Most natural soils exhibit a certain degree of soil structure which, in general, leads to increased strength and stiffness properties. However, the mechanical characterization of these soils based on conventional laboratory testing proves difficult in many cases due to sample disturbance. The present work aims to characterize the microstructure of a postglacial, normally consolidated, fine-grained deposit in Seekirchen, Austria, adopting in situ testing, laboratory testing on high-quality samples, and numerical analysis. The latter involves recalculating in situ piezocone penetration tests (CPTu) using an advanced constitutive model for structured soil. In contrast to existing in situ interpretation methods, the results of the numerical study, the mineralogical and hydrochemical testing, as well as the oedometer and bender element testing on undisturbed and reconstituted samples suggest that the soil is characterized by a significant amount of structure. It is demonstrated that the difference in shear wave velocity measured in situ and through bender element testing on reconstituted samples can be used as an indicator for soil structure. Ignoring the effects of structure may lead to inaccurate parameter determination for advanced constitutive models, which are subsequently employed to solve complex boundary value problems in geotechnical practice. As a consequence, the prediction of expected displacement may not be reliable.

In this paper, a computational framework based on the Smoothed Particle Finite Element Method is developed to study the coupled seepage-deformation process in unsaturated porous media. Governing equations are derived from the balance laws of solid and fluid phases considering partial saturation effects in porous media. Moreover, an hourglass control method is implemented to avoid the rank-deficiency issue in SPFEM and the moving least squares approximation technique (MLS) is implemented to eliminate the pore pressure oscillations when the low-order triangle element is used. The proposed coupled SPFEM formulation is validated through four elastic examples and one elasto-plastic example. Good agreement with the numerical or analytical results reported in the literature is obtained. Further, the rainfallinduced slope failure is studied, in which a suction-dependent elasto-plastic Mohr-Coulomb model is adopted to take account of the suction effect in unsaturated soil. The evolution of the suction and soil deformation during the rainfall period and the whole slope failure process are obtained. It is demonstrated that the proposed method is a promising tool in numerical investigations of both the triggering mechanisms and post-failure behavior of the rainfall-induced slope failure.

In this study, we present a novel nodal integration-based particle finite element method (N-PFEM) designed for the dynamic analysis of saturated soils. Our approach incorporates the nodal integration technique into a generalised Hellinger-Reissner (HR) variational principle, creating an implicit PFEM formulation. To mitigate the volumetric locking issue in low-order elements, we employ a node-based strain smoothing technique. By discretising field variables at the centre of smoothing cells, we achieve nodal integration over cells, eliminating the need for sophisticated mapping operations after re-meshing in the PFEM. We express the discretised governing equations as a min-max optimisation problem, which is further reformulated as a standard second-order cone programming (SOCP) problem. Stresses, pore water pressure, and displacements are simultaneously determined using the advanced primal-dual interior point method. Consequently, our numerical model offers improved accuracy for stresses and pore water pressure compared to the displacement-based PFEM formulation. Numerical experiments demonstrate that the N-PFEM efficiently captures both transient and long-term hydro-mechanical behaviour of saturated soils with high accuracy, obviating the need for stabilisation or regularisation techniques commonly employed in other nodal integration-based PFEM approaches. This work holds significant implications for the development of robust and accurate numerical tools for studying saturated soil dynamics. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).

A landslide is a common natural disaster that causes environmental damage, casualties and economic losses, which seriously affects the sustainable development of society. In geomechanics, it is one of the largest deformation problems. Herein, the GPU-accelerated explicit smoothed particle finite element method (eSPFEM) for large deformation analysis in geomechanics was developed on the CUDA platform based on high-performance computing using a self-designed eSPFEM program code. The eSPFEM combines the strain smoothing nodal integration techniques found in the particle finite element method (PFEM) framework, which allows for the use of low-order triangular elements without volume locking and avoids frequent information transfer and mapping errors between Gaussian points and particles in PFEM. A numerical simulation of slope instability using the eSPFEM and based on a strength reduction technique was conducted using various examples, including a cohesive homogeneous slope, a non-cohesive homogeneous slope, a non-homogeneous slope and a slope with a thin soft band. The calculation results show that the eSPFEM can be applied to slope stability analysis under different working conditions, simulating the entire process of slope instability initiation, sliding and reaccumulation, and obtaining reliable FOS values. A numerical simulation was conducted to analyse a landslide that occurred in the Zhangjiazhuang tunnel on the Lanzhou-Xinjiang high-speed railway line on 18 January 2016. A natural unsaturated soil slope, a soil slope with a high moisture content and a soil slope with a high moisture content subjected to an earthquake were analysed. The findings of this study are in good agreement with the actual slope failure conditions. The primary triggers identified for the landslide were heavy rainfall and earthquakes. The verification results indicate that the eSPFEM can effectively simulate an actual landslide case, showcasing high accuracy and applicability in simulating the large deformation behaviour of landslides.