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 discrete element method (DEM) has demonstrated significant advantages in simulating soil-tool interaction and an appropriate contact model notable affected the simulation accuracy. The accuracy of numerical simulation is compromised due to the variations in soil properties when tillage implements are employed in clay-moist soil conditions. This study aims to establish a discrete element model of clay-moist soil based on the Edinburgh Elasto-Plastic Adhesion (EEPA) contact model. Calibration tests using a combination of direct shear tests and cone penetration tests were conducted to identify sensitive parameters that need to be calibrated in the model and analyze the effects of each parameter. The results indicated that contact plasticity ratio and surface energy had significant influence on representing the mechanical properties of clay-moist soil. Then, by utilizing scanning technology to acquire furrow shape data, soil bin test was conducted to validate the reliability of the calibration parameters. Using sensitive parameters as variables, the actual value of clay-moist soil with a moisture content of 33 % as the target value obtained from experimental tests. The optimal combination was: the coefficient of static friction of 0.45, the coefficient of rolling friction of 0.18, and the surface energy of 27.95 J.m-2, the contact plasticity ratio of 0.59. The relative error between the simulated draft force value and the actual measured value was 7.98 %, and the relative errors in the furrow type parameters did not exceed 5 %. The accuracy of the calibration results was verified through comparative analysis of simulation and empirical results. This study provides a scientific approach for employing DEM in modeling clay-moist soil-tool interaction.

This paper deals with the contribution of the soil-structure interaction (SSI) effects to the seismic analysis of cultural heritage buildings. This issue is addressed by considering, as a case study, the Mosque-Cathedral of Cordoba (Spain). This study is focussed on the Abd al-Rahman I sector, which is the most ancient part, that dates from the 8th century. The building is a UNESCO World Heritage Site and it is located in a moderate seismic hazard zone. It is built on soft alluvial strata, which amplifies the SSI. Since invasive tests are not allowed in heritage buildings, in this work a non-destructive test campaign has been performed for the characterisation of the structure and the soil. Ambient vibration tests have been used to calibrate a refined 3D macro-mechanical-based finite element model. The soil parameters have been obtained through an in situ geotechnical campaign, that has included geophysical tests. The SSI has been accounted for by following the direct method. Nonlinear static and dynamic time-history analyses have been carried out to assess the seismic behaviour. The results showed that the performance of the building, if the SSI is accounted for, is reduced by up to 20 % and 13 % in the direction of the arcades and in the perpendicular direction, respectively. Also, if the SSI is taken into account, the damage increased. This study showed that considering the SSI is important to properly assess the seismic behaviour of masonry buildings on soft strata. Finally, it should be highlighted that special attention should be paid to the SSI, which is normally omitted in this type of studies, to obtain a reliable dynamic identification of the built heritage.

This paper establishes a novel full-process numerical simulation framework for analyzing the 3D seismic response of mountain tunnels induced by active faults. The framework employs a two-step approach to achieve wavefield transmission through equivalent seismic load: first, a highly efficient and accurate FMIBEM (Fast multipole indirect boundary element method) is used for large-scale 3D numerical simulations at the regional scale to generate broadband ground motions (1-5 Hz) for specific sites; subsequently, using the FEM (Finite element method), a refined simulation of the plastic deformation of surrounding rock and the elastoplastic behavior of the tunnel structure was conducted at the engineering scale. The accuracy of the framework has been validated. To further demonstrate its effectiveness, the framework is applied to analyze the impact of different fault movement mechanisms on the damage to mountain tunnels based on a scenario earthquake (Mw 6.7). By introducing tunnel structure damage classification and corresponding damage indicators, the structural damage levels of tunnels subjected to active fault movements are quantitatively evaluated. The findings demonstrate that the framework successfully simulates the entire process, from fault rupture and terrain amplification to the seismic response of tunnel structures. Furthermore, the severity of tunnel damage caused by different fault types is ranked as follows: reverse fault > normal fault > strike-slip fault.

Hidden soil caves pose a serious threat to the stability and safety of subgrades. In this study, using the two-dimensional particle flow discrete element code, a total of eight subgrade models with circular soil caves of different dimensions, depths, and locations were established. Under self-weight and superimposed loading, the deformation characteristics of fill subgrade models, such as the evolution of displacement field and crack development process, were analyzed. The results show that under the self-weight, after the fill subgrade model of soil caves with diameters of 2 m, 4 m, 6 m, and 8 m is stable, the overlying soil layer of the soil cave corresponds to the transformation of slag falling, block falling, collapse and rapid collapse, respectively. The larger the dimension of the soil cave, the larger the number of cracks and damage areas, and the more prone the fill subgrade is to collapse. The superimposed load makes the fill subgrade compress from shallow to deep, significantly increasing the overall subgrade deformation, the number of cracks, and the development range. The evolution of the displacement field and crack propagation of the fill subgrade are also controlled by the buried depth and location of the soil cave. Whether the fill subgrade collapses is comprehensively controlled by the dimension and buried depth of the soil cave, the mechanical parameters of the soil layer, the load, and its scope of action. Thus, a comprehensive criterion of cylindrical collapse of the soil layer above the soil cave is constructed.

Energy piles, which serve the dual functions of load-bearing and geothermal energy exchange, are often modeled with surrounding soil assumed to be either fully saturated or completely dry in existing design and computational methods. These simplifications neglect soil saturation variability, leading to reduced predictive accuracy of the thermomechanical response of energy piles. This study proposes a novel theoretical framework for predicting the thermo-hydro-mechanical (THM) behavior of energy piles in partially saturated soils. The framework incorporates the effects of temperature and hydraulic conditions on the mechanical properties of partially saturated soils and pile-soil interface. A modified cyclic generalized nonlinear softening model and a cyclic hyperbolic model were developed to describe the interface shear stress-displacement relationship at the pile shaft and base, respectively. Governing equations for the load-settlement behavior of energy piles in partially saturated soils were derived using the load transfer method (LTM) and solved numerically using the matrix displacement method. The proposed approach was validated against experimental data from both field and centrifuge tests, demonstrating strong predictive performance. Specifically, the average relative error (ARE) was less than 15% for saturated soils and below 23% for unsaturated soils when evaporation effects were considered. Finally, parametric analyses were conducted to assess the effects of flow rate, groundwater table position, and softening parameters on the THM behavior of energy piles. This framework can offer a valuable tool for predicting THM behavior of energy piles in partially saturated soils, supporting their broader application as a sustainable foundation solution in geotechnical engineering.

Pile penetration in soft ground involves complex mechanisms, including significant alterations in the soil state surrounding the pile, which influence the pile negative skin friction (NSF) over time. However, the pile penetration process is often excluded from finite element analysis. This paper investigates the impact of pile penetration on the generation of NSF and dragload. A stable node-based smoothed particle finite element method (SNS-PFEM) framework is introduced for two-dimensional axisymmetric conditions and coupled consolidation, incorporating the ANICREEP model of soft soil with a modified cutting-plane algorithm. A field case study with penetration process is simulated to verify the numerical model's performance, followed by a parametric analysis on the effect of penetration rate on NSF during consolidation. Results indicate that without the pile penetration process in NSF analysis can result in an unsafely low estimation of NSF and dragload magnitudes. The penetration rate affects dragload only at the initial consolidation stage. As consolidation progresses, dragload converges to nearly the same magnitude across different rates. Additionally, current design methods inadequately predict the beta value (where beta is an empirical factor correlating vertical effective stress of soil with the pile skin friction) and its time dependency, for which a new empirical formula for the time-dependent beta value is proposed and successfully applied to other field cases.

This study presents a hierarchical multiscale approach that combines the finite-element method (FEM) and the discrete-element method (DEM) to investigate tunneling-induced ground responses in coarse-grained soils. The approach considers both particle-scale physical characteristics and engineering-scale boundary value problems (BVPs) simultaneously, accurately reproducing typical tunneling-induced mechanical responses in coarsegrained soils, including soil arching and ground movement characteristics observed in laboratory tests and engineering practice. The study also unveils particle-scale mechanisms responsible for the evolution of soil arching through the underlying DEM-based RVEs. The results show that the rearrangement of microstructures and the deflection of strong contact force chains drive the rotation of macroscopic principal stress and the formation of soil arch. The microscopic fabric anisotropy direction can serve as a quantitative indicator for characterizing soil arching zones. Moreover, the effects of particle size distributions (PSD) and soil densities on ground deformation patterns are interpreted based on the stress-strain responses and contact network characteristics of DEM RVEs. These multiscale insights enrich the knowledge of tunneling-induced ground responses and the same approach can be applied to other geotechnical engineering analyses in coarse-grained soils.

Subsea pipelines in Arctic environments face the risk of damage from ice gouging, where drifting ice keels scour the seabed. To ensure pipeline integrity, burial using methods like ploughs, mechanical trenchers, jetting, or hydraulic dredging is the conventional protection method. Each method has capabilities and limitations, resulting in different trench profiles and backfill characteristics. This study investigates the influence of these trenching methods and their associated trench geometries on pipeline response and seabed failure mechanisms during ice gouging events. Using advanced large deformation finite element (LDFE) analyses with a Coupled Eulerian-Lagrangian (CEL) algorithm, the complex soil behavior, including strain-rate dependency and strainsoftening effects, is modeled. The simulations explicitly incorporate the pipeline, enabling a detailed analysis of its behavior under ice gouging loads. The simulations analyze subgouge soil displacement, pipeline displacement, strains, and ovalization. The findings reveal a direct correlation between increasing trench wall angle and width and the intensification of the backfill removal mechanism. Trench geometry significantly influences the pipeline's horizontal and vertical displacement, while axial displacement and ovalization are less affected. This study emphasizes the crucial role of trenching technique selection and trench shape design in mitigating the risks of ice gouging, highlighting the value of numerical modeling in optimizing pipeline protection strategies in these challenging environments.

Seismic fragility denotes the probabilities of a system exceeding some prescribed damage levels under a range of seismic intensities. Classical seismic fragility studies in slope engineering usually construct fragility functions by making some assumptions for fragility curve shape, and always neglect spatial variability of soil materials. In this study, an assumption-free method on the basis of probability density evolution theory (PDET) is proposed for seismic fragility assessment of slopes. The random input earthquakes and spatially-variable soil parameters in slope are simultaneously quantified. By the proposed method, assumption-free fragility curves of a slope are established without limiting the fragility curve shape. The obtained fragility results are also compared with those from two classic parametric fragility methods (linear regression and maximum likelihood estimation) and Monte Carlo simulation. The results demonstrate that the proposed assumption-free method has potential to gives more rigorous and accurate fragility results than classical parametric fragility analysis methods. With the proposed method, more reliable fragility results can be obtained for slope seismic risk assessment.