High-speed train (HST) running in the saturated soft ground induces significant vibration that may threaten the running safety and serviceability of high-speed railway (HSR). Extensive studies have been conducted on the dynamic responses of HSR, yet, the soil-water coupling and plastic behavior in the saturated soft ground are rarely considered, and thus the build-up of excess pore water pressure (EPWP) and displacement cannot be accurately calculated. In this study, 2D soil-water coupling elastoplastic FEM was employed to investigate HST induced vibration in the pile-supported embankment using FE code called DBLEAVES. Dynamic soil stress, EPWP, acceleration and displacement under different cases were numerically analyzed in detail. Numerical tests confirm that liquid phase in soft ground plays important influence on the dynamic responses that vertical acceleration and displacement will be overestimated while the horizontal acceleration and displacement as well as EPWP will be underestimated if soil-water coupling is not considered. Single-phase analysis also exaggerates the acceleration attenuation and underestimate the vibration amplification in soft ground. The existence of piles can induce significant soil arching effect in the embankment, the distributions of vertical acceleration and EPWP are partitioned sharply by the piles while vertical displacement in soft ground becomes more uniform along the depth direction within the pile reinforced area. The existence of piles also induces stronger vibration beneath the pile end so that larger EPWP is generated below the pile end than around the pile body. The main influence area due to HST vibration for pile-supported embankment is overall 20 m away from the centerline of HSR track, therefore, it is reasonable to improve the ground by properly increasing the number of pile within this area. When the number of pile is determined, increasing the length of pile or reducing the pile spacing are two effective ways to mitigate the dynamic response.

Dynamic soil -water coupling analyses, based on the u -p formulation, are inapplicable to highly permeable soils, causing numerical instability. In this study, it is demonstrated that theoretical solutions to the u -p formulation itself certainly exhibit unconditional convergence regardless of the permeability coefficient. This suggests that the instability is only numerical and can be observed in a temporally discretized system. Firstly, the linearized governing equation for the u -p formulation was proven to be reduced to a damped wave equation under a one-dimensional condition, similar to the Full formulation. Secondly, theoretical solutions for the u -p formulation were derived and their unconditional convergence was confirmed. Then, the essential characteristics of the u -p theoretical solutions, that is, the underestimation of permeability, overestimation of compression wave celerity, and occurrence of negative pore water pressure against positive load application, were described and compared with theoretical solutions for the Full formulation. (c) 2024 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BYNC -ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

In this study, a single-layer SPH approach that takes into account full soil-water interactions is proposed. The approach updates the propagation of pore pressure through combination of volumetric strain and Darcy's law, accounting for the momentum equation, soil constitutive behavior, and the development of pore pressure at each timestep of the simulation. The proposed method is validated by analytical solutions of consolidation problems. To showcase its capability in simulating large-deformation problems with hydro-mechanical interactions, a physical test of a seepage-induced sinkhole was simulated using the proposed SPH method. The good agreements suggest that the proposed method can capture the key features of sinkhole developments and serve as a promising tool to explore the associated failure mechanism. A series of parametric studies are then conducted to reveal the influences of material properties and hydraulic conditions on the failure behavior of sinkholes, including failure patterns, influence zone, and surface settlement.