Yuqiong Li

In this study, the mechanisms of strength weakening in clay-rich rocks following water exposure were investigated by examining the relationship between mineral composition, microscopic pore structure and gaseous water adsorption. X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and molecular dynamics (MD) simulations were used to characterise mineralogy, pore features and clay–water interactions. Results showed that water absorption is positively correlated with total clay content, particularly montmorillonite (MMT). A novel contribution of this work is the quantitative determination of weight coefficients for the main influencing factors, which clarifies the relative roles of hydrophilic mineral composition and pore structure in post-absorption strength reduction – an aspect not addressed in prior studies. The weight coefficients ranked as follows: pore fractal dimension > effective porosity > clay mineral (MMT) content. MMT content exhibited a negative correlation with post-absorption strength, with MMT identified as the primary mineral driving strength softening. MD simulations further demonstrated the micro-scale weakening effect of hydrated MMT. These findings provide new insight into the water sensitivity of clay-rich rocks and support improved assessment and mitigation of water-induced engineering failures.

To enable in-situ geotechnical investigations in human-inaccessible areas, the impact penetration technique facilitates remote, rapid and in-situ characterization of soil mechanical properties. However, existing research has predominantly focused on quasi-static or low-velocity penetration, with the micromechanical mechanisms governing penetration resistance in saturated sand remaining poorly understood for high-velocity impact penetration within the range of 10-40 m/s. Moreover, the conventional Discrete Element Method (DEM) fails to capture the dynamic fluid-solid interactions between pore water and soil particles. To address these knowledge gaps, a numerical model for simulating impact penetration in dry and saturated sand is developed based on a coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) framework, which is calibrated and validated against experimental data from laboratory impact penetration tests. Results show that penetration resistance increases significantly with rising velocity for both sand states, and saturated sand exhibits consistently higher resistance and markedly stronger rate dependence than dry sand, confirming that pore water substantially amplifies the velocity sensitivity of sand under high-velocity impact. Multi-scale analysis establishes a complete causal chain between macroscopic penetration resistance and micromechanical mechanisms: fluid drag force concentrated around the cone tip is the fundamental origin of pore water confinement, which restricts particle dispersive motion and cone tip-soil interface separation, stabilizes the interparticle force chain network, and ultimately drives the distinct macroscopic response of saturated sand. These findings provide critical insights into the formation mechanism of penetration resistance at multi-scale, and provide a micromechanical basis for the interpretation of in-situ impact penetration test data.

Rapid geotechnical investigation in geological hazard-affected areas is crucial for assessing vehicle passage capacity and securing relief access. This study presents an unmanned aerial vehicle (UAV) based cone impact penetration method designed for rapid soil characterization in hazardous environments. Addressing the need for accurate dynamic penetration models, we derive a theoretical model for sand based on the integration of the oval cavity boundary concepts and the shear band patterns defined by the zero-extension line (ZEL). Experimental impact penetration tests provided rigorous validation: penetrometer acceleration time-history data aligned with the theoretical model predictions, while observed arc-shaped sand displacement contours corroborated the oval cavity boundary condition. Further analysis of sand strain data based on ZEL identified the shear band patterns, which verify the existence of an ogival shear region and effectively linking theoretical assumptions to actual sand shear failure mechanisms. Finally, by combining the theoretical model with the multi-island genetic algorithm (MIGA), the cohesion (C) and internal friction angle (φ) of sand were inverted, with the errors being less than 30% and 40% respectively, demonstrating the method’s potential for practical geotechnical investigations.

Vehicle repeated passes over soft terrain alter the soil’s bearing and shear behavior, thereby affecting vehicle mobility and energy consumption. To address this issue, this study conducted cyclic compression and shear tests on beach sand with moisture contents of 5%, 15%, and 25%. A constitutive model incorporating the coupling effects of loading cycles (N) and moisture content (ω) was developed based on the Bekker and Janosi model framework. The model expresses compression parameters as functions of N and ω, and describes shear behavior through the strength evolution function k(N,ω) and deformation modulus function h(N,ω). Results show excellent agreement between the model predictions and experimental data (R² > 0.92). Furthermore, a vehicle–soil coupled dynamics model was established based on the proposed constitutive model, forming a comprehensive analytical framework that integrates soil meso-mechanics with full vehicle–terrain interaction. This work provides valuable theoretical and technical support for predicting vehicle trafficability on coastal soft soils and optimizing vehicle suspension systems.

In this paper, the contact parameters of beach sand are calibrated based on the discrete element method and the optimal design method, and the obtained parameters by calibration are used as input for the angle of repose simulation. The relative error between angle of repose simulation results and experimental results is 3.27%. Based on the penetration and shear tests, simulation models were constructed to study the pressure shear failure mechanism of beach sand under high-speed conditions. The high-speed penetration simulation shows that with the increase of the penetration rate, the influence area of the sinkage plate gradually increases, and the stress of sand particles also increases. When the penetration rate increased from 0.5 m/s to 8 m/s, the pressure on the plate increased 12.7 times, indicating that the bearing capacity of the sand increased significantly with the increase of the penetration rate. The high-speed shear simulation shows that in the stable shear stage, the average shear torque initially increases slightly with the increase of speed, and then decreases significantly when the speed exceeds 4 m/s. This is because as the shear rate increases, the disturbance of the soil by the shear plate increases, the velocity of soil particles increases, resulting in a decrease in the number of soil particles in contact with the shear plate, thereby reducing the shear torque.