In this paper, a modeling procedure is carried out to numerically investigate the end bearing cap... more In this paper, a modeling procedure is carried out to numerically investigate the end bearing capacity of drilled shafts in layered soils. For the case of sand overlying clay, the reliable depth for full mobilization of the end bearing capacity of drilled shafts is also discussed. The modeling procedure in homogenous soil and the constitutive law are first described. The modeling procedure in layered soils is explained next. Numerical analyses show that when the pile tip is located in the sand and close to the clay layer below, the distance that pile tip senses the presence of the clay layer depends on the ratio of the fully mobilized end bearing capacity of clay to the fully mobilized end bearing capacity of sand. Finally, numerical results are compared with experimental data suggested by other researchers.
International Journal of Geomechanics, Aug 27, 2010
ABSTRACT Using a high-strength geosynthetic for encasement of granular columns increases the stre... more ABSTRACT Using a high-strength geosynthetic for encasement of granular columns increases the strength of a given column and improves its stress-displacement response. This paper describes the results from a series of three-dimensional finite-element analyses that were performed to simulate the behavior of a single geosynthetic-encased column in soft clay. To examine the sensitivity of the results to the constitutive model that was used to simulate the behavior of the encased granular soil, analyses were performed using models for the encased soil possessing various levels of sophistication. For each model that was studied, comparative analyses were performed to simulate the behavior of a dense and a loose granular soil within the encasement. The results demonstrate the importance of selecting a constitutive model that accurately captures the shear-induced volume-change behavior of the encased granular soil. Additional findings provide guidance for other researchers seeking to model the behavior of geosynthetic-encased columns and are useful for practitioners looking to enhance their understanding of the performance of different constitutive models for simulating the behavior of similar foundation elements. (c) 2012 American Society of Civil Engineers.
ABSTRACT Stone columns are commonly used as ground improvement elements since they act as reinfor... more ABSTRACT Stone columns are commonly used as ground improvement elements since they act as reinforcing inclusions. However, due to the lack of sufficient lateral confinement for the columns, this technique is not applicable for the improvement of grounds that consist of very soft soils. In order to provide lateral confinement and increase the load bearing capacity of stone columns installed in very soft clay soils, they are usually encased with suitable geosynthetic materials, forming geosynthetic-encased columns (GECs). In this paper, a 3D numerical approach is used to study the effect of varying the encasement length of different columns of a group of GECs on the overall group behavior. These results are compared with those obtained from a group of fully encased columns, through comparison of the settlements and lateral deformations (bulging) of the columns. The analyses are calibrated through modeling the behavior of GECs used in a ground reclamation project in Hamburg, Germany. Parametric studies are also carried out to investigate the effects of factors such as stiffness of the geosynthetic encasement, column diameter, and modulus of elasticity and friction angle of the column material on the overall behavior of the GEC group. The results indicated that encasing only the outer columns of the stone column group is sufficient in providing an optimal design. It was also shown that increasing the stiffness of the encasement and the column diameter enhance the overall behavior of the GEC group through increasing the overall stiffness of the stone columns and the ratio of the soft soil replaced by the stone columns (i.e. the area replacement ratio), respectively. Moreover, it was observed that the performance of GECs is comparatively less sensitive to the internal friction angle of the column material, and that, in general, the modulus of elasticity of the column material has only a small effect on the group behavior.
In this paper, a modeling procedure is carried out to numerically analyze the end bearing capacit... more In this paper, a modeling procedure is carried out to numerically analyze the end bearing capacity of drilled shafts in sand. The Mohr–Coulomb elastic plastic constitutive law with stress dependent elastic parameters is used for all numerical analyses performed in this study. The numerical results are compared with the available experimental equations. It is seen that numerical results are in
ABSTRACT Using a high-strength geosynthetic for encasement of granular columns increases the stre... more ABSTRACT Using a high-strength geosynthetic for encasement of granular columns increases the strength of a given column and improves its stress-displacement response. This paper describes the results from a series of three-dimensional finite-element analyses that were performed to simulate the behavior of a single geosynthetic-encased column in soft clay. To examine the sensitivity of the results to the constitutive model that was used to simulate the behavior of the encased granular soil, analyses were performed using models for the encased soil possessing various levels of sophistication. For each model that was studied, comparative analyses were performed to simulate the behavior of a dense and a loose granular soil within the encasement. The results demonstrate the importance of selecting a constitutive model that accurately captures the shear-induced volume-change behavior of the encased granular soil. Additional findings provide guidance for other researchers seeking to model the behavior of geosynthetic-encased columns and are useful for practitioners looking to enhance their understanding of the performance of different constitutive models for simulating the behavior of similar foundation elements. (c) 2012 American Society of Civil Engineers.
In this paper, a modeling procedure is carried out to numerically investigate the end bearing cap... more In this paper, a modeling procedure is carried out to numerically investigate the end bearing capacity of drilled shafts in layered soils. For the case of sand overlying clay, the reliable depth for full mobilization of the end bearing capacity of drilled shafts is also discussed. The modeling procedure in homogenous soil and the constitutive law are first described. The modeling procedure in layered soils is explained next. Numerical analyses show that when the pile tip is located in the sand and close to the clay layer below, the distance that pile tip senses the presence of the clay layer depends on the ratio of the fully mobilized end bearing capacity of clay to the fully mobilized end bearing capacity of sand. Finally, numerical results are compared with experimental data suggested by other researchers.
International Journal of Geomechanics, Aug 27, 2010
ABSTRACT Using a high-strength geosynthetic for encasement of granular columns increases the stre... more ABSTRACT Using a high-strength geosynthetic for encasement of granular columns increases the strength of a given column and improves its stress-displacement response. This paper describes the results from a series of three-dimensional finite-element analyses that were performed to simulate the behavior of a single geosynthetic-encased column in soft clay. To examine the sensitivity of the results to the constitutive model that was used to simulate the behavior of the encased granular soil, analyses were performed using models for the encased soil possessing various levels of sophistication. For each model that was studied, comparative analyses were performed to simulate the behavior of a dense and a loose granular soil within the encasement. The results demonstrate the importance of selecting a constitutive model that accurately captures the shear-induced volume-change behavior of the encased granular soil. Additional findings provide guidance for other researchers seeking to model the behavior of geosynthetic-encased columns and are useful for practitioners looking to enhance their understanding of the performance of different constitutive models for simulating the behavior of similar foundation elements. (c) 2012 American Society of Civil Engineers.
ABSTRACT Stone columns are commonly used as ground improvement elements since they act as reinfor... more ABSTRACT Stone columns are commonly used as ground improvement elements since they act as reinforcing inclusions. However, due to the lack of sufficient lateral confinement for the columns, this technique is not applicable for the improvement of grounds that consist of very soft soils. In order to provide lateral confinement and increase the load bearing capacity of stone columns installed in very soft clay soils, they are usually encased with suitable geosynthetic materials, forming geosynthetic-encased columns (GECs). In this paper, a 3D numerical approach is used to study the effect of varying the encasement length of different columns of a group of GECs on the overall group behavior. These results are compared with those obtained from a group of fully encased columns, through comparison of the settlements and lateral deformations (bulging) of the columns. The analyses are calibrated through modeling the behavior of GECs used in a ground reclamation project in Hamburg, Germany. Parametric studies are also carried out to investigate the effects of factors such as stiffness of the geosynthetic encasement, column diameter, and modulus of elasticity and friction angle of the column material on the overall behavior of the GEC group. The results indicated that encasing only the outer columns of the stone column group is sufficient in providing an optimal design. It was also shown that increasing the stiffness of the encasement and the column diameter enhance the overall behavior of the GEC group through increasing the overall stiffness of the stone columns and the ratio of the soft soil replaced by the stone columns (i.e. the area replacement ratio), respectively. Moreover, it was observed that the performance of GECs is comparatively less sensitive to the internal friction angle of the column material, and that, in general, the modulus of elasticity of the column material has only a small effect on the group behavior.
In this paper, a modeling procedure is carried out to numerically analyze the end bearing capacit... more In this paper, a modeling procedure is carried out to numerically analyze the end bearing capacity of drilled shafts in sand. The Mohr–Coulomb elastic plastic constitutive law with stress dependent elastic parameters is used for all numerical analyses performed in this study. The numerical results are compared with the available experimental equations. It is seen that numerical results are in
ABSTRACT Using a high-strength geosynthetic for encasement of granular columns increases the stre... more ABSTRACT Using a high-strength geosynthetic for encasement of granular columns increases the strength of a given column and improves its stress-displacement response. This paper describes the results from a series of three-dimensional finite-element analyses that were performed to simulate the behavior of a single geosynthetic-encased column in soft clay. To examine the sensitivity of the results to the constitutive model that was used to simulate the behavior of the encased granular soil, analyses were performed using models for the encased soil possessing various levels of sophistication. For each model that was studied, comparative analyses were performed to simulate the behavior of a dense and a loose granular soil within the encasement. The results demonstrate the importance of selecting a constitutive model that accurately captures the shear-induced volume-change behavior of the encased granular soil. Additional findings provide guidance for other researchers seeking to model the behavior of geosynthetic-encased columns and are useful for practitioners looking to enhance their understanding of the performance of different constitutive models for simulating the behavior of similar foundation elements. (c) 2012 American Society of Civil Engineers.
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