Experimental study on surface protection support using polymer thin spray-on layer

Experimental study on surface protection support using polymer thin spray-on layer | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Experimental study on surface protection support using polymer thin spray-on layer Han LIANG, ZHANG Zedi, Yunjing SHI, BAI Zihan, CAO Chen This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6927620/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 12 You are reading this latest preprint version Abstract The Thin Spray-on Layer (TSL) is widely used in seal engineering of mine. TSL with high bearing capability is a new method to replace the metal mesh in the roadway support of underground coal mines, which has the advantages of fast development, automation and applicability of geo-conditions. Based on the deformational process of TSL in soft rock roadway, the support theories of TSL are analyzed. It shows that TSL coheres and repairs the surrounding rock surface to form a bonding layer, which has a confinement effect on the deformation of deep rock mass. Under the condition of large deformation of surrounding rock, TSL forms a thin shell structure, which produces supporting effect. Experiments were conducted to compare the support effects of different surface protection methods using large-scale briquette coal pillar samples and a newly developed polymer TSL material. The results show that the confining effect of TSL is greater than that of the metal mesh, and the bearing capacity of the sample is increased by 28.3%. The residual strength of the TSL specimen is also higher, and the energy dissipation of the system increases by 44.1%. The support effect of TSL thin shell structure is experimentally studied for the first time on different rock mass. The results showed that the TSL shell structure reduced surface rock deformation by bearing compressive stress, and the bearing capacity of lignite and sandstone samples increased by 44.6% and 20.4%, respectively, while energy dissipation increased by about 2 times. The numerical method was used to analyze stress distribution of TSL and mechanism of surrounding rock deformation in the experiments, and results were compared with experimental observations. This study provides a theoretical basis for the practice of TSL support engineering and an experimental research method for predicting the effect of TSL support in underground coal mine roadway. Physical sciences/Engineering/Civil engineering Earth and environmental sciences/Environmental sciences/Environmental impact TSL roadway support restraint shell structure bearing 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 1. Introduction Thin spray-on liner (TSL) is a protective technology for spraying thin films on the surface of rock mass, which is widely used in mine sealing projects, such as water sealing, airtight and gas extraction closure (Mpunzi et al. 2015). TSL support is a new method to replace the metal mesh in roadway support, which has the advantages of fast operation and automation, and has great application potentials in the rapid excavation and anchoring automation of underground coal mine roadway (Kang et al. 2024). Supporting TSL materials can be classified as polymer or cement-based non-reactive types. In the past three decades, a variety of mining support TSL materials has been developed, and experimental research on the physical and mechanical properties of the materials was carried out, including the adhesive, tensile, shearing, compressive, bending and tearing properties of the materials (Chen et al.2024; Wang et al.2023), a few experimental studies on fire resistance, blastability and fiber reinforcement. From the perspective of support manner, TSL is a kind of active support, that is, when the surrounding rock is slightly deformed, the support resistance of the TSL is generated to reduce the fracture propagation or broken rock fall off (Han et al. 2024; Lacerda et al.2002). Metal mesh is a kind of passive support, which produces a supporting effect after the surrounding rock is largely deformed or falls off. Shotcrete support relies on its own structural strength to provide large rigid constraints in the early stage of surrounding rock deformation, but its curing time is long, the flexibility is poor, and the small displacement under tensile, shear or torsion conditions can cause slag dropping and cracking of the sprayed layer, which is mostly used in permanent roadways with small deformation, and is not suitable for rapid excavation or large deformation roadways (Tannant et al. 1995 and 1997;). Therefore, TSL support is a more flexible support method between metal mesh and shotcrete (Tannant et al. 2001). In particular, the chemical reaction time of polymer TSL is about tens of seconds, which has the effect of "spraying and using", and their mechanical performances are more diverse, which can meet the support needs of different mining geological conditions. The performance of TSL is the premise of support design, which is of great research significance. After spraying, TSL forms a composite structure with the bonded surrounding rock, and its load-bearing and deformation law determines the supporting effect of TSL. At present, the research on TSL support performance mainly adopts the method of comparative test. For example, the comparative test of TSL support effect of hard rock pillar (Archibald et al.2001; Ozturk et al.2017; Qiao et al. 2014) and the bearing basket of broken rock mass (Nemcik et al.2011). The results show that TSL has a better supporting effect than steel mesh for soft rock (Qiao et al. 2015), loose rock mass (Kristie et al. 2006), jointed rock mass (Nemcik et al. 2014; Shan et al. 2018 and 2020) or rock mass with weak interlayer (Qiao et al. 2015). In summary, TSL support is a new method of fast and efficient surface protection, and the active support effect of the composite structure formed by TSL and bonded surrounding rock is more significant, especially for the weak and jointed rock mass of coal measure strata. However, the experimental research on TSL support is mostly for hard rock samples, and there are very few studies on soft rock in coal measure. The geological conditions and mining methods of metal mines are very different from those of underground coal mines, and the experimental design methods and research results of hard rock TSL support cannot be copied to the application of underground coal mines. Therefore, considering the application scenarios of TSL in underground coal mines, this paper firstly analyzes the supporting effect of TSL in different deformation stages, carries out experimental research on the support performance of TSL, and uses numerical methods to analyze the mechanism of the TSL support, so as to provide a basis for the application of TSL in underground coal roadway. 2. TSL deformation process and supporting effect Based on the application process and bearing characteristics, TSL support can be divided into three stages: bonding, flexural deformation, and thin shell structure (Stacey et al. 2004), which correspond to the three main supporting effects of cemented wedge, confinement and thin shell structure, respectively. 2.1 Cementation wedge effect After spraying, the TSL is bonded to the surrounding rock surface, causing the scattered rock to form rock interlocks (Fig. 1a). The bonding strength between TSL and rock is more than 3 times that of shotcrete (Ozturk et al. 2010; Chen et al. 2020; Wei et al. 2020), which can improve the integrity of loose rock mass effectively. Compared with shotcrete, TSL material also has better fluidity, and penetrates the cracks on the surface of the rock during the spraying process to repair the fractured surrounding rock. The experimental results show (Tannant et al. 2006) that the material can penetrate 20~50 mm depth for the crack width of 1~2 mm during the spraying process. Experimental results show that the airtightness of TSL can also reduce the deformation of surrounding rock (Finn et al. 2018). In the process of rock mass fracture and migration, gaps are formed between rock blocks, which cause the surrounding rock to expand. If no air enters, negative pressure can cause suction between rock blocks to prevent cracks from developing into fractures and dislocation (Coates et al. 1966). At the same time, the sealing effect of TSL can also prevent the weathering and deliquescent of the surface rock, which has a positive effect on maintaining the stability of sensitive rock mass. In the early stage of TSL support, it has a more active effect than metal mesh support by interlocking surface rock masses, repairing surrounding rock cracks, and preventing small rock blocks from loosening and falling. The support effect mainly depends on the adhesive performance of TSL, the infiltration ability to the rock joint, the thickness of the spray layer and the surface characteristics of the surrounding rock. After the TSL is solidified, it is deformed together with the bonded rock mass, and the TSL support enters the flexure stage, and the main role of the TSL support in this stage is the confining effect. 2.2 Confining effect After the excavation of the underground space, the normal stress of the exposed surface is reduced to 0, and the surface rock mass changes from a three-way stress state to a two-way stress state. In the process of stress redistribution, if the load of the shallow surrounding rock is greater than its strength, the rock mass enters plastic deformation or even breakage, and the load is transferred to the deep rock mass until the bearing unit is in elastic deformation. The shallow surrounding rocks located in the fracture zone and plastic deformation zone are collectively referred to as the loosening zone of the surrounding rock. With the increase of the deformation of the surrounding rock of the roadway, the TSL and the cohesive rock mass enter the deflection deformation stage. In the flexural stage, TSL and the bonded surrounding rock form a composite structure to bear and deform together, and the TSL retaining layer makes the surface rock mass in a three-way stress state through its own bearing, establishes a restraint layer for the internal surrounding rock, and achieves the purpose of narrowing the loosening zone. Therefore, the main support of TSL in the flexural stage is the restraining effect on the deformation of the deep surrounding rock. The confinement effect of TSL depends on the displacement coupling with the cohesive rock mass, which is essentially a modification of the surface rock mass. The experimental results show that the compressive strength (Qiao et al. 2015;Wei et al.2020) and shear resistance of TSL specimens are significantly improved. Especially for coal measure strata, there are generally multiple weak structural planes, such as joints, cleats, cracks, etc., which have the characteristics of low strength and large loosening range, and the restraining effect of TSL enhances the stability of the surrounding rock structure. In the flexural stage, TSL produces tensile, shearing, bending and torsional deformation. In the experimental study of TSL support of soft rock and jointed rock mass, TSL mainly bears tensile stress and shear stress in this deformation stage (Qiao et al. 2015; Kristie et al. 2006; Nemcik et al. 2014; Shan et al. 2018). After the surrounding rock enters the stage of large deformation, TSL and the cohesive rock mass form a thin shell structure to produce support. 2.3 Thin shell structure effect In the final stage of TSL support, when the roadway displacement is large and the surface rock blocks are scattered, TSL, like the metal mesh, can produce a kind of bearing basket effect on the loose rock blocks. Due to the restraining effect of TSL or metal mesh and the anchorage of the rock bolt, the loose rock block has a certain bearing capacity, which can not only prevent the rock mass from falling and further free expansion of the cracks, but also transfer load from shallow loose rock mass to the deep stable rock mass through the bolt, so as to improve the stability of the surrounding rock. The ductility of the surface support material determines the support effect of the bearing basket, and the effect of TSL and metal mesh has advantages over shotcrete. The experimental results showed that the fiber-reinforced TSL greatly improved the bearing capacity of the basket. Shotcrete is considered to form a "shell structure" to be the main supporting role. Although there is local debonding, twisting, tearing and leakage in the final stage of support, the main part of TSL is still bonded to the surrounding rock. TSL and cohesive rock mass, including rocks within the bearing basket, can form a thin shell structure for bearing. In this case, the equivalent thickness of the crust is the thickness of the TSL bonded surrounding rock (t in Fig. 1). The mechanism of shell structures is a classic research topic in the field of shotcrete. Generally, it is assumed that the roadway is a semicircular section, and the plane stress or plane strain method is used for analysis. When the thickness of the spray layer is negligible to the roadway radius, the constitutive equation of the thin shell in the classical elastic theory is as follows: (1) where and are deflection and stress, r and θ are the radius direction and angle, E is the Young's modulus, and I is the moment of inertia of the cross-section. Consider the actual field to determine the boundary conditions for solving. However, the surface rock mass of the underground coal mine roadway is in a state of plastic deformation or even fractured, and its main bearing body is a pressure arch along the loose circle. Therefore, it is not appropriate to use the elastic shell structure theory or the linear bearing analysis method to analyze the supporting effect of TSL thin shell structure in underground coal mines. It is a new research topic to establish an analytical method for the supporting effect of TSL thin shell structure under the condition of large deformation of soft rock. In summary, TSL bonds the rock surface and repairs the fractured rock mass. With the increase of the surrounding rock deformation, TSL enters the flexural deformation stage and produces the bearing basket effect of the loose rock blocks, which has a restraining effect on the deformation of the surrounding rock. At the same time, TSL and the cohesive rock mass form a thin shell structure for bearing. In the follow-up study, a newly developed polymer TSL material was used to compare and analyze the confining effect of TSL on the deformation of coal pillars and the supporting effect of thin shell structure by experimental methods, and the load- deformation law of TSL and the mechanism of roadway surrounding rock were revealed by numerical methods, so as to provide theoretical guidance for the practical TSL engineering of underground coal mines. 3. TSL confinement effect for coal pillar Oztuck and Guner (2017) and Qiao et al (2014) conducted a comparative experimental study on TSL support for cylindrical hard rock pillars in metal mines. In this paper, the TSL support of the cuboid coal pillar of the underground mine is studied experimentally, and the comparison is carried out with the metal mesh support. 3.1 Materials and methods The width of the common coal pillar in underground mines is 5 m, the spacing of the connecting roadway is 20 m, and the height of the roadway is about 4 m. The coal pillar sample is determined to be 500 mm long, 125 mm wide and 100 mm high according to geometric similarity. The coal pillar specimen was prepared by pressing briquette. After crushing the lignite, the pulverized coal is screened using an 80-mesh sieve (Fig 2a). High-strength Portland cement is selected as the binder, and the mass ratio of pulverized coal to cement is 5:1 and the water-cement ratio is 0.4. Place the mixture into an internal space 500×125×100 mm metal mold (Fig 2b). The WAW-600C microcomputer controlled the electro-hydraulic servo-universal testing machine was used for compression, and the pressure was 3.2 MPa for 30 min (Fig. 2c). Leave the specimen at room temperature for 7 days before demoulding (Fig 2d). In order to carry out numerical calculations, the mechanical parameters of the briquette were measured using the standard experimental method of rock mechanics, and the results are shown in Table 1. Table 1 Mechanical properties of briquette used in the test Bulk modulus/Pa Shear modulus/Pa Cohesiveness/Pa Tensile strength/Pa Internal friction angle/° 0.54E9 0.25E9 3.0E6 0.10E6 35 The TSL used in the test is a self-developed two-component polyurethane substrate temperature-limiting modified material (patent number: CN113153373A), the composition of which is shown in Fig 3a, and the small figure shows the tensile interface. The mechanical properties are shown in Table 2 (Han et al.2021). The TSL specimen was placed into the center of the organic rubber frame with an internal dimension of 510×135×100 mm, mixed and stirred the TSL two-component material, poured into the gap between the coal pillar and the frame, and was released after curing. The galvanized diamond-shaped mesh of 10×20 mm aperture (Fig. 3b) is tightly fastened with iron wire around the specimen after cutting. The control specimen does not have any surface protection arrangement. A total of three samples were prepared, including TSL, diamond mesh and none surface protection (Fig. 3c). The testing machine uses the WAW-600C, the loading rate is 1 mm/min, and the test process is shown in Fig 3d. Table 2 Mechanical parameters of TSL for test Average compressive strength ( standard deviation ) / MPa Average deformation / mm Average tensile strength ( standard deviation ) / MPa Elongation at break / % Cohesion / MPa Internal friction angle / ° Average bond strength with coal ( standard deviation ) / MPa 52.62（4.02） 14.28 12.73（1.230） 6.29 6.15 33.60 1.63（0.36） 3.2 Results and Analysis The load-displacement curves of the coal pillar samples with three different surface protection methods are shown in Fig 4, and the experimental results are shown in Table 3. Table 3 Supporting performance of coal pillar specimens under different support methods Yield load/kN (displacement under yield load/mm). Peak load/kN (displacement at peak load/mm). Energy absorption capacity/J None 309.4（5.29） 313.5（6.12） 2549 Diamond-shaped mesh 298.7（7.42） 316.7（10.15） 3004 TSL 384.5（12.52） 406.2（14.48） 4329 The test results show that the yield and peak loads of the diamond-shaped mesh and the control specimen are similar, but the displacement of the metal mesh specimen is higher than that of the control specimen. It shows that after the yield and failure of the coal pillar, the mesh has the effect of holding the broken coal. The total energy absorption of the mesh support system is increased by 18% compared with that without support. The yield load of the TSL specimen is increased by 24% and the peak load is increased by 30% compared with the unprotected specimen. TSL had a vertical penetrating fracture at the peak of the test force, but it still had a high residual strength, indicating that the TSL support significantly improved the bearing capacity of the coal pillar. Compared with other specimens, the displacement of TSL under yielding load and peak load is larger, and it is more continuous than the diamond mesh after the material is broken, and the system energy absorption of TSL specimens is about 70% higher than that of the control specimens. During the test, it was observed that the control sample had a large collapsed at the corner of the coal pillar under yield load, which belonged to the brittle failure type. At the peak load, compression-shear failure type occurred. The diamond-shaped mesh specimen begins to break when the coal body is under yield load, but the diamond-shaped mesh plays a blocking role in the thrown coal. At the peak load, the diamond-shaped mesh spreads out, part of the wire breaks, and the broken coal is thrown out. Local cracks appeared in the TSL before the yield load (Fig. 4), and penetrating tensile fracture appeared in the TSL under yield load, and the TSL fracture was further expanded under continuous loading, but it could still restrain the deformation of the coal pillar. Finally, the coal pillar was completely damaged after multiple penetrating failures in TSL (Fig. 4), but the TSL sample did not exhibit coal ejection at the end of the test. The experimental results show that the bonding between TSL and the coal pillar improves the strength and ductility of the rock mass and prevents sudden brittle failure. In particular, the high residual strength and large displacement after the peak significantly improve the energy dissipation of the system, which is a new method of surface protection support for large deformation roadways. 3.3 Numerical Calculations Numerical method is used to analyze the bearing state of TSL and the influence on the stress distribution of coal pillars during the test, which can be hardly observed and analyzed in the test. 3.3.1 Model establishment and validation FLAC3D 5.01 （FLAC3D 5.01 https://www.itascacg.com/software/flac3d）was used to establish the numerical models of TSL and unreinforced coal pillars. The geometry of the model is the same as that of the test specimen. The Mohr-Colomb failure criterion was used. The mechanical parameters of the model are shown in Table 1, and the mechanical parameters of TSL are shown in Table 2. The bottom of the model is bound in the x, y, and z directions, and the rest are free faces. The calculation results are compared with the experimental results to verify the reliability of the calculation model. The results of the coal pillar test show that the peak load of the unsupported sample is 313.5 kN（5.01 MPa）. The calculation model of the coal pillar without surface protection is loaded to 2.5 MPa (50% peak load) and 5.0 MPa (peak load), respectively, and the plastic zone of the coal pillar is shown in Fig. 5. Under 2.5 MPa loading, the upper part of the coal pillar model began to undergo tensile plastic deformation, especially at the corner of the coal pillar. When the loading stress is 5.0 MPa, most of the coal pillar model elements are in the plastic zone, which is mostly consistent with the experimental observation, and it is considered that the stress distribution state and evolution law of the model are consistent with the experimental results. 3.3.2 Effect of TSL on the maximum principal stress of coal pillar Fig. 6 shows the maximum principal stress distribution of the TSL supported and unsupported coal pillar models under the condition that the vertical stresses are 2.5 MPa and 5.0 MPa, respectively. The calculation results show that the model is mostly tensile except for the lower part of the model under the loading condition of 2.5 MPa, and the maximum tensile stress is 0.08 MPa, and the outside of the model is more concentrated. When the loading stress is 5.0 MPa, except for the binding area on the lower surface, the coal pillar is in tension, and the maximum tensile stress is 0.10 MPa. At 2.5 MPa of TSL coal pillar, most of the coal pillar units are in the compression state, and the maximum tensile stress is at the corner of the bond between the TSL and the coal pillar. Under the loading condition of 5.0 MPa, most of the TSL coal pillar units are still under compression. The confining effect of TSL on the coal pillar improves the bearing state of the coal pillar element and increases the stability of the coal pillar. 3.3.3 Load-bearing characteristics of the TSL The peak load of the laboratory TSL specimen is 406.2 kN, or 6.50 MPa. The TSL calculation model was loaded to 3.25 MPa (50% peak load) and 6.50 MPa, respectively, and Fig. 7 shows the distribution contour of the maximum principal stress and maximum shear stress of the TSL itself. The maximum principal stress contour shows that the maximum principal stress of the TSL element is tensile stress, and the maximum principal stress of the coal pillar element near the TSL is also in tensile stress. The stress concentration is mainly at the corner where the TSL is bonded to the coal pillar. With the increase of loading stress, the maximum principal stress in the TSL element increases, and the maximum principal stress of the TSL element reaches 2.5 MPa when the loading stress is 6.50 MPa. In the laboratory test, the TSL failure is tensile break of the spray layer, which is due to the high tensile stress of the spray layer. The maximum shear stress contour shows that the TSL element is the shear stress concentration area, and the TSL shear stress on the two sides of the corner of the coal pillar is the largest. As the loading stress increases, the maximum shear stress in the TSL element increases and expands to both sides. The shear stress of the coal pillar element bonded to TSL is also larger, and the internal shear stress of the coal pillar is smaller. When loaded to 6.50 MPa, the maximum shear stress of TSL and bonded coal pillar elements reaches 5.0 MPa, but the shear stress of most coal pillar elements inside the coal pillar is small. It shows that TSL significantly improves the bearing capacity of the surface rock mass through its own bearing, and establishes a restraining effect for the deformation of the deep rock mass. Moreover, the stress state of the rock mass around TSL is similiar to that of the layer, that is, this restraining effect is jointly established by TSL and the cohesive rock mass. Subsequently, experimental and numerical methods were used to study the supporting effect of the thin shell structure formed by TSL and the cohesive rock mass under the condition of large deformation of the surrounding rock. 4. TSL thin shell structure support The supporting role of shell structures formed by sprayed concrete has been widely recognized by the academic community. However, the development of TSL is relatively short, and the research on support theory is seriously insufficient. In this study, it is believed that after the large deformation of the surrounding rock of the roadway, TSL and the bonded surrounding rock form a similar thin shell structure. The numerical study results of the confinement effect of TSL coal pillars also show that the bearing state of the medium bonded by TSL is very similar to that of TSL, but is quite different from that of the deep medium, which also provides a theoretical basis for the formation of thin shell structure at the end of TSL support stage. However, there is still a gap in the research on related basic theories. Therefore, the bearing performance and deformation characteristics of TSL thin shell structures were studied experimentally, followed by numerical method used to analyze the stress evolution law between TSL and the bonded rock mass during the bearing process. 4.1 Materials and methods Two kinds of rocks, lignite and sandstone, were used as the sample substrates to study the TSL thin shell support effect of hard rock and soft rock. The mechanical properties of them are shown in Table 4. Two types of rock were processed into 200 mm x 200 mm x 150 mm substrate specimens, 3 of each rock. In order to make the experimental results more obvious and to facilitate comparison with the current shotcrete research results, a circular hole with a diameter of 50 mm was drilled in the center of the substrate to simulate the underground roadway, and the drilled substrate is shown in Fig 8a. Table 4 Mechanical parameters of sandstone and lignite for testing Bulk modulus/Pa Shear modulus/Pa Cohesiveness/Pa Tensile strength/Pa Internal friction angle/° lignite 1.0E9 6.0E8 2.0E6 1.0E6 25 sandstone 2.0E10 1.3E10 1.8E7 9.0E6 40 Three kinds of samples were made on two substrates, TSL support, diamond mesh support and unsupported. The material properties of TSL and diamond mesh are the same as those of the coal pillar confinement experiment. A PVC pipe with an outer diameter of 4.0 mm was used for the TSL specimens. It was placed in the center of the hole after lubrication, TSL materials were mixed and stirred with the same volume and poured into the gap between the PVC pipe and the hole. The PVC pipe was withdrawn after 2 minutes (Fig. 8b). The diamond-shaped mesh was cut into 200×150 mm, rolled into a cylindrical shape, and arranged in a circular hole of the sample with iron wire connection (Fig. 8c). There is no surface protection for the circular hole in the control samples. The testing machine is WAW-600C and the loading mode is displacement loading at the loading rate of 1 mm/min. The load and displacement are monitored and and the test process is shown in Fig 8d. 4.2 Results and Analysis Fig. 9 shows the load-displacement curves for different lithologies and different surface protection methods. The experimental results are summarized in Table 5. Table 5 Experimental results of different substrate and surface protection methods Support method Yield load (kN)/ Displacement(mm) Peak load (kN)/ Displacement (mm) Energy Absorption(J) None 105.5 (3.91) 118.5 (4.14) 128.4 Lignite Mesh 115.0 (4.10) 119.9 (4.34) 151.2 TSL 136.9 (4.92) 171.3 (6.27) 386.4 None 278.0 (6.46) 309.7 (7.04) 887.9 Sandstone Mesh 310.5 (7.63) 315.3 (8.07) 922.1 TSL 321.0 (8.92) 373.0 (11.76) 2712 The patterns of load-displacement curves are very similar for the two rock substrate specimens. The results show that the yield and peak load of the diamond mesh specimens are close to those of the unsupported specimens. The reason is that the diamond mesh supports the rock mass when its displacement is large. The bearing capacity and ductility of the TSL specimen were significantly improved, and the dissipation energy was increased by 201% compared with the control specimen, and 156% higher than that of the diamond-shaped mesh specimen. Compared with sandstone and lignite, sandstone has high strength, and the yield, peak and residual strength of the sample are higher than those of the lignite samples. However, the improvement of the supporting performance of the sandstone TSL sample is less than that of the lignite sample, and the same TSL has a more significant supporting effect on the soft rock. The failure process of the two substrate specimens is similar. The unprotected specimen and the diamond-shaped mesh specimen underwent a brittle failure around the hole under yield load and expanded rapidly, and the failure was completely carried out under peak load. The failure of the TSL specimen first occurs in the brittle failure at the corner of the specimen, and the medium around the hole also begins to fail after the yield load is reached, and the specimen is completely destroyed after the complete failure of the TSL ring. Fig 10 shows that the lignite substrate TSL sample has undergone complete brittle failure, and the upper part of the TSL ring is basically debonded from the substrate, but the lower TSL is still bonded to the substrate. 4.3 Numerical calculations 4.3.1 Model establishment and verification Numerical calculation method is used to analyze the bearing state of TSL thin shell structure and its influence on the stress distribution of surrounding rock during the test. The dimensions of the calculated model are the same as those for the shell structure bearing test, which is 200×200×150 mm. The computational model uses the Mohr-Coulomb criterion. The deformation laws of different substrate samples are similar, only the simulation results of lignite are shown. The mechanical parameters of the model material are shown in Table 4. The bottom surface of the model is bound in the x, y, and z directions, and the rest is free surface, as shown in Fig 11. The TSL is simulated using shell structure element in the numerical model. First, the computational model is to be verified. The yield load of the non-surface protection specimen in the test is 2.75 MPa, and the stress of 2.75 MPa is applied to the upper part of the two calculation models, respectively. The calculation results of the plastic zone of the non-surface and TSL shell models are shown in Fig. 12. The calculation results of the plastic zone show that most of the elements of the non-protection coal model are in tensile yield state under the load of yield stress (2.75 MPa), and the elements on both sides of the round hole are in the shear plastic deformation state, which is consistent with the brittle failure phenomenon round hole in the test. Under the same stress loading, the tensile and shear plastic deformation of the coal unit occurred above the hole, but the TSL shell structure was in the elastic stage, which was consistent with the experimental observation. 4.3.2 The influence of thin shell on the deformation of surrounding rock The distribution law of surrounding rock deformation under different support conditions was compared. The numerical calculation model was loaded to 3.75 MPa (TSL specimen yield stress) and the displacement contour is shown in Fig 13. The results show that under the stress load of 3.75 MPa, the elements around the hole of the model without a protective surface are seriously deformed, with a maximum displacement of 13.06 mm, which is located above the round hole, and the hole is completely collapsed in the experiment. The maximum displacement of the TSL model is 12.28 mm, but the maximum displacement element is at the upper corner of the model, and the displacement of the elements around the round hole is not large, and the shape of the round hole is basically intact, which is consistent with the experimental phenomenon. Under the condition of no support, the deformation caused by the stress of the rock mass is freely propagated around the hole, resulting in the large deformation of the surface surrounding rock, which is shown in engineering practice as the surrounding rock of the roadway is broken and falling. The restraint effect is lost, resulting in the further expansion of the loosening circle of the roadway. Under the condition that there is a shell structure around the hole, the shell structure prevents the large deformation of the rock mass around the hole and maintains the stability of the roadway. 4.3.3 Load-bearing state of thin shell structure The shell structure in the calculation model was taken out separately to analyze its deformation and stress-bearing state under different stresses. When the loading stress is 3.75 MPa, the displacement calculation results of the TSL shell structure are shown in Fig. 14a. The results show that the overall displacement of the shell structure is small, with a maximum displacement of 0.38 mm on the upper surface and a gradual decrease from top to bottom, and the maximum displacement on the lower surface is about 0.31 mm. In the experiment, the upper part of the TSL ring was debonded and broken, but the lower part was relatively intact and bonded to the coal base. The maximum principal stress contour of the TSL shell structure under 3.75 MPa loading is shown in 14b. The results show that the whole shell structure is in a state of compressive stress, and the maximum principal stress on the upper and lower surfaces reaches 6.14 MPa, and the smaller one on both sides is only 1.0 MPa. It is believed that the effective shell structure can significantly improve the stress distribution state of the rock mass on the surface of the roadway and increase the stability of the supporting structure. 5. Conclusion TSL support has the advantages of fast development, automation and wide range of application, and is a new method to replace the metal mesh support of underground coal mines. In this study, laboratory experiments and numerical calculations were used to compare and analyze the supporting effect of a new polymer TSL in coal mine roadway, and the following conclusions were drawn: (1) After the TSL is bonded with the surface surrounding rock, the rock is interlocked, and the bond layer has a confining effect on the deformation of the deep rock mass. TSL restraint is earlier than metal mesh and more resilient than shotcrete. In the large deformation stage of the surrounding rock, TSL forms a thin shell structure with the cohesive rock mass and the loose rock blocks in the bearing basket, which produces the surface protection support effect through its own bearing compressive stress. (2) For large briquette pillar samples, the restraining effect of TSL is earlier and stronger than that of diamond mesh, and the bearing capacity of the sample is increased by 28.3%. At the same time, the ductility of TSL tensile is better, the residual strength of the specimen is higher, the post-peak displacement is larger, and the total energy dissipation of the specimen is increased by 44.1%. (3) In the large deformation stage of the roadway, the TSL and the confined rock mass form a thin shell structure, and the deformation of the surface rock mass is reduced by the compressive stress of the self-bearing, and the bearing capacity of the lignite and sandstone TSL thin shell structure specimens increases by 44.6% and 20.4%, respectively, and the energy dissipation increases by about 2 times. This study provides a theoretical basis for the practice of TSL support engineering and an experimental research method for the prediction of TSL support effect in coal mine roadway. Declarations Fund Project National Natural Science Foundation of China Youth Project ( 52304135 ) Author Contribution L. and Z. wrote the main manuscript text , S. and B. prepared figures 1-3. All authors reviewed the manuscript. Data Availability The main raw data has been provided in the article. The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. References J.F. Archibald, Assessing acceptance criteria for and capabilities of liners for mitigating ground falls, in: Mining Health and Safety Conference 2001, Sudbury, Ontario, 2001, pp. 209–215. DOI: N/A. L. Chen, Z. Zhou, G. Liu, et al., Effects of substrate materials and liner thickness on the adhesive strength of the novel thin spray-on liner, Advances in Mechanical Engineering 12 (2) (2020) 1–13. DOI:10.1177/1687814020904574. Q.F. Chen, W.X. Yang, J.Y. Wu, W.J. Niu, Macro and micro experimental study on the effect of water-cement ratio on the tensile properties of thin spray lining materials, Materials Reports 38 (8) (2024) 281–287 (in Chinese). DOI: 10.11896/cldb.22090309. D.F. Coates, Rock Mechanics Principles, Geoscience Abstracts (1966). DOI: N/A. 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Guner, Failure analysis of thin spray-on liner coated rock cores, Engineering Failure Analysis 79 (2017) 25–33. DOI: 10.1016/j.engfailanal.2017.03.024. H. Ozturk, D. Tannant, Thin spray-on liner adhesive strength test method and effect of liner thickness on adhesion, International Journal of Rock Mechanics and Mining Sciences 47 (5) (2010) 808–815. DOI: 10.1016/j.ijrmms.2010.05.004. Q. Qiao, Experimental and numerical analysis of thin spray-on liner materials for use in underground mines, Doctoral dissertation, University of Wollongong, 2015. DOI: N/A. Q. Qiao, J. Nemcik, I. Porter, E. Baafi, Laboratory investigation on support mechanism of thin spray-on liner for pillar reinforcement, Géotechnique Letters 4 (2014) 317–321. DOI: 10.1680/geolett.14.00076. Q. Qiao, J. Nemcik, I. Porter, et al., Laboratory tests on thin spray-on liner penetrated rock joints in direct shear, Rock Mechanics and Rock Engineering 48 (5) (2015) 2173–2177. DOI: 10.1007/s00603-014-0669-7. Z. Shan, I. Porter, J. Nemcik, et al., Investigating the behaviour of fibre reinforced polymers and steel mesh when supporting coal mine roof strata subject to buckling, Rock Mechanics and Rock Engineering 52 (6) (2018) 1857–1869. DOI: 10.1007/s00603-018-1656-1. Z. Shan, I. Porter, J. Nemcik, et al., Investigation on the rock surface support performance of welded steel mesh and thin spray-on liners using full-scale laboratory testing, Rock Mechanics and Rock Engineering 53 (1) (2020) 171–183. DOI: 10.1007/s00603-019-01895-5. T.R. Stacey, X. Yu, Investigations into mechanisms of rock support provided by sprayed liners, in: Proceedings of Fifth International Symposium on Ground Support, Perth, Australia, 2004, pp. 209–215. DOI: 10.1201/9780203023921-71. D. Tannant, Load capacity and stiffness of welded-wire mesh, in: Proceedings of the 48th Canadian Geotechnical Conference, Canada, 1995. DOI: N/A. D. Tannant, Thin spray-on liners for underground rock support, in: 17th International Mining Congress and Exhibition of Turkey (IMCET 2001), Ankara, 2001. DOI: http://dx.doi.org/. D. Tannant, P. Kaiser, S. Maloney, Load-displacement properties of welded-wire, chain-link and expanded metal mesh, in: International Symposium on Rock Support: Applied Solutions for Underground Structures, Lillehammer, 1997, pp. 651–659. DOI: N/A. Q. Wei, Mechanism of spraying flexible film in bolt support, Doctoral dissertation, China University of Mining and Technology, Xuzhou, 2020 (in Chinese). DOI: 10.27623/d.cnki.gzkyu.2020.000868. S. Wang, X. Xiong, J. Wang, S. Yan, Q. Wu, L. Weng, Experimental study on dynamic tensile properties of sandstone under TSL material protection, Journal of Vibration and Shock 42 (21) (2023) 192-199+218. (in Chinese).2023.21.023. Additional Declarations No competing interests reported. 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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-6927620","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":482042605,"identity":"0c7dd9cd-bd90-4c05-ab40-b504730fd12b","order_by":0,"name":"Han LIANG","email":"","orcid":"","institution":"Liaoning Technical University","correspondingAuthor":false,"prefix":"","firstName":"Han","middleName":"","lastName":"LIANG","suffix":""},{"id":482042606,"identity":"8a4ccf47-6312-486a-bb5a-de9566f8fb5d","order_by":1,"name":"ZHANG 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1","display":"","copyAsset":false,"role":"figure","size":108805,"visible":true,"origin":"","legend":"\u003cp\u003eTSL bond and infiltrate into the fractured rock mass to produce rock interlocking (t is the thickness of the cohesive rock layer).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/f73aec981ea934e58b66f9a8.png"},{"id":86319830,"identity":"3f079128-d609-4882-b178-7293895c1662","added_by":"auto","created_at":"2025-07-09 09:31:06","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":58696,"visible":true,"origin":"","legend":"\u003cp\u003eTSL coal pillar experiment (a) screened pulverized coal (b) sample pouring (c) sample pressing (d) samples.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/440baa1c3d1e09b0a87fc20d.jpg"},{"id":86318595,"identity":"e8913d4f-34bb-4b8b-998d-10472b0c96a6","added_by":"auto","created_at":"2025-07-09 09:23:06","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":55908,"visible":true,"origin":"","legend":"\u003cp\u003eCoal pillar test for surface protection in laboratory ( a ) TSL material diagram ( b ) diamond mesh after cutting ( c ) coal pillar sample for surface protection layout ( d ) test process\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/c2dd7f0895b0784e2687ff7f.jpg"},{"id":86318599,"identity":"a103bdf8-7bb6-482e-9a99-a11d500add68","added_by":"auto","created_at":"2025-07-09 09:23:06","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":112516,"visible":true,"origin":"","legend":"\u003cp\u003eLoad-displacement curves and test phenomenon of coal pillar specimen\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/a5d305b6fb0467d573dc8f88.jpg"},{"id":86319832,"identity":"b832602f-06d7-4ed9-aee6-13b70ea6737b","added_by":"auto","created_at":"2025-07-09 09:31:06","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":104828,"visible":true,"origin":"","legend":"\u003cp\u003ePlastic zones of 2.5 MPa and 5.0 MPa in numerical model\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/5e6975996f62892051788f25.jpg"},{"id":86318609,"identity":"af814a78-716a-41f0-bbf8-861ac994e7f8","added_by":"auto","created_at":"2025-07-09 09:23:06","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":201275,"visible":true,"origin":"","legend":"\u003cp\u003eMaximum principal stress contours of different supports under 2.5 MPa and 5.0 MPa loading conditions\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/43d7534294d817cc00208395.jpg"},{"id":86318603,"identity":"ff0e8de1-724f-48b3-95fc-af008d2dac67","added_by":"auto","created_at":"2025-07-09 09:23:06","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":251963,"visible":true,"origin":"","legend":"\u003cp\u003eTSL bearer state under 3.25 MPa and 6.5 MPa loading conditions\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/af66a540dd9c3100940e8220.jpg"},{"id":86319845,"identity":"14ad1968-6ecb-4e73-a410-d1f847fd2c80","added_by":"auto","created_at":"2025-07-09 09:31:07","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":66867,"visible":true,"origin":"","legend":"\u003cp\u003eComparative test of bearing capacity ( a ) specimen ( b ) TSL specimen ( c ) diamond mesh specimen ( d ) test process\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/a1a6c2889f98e4c217db1a49.jpg"},{"id":86319835,"identity":"0080df8a-09fd-4d27-8fee-ad07d35a8218","added_by":"auto","created_at":"2025-07-09 09:31:06","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":66350,"visible":true,"origin":"","legend":"\u003cp\u003eLoad-displacement curves of samples with different substrates (TSL, diamond mesh, no support)\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/95a73f076a2e1d1f9ee7647a.jpg"},{"id":86318610,"identity":"c94cbc82-0b73-42c2-a8d6-763ec84d3309","added_by":"auto","created_at":"2025-07-09 09:23:06","extension":"jpeg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":62544,"visible":true,"origin":"","legend":"\u003cp\u003eLignite TSL specimen after failure\u003c/p\u003e","description":"","filename":"10.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/5346e08278717073f17b6217.jpeg"},{"id":86319839,"identity":"6640295e-3c0e-4e0a-8cdf-9c59723cbaa4","added_by":"auto","created_at":"2025-07-09 09:31:06","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":85450,"visible":true,"origin":"","legend":"\u003cp\u003eNumerical model of shell structure\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/5f600fa85d50348e25fd226a.jpg"},{"id":86318608,"identity":"2c21a245-659e-4df3-b1fc-ac88bb812a65","added_by":"auto","created_at":"2025-07-09 09:23:06","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":97882,"visible":true,"origin":"","legend":"\u003cp\u003eNumerical model plastic zone of coal substrate under loading stress of 2.75 MPa\u003c/p\u003e","description":"","filename":"12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/1c6666d1f40a343a45c5fca9.jpg"},{"id":86319836,"identity":"70f2a0c2-6e54-4bf8-a9d1-7cbb767cd911","added_by":"auto","created_at":"2025-07-09 09:31:06","extension":"jpg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":189040,"visible":true,"origin":"","legend":"\u003cp\u003eDisplacement contour of the numerical model of coal substrate under loading stress of 3.75 MPa\u003c/p\u003e","description":"","filename":"13.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/8d4398b19eed4814e90e608e.jpg"},{"id":86318629,"identity":"8352f18a-f16e-484b-9b14-f4e29a3fd2bd","added_by":"auto","created_at":"2025-07-09 09:23:07","extension":"jpg","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":128130,"visible":true,"origin":"","legend":"\u003cp\u003eMaximum principal stress contour of TSL shell structure loaded into 3.75 MPa\u003c/p\u003e","description":"","filename":"14.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/8fac171748d9be0b489f748a.jpg"},{"id":86320883,"identity":"89d408f3-4171-4210-b734-ac8c4c81075b","added_by":"auto","created_at":"2025-07-09 09:39:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2314381,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6927620/v1/663832fb-c2e5-4443-84e6-77b462a237de.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Experimental study on surface protection support using polymer thin spray-on layer","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThin spray-on liner (TSL) is a protective technology for spraying thin films on the surface of rock mass, which is widely used in mine sealing projects, such as water sealing, airtight and gas extraction closure (Mpunzi et al. 2015). TSL support is a new method to replace the metal mesh in roadway support, which has the advantages of fast operation and automation, and has great application potentials in the rapid excavation and anchoring automation of underground coal mine roadway (Kang et al. 2024).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSupporting TSL materials can be classified as polymer or cement-based non-reactive types. In the past three decades, a variety of mining support TSL materials has been developed, and experimental research on the physical and mechanical properties of the materials was carried out, including the adhesive, tensile, shearing, compressive, bending and tearing properties of the materials (Chen et al.2024; Wang et al.2023), a few experimental studies on fire resistance, blastability and fiber reinforcement.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFrom the perspective of support manner, TSL is a kind of active support, that is, when the surrounding rock is slightly deformed, the support resistance of the TSL is generated to reduce the fracture propagation or broken rock fall off (Han et al. 2024; Lacerda et al.2002). Metal mesh is a kind of passive support, which produces a supporting effect after the surrounding rock is largely deformed or falls off. Shotcrete support relies on its own structural strength to provide large rigid constraints in the early stage of surrounding rock deformation, but its curing time is long, the flexibility is poor, and the small displacement under tensile, shear or torsion conditions can cause slag dropping and cracking of the sprayed layer, which is mostly used in permanent roadways with small deformation, and is not suitable for rapid excavation or large deformation roadways (Tannant et al. 1995 and 1997;). Therefore, TSL support is a more flexible support method between metal mesh and shotcrete (Tannant et al. 2001). In particular, the chemical reaction time of polymer TSL is about tens of seconds, which has the effect of \u0026quot;spraying and using\u0026quot;, and their mechanical performances are more diverse, which can meet the support needs of different mining geological conditions.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe performance of TSL is the premise of support design, which is of great research significance. After spraying, TSL forms a composite structure with the bonded surrounding rock, and its load-bearing and deformation law determines the supporting effect of TSL. At present, the research on TSL support performance mainly adopts the method of comparative test. For example, the comparative test of TSL support effect of hard rock pillar (Archibald et al.2001; Ozturk et al.2017; Qiao et al. 2014) and the bearing basket of broken rock mass (Nemcik et al.2011). The results show that TSL has a better supporting effect than steel mesh for soft rock (Qiao et al. 2015), loose rock mass (Kristie et al. 2006), jointed rock mass (Nemcik et al. 2014; Shan et al. 2018 and 2020) or rock mass with weak interlayer (Qiao et al. 2015).\u003c/p\u003e\n\u003cp\u003eIn summary, TSL support is a new method of fast and efficient surface protection, and the active support effect of the composite structure formed by TSL and bonded surrounding rock is more significant, especially for the weak and jointed rock mass of coal measure strata. However, the experimental research on TSL support is mostly for hard rock samples, and there are very few studies on soft rock in coal measure. The geological conditions and mining methods of metal mines are very different from those of underground coal mines, and the experimental design methods and research results of hard rock TSL support cannot be copied to the application of underground coal mines. Therefore, considering the application scenarios of TSL in underground coal mines, this paper firstly analyzes the supporting effect of TSL in different deformation stages, carries out experimental research on the support performance of TSL, and uses numerical methods to analyze the mechanism of the TSL support, so as to provide a basis for the application of TSL in underground coal roadway.\u003c/p\u003e"},{"header":"2. TSL deformation process and supporting effect","content":"\u003cp\u003eBased on the application process and bearing characteristics, TSL support can be divided into three stages: bonding, flexural deformation, and thin shell structure (Stacey et al. 2004), which correspond to the three main supporting effects of cemented wedge, confinement and thin shell structure, respectively.\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003e2.1 Cementation wedge effect\u003c/h3\u003e\n\u003cp\u003eAfter spraying, the TSL is bonded to the surrounding rock surface, causing the scattered rock to form rock interlocks (Fig. 1a). The bonding strength between TSL and rock is more than 3 times that of shotcrete (Ozturk et al. 2010; Chen et al. 2020; Wei et al. 2020), which can improve the integrity of loose rock mass effectively. Compared with shotcrete, TSL material also has better fluidity, and penetrates the cracks on the surface of the rock during the spraying process to repair the fractured surrounding rock. The experimental results show (Tannant et al. 2006) that the material can penetrate 20~50 mm depth for the crack width of 1~2 mm during the spraying process.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eExperimental results show that the airtightness of TSL can also reduce the deformation of surrounding rock (Finn et al. 2018). In the process of rock mass fracture and migration, gaps are formed between rock blocks, which cause the surrounding rock to expand. If no air enters, negative pressure can cause suction between rock blocks to prevent cracks from developing into fractures and dislocation (Coates et al. 1966). At the same time, the sealing effect of TSL can also prevent the weathering and deliquescent of the surface rock, which has a positive effect on maintaining the stability of sensitive rock mass.\u003c/p\u003e\n\u003cp\u003eIn the early stage of TSL support, it has a more active effect than metal mesh support by interlocking surface rock masses, repairing surrounding rock cracks, and preventing small rock blocks from loosening and falling. The support effect mainly depends on the adhesive performance of TSL, the infiltration ability to the rock joint, the thickness of the spray layer and the surface characteristics of the surrounding rock. After the TSL is solidified, it is deformed together with the bonded rock mass, and the TSL support enters the flexure stage, and the main role of the TSL support in this stage is the confining effect.\u003c/p\u003e\n\u003ch3\u003e2.2 Confining effect\u003c/h3\u003e\n\u003cp\u003eAfter the excavation of the underground space, the normal stress of the exposed surface is reduced to 0, and the surface rock mass changes from a three-way stress state to a two-way stress state. In the process of stress redistribution, if the load of the shallow surrounding rock is greater than its strength, the rock mass enters plastic deformation or even breakage, and the load is transferred to the deep rock mass until the bearing unit is in elastic deformation. The shallow surrounding rocks located in the fracture zone and plastic deformation zone are collectively referred to as the loosening zone of the surrounding rock.\u003c/p\u003e\n\u003cp\u003eWith the increase of the deformation of the surrounding rock of the roadway, the TSL and the cohesive rock mass enter the deflection deformation stage. In the flexural stage, TSL and the bonded surrounding rock form a composite structure to bear and deform together, and the TSL retaining layer makes the surface rock mass in a three-way stress state through its own bearing, establishes a restraint layer for the internal surrounding rock, and achieves the purpose of narrowing the loosening zone. Therefore, the main support of TSL in the flexural stage is the restraining effect on the deformation of the deep surrounding rock.\u003c/p\u003e\n\u003cp\u003eThe confinement effect of TSL depends on the displacement coupling with the cohesive rock mass, which is essentially a modification of the surface rock mass. The experimental results show that the compressive strength (Qiao et al. 2015;Wei et al.2020) and shear resistance of TSL specimens are significantly improved. Especially for coal measure strata, there are generally multiple weak structural planes, such as joints, cleats, cracks, etc., which have the characteristics of low strength and large loosening range, and the restraining effect of TSL enhances the stability of the surrounding rock structure.\u003c/p\u003e\n\u003cp\u003eIn the flexural stage, TSL produces tensile, shearing, bending and torsional deformation. In the experimental study of TSL support of soft rock and jointed rock mass, TSL mainly bears tensile stress and shear stress in this deformation stage (Qiao et al. 2015; Kristie et al. 2006; Nemcik et al. 2014; Shan et al. 2018). After the surrounding rock enters the stage of large deformation, TSL and the cohesive rock mass form a thin shell structure to produce support.\u003c/p\u003e\n\u003ch3\u003e2.3 Thin shell structure effect\u003c/h3\u003e\n\u003cp\u003eIn the final stage of TSL support, when the roadway displacement is large and the surface rock blocks are scattered, TSL, like the metal mesh, can produce a kind of bearing basket effect on the loose rock blocks. Due to the restraining effect of TSL or metal mesh and the anchorage of the rock bolt, the loose rock block has a certain bearing capacity, which can not only prevent the rock mass from falling and further free expansion of the cracks, but also transfer load from shallow loose rock mass to the deep stable rock mass through the bolt, so as to improve the stability of the surrounding rock.\u003c/p\u003e\n\u003cp\u003eThe ductility of the surface support material determines the support effect of the bearing basket, and the effect of TSL and metal mesh has advantages over shotcrete. The experimental results showed that the fiber-reinforced TSL greatly improved the bearing capacity of the basket.\u003c/p\u003e\n\u003cp\u003eShotcrete is considered to form a \u0026quot;shell structure\u0026quot; to be the main supporting role. Although there is local debonding, twisting, tearing and leakage in the final stage of support, the main part of TSL is still bonded to the surrounding rock. TSL and cohesive rock mass, including rocks within the bearing basket, can form a thin shell structure for bearing. In this case, the equivalent thickness of the crust is the thickness of the TSL bonded surrounding rock (t in Fig. 1).\u003c/p\u003e\n\u003cp\u003eThe mechanism of shell structures is a classic research topic in the field of shotcrete. Generally, it is assumed that the roadway is a semicircular section, and the plane stress or plane strain method is used for analysis. When the thickness of the spray layer is negligible to the roadway radius, the constitutive equation of the thin shell in the classical elastic theory is as follows:\u003c/p\u003e\n\u003cp\u003e\u003cimg width=\"162\" height=\"24\" src=\"data:image/png;base64,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\" alt=\"image\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; (1)\u003c/p\u003e\n\u003cp\u003ewhere\u0026nbsp;\u003cimg width=\"7\" height=\"16\" src=\"data:image/png;base64,R0lGODlhBwAQAHcAMSH+GlNvZnR3YXJlOiBNaWNyb3NvZnQgT2ZmaWNlACH5BAEAAAAALAAABQAHAAYAhAAAAAAAOgA6ZgBmtjo6kDqQ22YAZmY6AGZmOma2/5A6AJCQ25DbtpDb/7ZmALZmOraQkLb//9uQOtuQkNu2Ztv///+2Zv/bkP//tv//2wECAwECAwECAwECAwECAwECAwUfIHYMAGZEEEVeRAVICWAVAPA0mRKb0YQwi1wg4RBEQgA7\" alt=\"image\"\u003e\u0026nbsp;and\u0026nbsp;\u003cimg width=\"7\" height=\"16\" src=\"data:image/png;base64,R0lGODlhBwAQAHcAMSH+GlNvZnR3YXJlOiBNaWNyb3NvZnQgT2ZmaWNlACH5BAEAAAAALAAABQAHAAYAhAAAAAAAAAAAZgA6ZgA6kDoAADo6kDpmtjqQ22a2/5A6AJDb/7ZmOraQZrb//9uQOtu2Ztv////bkP//2wECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwUfIDA1RRAQAHNEzAJIRgQ8yFxPSjIfACQ4IkVg4AKEAAA7\" alt=\"image\"\u003e\u0026nbsp;are deflection and stress, r and \u0026theta; are the radius direction and angle, E is the Young\u0026apos;s modulus, and I is the moment of inertia of the cross-section. Consider the actual field to determine the boundary conditions for solving. However, the surface rock mass of the underground coal mine roadway is in a state of plastic deformation or even fractured, and its main bearing body is a pressure arch along the loose circle. Therefore, it is not appropriate to use the elastic shell structure theory or the linear bearing analysis method to analyze the supporting effect of TSL thin shell structure in underground coal mines. It is a new research topic to establish an analytical method for the supporting effect of TSL thin shell structure under the condition of large deformation of soft rock.\u003c/p\u003e\n\u003cp\u003eIn summary, TSL bonds the rock surface and repairs the fractured rock mass. With the increase of the surrounding rock deformation, TSL enters the flexural deformation stage and produces the bearing basket effect of the loose rock blocks, which has a restraining effect on the deformation of the surrounding rock. At the same time, TSL and the cohesive rock mass form a thin shell structure for bearing. In the follow-up study, a newly developed polymer TSL material was used to compare and analyze the confining effect of TSL on the deformation of coal pillars and the supporting effect of thin shell structure by experimental methods, and the load- deformation law of TSL and the mechanism of roadway surrounding rock were revealed by numerical methods, so as to provide theoretical guidance for the practical TSL engineering of underground coal mines.\u003c/p\u003e"},{"header":"3. TSL confinement effect for coal pillar ","content":"\u003cp\u003eOztuck and Guner (2017) and Qiao\u003csup\u003e\u0026nbsp;\u003c/sup\u003eet al (2014)\u003csup\u003e\u0026nbsp;\u003c/sup\u003econducted a comparative experimental study on TSL support for cylindrical hard rock pillars in metal mines. In this paper, the TSL support of the cuboid coal pillar of the underground mine is studied experimentally, and the comparison is carried out with the metal mesh support.\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003e3.1 Materials and methods\u003c/h3\u003e\n\u003cp\u003eThe width of the common coal pillar in underground mines is 5 m, the spacing of the connecting roadway is 20 m, and the height of the roadway is about 4 m. The coal pillar sample is determined to be 500 mm long, 125 mm wide and 100 mm high according to geometric similarity. The coal pillar specimen was prepared by pressing briquette. After crushing the lignite, the pulverized coal is screened using an 80-mesh sieve (Fig 2a). High-strength Portland cement is selected as the binder, and the mass ratio of pulverized coal to cement is 5:1 and the water-cement ratio is 0.4. Place the mixture into an internal space 500\u0026times;125\u0026times;100 mm metal mold (Fig 2b). The WAW-600C microcomputer controlled the electro-hydraulic servo-universal testing machine was used for compression, and the pressure was 3.2 MPa for 30 min (Fig. 2c). Leave the specimen at room temperature for 7 days before demoulding (Fig 2d).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn order to carry out numerical calculations, the mechanical parameters of the briquette were measured using the standard experimental method of rock mechanics, and the results are shown in Table 1.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1\u0026nbsp;\u003c/strong\u003eMechanical properties of briquette used in the test\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"532\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 20%;\"\u003e\n \u003cp\u003eBulk modulus/Pa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20%;\"\u003e\n \u003cp\u003eShear modulus/Pa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20%;\"\u003e\n \u003cp\u003eCohesiveness/Pa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20%;\"\u003e\n \u003cp\u003eTensile strength/Pa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20%;\"\u003e\n \u003cp\u003eInternal friction angle/\u0026deg;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 20%;\"\u003e\n \u003cp\u003e0.54E9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20%;\"\u003e\n \u003cp\u003e0.25E9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20%;\"\u003e\n \u003cp\u003e3.0E6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20%;\"\u003e\n \u003cp\u003e0.10E6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20%;\"\u003e\n \u003cp\u003e35\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe TSL used in the test is a self-developed two-component polyurethane substrate temperature-limiting modified material (patent number: CN113153373A), the composition of which is shown in Fig 3a, and the small figure shows the tensile interface. The mechanical properties are shown in Table 2 (Han et al.2021). The TSL specimen was placed into the center of the organic rubber frame with an internal dimension of 510\u0026times;135\u0026times;100 mm, mixed and stirred the TSL two-component material, poured into the gap between the coal pillar and the frame, and was released after curing. The galvanized diamond-shaped mesh of 10\u0026times;20 mm aperture (Fig. 3b) is tightly fastened with iron wire around the specimen after cutting. The control specimen does not have any surface protection arrangement. A total of three samples were prepared, including TSL, diamond mesh and none surface protection (Fig. 3c). The testing machine uses the WAW-600C, the loading rate is 1 mm/min, and the test process is shown in Fig 3d.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2\u003c/strong\u003e Mechanical parameters of TSL for test\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAverage compressive strength ( standard deviation ) / MPa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAverage deformation / mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAverage tensile strength ( standard deviation ) / MPa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eElongation at break / %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCohesion / MPa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eInternal friction angle / \u0026deg;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAverage bond strength with coal ( standard deviation ) / MPa\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e52.62（4.02）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e14.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e12.73（1.230）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e6.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e6.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e33.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.63（0.36）\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003ch3\u003e3.2 Results and Analysis\u003c/h3\u003e\n\u003cp\u003eThe load-displacement curves of the coal pillar samples with three different surface protection methods are shown in Fig 4, and the experimental results are shown in Table 3.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3\u003c/strong\u003e Supporting performance of coal pillar specimens under different support methods\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003eYield load/kN\u003c/p\u003e\n \u003cp\u003e(displacement under yield load/mm).\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 154px;\"\u003e\n \u003cp\u003ePeak load/kN\u003c/p\u003e\n \u003cp\u003e(displacement at peak load/mm).\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003eEnergy absorption capacity/J\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003eNone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003e309.4（5.29）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 154px;\"\u003e\n \u003cp\u003e313.5（6.12）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e2549\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003eDiamond-shaped mesh\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003e298.7（7.42）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 154px;\"\u003e\n \u003cp\u003e316.7（10.15）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e3004\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 101px;\"\u003e\n \u003cp\u003eTSL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003e384.5（12.52）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 154px;\"\u003e\n \u003cp\u003e406.2（14.48）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e4329\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe test results show that the yield and peak loads of the diamond-shaped mesh and the control specimen are similar, but the displacement of the metal mesh specimen is higher than that of the control specimen. It shows that after the yield and failure of the coal pillar, the mesh has the effect of holding the broken coal. The total energy absorption of the mesh support system is increased by 18% compared with that without support.\u003c/p\u003e\n\u003cp\u003eThe yield load of the TSL specimen is increased by 24% and the peak load is increased by 30% compared with the unprotected specimen. TSL had a vertical penetrating fracture at the peak of the test force, but it still had a high residual strength, indicating that the TSL support significantly improved the bearing capacity of the coal pillar. Compared with other specimens, the displacement of TSL under yielding load and peak load is larger, and it is more continuous than the diamond mesh after the material is broken, and the system energy absorption of TSL specimens is about 70% higher than that of the control specimens.\u003c/p\u003e\n\u003cp\u003eDuring the test, it was observed that the control sample had a large collapsed at the corner of the coal pillar under yield load, which belonged to the brittle failure type. At the peak load, compression-shear failure type occurred. The diamond-shaped mesh specimen begins to break when the coal body is under yield load, but the diamond-shaped mesh plays a blocking role in the thrown coal. At the peak load, the diamond-shaped mesh spreads out, part of the wire breaks, and the broken coal is thrown out. Local cracks appeared in the TSL before the yield load (Fig. 4), and penetrating tensile fracture appeared in the TSL under yield load, and the TSL fracture was further expanded under continuous loading, but it could still restrain the deformation of the coal pillar. Finally, the coal pillar was completely damaged after multiple penetrating failures in TSL (Fig. 4), but the TSL sample did not exhibit coal ejection at the end of the test.\u003c/p\u003e\n\u003cp\u003eThe experimental results show that the bonding between TSL and the coal pillar improves the strength and ductility of the rock mass and prevents sudden brittle failure. In particular, the high residual strength and large displacement after the peak significantly improve the energy dissipation of the system, which is a new method of surface protection support for large deformation roadways.\u003c/p\u003e\n\u003ch3 id=\"_Toc86628417\"\u003e3.3 Numerical Calculations\u003c/h3\u003e\n\u003cp\u003eNumerical method is used to analyze the bearing state of TSL and the influence on the stress distribution of coal pillars during the test, which can be hardly observed and analyzed in the test.\u003c/p\u003e\n\u003ch4\u003e3.3.1 Model establishment and validation\u003c/h4\u003e\n\u003cp\u003eFLAC3D 5.01\u0026nbsp;（FLAC3D 5.01 https://www.itascacg.com/software/flac3d）was used to establish the numerical models of TSL and unreinforced coal pillars. The geometry of the model is the same as that of the test specimen. The Mohr-Colomb failure criterion was used. The mechanical parameters of the model are shown in Table 1, and the mechanical parameters of TSL are shown in Table 2. \u0026nbsp;The bottom of the model is bound in the x, y, and z directions, and the rest are free faces.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe calculation results are compared with the experimental results to verify the reliability of the calculation model. The results of the coal pillar test show that the peak load of the unsupported sample is 313.5 kN（5.01 MPa）. The calculation model of the coal pillar without surface protection is loaded to 2.5 MPa (50% peak load) and 5.0 MPa (peak load), respectively, and the plastic zone of the coal pillar is shown in Fig. 5.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eUnder 2.5 MPa loading, the upper part of the coal pillar model began to undergo tensile plastic deformation, especially at the corner of the coal pillar. When the loading stress is 5.0 MPa, most of the coal pillar model elements are in the plastic zone, which is mostly consistent with the experimental observation, and it is considered that the stress distribution state and evolution law of the model are consistent with the experimental results.\u003c/p\u003e\n\u003ch4\u003e3.3.2 Effect of TSL on the maximum principal stress of coal pillar\u003c/h4\u003e\n\u003cp\u003eFig. 6 shows the maximum principal stress distribution of the TSL supported and unsupported coal pillar models under the condition that the vertical stresses are 2.5 MPa and 5.0 MPa, respectively.\u003c/p\u003e\n\u003cp\u003eThe calculation results show that the model is mostly tensile except for the lower part of the model under the loading condition of 2.5 MPa, and the maximum tensile stress is 0.08 MPa, and the outside of the model is more concentrated. When the loading stress is 5.0 MPa, except for the binding area on the lower surface, the coal pillar is in tension, and the maximum tensile stress is 0.10 MPa. At 2.5 MPa of TSL coal pillar, most of the coal pillar units are in the compression state, and the maximum tensile stress is at the corner of the bond between the TSL and the coal pillar. Under the loading condition of 5.0 MPa, most of the TSL coal pillar units are still under compression. The confining effect of TSL on the coal pillar improves the bearing state of the coal pillar element and increases the stability of the coal pillar.\u003c/p\u003e\n\u003ch4\u003e3.3.3 Load-bearing characteristics of the TSL\u003c/h4\u003e\n\u003cp\u003eThe peak load of the laboratory TSL specimen is 406.2 kN, or 6.50 MPa. The TSL calculation model was loaded to 3.25 MPa (50% peak load) and 6.50 MPa, respectively, and Fig. 7 shows the distribution contour of the maximum principal stress and maximum shear stress of the TSL itself.\u003c/p\u003e\n\u003cp\u003eThe maximum principal stress contour shows that the maximum principal stress of the TSL element is tensile stress, and the maximum principal stress of the coal pillar element near the TSL is also in tensile stress. The stress concentration is mainly at the corner where the TSL is bonded to the coal pillar. With the increase of loading stress, the maximum principal stress in the TSL element increases, and the maximum principal stress of the TSL element reaches 2.5 MPa when the loading stress is 6.50 MPa. In the laboratory test, the TSL failure is tensile break of the spray layer, which is due to the high tensile stress of the spray layer.\u003c/p\u003e\n\u003cp\u003eThe maximum shear stress contour shows that the TSL element is the shear stress concentration area, and the TSL shear stress on the two sides of the corner of the coal pillar is the largest. As the loading stress increases, the maximum shear stress in the TSL element increases and expands to both sides. The shear stress of the coal pillar element bonded to TSL is also larger, and the internal shear stress of the coal pillar is smaller. When loaded to 6.50 MPa, the maximum shear stress of TSL and bonded coal pillar elements reaches 5.0 MPa, but the shear stress of most coal pillar elements inside the coal pillar is small.\u003c/p\u003e\n\u003cp\u003eIt shows that TSL significantly improves the bearing capacity of the surface rock mass through its own bearing, and establishes a restraining effect for the deformation of the deep rock mass. Moreover, the stress state of the rock mass around TSL is similiar to that of the layer, that is, this restraining effect is jointly established by TSL and the cohesive rock mass. Subsequently, experimental and numerical methods were used to study the supporting effect of the thin shell structure formed by TSL and the cohesive rock mass under the condition of large deformation of the surrounding rock.\u003c/p\u003e"},{"header":"4. TSL thin shell structure support","content":"\u003cp\u003eThe supporting role of shell structures formed by sprayed concrete has been widely recognized by the academic community. However, the development of TSL is relatively short, and the research on support theory is seriously insufficient. In this study, it is believed that after the large deformation of the surrounding rock of the roadway, TSL and the bonded surrounding rock form a similar thin shell structure. The numerical study results of the confinement effect of TSL coal pillars also show that the bearing state of the medium bonded by TSL is very similar to that of TSL, but is quite different from that of the deep medium, which also provides a theoretical basis for the formation of thin shell structure at the end of TSL support stage. However, there is still a gap in the research on related basic theories. Therefore, the bearing performance and deformation characteristics of TSL thin shell structures were studied experimentally, followed by numerical method used to analyze the stress evolution law between TSL and the bonded rock mass during the bearing process.\u003c/p\u003e\n\u003ch3\u003e4.1 Materials and methods\u003c/h3\u003e\n\u003cp\u003eTwo kinds of rocks, lignite and sandstone, were used as the sample substrates to study the TSL thin shell support effect of hard rock and soft rock. The mechanical properties of them are shown in Table 4. Two types of rock were processed into 200 mm x 200 mm x 150 mm substrate specimens, 3 of each rock. In order to make the experimental results more obvious and to facilitate comparison with the current shotcrete research results, a circular hole with a diameter of 50 mm was drilled in the center of the substrate to simulate the underground roadway, and the drilled substrate is shown in Fig 8a.\u003c/p\u003e\n\u003cp\u003eTable 4 Mechanical parameters of sandstone and lignite for testing\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"554\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003eBulk modulus/Pa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003eShear modulus/Pa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 115px;\"\u003e\n \u003cp\u003eCohesiveness/Pa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003eTensile strength/Pa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 80px;\"\u003e\n \u003cp\u003eInternal friction angle/\u0026deg;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003elignite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e1.0E9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e6.0E8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 115px;\"\u003e\n \u003cp\u003e2.0E6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e1.0E6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 80px;\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003esandstone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e2.0E10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e1.3E10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 115px;\"\u003e\n \u003cp\u003e1.8E7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e9.0E6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 80px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThree kinds of samples were made on two substrates, TSL support, diamond mesh support and unsupported. The material properties of TSL and diamond mesh are the same as those of the coal pillar confinement experiment. A PVC pipe with an outer diameter of 4.0 mm was used for the TSL specimens. It was placed in the center of the hole after lubrication, TSL materials were mixed and stirred with the same volume and poured into the gap between the PVC pipe and the hole. The PVC pipe was withdrawn after 2 minutes (Fig. 8b). The diamond-shaped mesh was cut into 200\u0026times;150 mm, rolled into a cylindrical shape, and arranged in a circular hole of the sample with iron wire connection (Fig. 8c). There is no surface protection for the circular hole in the control samples. The testing machine is WAW-600C and the loading mode is displacement loading at the loading rate of 1 mm/min. The load and displacement are monitored and and the test process is shown in Fig 8d.\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003e4.2 Results and Analysis\u003c/h3\u003e\n\u003cp\u003eFig. 9 shows the load-displacement curves for different lithologies and different surface protection methods. The experimental results are summarized in Table 5.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 5\u003c/strong\u003e Experimental results of different substrate and surface protection methods\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 9.5317%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 10.5292%;\"\u003e\n \u003cp\u003eSupport method\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 16.5143%;\"\u003e\n \u003cp\u003eYield load (kN)/\u003c/p\u003e\n \u003cp\u003eDisplacement(mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 15.8493%;\"\u003e\n \u003cp\u003ePeak load (kN)/\u003c/p\u003e\n \u003cp\u003eDisplacement (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.6412%;\"\u003e\n \u003cp\u003eEnergy Absorption(J)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 9.5317%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 10.5292%;\"\u003e\n \u003cp\u003eNone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 16.5143%;\"\u003e\n \u003cp\u003e105.5 (3.91)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 15.8493%;\"\u003e\n \u003cp\u003e118.5 (4.14)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 5.3821%;\"\u003e\n \u003cp\u003e128.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 9.5317%;\"\u003e\n \u003cp\u003eLignite\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 10.5292%;\"\u003e\n \u003cp\u003eMesh\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 16.5143%;\"\u003e\n \u003cp\u003e115.0 (4.10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 15.8493%;\"\u003e\n \u003cp\u003e119.9 (4.34)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 5.3821%;\"\u003e\n \u003cp\u003e151.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 9.5317%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 10.5292%;\"\u003e\n \u003cp\u003eTSL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 16.5143%;\"\u003e\n \u003cp\u003e136.9 (4.92)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 15.8493%;\"\u003e\n \u003cp\u003e171.3 (6.27)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 5.3821%;\"\u003e\n \u003cp\u003e386.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 9.5317%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 9.8642%;\"\u003e\n \u003cp\u003eNone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 16.5143%;\"\u003e\n \u003cp\u003e278.0 (6.46)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 15.7384%;\"\u003e\n \u003cp\u003e309.7 (7.04)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5292%;\"\u003e\n \u003cp\u003e887.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 9.5317%;\"\u003e\n \u003cp\u003eSandstone\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 9.8642%;\"\u003e\n \u003cp\u003eMesh\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 16.5143%;\"\u003e\n \u003cp\u003e310.5 (7.63)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 15.7384%;\"\u003e\n \u003cp\u003e315.3 (8.07)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5292%;\"\u003e\n \u003cp\u003e922.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 9.5317%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 9.8642%;\"\u003e\n \u003cp\u003eTSL\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 16.5143%;\"\u003e\n \u003cp\u003e321.0 (8.92)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 15.7384%;\"\u003e\n \u003cp\u003e373.0 (11.76)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5292%;\"\u003e\n \u003cp\u003e2712\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe patterns of load-displacement curves are very similar for the two rock substrate specimens. The results show that the yield and peak load of the diamond mesh specimens are close to those of the unsupported specimens. The reason is that the diamond mesh supports the rock mass when its displacement is large. The bearing capacity and ductility of the TSL specimen were significantly improved, and the dissipation energy was increased by 201% compared with the control specimen, and 156% higher than that of the diamond-shaped mesh specimen.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCompared with sandstone and lignite, sandstone has high strength, and the yield, peak and residual strength of the sample are higher than those of the lignite samples. However, the improvement of the supporting performance of the sandstone TSL sample is less than that of the lignite sample, and the same TSL has a more significant supporting effect on the soft rock.\u003c/p\u003e\n\u003cp\u003eThe failure process of the two substrate specimens is similar. The unprotected specimen and the diamond-shaped mesh specimen underwent a brittle failure around the hole under yield load and expanded rapidly, and the failure was completely carried out under peak load. The failure of the TSL specimen first occurs in the brittle failure at the corner of the specimen, and the medium around the hole also begins to fail after the yield load is reached, and the specimen is completely destroyed after the complete failure of the TSL ring. Fig 10 shows that the lignite substrate TSL sample has undergone complete brittle failure, and the upper part of the TSL ring is basically debonded from the substrate, but the lower TSL is still bonded to the substrate.\u003c/p\u003e\n\u003ch3\u003e4.3 Numerical calculations\u003c/h3\u003e\n\u003ch4\u003e4.3.1 Model establishment and verification\u003c/h4\u003e\n\u003cp\u003eNumerical calculation method is used to analyze the bearing state of TSL thin shell structure and its influence on the stress distribution of surrounding rock during the test. The dimensions of the calculated model are the same as those for the shell structure bearing test, which is 200\u0026times;200\u0026times;150 mm. The computational model uses the Mohr-Coulomb criterion. The deformation laws of different substrate samples are similar, only the simulation results of lignite are shown. The mechanical parameters of the model material are shown in Table 4. The bottom surface of the model is bound in the x, y, and z directions, and the rest is free surface, as shown in Fig 11. The TSL is simulated using shell structure element in the numerical model.\u003c/p\u003e\n\u003cp\u003eFirst, the computational model is to be verified. The yield load of the non-surface protection specimen in the test is 2.75 MPa, and the stress of 2.75 MPa is applied to the upper part of the two calculation models, respectively. The calculation results of the plastic zone of the non-surface and TSL shell models are shown in Fig. 12.\u003c/p\u003e\n\u003cp\u003eThe calculation results of the plastic zone show that most of the elements of the non-protection coal model are in tensile yield state under the load of yield stress (2.75 MPa), and the elements on both sides of the round hole are in the shear plastic deformation state, which is consistent with the brittle failure phenomenon round hole in the test. Under the same stress loading, the tensile and shear plastic deformation of the coal unit occurred above the hole, but the TSL shell structure was in the elastic stage, which was consistent with the experimental observation.\u0026nbsp;\u003c/p\u003e\n\u003ch4\u003e4.3.2 The influence of thin shell on the deformation of surrounding rock\u003c/h4\u003e\n\u003cp\u003eThe distribution law of surrounding rock deformation under different support conditions was compared. The numerical calculation model was loaded to 3.75 MPa (TSL specimen yield stress) and the displacement contour is shown in Fig 13.\u003c/p\u003e\n\u003cp\u003eThe results show that under the stress load of 3.75 MPa, the elements around the hole of the model without a protective surface are seriously deformed, with a maximum displacement of 13.06 mm, which is located above the round hole, and the hole is completely collapsed in the experiment. The maximum displacement of the TSL model is 12.28 mm, but the maximum displacement element is at the upper corner of the model, and the displacement of the elements around the round hole is not large, and the shape of the round hole is basically intact, which is consistent with the experimental phenomenon.\u003c/p\u003e\n\u003cp\u003eUnder the condition of no support, the deformation caused by the stress of the rock mass is freely propagated around the hole, resulting in the large deformation of the surface surrounding rock, which is shown in engineering practice as the surrounding rock of the roadway is broken and falling. The restraint effect is lost, resulting in the further expansion of the loosening circle of the roadway. Under the condition that there is a shell structure around the hole, the shell structure prevents the large deformation of the rock mass around the hole and maintains the stability of the roadway.\u003c/p\u003e\n\u003ch4\u003e4.3.3 Load-bearing state of thin shell structure\u003c/h4\u003e\n\u003cp\u003eThe shell structure in the calculation model was taken out separately to analyze its deformation and stress-bearing state under different stresses. When the loading stress is 3.75 MPa, the displacement calculation results of the TSL shell structure are shown in Fig. 14a. The results show that the overall displacement of the shell structure is small, with a maximum displacement of 0.38 mm on the upper surface and a gradual decrease from top to bottom, and the maximum displacement on the lower surface is about 0.31 mm. In the experiment, the upper part of the TSL ring was debonded and broken, but the lower part was relatively intact and bonded to the coal base.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe maximum principal stress contour of the TSL shell structure under 3.75 MPa loading is shown in 14b. The results show that the whole shell structure is in a state of compressive stress, and the maximum principal stress on the upper and lower surfaces reaches 6.14 MPa, and the smaller one on both sides is only 1.0 MPa. It is believed that the effective shell structure can significantly improve the stress distribution state of the rock mass on the surface of the roadway and increase the stability of the supporting structure.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eTSL support has the advantages of fast development, automation and wide range of application, and is a new method to replace the metal mesh support of underground coal mines. In this study, laboratory experiments and numerical calculations were used to compare and analyze the supporting effect of a new polymer TSL in coal mine roadway, and the following conclusions were drawn:\u003c/p\u003e\n\u003cp\u003e(1) After the TSL is bonded with the surface surrounding rock, the rock is interlocked, and the bond layer has a confining effect on the deformation of the deep rock mass. TSL restraint is earlier than metal mesh and more resilient than shotcrete. In the large deformation stage of the surrounding rock, TSL forms a thin shell structure with the cohesive rock mass and the loose rock blocks in the bearing basket, which produces the surface protection support effect through its own bearing compressive stress.\u003c/p\u003e\n\u003cp\u003e(2) For large briquette pillar samples, the restraining effect of TSL is earlier and stronger than that of diamond mesh, and the bearing capacity of the sample is increased by 28.3%. At the same time, the ductility of TSL tensile is better, the residual strength of the specimen is higher, the post-peak displacement is larger, and the total energy dissipation of the specimen is increased by 44.1%.\u003c/p\u003e\n\u003cp\u003e(3) In the large deformation stage of the roadway, the TSL and the confined rock mass form a thin shell structure, and the deformation of the surface rock mass is reduced by the compressive stress of the self-bearing, and the bearing capacity of the lignite and sandstone TSL thin shell structure specimens increases by 44.6% and 20.4%, respectively, and the energy dissipation increases by about 2 times.\u003c/p\u003e\n\u003cp\u003eThis study provides a theoretical basis for the practice of TSL support engineering and an experimental research method for the prediction of TSL support effect in coal mine roadway.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eFund Project\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNational Natural Science Foundation of China Youth Project ( 52304135 )\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eL. and Z. wrote the main manuscript text , S. and B. prepared figures 1-3. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe main raw data has been provided in the article. The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eJ.F. Archibald, Assessing acceptance criteria for and capabilities of liners for mitigating ground falls, in: Mining Health and Safety Conference 2001, Sudbury, Ontario, 2001, pp. 209\u0026ndash;215. DOI: N/A.\u003c/li\u003e\n\u003cli\u003eL. Chen, Z. Zhou, G. Liu, et al., Effects of substrate materials and liner thickness on the adhesive strength of the novel thin spray-on liner, Advances in Mechanical Engineering 12 (2) (2020) 1\u0026ndash;13. DOI:10.1177/1687814020904574.\u003c/li\u003e\n\u003cli\u003eQ.F. Chen, W.X. Yang, J.Y. Wu, W.J. Niu, Macro and micro experimental study on the effect of water-cement ratio on the tensile properties of thin spray lining materials, Materials Reports 38 (8) (2024) 281\u0026ndash;287 (in Chinese). DOI: 10.11896/cldb.22090309.\u003c/li\u003e\n\u003cli\u003eD.F. Coates, Rock Mechanics Principles, Geoscience Abstracts (1966). DOI: N/A.\u003c/li\u003e\n\u003cli\u003eENC 250TSL v7.2 25-07-08, Specification and guidelines on thin spray-on liners for mining and tunnelling, 2008. DOI: N/A.\u003c/li\u003e\n\u003cli\u003eD.J. Finn, P. Teasdale, C.R. Windsor, In-situ trials and field testing of two polymer restraint membranes, in: Proceedings of the Conference, Rotterdam, 2018. DOI: 10.1201/9780203740460-13.\u003c/li\u003e\n\u003cli\u003eJ. Han, T.Y. Zhang, H. Liang, et al., A surface support method for coal mine roadway with reactive resin thin spray material, China Patent CN113153373A, 2021 (in Chinese). DOI: N/A.\u003c/li\u003e\n\u003cli\u003eY. Han, S.C. Li, C. Yuan, X.D. Feng, X.W. Wang, Analysis of mechanical properties and crack propagation characteristics of thin-fissure red sandstone under uniaxial compression, Rock and Soil Mechanics 45 (9) (2024) 2583\u0026ndash;2594 (in Chinese). DOI: 10.16285/j.rsm.2023.1682.\u003c/li\u003e\n\u003cli\u003eH.P. Kang, P.F. Jiang, Z.Y. Wang, et al., Rapid excavation technology and equipment and application of drilling and anchoring integration in coal roadway, Journal of China Coal Society 49 (1) (2024) 131\u0026ndash;151 (in Chinese). DOI: 10.13225/j.cnki.jccs.2023.1675.\u003c/li\u003e\n\u003cli\u003eT. Kristie, Laboratory testing procedures for evaluating thin spray-on membrane liners, in: Proceeding of the CORE Project on Deep Mining, 2006. DOI: 10.1007/s00603-014-0669-7.\u003c/li\u003e\n\u003cli\u003eL. Lacerda, M. Rispin, Current ground support membrane applications in North American underground mines, in: 2nd International Seminar on Surface Support, South Africa, 2002. DOI: N/A.\u003c/li\u003e\n\u003cli\u003eP. Mpunzi, R. Masethe, M. Rizwan, et al., Enhancement of the tensile strengths of rock and shotcrete by thin spray-on liners, Tunneling and Underground Space Technology 49 (2015) 369\u0026ndash;375. DOI:10.1016/j.tust.2015.05.013.\u003c/li\u003e\n\u003cli\u003eJ. Nemcik, I. Porter, E. Baafi, J. Towns, Bearing capacity of a glass fibre reinforced polymer liner, in: Proceedings of 11th Coal Operator\u0026rsquo;s Conference, Wollongong, Australia, 2011, pp. 148\u0026ndash;153. DOI: N/A.\u003c/li\u003e\n\u003cli\u003eJ. Nemcik, Stress in Underground Mines, Lecture notes distributed for MINE323 Mining GeoMechanics, Wollongong, 2014. DOI: N/A.\u003c/li\u003e\n\u003cli\u003eH. Ozturk, D. Guner, Failure analysis of thin spray-on liner coated rock cores, Engineering Failure Analysis 79 (2017) 25\u0026ndash;33. DOI: 10.1016/j.engfailanal.2017.03.024.\u003c/li\u003e\n\u003cli\u003eH. Ozturk, D. 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DOI: N/A.\u003c/li\u003e\n\u003cli\u003eD. Tannant, Thin spray-on liners for underground rock support, in: 17th International Mining Congress and Exhibition of Turkey (IMCET 2001), Ankara, 2001. DOI: http://dx.doi.org/.\u003c/li\u003e\n\u003cli\u003eD. Tannant, P. Kaiser, S. Maloney, Load-displacement properties of welded-wire, chain-link and expanded metal mesh, in: International Symposium on Rock Support: Applied Solutions for Underground Structures, Lillehammer, 1997, pp. 651\u0026ndash;659. DOI: N/A.\u003c/li\u003e\n\u003cli\u003eQ. Wei, Mechanism of spraying flexible film in bolt support, Doctoral dissertation, China University of Mining and Technology, Xuzhou, 2020 (in Chinese). DOI: 10.27623/d.cnki.gzkyu.2020.000868.\u003c/li\u003e\n\u003cli\u003eS. Wang, X. Xiong, J. Wang, S. Yan, Q. Wu, L. Weng, Experimental study on dynamic tensile properties of sandstone under TSL material protection, Journal of Vibration and Shock 42 (21) (2023) 192-199+218. (in Chinese).2023.21.023.\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":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"TSL, roadway support, restraint, shell structure, bearing mechanism","lastPublishedDoi":"10.21203/rs.3.rs-6927620/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6927620/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe Thin Spray-on Layer (TSL) is widely used in seal engineering of mine. TSL with high bearing capability is a new method to replace the metal mesh in the roadway support of underground coal mines, which has the advantages of fast development, automation and applicability of geo-conditions. Based on the deformational process of TSL in soft rock roadway, the support theories of TSL are analyzed. It shows that TSL coheres and repairs the surrounding rock surface to form a bonding layer, which has a confinement effect on the deformation of deep rock mass. Under the condition of large deformation of surrounding rock, TSL forms a thin shell structure, which produces supporting effect. Experiments were conducted to compare the support effects of different surface protection methods using large-scale briquette coal pillar samples and a newly developed polymer TSL material. The results show that the confining effect of TSL is greater than that of the metal mesh, and the bearing capacity of the sample is increased by 28.3%. The residual strength of the TSL specimen is also higher, and the energy dissipation of the system increases by 44.1%. The support effect of TSL thin shell structure is experimentally studied for the first time on different rock mass. The results showed that the TSL shell structure reduced surface rock deformation by bearing compressive stress, and the bearing capacity of lignite and sandstone samples increased by 44.6% and 20.4%, respectively, while energy dissipation increased by about 2 times. The numerical method was used to analyze stress distribution of TSL and mechanism of surrounding rock deformation in the experiments, and results were compared with experimental observations. This study provides a theoretical basis for the practice of TSL support engineering and an experimental research method for predicting the effect of TSL support in underground coal mine roadway.\u003c/p\u003e","manuscriptTitle":"Experimental study on surface protection support using polymer thin spray-on layer","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-09 09:23:01","doi":"10.21203/rs.3.rs-6927620/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-11T09:27:07+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-11T07:11:05+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-10T09:27:26+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"194943840894418118582498120704524119642","date":"2025-07-08T00:28:13+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"294182310101415633673009063907769485698","date":"2025-07-07T13:26:49+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"101031458662314811701779930161255649306","date":"2025-07-07T12:26:04+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"21468376176581349633625221382911866792","date":"2025-07-07T12:09:18+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-07T10:01:12+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-07T09:55:55+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-07-07T08:48:54+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-30T17:40:35+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-06-30T17:37:35+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"873f3c0c-dc09-4c89-b109-acbd390d26c9","owner":[],"postedDate":"July 9th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":51180362,"name":"Physical sciences/Engineering/Civil engineering"},{"id":51180363,"name":"Earth and environmental sciences/Environmental sciences/Environmental impact"}],"tags":[],"updatedAt":"2025-08-01T07:08:26+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-09 09:23:01","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6927620","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6927620","identity":"rs-6927620","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}