The pullout behaviour of cement-grouted soil nails, particularly in field conditions, is not yet ... more The pullout behaviour of cement-grouted soil nails, particularly in field conditions, is not yet fully understood. In this study, a series of tests was conducted to evaluate the pullout response of grouted soil nails in a field slope. A new innovative grouting packer system was developed to control the grouted length and maintain the cement grout pressure of the grouted part. By using the grouting packer system, a total of 10 soil nails placed at different soil depths were grouted with different pressures in the field. The pullout results of present field tests and a number of past laboratory tests indicate that the apparent coefficient of friction (ACF) decreases with the increase of overburden stress even though grouting pressure is applied. In addition, when the overburden stress is unchanged, the obtained ACF values in the field tests appear to increase almost linearly with the increase of grouting pressure. After the soil nails were completely pulled out of the ground, the surfaces of the soil nails and surrounding soil were examined. It is found that the water content of the soil samples at the soil-nail interfaces decrease substantially compared to the water content of soil samples in drill holes. Measurement results also show that the failure surfaces of soil nails shifted about 16 mm on average into the surrounding soil due to the application of grouting pressure.
The authors wish to thank the discussers for their interest in our paper and for their suggestion... more The authors wish to thank the discussers for their interest in our paper and for their suggestions. The first method advocated by the discussers is what the authors used in the paper. The second method suggested by the discussers was to use a cylindrical cavity expansion model, proposed by Jiang and Shen [1], to consider the softening behaviour of a dilative soil. They consider that the second method can be used to analytically calculate the stress and strain distributions in the soil surrounding the soil nail, but did not show how it can be used in soil nail pullout analysis. It should be noted that the actual stress and strain distributions in the perimetric and axial directions around the soil nail are not uniform (see Fig. 2 in the paper for the former case). In the axial direction the soil nail pullout resistance is developed in a progressive way, as in the simple method proposed by the authors. In addition, the proper evaluation of the model parameters, for example how the elastic and plastic regions along the soil nail are defined, is also important in the development of the new method. Reference [1] Jiang JM, Shen ZJ. On expansion of cylindrical cavity with linear softening and shear dilatation behavior.
The pullout behaviour of cement-grouted soil nails, particularly in field conditions, is not yet ... more The pullout behaviour of cement-grouted soil nails, particularly in field conditions, is not yet fully understood. In this study, a series of tests was conducted to evaluate the pullout response of grouted soil nails in a field slope. A new innovative grouting packer system was developed to control the grouted length and maintain the cement grout pressure of the grouted part. By using the grouting packer system, a total of 10 soil nails placed at different soil depths were grouted with different pressures in the field. The pullout results of present field tests and a number of past laboratory tests indicate that the apparent coefficient of friction (ACF) decreases with the increase of overburden stress even though grouting pressure is applied. In addition, when the overburden stress is unchanged, the obtained ACF values in the field tests appear to increase almost linearly with the increase of grouting pressure. After the soil nails were completely pulled out of the ground, the surfaces of the soil nails and surrounding soil were examined. It is found that the water content of the soil samples at the soil–nail interfaces decrease substantially compared to the water content of soil samples in drill holes. Measurement results also show that the failure surfaces of soil nails shifted about 16 mm on average into the surrounding soil due to the application of grouting pressure. Résumé : Le comportement en retrait de clous de sol avec coulis en ciment n'est pas encore totalement compris, particulière-ment dans les conditions de terrain. Dans cette étude, une série d'essais a été réalisée pour évaluer le comportement en retrait de clous de sol cimentés dans une pente sur le terrain. Un nouveau système innovateur de coulis étanche a été développé afin de contrôler la longueur cimentée et de maintenir la pression du coulis de la partie cimentée. À l'aide du système de coulis étanche, un total de dix clous de sol placés a ` différentes profondeurs dans le sol sur le terrain ont été cimentés avec différentes pressions. Les résultats de retrait des présents essais de terrain et de nombreux essais en laboratoire précédents indiquent que le coefficient de friction apparente (CFA) diminue lorsque la contrainte des terres augmente, même si une pression de ciment est appliquée. De plus, lorsque la contrainte des terres demeure inchangée, les valeurs de CFA obtenues dans les essais semblent augmenter de façon presque linéaire avec l'augmentation de la pression du coulis. Une fois que les clous de sol ont été complètement retirés du sol, les surfaces des clous de sol et du sol environnant ont été examinées. Il a été déterminé que les teneurs en eau des échantillons de sol aux interfaces sol-clou diminuent substantiellement comparativement aux teneurs en eau des échantillons de sol dans les trous de forage. Les résultats de mesures démontrent aussi que les surfaces de rupture des clous de sol se déplacent d'environ 16 mm en moyenne dans le sol environnant en raison de l'application de coulis sous pression. [Traduit par la Rédaction] Mots-clés : clou de sol, pression de coulis de ciment, coefficient de friction apparente, contrainte des terres.
In this study, the accuracy and reliability of fully nonlinear method against equivalent linear m... more In this study, the accuracy and reliability of fully nonlinear method against equivalent linear method for dynamic analysis of soil-structure interaction is investigated comparing the predicted results of both numerical procedures with the results of experimental shaking table tests. An enhanced numerical soil-structure model has been developed which treats the behaviour of the soil and the structure with equal rigour. The soil-structural model comprises a 15 storey structural model resting on a soft soil inside a laminar soil container. The structural model was analysed under three different conditions: (i) fixed base model performing conventional time history dynamic analysis, (ii) flexible base model (considering full soil-structure interaction) conducting equivalent linear dynamic analysis, and (iii) flexible base model performing fully nonlinear dynamic analysis. The results of the above mentioned three cases in terms of lateral storey deflections and inter-storey drifts are determined and compared with the experimental results of shaking table tests. Comparing the experimental results with the numerical analysis predictions, it is noted that equivalent linear method of dynamic analysis underestimates the inelastic seismic response of mid-rise moment resisting building frames resting on soft soils in comparison to the fully nonlinear dynamic analysis method. Thus, inelastic design procedure, using equivalent linear method, cannot adequately guarantee the structural safety for mid-rise building frames resting on soft soils. However, results obtained from the fully nonlinear method of analysis fit the experimental results reasonably well. Therefore, this method is recommended to be used by practicing engineers.
Unsaturated soil is common in practical geotechnical engineering and is defined by more character... more Unsaturated soil is common in practical geotechnical engineering and is defined by more characteristics than saturated soil. Based on the Fredlund and Rahardjo's one-dimensional (1-D) consolidation theories of unsaturated soil, the behaviors of unsaturated soil under different initial and boundary conditions are investigated. The differential quadrature method (DQM) is employed to obtain the solutions that consider different boundary conditions and various initial pore water and air distributions. DQM is an efficient numerical technique for initial and/or boundary problems, and it can obtain sufficient accuracy with a small number of discretized points. It can avoid cumbersome computations in solving eigen-equations encountered with the analytical solution. A special case for which the analytical solution is available in the literature is employed to compare with and verify the accuracy of the DQM solution. Good agreements are found in the comparisons. Then the average degree of consolidation is studied for the different boundary conditions. Finally, the characteristics of the 1-D consolidation of unsaturated soil are investigated under various initial pore pressure distributions. It is found that the initial and boundary conditions have a significant influence on the consolidation of unsaturated soil.
Japanese Geotechnical Society Special Publication, 2016
The shear strength of unsaturated completely decomposed granite (CDG) soil was studied by perform... more The shear strength of unsaturated completely decomposed granite (CDG) soil was studied by performing a series of unsaturated direct shear tests under different combinations of net normal stress and matric suction conditions. The axis-translation technique is applied to control matric suction. A series of typical soil water characteristic curves (SWCC) of CDG soil under different net normal stresses were obtained considering consolidation process by monitoring the vertical displacement throughout the tests. Experimental results show that both unsaturated shear strength and SWCC are affected by the soil stress states. Shear dilation behavior is observed significantly obvious at higher suction and lower net normal stress state, and the shear strength of unsaturated CDG soil increases with matric suction and net normal stress.
The present study focuses on the pullout resistance of grouted soil nails which are commonly used... more The present study focuses on the pullout resistance of grouted soil nails which are commonly used in Hong Kong. Data from a series of laboratory and field pullout tests are presented for investigation of key influencing factors on the fundamental interaction mechanism of soil nail pullout resistance. Laboratory soil nail pullout tests were carried out on a completely decomposed granite (CDG) soil in a nearly saturated condition under a combination of different grouting pressures and overburden stresses. In addition, a total of 8 pullout tests were conducted in a slope site with different overburden stresses and grouting pressures. The study shows that the grouting pressure and overburden stress have interactional influence on the soil nail pullout resistance. New understandings and findings from the study are presented.
,"A new simulation approach of genetic programming in modelling of soil water retention property ... more ,"A new simulation approach of genetic programming in modelling of soil water retention property of unsaturated soil", Engineering Computations, Vol. 32 Iss 3 pp. 914 -930 Permanent link to this document: http://dx.
The design of preloading involves loading schedule design and prediction of post-construction set... more The design of preloading involves loading schedule design and prediction of post-construction settlement. As the in situ measurement data are usually unavailable during the loading schedule design, it is difficult to estimate the preloading effects before construction. In this Reply, we first discuss the satisfied conditions of eq. (D4) in the Discussion (Mesri and Wang 2015) based on Bjerrum's creep diagram and Yin-Graham's model . Then the research objective and significance of the paper under discussion ) are addressed.
Based on Fredlund's one-dimensional (1-D) consolidation theory for unsaturated soils, the solutio... more Based on Fredlund's one-dimensional (1-D) consolidation theory for unsaturated soils, the solution to consolidation of a two-layer system for unsaturated soil is obtained in matrix form by using differential quadrature method (DQM). DQ solution can produce highly accurate solution with a considerable small number of sample points. Due to the uniform matrix structure of the present solution, it is easy to program and many complicated in situ factors can be considered. In addition, the solution can be easily extended for multi-layered unsaturated soil profile. In the case study, the influences of different saturated water permeability ratios ,2 ,1 / w w k k and thickness ratios 2 1 / h h on the dissipation of both water and air phases subjected to instantaneous loading are investigated. The variation of average degree of consolidation versus time and the isochrones along depth for both water and air phases are presented and discussed. It is found that the saturated water permeability ratio has much influence on the dissipation process of both water and air phases.
To investigate the soil-pile interactive performance under lateral loads, a set of laboratory mod... more To investigate the soil-pile interactive performance under lateral loads, a set of laboratory model tests was conducted on remoulded test bed of soft clay and medium dense sand. Then, a simplified boundary element analysis had been carried out assuming floating pile. In case of soft clay, it has been observed that lateral loads on piles can initiate the formation of a gap, soil heave and the tension crack in the vicinity of the soil surface and the interface, whereas in medium dense sand, a semi-elliptical depression zone can develop. Comparison of test and boundary element results indicates the accuracy of the solution developed. However, in the boundary element analysis, the possible shear stresses likely to be developed at the interface are ignored in order to simplify the existing complex equations. Moreover, it is unable to capture the influence of base restraint in case of a socketed pile. To bridge up this gap and to study the influence of the initial stress state and interfa...
Soil nailing is the most popular technique for stabilizing newly formed and existing sub-standard... more Soil nailing is the most popular technique for stabilizing newly formed and existing sub-standard slopes in Hong Kong because of its economic and technical advantages. The nail-soil interface shear resistance is an important parameter in design of soil nailed structures. A three-dimensional finite element model was established and used for simulating soil nail pull-out tests. The finite element model was verified by comparing simulated results with measured data. The agreement between the experimental and simulated results in terms of both average pull-out shear stress and stress variation was very good. Using this finite element model, a parametric study was carried out to study the influences of the overburden pressure and soil dilation angle on the soil nail pull-out resistance. The simulated peak pull-out resistance was not directly related to the overburden pressure, which was coincident with the observations in laboratory pull-out tests. The simulated pull-out resistance increased significantly with the increase in dilation angle of the shearing zone. This analysis indicated that the constrained dilatancy of the nail-soil interface and the soil surrounding the nail contributed a lot to the development of peak pull-out resistance.
Soil nailing technology has been commonly used for upgrading geotechnical structures such as reta... more Soil nailing technology has been commonly used for upgrading geotechnical structures such as retaining walls, excavations or slopes, etc. The reinforcing effect of a soil nail in the geotechnical structures is largely related to the soil nail cement grout quality, which is however invisible while the soil nail is installed inside the geotechnical structures. This paper presents a study on the cement grout quality of model soil nails measured using Long Gage fiber Bragg grating (FBG) sensing technology and by carrying a pullout test. In this study, a series of pullout tests were performed for model soil nails grouted with various cavity defects. Long-Gauge FBG (LGFBG) sensing array was then used for measuring the strain distributions along the model soil nails. Test results indicate that the presence of cavity defects due to poor grouting quality can be identified within a specific range by using the LGFBG sensing array.
This paper presents a study on the soil nail pullout resistance based on results from a series of... more This paper presents a study on the soil nail pullout resistance based on results from a series of laboratory soil nail pullout tests.
Grouted soil nails are widely used in the slope stabilization projects. It is of great interests ... more Grouted soil nails are widely used in the slope stabilization projects. It is of great interests to engineers and researchers to study the mechanism of the soil nail pullout resistance under different conditions. In this paper, a three-dimensional (3D) finite element (FE) model is developed to simulate the behavior of soil nail considering the effects of overburden pressure and dilation. The Mohr-Coulomb model is adopted to simulate the soil behavior. The interaction between the soil nail surface and the surrounding soil is modeled by Coulomb model. Contact pairs are used at the soil-nail interface so that the sliding failure can be considered during the pullout analysis. The model parameters are calibrated by the triaxial soil test data. It is found that the selected model can represent the soil stress-strain behaviour under different confining pressures. Large scale laboratory pullout test data are used to compare with the modelling results and verify the model. The soil stress variations surrounding the soil nail before and during pullout are demonstrated in FE modelling. Parametric analysis is carried out to investigate the effects of soil dilation and overburden pressure on the soil nail pullout resistance. It is found that the effect of interface soil dilation under small overburden pressures is not so significant as that under OP = 200 kPa and 300 kPa.
The pullout behaviour of cement-grouted soil nails, particularly in field conditions, is not yet ... more The pullout behaviour of cement-grouted soil nails, particularly in field conditions, is not yet fully understood. In this study, a series of tests was conducted to evaluate the pullout response of grouted soil nails in a field slope. A new innovative grouting packer system was developed to control the grouted length and maintain the cement grout pressure of the grouted part. By using the grouting packer system, a total of 10 soil nails placed at different soil depths were grouted with different pressures in the field. The pullout results of present field tests and a number of past laboratory tests indicate that the apparent coefficient of friction (ACF) decreases with the increase of overburden stress even though grouting pressure is applied. In addition, when the overburden stress is unchanged, the obtained ACF values in the field tests appear to increase almost linearly with the increase of grouting pressure. After the soil nails were completely pulled out of the ground, the surfaces of the soil nails and surrounding soil were examined. It is found that the water content of the soil samples at the soil-nail interfaces decrease substantially compared to the water content of soil samples in drill holes. Measurement results also show that the failure surfaces of soil nails shifted about 16 mm on average into the surrounding soil due to the application of grouting pressure.
The authors wish to thank the discussers for their interest in our paper and for their suggestion... more The authors wish to thank the discussers for their interest in our paper and for their suggestions. The first method advocated by the discussers is what the authors used in the paper. The second method suggested by the discussers was to use a cylindrical cavity expansion model, proposed by Jiang and Shen [1], to consider the softening behaviour of a dilative soil. They consider that the second method can be used to analytically calculate the stress and strain distributions in the soil surrounding the soil nail, but did not show how it can be used in soil nail pullout analysis. It should be noted that the actual stress and strain distributions in the perimetric and axial directions around the soil nail are not uniform (see Fig. 2 in the paper for the former case). In the axial direction the soil nail pullout resistance is developed in a progressive way, as in the simple method proposed by the authors. In addition, the proper evaluation of the model parameters, for example how the elastic and plastic regions along the soil nail are defined, is also important in the development of the new method. Reference [1] Jiang JM, Shen ZJ. On expansion of cylindrical cavity with linear softening and shear dilatation behavior.
The pullout behaviour of cement-grouted soil nails, particularly in field conditions, is not yet ... more The pullout behaviour of cement-grouted soil nails, particularly in field conditions, is not yet fully understood. In this study, a series of tests was conducted to evaluate the pullout response of grouted soil nails in a field slope. A new innovative grouting packer system was developed to control the grouted length and maintain the cement grout pressure of the grouted part. By using the grouting packer system, a total of 10 soil nails placed at different soil depths were grouted with different pressures in the field. The pullout results of present field tests and a number of past laboratory tests indicate that the apparent coefficient of friction (ACF) decreases with the increase of overburden stress even though grouting pressure is applied. In addition, when the overburden stress is unchanged, the obtained ACF values in the field tests appear to increase almost linearly with the increase of grouting pressure. After the soil nails were completely pulled out of the ground, the surfaces of the soil nails and surrounding soil were examined. It is found that the water content of the soil samples at the soil–nail interfaces decrease substantially compared to the water content of soil samples in drill holes. Measurement results also show that the failure surfaces of soil nails shifted about 16 mm on average into the surrounding soil due to the application of grouting pressure. Résumé : Le comportement en retrait de clous de sol avec coulis en ciment n'est pas encore totalement compris, particulière-ment dans les conditions de terrain. Dans cette étude, une série d'essais a été réalisée pour évaluer le comportement en retrait de clous de sol cimentés dans une pente sur le terrain. Un nouveau système innovateur de coulis étanche a été développé afin de contrôler la longueur cimentée et de maintenir la pression du coulis de la partie cimentée. À l'aide du système de coulis étanche, un total de dix clous de sol placés a ` différentes profondeurs dans le sol sur le terrain ont été cimentés avec différentes pressions. Les résultats de retrait des présents essais de terrain et de nombreux essais en laboratoire précédents indiquent que le coefficient de friction apparente (CFA) diminue lorsque la contrainte des terres augmente, même si une pression de ciment est appliquée. De plus, lorsque la contrainte des terres demeure inchangée, les valeurs de CFA obtenues dans les essais semblent augmenter de façon presque linéaire avec l'augmentation de la pression du coulis. Une fois que les clous de sol ont été complètement retirés du sol, les surfaces des clous de sol et du sol environnant ont été examinées. Il a été déterminé que les teneurs en eau des échantillons de sol aux interfaces sol-clou diminuent substantiellement comparativement aux teneurs en eau des échantillons de sol dans les trous de forage. Les résultats de mesures démontrent aussi que les surfaces de rupture des clous de sol se déplacent d'environ 16 mm en moyenne dans le sol environnant en raison de l'application de coulis sous pression. [Traduit par la Rédaction] Mots-clés : clou de sol, pression de coulis de ciment, coefficient de friction apparente, contrainte des terres.
In this study, the accuracy and reliability of fully nonlinear method against equivalent linear m... more In this study, the accuracy and reliability of fully nonlinear method against equivalent linear method for dynamic analysis of soil-structure interaction is investigated comparing the predicted results of both numerical procedures with the results of experimental shaking table tests. An enhanced numerical soil-structure model has been developed which treats the behaviour of the soil and the structure with equal rigour. The soil-structural model comprises a 15 storey structural model resting on a soft soil inside a laminar soil container. The structural model was analysed under three different conditions: (i) fixed base model performing conventional time history dynamic analysis, (ii) flexible base model (considering full soil-structure interaction) conducting equivalent linear dynamic analysis, and (iii) flexible base model performing fully nonlinear dynamic analysis. The results of the above mentioned three cases in terms of lateral storey deflections and inter-storey drifts are determined and compared with the experimental results of shaking table tests. Comparing the experimental results with the numerical analysis predictions, it is noted that equivalent linear method of dynamic analysis underestimates the inelastic seismic response of mid-rise moment resisting building frames resting on soft soils in comparison to the fully nonlinear dynamic analysis method. Thus, inelastic design procedure, using equivalent linear method, cannot adequately guarantee the structural safety for mid-rise building frames resting on soft soils. However, results obtained from the fully nonlinear method of analysis fit the experimental results reasonably well. Therefore, this method is recommended to be used by practicing engineers.
Unsaturated soil is common in practical geotechnical engineering and is defined by more character... more Unsaturated soil is common in practical geotechnical engineering and is defined by more characteristics than saturated soil. Based on the Fredlund and Rahardjo's one-dimensional (1-D) consolidation theories of unsaturated soil, the behaviors of unsaturated soil under different initial and boundary conditions are investigated. The differential quadrature method (DQM) is employed to obtain the solutions that consider different boundary conditions and various initial pore water and air distributions. DQM is an efficient numerical technique for initial and/or boundary problems, and it can obtain sufficient accuracy with a small number of discretized points. It can avoid cumbersome computations in solving eigen-equations encountered with the analytical solution. A special case for which the analytical solution is available in the literature is employed to compare with and verify the accuracy of the DQM solution. Good agreements are found in the comparisons. Then the average degree of consolidation is studied for the different boundary conditions. Finally, the characteristics of the 1-D consolidation of unsaturated soil are investigated under various initial pore pressure distributions. It is found that the initial and boundary conditions have a significant influence on the consolidation of unsaturated soil.
Japanese Geotechnical Society Special Publication, 2016
The shear strength of unsaturated completely decomposed granite (CDG) soil was studied by perform... more The shear strength of unsaturated completely decomposed granite (CDG) soil was studied by performing a series of unsaturated direct shear tests under different combinations of net normal stress and matric suction conditions. The axis-translation technique is applied to control matric suction. A series of typical soil water characteristic curves (SWCC) of CDG soil under different net normal stresses were obtained considering consolidation process by monitoring the vertical displacement throughout the tests. Experimental results show that both unsaturated shear strength and SWCC are affected by the soil stress states. Shear dilation behavior is observed significantly obvious at higher suction and lower net normal stress state, and the shear strength of unsaturated CDG soil increases with matric suction and net normal stress.
The present study focuses on the pullout resistance of grouted soil nails which are commonly used... more The present study focuses on the pullout resistance of grouted soil nails which are commonly used in Hong Kong. Data from a series of laboratory and field pullout tests are presented for investigation of key influencing factors on the fundamental interaction mechanism of soil nail pullout resistance. Laboratory soil nail pullout tests were carried out on a completely decomposed granite (CDG) soil in a nearly saturated condition under a combination of different grouting pressures and overburden stresses. In addition, a total of 8 pullout tests were conducted in a slope site with different overburden stresses and grouting pressures. The study shows that the grouting pressure and overburden stress have interactional influence on the soil nail pullout resistance. New understandings and findings from the study are presented.
,"A new simulation approach of genetic programming in modelling of soil water retention property ... more ,"A new simulation approach of genetic programming in modelling of soil water retention property of unsaturated soil", Engineering Computations, Vol. 32 Iss 3 pp. 914 -930 Permanent link to this document: http://dx.
The design of preloading involves loading schedule design and prediction of post-construction set... more The design of preloading involves loading schedule design and prediction of post-construction settlement. As the in situ measurement data are usually unavailable during the loading schedule design, it is difficult to estimate the preloading effects before construction. In this Reply, we first discuss the satisfied conditions of eq. (D4) in the Discussion (Mesri and Wang 2015) based on Bjerrum's creep diagram and Yin-Graham's model . Then the research objective and significance of the paper under discussion ) are addressed.
Based on Fredlund's one-dimensional (1-D) consolidation theory for unsaturated soils, the solutio... more Based on Fredlund's one-dimensional (1-D) consolidation theory for unsaturated soils, the solution to consolidation of a two-layer system for unsaturated soil is obtained in matrix form by using differential quadrature method (DQM). DQ solution can produce highly accurate solution with a considerable small number of sample points. Due to the uniform matrix structure of the present solution, it is easy to program and many complicated in situ factors can be considered. In addition, the solution can be easily extended for multi-layered unsaturated soil profile. In the case study, the influences of different saturated water permeability ratios ,2 ,1 / w w k k and thickness ratios 2 1 / h h on the dissipation of both water and air phases subjected to instantaneous loading are investigated. The variation of average degree of consolidation versus time and the isochrones along depth for both water and air phases are presented and discussed. It is found that the saturated water permeability ratio has much influence on the dissipation process of both water and air phases.
To investigate the soil-pile interactive performance under lateral loads, a set of laboratory mod... more To investigate the soil-pile interactive performance under lateral loads, a set of laboratory model tests was conducted on remoulded test bed of soft clay and medium dense sand. Then, a simplified boundary element analysis had been carried out assuming floating pile. In case of soft clay, it has been observed that lateral loads on piles can initiate the formation of a gap, soil heave and the tension crack in the vicinity of the soil surface and the interface, whereas in medium dense sand, a semi-elliptical depression zone can develop. Comparison of test and boundary element results indicates the accuracy of the solution developed. However, in the boundary element analysis, the possible shear stresses likely to be developed at the interface are ignored in order to simplify the existing complex equations. Moreover, it is unable to capture the influence of base restraint in case of a socketed pile. To bridge up this gap and to study the influence of the initial stress state and interfa...
Soil nailing is the most popular technique for stabilizing newly formed and existing sub-standard... more Soil nailing is the most popular technique for stabilizing newly formed and existing sub-standard slopes in Hong Kong because of its economic and technical advantages. The nail-soil interface shear resistance is an important parameter in design of soil nailed structures. A three-dimensional finite element model was established and used for simulating soil nail pull-out tests. The finite element model was verified by comparing simulated results with measured data. The agreement between the experimental and simulated results in terms of both average pull-out shear stress and stress variation was very good. Using this finite element model, a parametric study was carried out to study the influences of the overburden pressure and soil dilation angle on the soil nail pull-out resistance. The simulated peak pull-out resistance was not directly related to the overburden pressure, which was coincident with the observations in laboratory pull-out tests. The simulated pull-out resistance increased significantly with the increase in dilation angle of the shearing zone. This analysis indicated that the constrained dilatancy of the nail-soil interface and the soil surrounding the nail contributed a lot to the development of peak pull-out resistance.
Soil nailing technology has been commonly used for upgrading geotechnical structures such as reta... more Soil nailing technology has been commonly used for upgrading geotechnical structures such as retaining walls, excavations or slopes, etc. The reinforcing effect of a soil nail in the geotechnical structures is largely related to the soil nail cement grout quality, which is however invisible while the soil nail is installed inside the geotechnical structures. This paper presents a study on the cement grout quality of model soil nails measured using Long Gage fiber Bragg grating (FBG) sensing technology and by carrying a pullout test. In this study, a series of pullout tests were performed for model soil nails grouted with various cavity defects. Long-Gauge FBG (LGFBG) sensing array was then used for measuring the strain distributions along the model soil nails. Test results indicate that the presence of cavity defects due to poor grouting quality can be identified within a specific range by using the LGFBG sensing array.
This paper presents a study on the soil nail pullout resistance based on results from a series of... more This paper presents a study on the soil nail pullout resistance based on results from a series of laboratory soil nail pullout tests.
Grouted soil nails are widely used in the slope stabilization projects. It is of great interests ... more Grouted soil nails are widely used in the slope stabilization projects. It is of great interests to engineers and researchers to study the mechanism of the soil nail pullout resistance under different conditions. In this paper, a three-dimensional (3D) finite element (FE) model is developed to simulate the behavior of soil nail considering the effects of overburden pressure and dilation. The Mohr-Coulomb model is adopted to simulate the soil behavior. The interaction between the soil nail surface and the surrounding soil is modeled by Coulomb model. Contact pairs are used at the soil-nail interface so that the sliding failure can be considered during the pullout analysis. The model parameters are calibrated by the triaxial soil test data. It is found that the selected model can represent the soil stress-strain behaviour under different confining pressures. Large scale laboratory pullout test data are used to compare with the modelling results and verify the model. The soil stress variations surrounding the soil nail before and during pullout are demonstrated in FE modelling. Parametric analysis is carried out to investigate the effects of soil dilation and overburden pressure on the soil nail pullout resistance. It is found that the effect of interface soil dilation under small overburden pressures is not so significant as that under OP = 200 kPa and 300 kPa.
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