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© 2019 American Society of Civil Engineers. According to the characteristics of the time-dependent dispersion coefficient of pollutant migration in soils, a one-dimensional pollutant migration model considering solute decay is established in the finite thickness soil. Based on the proposed model, the time-dependent boundary condition variable is considered, and different types of time-dependent dispersion coefficients are also assumed. The variable parameter k for pollutant diffusion time is used to control the time-dependent model. The analytical solution is obtained by separating the variable method. The results calculated by the presented analytical solution compared with those in the literature indicate solution accuracy and program reliability. According to the parameter study, variable k in the time-dependent model has a particular influence on the results, and the time-dependent and constant boundary conditions have a significant difference. The proposed method can be a reference for the landfill liner design.

© 2019 American Society of Civil Engineers. According to the characteristics of the time-dependent dispersion coefficient of pollutant migration in soils, a one-dimensional pollutant migration model considering solute decay is established in the finite thickness soil. Based on the proposed model, the time-dependent boundary condition variable is considered, and different types of time-dependent dispersion coefficients are also assumed. The variable parameter k for pollutant diffusion time is used to control the time-dependent model. The analytical solution is obtained by separating the variable method. The results calculated by the presented analytical solution compared with those in the literature indicate solution accuracy and program reliability. According to the parameter study, variable k in the time-dependent model has a particular influence on the results, and the time-dependent and constant boundary conditions have a significant difference. The proposed method can be a reference for the landfill liner design.

© 2018 American Society of Civil Engineers. Seismic pounding occurs when the separation gap between buildings and structures is not wide enough, particularly during major earthquake events; this can cause them to collide, causing local damage or, in extreme cases, collapse. This study investigated the impact that this separation gap has on the seismic response of midrise buildings supported on piles while considering seismic soil-pile-structure interaction (SSPSI). To achieve this aim, three 15-story reinforced concrete buildings sitting on pile foundations and with five different separation gaps under excitations from the 1994 Northridge and 1995 Kobe earthquakes were numerically simulated. This study used three-dimensional numerical modeling to simultaneously capture the effects of seismic pounding and SSPSI. Because the considered structure, pile foundation, and soil deposit are three-dimensional in nature, the adopted three-dimensional numerical modeling can provide a more realistic simulation to capture the seismic behavior of the system. The nonlinear behavior of structural elements was included, and the dynamic soil properties were obtained from field data and backbone curves. A contact pair interface with small-sliding surface-to-surface formulation between buildings was used to capture possible seismic pounding, and contact interfaces with a finite-sliding formulation were used to simulate the interaction between the piles and the soil. The results, including lateral building deflections, interstory drifts, structural shear forces, foundation rocking, lateral pile deflections, and the distributions of bending moments and shear forces of the piles, are presented and discussed. The findings of this study will give engineers a better insight into the possible effects of seismic pounding on the seismic performance of buildings, and the response of endbearing piles in soft soils.

© 2018 American Society of Civil Engineers. Seismic pounding occurs when the separation gap between buildings and structures is not wide enough, particularly during major earthquake events; this can cause them to collide, causing local damage or, in extreme cases, collapse. This study investigated the impact that this separation gap has on the seismic response of midrise buildings supported on piles while considering seismic soil-pile-structure interaction (SSPSI). To achieve this aim, three 15-story reinforced concrete buildings sitting on pile foundations and with five different separation gaps under excitations from the 1994 Northridge and 1995 Kobe earthquakes were numerically simulated. This study used three-dimensional numerical modeling to simultaneously capture the effects of seismic pounding and SSPSI. Because the considered structure, pile foundation, and soil deposit are three-dimensional in nature, the adopted three-dimensional numerical modeling can provide a more realistic simulation to capture the seismic behavior of the system. The nonlinear behavior of structural elements was included, and the dynamic soil properties were obtained from field data and backbone curves. A contact pair interface with small-sliding surface-to-surface formulation between buildings was used to capture possible seismic pounding, and contact interfaces with a finite-sliding formulation were used to simulate the interaction between the piles and the soil. The results, including lateral building deflections, interstory drifts, structural shear forces, foundation rocking, lateral pile deflections, and the distributions of bending moments and shear forces of the piles, are presented and discussed. The findings of this study will give engineers a better insight into the possible effects of seismic pounding on the seismic performance of buildings, and the response of endbearing piles in soft soils.

© 2017 Elsevier B.V. The swelling prediction of bentonite–sand mixtures due to wetting is very important in evaluating the long term performance of the engineered barrier in the high level radioactive waste disposal system and the hydraulic barriers in geoenvironmental constructions. Sun et al. (2015) proposed the swelling prediction model of bentonite-sand mixtures due to full hydration, and predicted the swelling of different types of bentonite-sand mixtures, which was verified, to be consistent with the swelling test results. However, the predicted swelling results of bentonite-sand mixtures with extremely high sand content obtained by the original swelling prediction model have a large deviation from the test results. The reason is that the original model is based on an assumption that all the pores and available water are only associated with bentonite/montmorillonite fraction. However, for mixtures with extremely high sand content, the sand skeleton exists and resists the external stress from the very beginning. At the same time, the bentonite, dispersing in the sand skeleton, in contact with the pore fluid, swells freely to fully saturated state, however, still fails to fill the sand skeleton voids completely. In this research, the original swelling prediction model is extended by introducing the concept of critical filling sand content and critical contact stress. When sand content is more than the critical filling sand content, the deformation of the mixture is mainly due to the sand skeleton deformation. After the stress increases greater than the critical contact stress, the saturated bentonite fills the sand skeleton voids completely, and the swelling can still be predicted by the original swelling prediction model. In the extended model, the swelling prediction can be divided into three zones according to the two limit values of critical sand content and critical filling sand content. In different zones, the distribution ratio of the vertical stress tha

© 2017 Elsevier B.V. The swelling prediction of bentonite–sand mixtures due to wetting is very important in evaluating the long term performance of the engineered barrier in the high level radioactive waste disposal system and the hydraulic barriers in geoenvironmental constructions. Sun et al. (2015) proposed the swelling prediction model of bentonite-sand mixtures due to full hydration, and predicted the swelling of different types of bentonite-sand mixtures, which was verified, to be consistent with the swelling test results. However, the predicted swelling results of bentonite-sand mixtures with extremely high sand content obtained by the original swelling prediction model have a large deviation from the test results. The reason is that the original model is based on an assumption that all the pores and available water are only associated with bentonite/montmorillonite fraction. However, for mixtures with extremely high sand content, the sand skeleton exists and resists the external stress from the very beginning. At the same time, the bentonite, dispersing in the sand skeleton, in contact with the pore fluid, swells freely to fully saturated state, however, still fails to fill the sand skeleton voids completely. In this research, the original swelling prediction model is extended by introducing the concept of critical filling sand content and critical contact stress. When sand content is more than the critical filling sand content, the deformation of the mixture is mainly due to the sand skeleton deformation. After the stress increases greater than the critical contact stress, the saturated bentonite fills the sand skeleton voids completely, and the swelling can still be predicted by the original swelling prediction model. In the extended model, the swelling prediction can be divided into three zones according to the two limit values of critical sand content and critical filling sand content. In different zones, the distribution ratio of the vertical stress tha

© 2016 The Authors. It is particularly necessary to study the deformation, strength and the changes of pore water pressure of bentonite-based buffer/backfill materials under the undrained condition. A series of isotropic compression tests and triaxial shear tests under undrained conditions were conducted on the compacted saturated/unsaturated GMZ bentonite-sand mixtures with dry mass ratio of bentonite/sand of 30:70. During the tests, the images of the sample were collected by photographic equipment and subsequently were cropped, binarized and centroids marked by image processing technique. Based on identification of the variation of the position of marked centroids, the deformation of the sample can be determined automatically in real-time. Finally, the hydro-mechanical behaviour of saturated and unsaturated bentonite-sand mixtures under the undrained condition can be obtained. From results of triaxial shear tests on unsaturated samples under constant water content, inflated volumetric deformation transforms to contractive volumetric deformation due to the increase of the confining pressure and lateral expansion deformation are observed due to the increase in the shearing stress. Moreover, the net mean stress affects the initial stiffness, undrained shear strength and deformation of the sample during the undrained shear tests.

© 2016 The Authors. It is particularly necessary to study the deformation, strength and the changes of pore water pressure of bentonite-based buffer/backfill materials under the undrained condition. A series of isotropic compression tests and triaxial shear tests under undrained conditions were conducted on the compacted saturated/unsaturated GMZ bentonite-sand mixtures with dry mass ratio of bentonite/sand of 30:70. During the tests, the images of the sample were collected by photographic equipment and subsequently were cropped, binarized and centroids marked by image processing technique. Based on identification of the variation of the position of marked centroids, the deformation of the sample can be determined automatically in real-time. Finally, the hydro-mechanical behaviour of saturated and unsaturated bentonite-sand mixtures under the undrained condition can be obtained. From results of triaxial shear tests on unsaturated samples under constant water content, inflated volumetric deformation transforms to contractive volumetric deformation due to the increase of the confining pressure and lateral expansion deformation are observed due to the increase in the shearing stress. Moreover, the net mean stress affects the initial stiffness, undrained shear strength and deformation of the sample during the undrained shear tests.

© 2015 Elsevier B.V. The swelling characteristic of bentonite-sand mixtures is an important index in evaluating the long term performance of the deep geological repository of nuclear waste. In this study the swelling characteristics of different types of bentonite-sand mixtures with various sand contents are compared. It is concluded that for pure bentonite and bentonite-sand mixtures with less sand than the critical sand content, the relationship between montmorillonite void ratio and vertical stress can be expressed as a unique line in a double logarithmic plot, and volumetric strain under a given vertical stress and swelling pressure at a constant volume after full saturation can be predicted based on this line; however, for mixtures with more sand than the critical sand content, the above relationship deviates from the line when the stress is larger than the starting deviation stress, which can be determined using the sand skeleton void ratio. Before the sand skeleton forms, the vertical stress is borne mainly by montmorillonite particles and the amount of swelling at full saturation is determined by the content of montmorillonite per unit volume, however, after the sand skeleton forms the vertical stress is borne by both the montmorillonite and the sand skeleton. The stress distribution coefficient is proposed to present a proportion of the vertical stress that is borne by both parts. A predictive method, verified by the swelling tests on bentonite-sand mixtures with various sand contents, is suggested to predict the amount of swelling due to saturation in the full range of sand content.

© 2015 Elsevier B.V. The swelling characteristic of bentonite-sand mixtures is an important index in evaluating the long term performance of the deep geological repository of nuclear waste. In this study the swelling characteristics of different types of bentonite-sand mixtures with various sand contents are compared. It is concluded that for pure bentonite and bentonite-sand mixtures with less sand than the critical sand content, the relationship between montmorillonite void ratio and vertical stress can be expressed as a unique line in a double logarithmic plot, and volumetric strain under a given vertical stress and swelling pressure at a constant volume after full saturation can be predicted based on this line; however, for mixtures with more sand than the critical sand content, the above relationship deviates from the line when the stress is larger than the starting deviation stress, which can be determined using the sand skeleton void ratio. Before the sand skeleton forms, the vertical stress is borne mainly by montmorillonite particles and the amount of swelling at full saturation is determined by the content of montmorillonite per unit volume, however, after the sand skeleton forms the vertical stress is borne by both the montmorillonite and the sand skeleton. The stress distribution coefficient is proposed to present a proportion of the vertical stress that is borne by both parts. A predictive method, verified by the swelling tests on bentonite-sand mixtures with various sand contents, is suggested to predict the amount of swelling due to saturation in the full range of sand content.