\u003e)(AlSi\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCalcite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCaCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.08\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \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\u003eChemical components of the organic dispersant\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\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 \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComponent\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCategory\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMass percentage/%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDodecyl trimethyl ammonium chloride\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCationic surfactant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePolyethylene glycol\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNonionic surfactant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLauryl Alkaline-8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNonionic surfactant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSodium alkane sulfonate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAnionic surfactant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWater\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolvent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e92.0\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=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eTesting approach\u003c/h2\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003eAtterberg limit tests\u003c/h2\u003e \u003cp\u003eDispersants can reduce the liquid limit of clay to increase its flowability and decrease adhesion strength, thereby reducing the risk of muck clogging during shield tunnelling(Liu et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Therefore, the Atterberg limit test was conducted to compare the effects of the organic and inorganic dispersants. Firstly, dispersants and pure water were mixed according to a certain dispersant content (the dispersant content was defined as the mass ratio of dispersant to dry clay) and water content, and then the conditioned soil was placed in a sealed chamber for 24 hours. The Atterberg limits were then determined using the fall cone. The testing conditions are listed in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe Atterberg limit testing conditions\u003c/p\u003e \u003c/div\u003e \u003c/caption\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 \u003cp\u003eThe reagent mixed with soil\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDispersant content /%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInorganic dispersant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e0.0, 0.5, 1.0, 2.0, 3.0, 5.0, 7.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOrganic dispersant\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 \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eSlaking tests\u003c/h2\u003e \u003cp\u003eSlaking tests are commonly used to assess the slaking characteristics of clays because they allow visualization of the slaking process of clay blocks and obtain the time-varying parameters of slaking (Moriwaki and Mitchell \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Du et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Huang et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the slaking apparatus mainly consists of an organic cylinder, a high-precision buoyancy scale (with an accuracy of 0.001g and a weighing range of 500g), and a mesh plate. The square mesh size is the main parameter determining whether the soil pieces will fall off after slaking. Preliminary tests have shown that the soil pieces were usually smaller than 5 mm after slaking. Thus, the square mesh size was set to 10 mm to prevent soil pieces from blocking the mesh(GB/T 50123\u0026thinsp;\u0026minus;\u0026thinsp;2019). The slaking percentage of the clay block can be obtained using Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), which represents the ratio of the volume of the slaked part (from the soil block) to that of the initial soil block(Gro\u0026szlig;e et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$${A_t}=\\frac{{{R_{\\text{0}}} - {R_t}}}{{{R_{\\text{0}}}-{R_{\\text{z}}}}} \\times 100\\%$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere At is the slaking percentage (%) of the clay block at time t; R0 is the initial reading on the buoyancy scale when the soil block starts to slake; Rt is the buoyancy scale reading at time t; Rz is the buoyancy scale reading when the soil block is completely slaked.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIf the soil block is a polygon with corners, the soil in the corner will slake first, causing the soil block to become more circular(Wang et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). To reduce the influence of the shape changes during clay slaking, cylindrical soil blocks with a radius (R) of 25 mm and a height (H) of 35 mm were prepared for the slaking test. The consistency index of the tested soil was designed to be 0.5 in the tests (with a water content of 40.95%). Since the mud cake became compact under the thrust of the shield machine in practice, all clay specimens were fully compacted with a dry density of 1.347 g/cm3, a void ratio of 1.089, and a saturation of 100%. Each slaking test was conducted with the following main procedures:\u003c/p\u003e\u003cp\u003e(a) To achieve a specified water or dispersant content, a certain amount of dry clay is mixed with water or dispersant and stirred thoroughly. The mixture is then sealed in a chamber for 24 hours, allowing uniform distribution of water or dispersant in the soil blocks.\u003c/p\u003e\u003cp\u003e(b) The soil for each specimen was divided into four parts of equal mass. After each part was dumped into the compaction mould, the soil was compacted by dropping a 482.5 g hammer from a height of 26.5 cm 10 times. The top layer was roughened before adding the soil of the next layer to ensure a strong bond between adjacent layers.\u003c/p\u003e \u003cp\u003e(c) Clean water or the prepared dispersant solution was dumped into a transparent cylinder to the predetermined water level. The soil block was placed in the center of the mesh plate. The mesh plate was hung under the buoyancy scale and quickly immersed in the solution, ensuring the soil block was positioned approximately 3 cm below the water level. Some photographs were taken at intervals of one minute or less to record readings of the buoyancy scale\u003c/p\u003e \u003cp\u003eThe slaking test conditions are shown in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, and each condition was tested three times.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe slaking test 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=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThe reagent mixed with soil\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDispersant content /%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSlaking solution\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSlaking solution concentration (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePure water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eInorganic dispersant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0, 2, 4, 6, 8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePure water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOrganic dispersant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0, 2, 4, 6, 8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInorganic dispersant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.0, 0.5, 1.0, 2.0, 3.0, 5.0, 7.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePure water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOrganic dispersant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.0, 0.5, 1.0, 2.0, 3.0, 5.0, 7.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePure water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e/\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=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eZeta potential tests\u003c/h2\u003e \u003cp\u003eThe change in Zeta potential can quantify electrostatic repulsion between clay particles, and therefore be used to indicate the microscopic origin for the cohesion of clay. It is natural to use Zeta potential to examine the dispersion capacity of clay under the action of dispersants (Liu et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Here, Zeta potential tests (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) were carried out to explore the electrochemical mechanisms of dispersants. The ZetaProbe device based on the multifrequency electroacoustic measurement technique was used to measure the Zeta potential of clay. A certain amount of dispersant was thoroughly mixed with 22 g dry clay and 220 g deionised water for each test, and the mixture was placed to the ZetaProbe equipment to measure the Zeta potential. The solid-liquid ratio of the experiment is 1:10, with a rotation speed of 300 rpm. The other testing conditions are the same as the Atterberg limits test (see Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eSwelling tests\u003c/h2\u003e \u003cp\u003eThe effects of organic and inorganic dispersants on the swelling characteristics of the mixed soil were determined to investigate the action mechanism of dispersants. Following the standard for geotechnical testing methods(GB/T 50123\u0026thinsp;\u0026minus;\u0026thinsp;2019), specimens were first prepared with a ring knife. Their water content and dry density were consistent with the blocks in the slaking tests. Subsequently, the filter paper and porous plate were arranged on the upper and lower surfaces of the specimens, respectively, and the specimens were placed in the swelling tester. After installing the cover plate and the dial indicators, pure water or dispersant solution was dumped to ensure the water level was 5 mm higher than the specimens. It is noted that two different dispersant solutions were prepared with a concentration of 6%, respectively for the sodium hexametaphosphate and the commercial dispersant. The dial indicator readings were recorded every minute.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eAnalysis of test results\u003c/h2\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003eVariations of atterberg limits under different dispersants\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows variations of the Atterberg limits of the soil with the dispersant content. As the content of the inorganic and organic dispersant increased, the liquid limit of the mixed soil reduced, and this reduction rate decreased. Compared with the liquid limit, the plastic limit of the soil did not change significantly due to a poorer effect of dispersant in the clay state of lower free water content. Thus, the plasticity index, which is the difference between the liquid and plastic limits, showed a similar trend as the liquid limit. The experimental results indicated that both organic and inorganic dispersants decreased the soil plasticity, reducing the risk of clay clogging.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eSlaking characteristics of dispersant-treated soil blocks immersed in pure water\u003c/h2\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003eSlaking process of the soil blocks\u003c/h2\u003e \u003cp\u003eAs indicated in Atterberg limits tests, the soil plasticity was reduced under the addition of inorganic and organic dispersants. Thus, to further explore the effect of dispersant on the soil conditioning for treating muck clogging, the slaking characteristics of the blocks of soil mixed with dispersant were investigated when they were placed in pure water. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, when the soil blocks with 2% inorganic dispersant content were immersed in pure water, the solution quickly became turbid, indicating that the clay particles dispersed rapidly into the solution and the dispersion slaking became significant. However, surface slaking was observed for the soil blocks with a 2% organic dispersant content in pure water(Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), and regardless of whether inorganic or organic dispersants were mixed with soil, the soil slaking was accelerating. When mixed with other inorganic and organic dispersant, the soil blocks also showed similar slaking phenomena in pure water.\u003c/p\u003e\u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eVariation of equivalent slaking thickness\u003c/h2\u003e \u003cp\u003eDuring the slaking process, the volume and surface area of the soil block decreased, reducing the solution-soil interaction area. The clay slaking rate slows down as the solution-soil interaction area decreases. Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) defines the equivalent slaking thickness (dt) as the ratio of the slaking volume to its surface area for a better understanding of the slaking characteristics. The equivalent slaking thickness can eliminate the effect of surface area when evaluating slaking characteristics. Therefore, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, the ratio of the volume of the soil block without slaking to the original volume is equivalent to the unslaked percentage and this index is utilised to establish Eq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) by assuming a uniform slaking rate across all positions of the soil block, based on the equivalent slaking thickness. The slaking percentage At is then converted into the equivalent slaking thickness dt of the soil block, representing the cumulative decrease in size during the slaking process.\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$${d_t}=\\frac{{{V_t}}}{{{S_t}}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere dt is the equivalent slaking thickness of the soil block at time t; Vt is the slaking volume of the soil block at time t; St is the surface area of the soil block at time t.\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\frac{{(H - 2 \\times {d_t}) \\times {{(R - {d_t})}^2} \\times \\pi }}{{H \\times {R^2} \\times \\pi }}=1 - {A_t}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere At is the slaking percentage at time t; H is the initial soil block height, with a value of 35 mm in this study; R is the original radius of the soil block, with a value of 25 mm in this study.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows the variation of equivalent slaking thickness of the soil blocks with inorganic dispersant content when placed in pure water. Due to the dense data points recorded, a continuous smooth curve was plotted. The slaking process of the soil block without dispersant added (dispersant content\u0026thinsp;=\u0026thinsp;0.0%) can be generally divided into the initial stable and rapid development periods, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. The water infiltrated the clay's pores during the initial stable period, weakening the interparticle bonding forces. However, it can be observed that the initial stable period of the mixed soil completely disappeared under the action of inorganic dispersant in the soil. This is because the soil mixed with inorganic dispersant immediately underwent dispersion slaking upon immersion in pure water (see Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). In Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, as the content of inorganic dispersant increased, the slaking rate of the rapid development period gradually increased and reached its maximum when the dispersant content was 2%. With higher dispersant content, the slaking rate during the rapid development period almost remained constant.\u003c/p\u003e\u003cp\u003eSimilar variations of equivalent slaking thickness were found with organic dispersant content in the soil blocks when immersed in pure water. As the content of organic dispersant increased, the slaking rate of the rapid development period gradually increased. However, it did not reach its maximum even when the dispersant content was as high as 7%.\u003c/p\u003e\u003cp\u003eThus, it is indicated that both inorganic and organic dispersants can be injected into the shield muck to facilitate the dispersion of clay blocks and to prevent soil clogging during shield tunnelling. However, the prerequisite is that dispersants are sufficiently mixed with the clayed muck.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eSlaking characteristics of soil blocks without dispersant when placed in dispersant solution\u003c/h2\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003eSlaking process of the soil blocks\u003c/h2\u003e \u003cp\u003eWhen the clayey muck is not properly conditioned during shield tunnelling, muck clogging easily happens. To treat the muck clogging, dispersants are commonly injected into the excavation chamber to remove the soil clogging on the cutterhead and cutters. Thus, the slaking characteristics of the soil blocks without dispersants were investigated when they were present in dispersant solutions. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the slaking process of the soil block when placed in a 6% concentration organic dispersant solution. It is evident that among the four slaking modes described by Moriwaki and Mitchell(1997), namely swelling slaking, dispersion slaking, surface slaking, and body slaking, the mixed soil mainly underwent surface slaking, with the surface debris of the soil block continuously peeled off, although it exhibited slight dispersion slaking since the solution became slightly turbid. Similar slaking phenomena were also observed under the actions of other concentration organic dispersant solutions.\u003c/p\u003e\u003cp\u003eHowever, when the soil blocks were placed in the inorganic dispersant solution, no slaking was observed even as long as 10 hours, indicating that the inorganic dispersant ions in the solution inhibited the soil slaking. Therefore, no relevant photos and curves for the soil slaking were obtained for those cases.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eVariation of equivalent slaking thickness\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e shows the variation of equivalent slaking thickness of the soil blocks in organic dispersant solution with different concentrations. The change rate in the equivalent slaking thickness gradually increased until it reached the maximum, which marks the transition into the rapid development period. Afterwards, the change rate in the equivalent slaking thickness of the clay remained relatively constant. Furthermore, due to an initial height of 35 mm for the soil block, soil block slaking was completed when the equivalent slaking thickness d equalling 17.5 mm. Additionally, when the size of the soil block was smaller than the mesh aperture, the overall fall of the soil block from the mesh plate caused a sudden change at the final moment of the slaking curve, manifesting as the vertical part at the end of the curve for each test. Furthermore, with an increase in organic dispersant concentration, the initial stable period of the mixed soil was significantly shortened, the slaking rate during the rapid development period gradually increased, and the total slaking time decreased.\u003c/p\u003e \u003cp\u003eThe findings suggest that the injection of organic dispersants can effectively alleviate soil clogging on the shield cutterhead and cutters during shield tunnelling. On the other hand, the use of inorganic dispersants does not provide significant assistance in this regard.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eMechanisms of clay slaking\u003c/h2\u003e \u003cp\u003eThe Zeta potential of the soil under the influence of different dispersants was determined to investigate the electrochemical mechanism of dispersants. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e shows the variation of the Zeta potential of the soil with dispersant content. With an increase in the inorganic dispersant content, the absolute value of the Zeta potential increased, but the increasing rate reduced gradually. After the content exceeds 2%, the Zeta potential almost remained constant. According to the Derjaguin\u0026ndash;Landau\u0026ndash;Verwey\u0026ndash;Overbeek (DLVO) theory, the maximum repulsive energy between clay particles increases with increasing absolute value of the Zeta potential, weakening particle connections(Luckham and Rossi \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). Therefore, when the inorganic dispersant content increases, the dispersibility of the soil particles is enhanced, and the soil plasticity is reduced. However, the Zeta potential did not change notably under the effect of organic dispersants, indicating that organic dispersant has little impact on the dispersibility of soil particles. Thus, the change in clay's dispersibility is not the reason for the decrease in soil plasticity under the influence of organic dispersants.\u003c/p\u003e \u003cp\u003eTo explore the reason why the soil plasticity decreased under the effect of the organic dispersant, swelling tests were conducted, as stated previously. Figure\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e shows the effect of organic and inorganic dispersants on the soil's swelling capacity (Sc). Compared with pure water, the inorganic dispersant solution inhibited the swelling of the mixed soil. In contrast, the organic dispersant solution promoted expansion. Thus, the soil structure was loosened under organic dispersant, reducing its shear strength and plasticity.\u003c/p\u003e \u003cp\u003eThe clay slaking depends on the relationship between the connecting and repulsive forces between particles. Assuming that the connecting force between clay particles remains constant, the solution infiltrates into the clay pores, and subsequently, the electrostatic repulsion, expansion (hydration) repulsion, and pore air pressure between particles continue to develop under the interaction between water and soil (Gro\u0026szlig;e et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Hu et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Eventually, the repulsion between particles surpasses the connecting forces, leading to the clay slaking. However, liquid infiltration into the soil blocks is a prerequisite for initiating the slaking under the dispersant solution as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e. The electrostatic repulsion between particles is not affected by organic dispersants (Zeta potential remains unchanged), but the organic dispersant promotes the expansion of the soil. Furthermore, the presence of surfactants in organic dispersants reduces the solution's surface tension, as reported in previous studies (Letey \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1975\u003c/span\u003e; Monteiro et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).. This decrease in surface tension facilitates the rapid infiltration of the solution into the clay through its pores, consequently causing an increase in pore air pressure. As a result, the slaking of clay was accelerated when organic dispersants were employed in the previous tests.\u003c/p\u003e \u003cp\u003eHowever, the inorganic dispersant in the soil and solution have different effects on the dispersion and slaking of the soils as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003e. With an increase in the inorganic dispersant content, the absolute value of the mixed soil's Zeta potential increases, leading to enhanced soil dispersion. Consequently, the dispersion slaking becomes more significant, and the dispersion of soils destroys the clay structure and promotes soil slaking. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e, the swelling of clay was limited when it was immersed in inorganic dispersant. Meanwhile, the total electrolyte concentration in the solution increases with the inorganic dispersant solution concentration, resulting in a decrease in the electric-double-layer thickness on the surface of clay particles and a reduction in the electrostatic repulsion between particles(Bissonnais \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). Under the influence of osmotic pressure, water molecules in the solution are more difficult to infiltrate into the clay, thus inhibiting the solution infiltration and further suppressing the soil dispersion and slaking.\u003c/p\u003e\u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThis study investigates the effect of dispersants on slaking characteristics of the clayey soil through Atterberg limits tests and slaking tests, and explores the mechanisms of dispersants through the Zeta potential and swelling characteristics. The main conclusions are drawn as follows:\u003c/p\u003e \u003cp\u003e(1)As the content of inorganic and organic dispersants in the soil increased, the soil plasticity decreased, indicating that both organic and inorganic dispersants can enhance the dispersity of the clay.\u003c/p\u003e \u003cp\u003e(2) Upon the inclusion of inorganic and organic dispersants in the preparation of the soil blocks, the slaking process in pure water was accelerated, and the initial stable period was eliminated. As the content of both inorganic and organic dispersants increased, the slaking rate during the rapid development period gradually intensified. However, the slaking rate reached its maximum at a 2% inorganic dispersant content and remained constant at higher concentrations. Consequently, both inorganic and organic dispersants can prevent soil clogging during shield tunnelling, provided that they are thoroughly mixed with the clayey muck.\u003c/p\u003e \u003cp\u003e(3) Increasing the concentration of organic dispersant significantly reduced the initial stable period and increased the slaking rate during the rapid development period. Conversely, it was found that the inorganic dispersions in the solution inhibited the soil slaking. Thus, organic dispersants are effective in removing soil clogging during shield tunnelling, while inorganic dispersants are not beneficial for this purpose.\u003c/p\u003e \u003cp\u003e(4) With an increase in the inorganic dispersant content, the absolute value of the Zeta potential increased, and clay plasticity reduced. The inorganic dispersant solution inhibited soil expansion by reducing electrostatic repulsion and impeding water infiltration due to osmotic pressure. Conversely, the Zeta potential remained unchanged with organic dispersant, but it promoted expansion and reduced the plasticity. Moreover, surfactants in the organic dispersants decreased solution surface tension, facilitating rapid infiltration through clay pores and increasing pore air pressure, accelerating soil slaking.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e \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\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis research is financially supported by the National Natural Science Foundation of China (No. 51778637, 52022112), the China Postdoctoral Science Foundation (No. 2022M723536) and the Fundamental Research Funds for the Central Universities of the Central South University (No. 2022ZZTS0689)\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eSW: conceptualization, writing \u0026mdash;original draft, methodology. HZ: lab experiments, investigation, methodology, writing\u0026mdash;review and editing.PL: supervision, writing (review and editing), methodology. TQ: formal analysis, writing (review and editing)\u003c/p\u003e\u003ch2\u003eAvailability of data and materials\u003c/h2\u003e \u003cp\u003eThe data sets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eASTM Standard D2487-17 (2017) Standard Practice for Classification of Soils for Engineering Purposes. ASTM International, West Conshohocken\u003c/li\u003e\n\u003cli\u003eBissonnais Y (1996) Aggregate stability and assessment of soil crustability and erodibility: I. Theory and methodology. Eur J Soil Sci 47:425\u0026ndash;437. https://doi.org/10.1111/j.1365-2389.1996.tb01843.x\u003c/li\u003e\n\u003cli\u003eDjeran-Maigre I, Dubujet P, Vogel TM (2018) Variation over time of excavated soil properties treated with surfactants. Environ Earth Sci 77:67. https://doi.org/10.1007/s12665-018-7230-z\u003c/li\u003e\n\u003cli\u003eDu C, Zhu H, Wang S, Zhang J (2022) Test and Application Study on Dispersion and Disintegration of Mud Cake on Slurry Shield. Tunnel Construction 42:847\u0026ndash;853\u003c/li\u003e\n\u003cli\u003eFang Y, Chen Z, Song T, et al (2023) New clogging potential assessment method for conditioned soil based on modified pullout and direct shear tests. Acta Geotech 18:3307\u0026ndash;3322. https://doi.org/10.1007/s11440-022-01760-w\u003c/li\u003e\n\u003cli\u003eFang Y, Yao Y, Song T, et al (2022) Study on disintegrating characteristics and mechanism of cutterhead mud-caking in cohesive strata. Bull Eng Geol Environ 81:510. https://doi.org/10.1007/s10064-022-03018-x\u003c/li\u003e\n\u003cli\u003eFu J, Xia Y, Lan H, et al (2021) A case study on TBM cutterhead temperature monitoring and mud cake formation discrimination method. Sci Rep 11:1\u0026ndash;12. https://doi.org/10.1038/s41598-021-99439-x\u003c/li\u003e\n\u003cli\u003eGB/T 50123-2019 (2019) Standard for geotechnical testing method. The Ministry of Water Resources of the People\u0026apos;s Republic of China, China Planning Press\u003c/li\u003e\n\u003cli\u003eGro\u0026szlig;e A-K, Cantr\u0026eacute; S, Saathoff F (2015) The applicability of disintegration tests for cohesive organic soils. J Environ Eng Landsc 23:1\u0026ndash;14. https://doi.org/10.3846/16486897.2014.919924\u003c/li\u003e\n\u003cli\u003eHu F, Liu J, Xu C, et al (2018) Soil internal forces initiate aggregate breakdown and splash erosion. Geoderma 320:43\u0026ndash;51. https://doi.org/10.1016/j.geoderma.2018.01.019\u003c/li\u003e\n\u003cli\u003eHuang K, Kang B, Zha F, et al (2022) Disintegration characteristics and mechanism of red-bed argillaceous siltstone under drying\u0026ndash;wetting cycle. Environ Earth Sci 81:336. https://doi.org/10.1007/s12665-022-10450-5\u003c/li\u003e\n\u003cli\u003eKhabbazi Basmenj A, Mirjavan A, Ghafoori M, Cheshomi A (2017) Assessment of the adhesion potential of kaolinite and montmorillonite using a pull-out test device. Bull Eng Geol Environ 76:1507\u0026ndash;1519. https://doi.org/10.1007/s10064-016-0921-3\u003c/li\u003e\n\u003cli\u003eLangmaack L, Feng Q (2005) Soil conditioning for EPB machines: Balance of functional and ecological properties. Underground Space Use: Analysis of the Past and Lessons for the Future - Proceedings of the 31st ITA-AITES World Tunnel Congress 2:729\u0026ndash;735\u003c/li\u003e\n\u003cli\u003eLangmaack L, Lee KF (2016) Difficult ground conditions? 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Tunnelling Underground Space Technol 95:103144. https://doi.org/10.1016/j.tust.2019.103144\u003c/li\u003e\n\u003cli\u003eWang S, Zhou Z, Liu P, et al (2023) On the critical particle size of soil with clogging potential in shield tunneling. Journal of Rock Mechanics and Geotechnical Engineering 15:477\u0026ndash;485. https://doi.org/10.1016/j.jrmge.2022.05.010\u003c/li\u003e\n\u003cli\u003eZhao S, Li S, Wan Z, et al (2021) Effects of anti-clay agents on bubble size distribution and stability of aqueous foam under pressure for earth pressure balance shield tunneling. Colloids Interface Sci Commun 42:100424. https://doi.org/10.1016/j.colcom.2021.100424\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-earth-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"enge","sideBox":"Learn more about [Environmental Earth Sciences](https://www.springer.com/journal/12665)","snPcode":"12665","submissionUrl":"https://submission.nature.com/new-submission/12665/3","title":"Environmental Earth Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Clay, Slaking characteristics, Organic dispersant, Inorganic dispersant, Atterberg limits, Influence mechanism","lastPublishedDoi":"10.21203/rs.3.rs-3792474/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3792474/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe adhesion of clay to the cutterhead and cutters presents a significant challenge during EPB shield excavation in clay strata. Dispersants are widely used to disintegrate clay adhering to metal surfaces, but their conditioning characteristics and working mechanisms remain elusive. This study investigates the effect of organic and inorganic dispersants on clay plasticity and slaking characteristics through Atterberg limit and slaking tests, complemented by Zeta potential and swelling tests to explore underlying mechanisms. The results demonstrate that increasing the content of inorganic and organic dispersants reduces soil plasticity and enhances the slaking rate during the rapid development period in pure water. Dispersion slaking occurs in soil blocks treated with inorganic dispersant in pure water, while soil blocks treated with organic dispersant primarily undergo surface slaking. A higher organic dispersant concentration significantly intensified the slaking rate. In contrast, inorganic dispersant solutions inhibit soil slaking. Inorganic dispersant solutions impede soil expansion and slaking due to reduced electrostatic repulsion and increasing difficulty in water infiltration. Conversely, organic dispersant solutions accelerate soil slaking by promoting soil expansion and solution infiltration, reducing surface tension, and increasing pore air pressure. The results may suggest injecting organic dispersant for removal of existing soil clogging in shield tunneling, but both inorganic and organic dispersants can serve to prevent the occurrence of soil clogging for shield tunnelling.\u003c/p\u003e","manuscriptTitle":"Soil Slaking under the effect of dispersants: characteristics and mechanism","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-01 15:21:10","doi":"10.21203/rs.3.rs-3792474/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-02-18T00:12:15+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-02-16T06:08:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"a2846edd-8b7f-4066-8773-955f7de7e789","date":"2024-01-16T03:57:34+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-01-15T07:32:39+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2023-12-29T05:50:57+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-12-29T05:50:57+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Earth Sciences","date":"2023-12-22T14:13:35+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-earth-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"enge","sideBox":"Learn more about [Environmental Earth Sciences](https://www.springer.com/journal/12665)","snPcode":"12665","submissionUrl":"https://submission.nature.com/new-submission/12665/3","title":"Environmental Earth Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"b267abdc-6038-4820-906d-db7dc310e7a5","owner":[],"postedDate":"January 1st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-06-21T15:16:59+00:00","versionOfRecord":{"articleIdentity":"rs-3792474","link":"https://doi.org/10.1007/s12665-024-11708-w","journal":{"identity":"environmental-earth-sciences","isVorOnly":false,"title":"Environmental Earth Sciences"},"publishedOn":"2024-06-17 15:16:59","publishedOnDateReadable":"June 17th, 2024"},"versionCreatedAt":"2024-01-01 15:21:10","video":"","vorDoi":"10.1007/s12665-024-11708-w","vorDoiUrl":"https://doi.org/10.1007/s12665-024-11708-w","workflowStages":[]},"version":"v1","identity":"rs-3792474","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3792474","identity":"rs-3792474","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}