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.
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...
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.
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...
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