Mesh-free methods, such as the Smooth Particle Hydrodynamics (SPH) method, have recently been successfully developed to model the entire wetting-induced slope collapse process, such as rainfall-induced landslides, from the onset to complete failure. However, the latest SPH developments still lack an advanced unsaturated constitutive model capable of capturing complex soil behaviour responses to wetting. This limitation reduces their ability to provide detailed insights into the failure processes and to correctly capture the complex behaviours of unsaturated soils. This paper addresses this research gap by incorporating an advanced unsaturated constitutive model for clay and sand (CASM-X) into a recently proposed fully coupled seepage flow-deformation SPH framework to simulate a field-scale wetting-induced slope collapse test. The CASM-X model is based on the unified critical state constitutive model for clay and sand (CASM) and incorporates a void-dependent water retention curve and a modified suction-dependent compression index law, enabling the accurate prediction various unsaturated soil behaviours. The integration of the proposed CASM-X model in the fully coupled flow deformation SPH framework enables the successful prediction of a field-scale wetting-induced slope collapse test, providing insights into slope failure mechanisms from initiation to post-failure responses.

Earthquake-induced soil liquefaction poses significant risks to the stability of geotechnical structures worldwide. An understanding of the liquefaction triggering, and the post-failure large deformation behaviour is essential for designing resilient infrastructure. The present study develops a Smoothed Particle Hydrodynamics (SPH) framework for earthquake-induced liquefaction hazard assessment of geotechnical structures. The coupled flowdeformation behaviour of soils subjected to cyclic loading is described using the PM4Sand model implemented in a three-phase, single-layer SPH framework. A staggered discretisation scheme based on the stress particle SPH approach is adopted to minimise numerical inaccuracies caused by zero-energy modes and tensile instability. Further, non-reflecting boundary conditions for seismic analysis of semi-infinite soil domains using the SPH method are proposed. The numerical framework is employed for the analysis of cyclic direct simple shear test, seismic analysis of a level ground site, and liquefaction-induced failure of the Lower San Fernando Dam. Satisfactory agreement for liquefaction triggering and post-failure behaviour demonstrates that the SPH framework can be utilised to assess the effect of seismic loading on field-scale geotechnical structures. The present study also serves as the basis for future advancements of the SPH method for applications related to earthquake geotechnical engineering.

Seepage-induced backward erosion is a complex and significant issue in geotechnical engineering that threatens the stability of infrastructure. Numerical prediction of the full development of backward erosion, pipe formation and induced failure remains challenging. For the first time, this study addresses this issue by modifying a recently developed five-phase smoothed particle hydrodynamics (SPH) erosion framework. Full development of backward erosion was subsequently analysed in a rigid flume test and a field-scale backward erosion-induced levee failure test. The seepage and erosion analysis provided results consistent with experimental data, including pore water pressure evolution, pipe length and water flux at the exit, demonstrating the good performance of the proposed numerical approach. Key factors influencing backward erosion, such as anisotropic flow and critical hydraulic gradient, are also investigated through a parametric study conducted with the rigid flume test. The results provide a better understanding of the mechanism of backward erosion, pipe formation and the induced post-failure process.

The seafloor environment is prone to rapid changes caused by landslides, which can result in significant human, financial, and environmental consequences. Previous research efforts have primarily focused on studying rigid submerged landslides using physical experiments and mesh-based numerical simulations. However, there is a need to investigate deformable soil masses due to their inherent complexity. In the current study, a smoothed particle hydrodynamics (SPH) method was developed to examine the behavior of submerged landslides. Three rheological models, namely Bingham, Herschel-Bulkley (H-B), and mu(I), were applied to characterize the properties of the sediment materials. The SPH governing equations were modified at the interface between the water and sediment phases to account for the density discontinuity between them. The viscosity term at this interface was determined using the Owens equation. The effective pressure, a crucial parameter in rheological models, was appropriately modified to reflect the influence of the water column on the sediment particles, utilizing a simple algorithm. For the mu(I) rheology, separate equations were applied to describe the behavior of dry and saturated conditions. Additionally, the Mohr-Coulomb criteria were utilized in the Bingham and H-B models to determine the yield stress. To validate the effectiveness of the proposed modeling approach, a column failure scenario was first simulated. Subsequently, a rigid submerged landslide was investigated to assess the capability and validity of the proposed framework in accurately capturing surge wave generation and calibrating the boundary friction factor. Finally, two deformable submerged landslides involving different materials, namely sand and glass beads, were simulated and compared with previous experimental and numerical studies at different time steps. Through these comprehensive investigations, the current understanding of the complex behavior exhibited by submerged landslides is enhanced, and valuable insight into landslide dynamics is provided. (c) 2024 International Research and Training Centre on Erosion and Sedimentation. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Earthquake-induced liquefaction and consequent failure of geomaterials have been recognised as a geohazard that causes significant damage to geotechnical infrastructures. Predicting such large deformation events has proven to be a challenging topic, which requires the development of powerful numerical tools and advanced soil models. The Smoothed Particle Hydrodynamics (SPH) method has been successfully applied to simulate large deformations and post-failure processes of geotechnical problems, including seismic large deformation analyses. However, the SPH simulation of earthquake-induced liquefaction and large deformation of geotechnical problems remains challenging, primarily due to the lack of a stabilised computational framework capable of capturing the complex responses of soil liquefaction. This study addresses this research question with the developments and applications of a fully coupled flow-deformation SPH framework incorporating the SANISAND model for solving earthquake-induced liquefaction problems. Several stabilisation techniques, including Rayleigh damping, stress diffusion and pore-pressure diffusion, are introduced to improve the stability and accuracy of SPH simulations. Additionally, a robust stress update method, combining the sub-stepping technique and cutting-plane algorithm, is proposed to effectively integrate the constitutive laws of the SANISAND model during large deformation SPH simulations. Verification of the proposed SPH framework against theoretical solutions shows its effectiveness before being applied to simulate several shaking table tests reported in the literature. The proposed SPH framework and model are able to reproduce experimental results in several simulations, demonstrating their potential and capability for the future prediction of earthquake-induced liquefaction and failure of geoinfrastructures.

This study adopts the Smoothed Particle Hydrodynamics (SPH) technique to accurately and efficiently replicate and forecast the mesoscopic behavior of soil-rock mixtures (SRM). It introduces a novel approach for generating rock blocks within the SRM, utilizing a method that randomly selects angles and lengths. In addition, this research proposes a method for discretizing any shaped region into free particles with specific material attributes, named the regional medium particle discretization method. It incorporates the Drucker-Prager constitutive model to develop the SPH numerical model for SRM. Furthermore, it examines the effects of different rock sizes and rock contents on the SRM's failure characteristics and mechanical properties. The findings revealed that, for identical rock contents, smaller rock samples exhibit a more dispersed failure surface with numerous secondary shear bands, whereas larger rock samples display a smoother and more concentrated failure surface. As the rock content decreases, shear bands typically form in the sample's center and are relatively straight. However, as the rock content increases, the shear bands' configuration becomes more intricate, often featuring multiple shear bands. This method offers a fresh perspective for exploring the mechanical properties of heterogeneous materials.

This study investigates the influence of many factors, specifically the strength parameters of geotechnical materials, on the run-out distance of flow-like landslides. Due to the limitations of field tests and laboratory experiments, strength parameters of soils usually exhibit significant spatial variability with different scales of fluctuation (SOF) in different directions, which is the anisotropy of SOF. Aiming at the influence mechanism of anisotropic SOF of the cohesion random field on the run-out distance of flow-like landslides, this study introduced the mid-point method based on the Cholesky decomposition to generate the anisotropic random field. The smoothed particle hydrodynamics (SPH) analysis method, combined with the Mohr-Coulomb failure criterion and the non-Newtonian fluid model, was used to simulate the sliding process and run-out distance of landslides. A stochastic analysis method for the flow-like landslide motion process was established within Monte Carlo simulation framework. Then, by simulating the Yangbaodi landslide and the horizontal strata model, the applicability of the SPH method and the random field discretization method was validated. Finally, a conceptual landslide case was constructed based on the topographic data of the Wangjiayan landslide that was triggered by the Wenchuan earthquake. The study discussed the movement process under the anisotropic SOF in the random field of cohesion and analyzed the probability distribution characteristics of run-out distances. The results show that an increase in the vertical fluctuation range results in a wider range of variation in run-out distance, and the sliding distances exhibit a discrete nature; on the premise that the cohesion parameter conforms to the lognormal distribution, the distribution of the run-out distance also conforms to the same lognormal distribution, which proves that the run-out distance distribution of flow-like landslides is closely related to the distribution characteristics of inputted parameters.