Accurately modeling soil-fluid coupling under large deformations is critical for understanding and predicting phenomena such as slope failures, embankment collapses, and other geotechnical hazards. This topic has been studied for decades and remains challenging due to the nonlinear responses of geotechnical structures, which typically result from plastic yielding and finite deformation of the soil skeleton. In this work, we comprehensively summarize the theory involved in the soil-fluid coupling problem. Within a finite strain framework, we employ an elasto-plastic constitutive model with linear hardening to represent the solid skeleton and a nearly incompressible model for water. The water content influences the behavior of the solid skeleton by affecting its cohesion. The governing equations are discretized by material point method and two sets of material points are employed to independently represent solid skeleton and fluid, respectively. The proposed method is validated by comparing simulation results with experimental results for the impact of water on dry soil and wet soil. The capability of the method is further demonstrated through two cases: (1) the impact of a rigid body on saturated soil, causing water seepage, and (2) the filling of a ditch, which considers the erosion of the foundation. This work may provide a versatile tool for analyzing the dynamic responses of fluid and solid interactions, considering both mixing and separation phenomena.

The piezocone (CPTu) dissipation test is used to characterize how the applied load from the penetrating cone is distributed between the soil and pore fluid during both penetrometer advancement and when penetration is paused. The coefficient of consolidation is often estimated from CPTu dissipation tests by interpreting the rate of excess porewater pressure ( triangle u ) decay to static conditions during a pause in cone penetration. Most CPTu dissipation test interpretation methods are based on Terzaghi consolidation theory for triangle u dissipation at the cone shoulder ( u 2 position) or cone face ( u 1 position) and assume that radial triangle u dissipation dominates the response. However, several recent studies show that vertical triangle u migration does contribute to the response. This study uses a large deformation direct axisymmetric cone penetration model to characterize the soil-water mechanical response during CPTu dissipation tests, and in particular, the role of vertical triangle u dissipation on the response at the u 1 and u 2 positions. Large deformations around the penetrating cone are accommodated with an Arbitrary Lagrangian Eulerian approach. Soil behavior is modeled with the MIT-S1 constitutive model calibrated for Boston blue clay (BBC) soil behavior. triangle u dissipation following undrained cone penetration is simulated with coupled consolidation for BBC with over-consolidation ratios (OCR) of 1, 2, and 4 and a range of hydraulic conductivity anisotropy. The simulated u 1 and u 2 dissipation responses are presented to study how they are affected by OCR and hydraulic conductivity anisotropy. A correction factor is recommended to account for hydraulic conductivity anisotropy when interpreting the horizontal coefficient of consolidation from CPTu dissipation tests.

Immense liquefaction damage was observed in the 2011 off the Pacific coast of Tohoku Earthquake. It was reported that, in Chiba Prefecture, Japan, the main shock oozed muddy water from the sandy ground and the aftershock which occurred 29 min after the main shock intensified the water spouting; thus, the aftershock expanded the liquefaction damage in the sandy ground. For comprehending such a phenomenon, using a soil-water-air coupled elastoplastic finite deformation analysis code, a rise in groundwater level induced by main shock is demonstrated, which may increase the potential of liquefaction damage during the aftershock. The authors wish to emphasize that these results cannot be obtained without soil-water-air coupled elastoplastic finite deformation analysis. This is because the rise in groundwater level is caused by the negative dilatancy behavior (plastic volume compression) of the saturated soil layer which supplies water to the upper unsaturated soil layer, and it is necessary to precisely calculate the settlement of ground and the amount of water drainage/absorption to investigate the groundwater level rise. This study provides insight into the mechanism of ground liquefaction during a series of earthquakes.