The shear behavior of gravel-block soil (GBS) is unique and significant for evaluation the failure mechanism of GBS landslide on the Qinghai-Tibet Plateau. This study focuses on interpreting the shear behavior observed in the GBS during large-scale direct shear tests conducted on a landslide in Jiacha County, Tibet, China. The tests considered coarse particle content (CPC), dry density, and moisture conditions. Additionally, a discrete element numerical model, scaled to match the laboratory testing dimensions, was developed to simulate the large-scale direct shear tests on GBS. Results indicated that an increase in CPC improves the strength of the GBS, as it enhances the framework strength through interlocking between gravel blocks and between gravel blocks and the soil mass. The critical CPC for shear failure of the GBS exhibits a decreasing trend as the dry density increases. Furthermore, particle crushing rate (PCR) of the GBS is positively correlated with CPC, vertical pressure, and dry density. The simulation results show good agreement with the test results, providing insights into the damage-shear fracture mechanism of typical GBS under large-scale direct shear tests. The research outcomes provide a theoretical basis for the prevention and control of geological hazards in the Qinghai-Tibet Plateau.

Particle size distribution (PSD) of coral sand is a critical factor that influences the mechanical properties at the coral sand-geogrid (CS-GG) interface, which is affected by both particle breakage and various temperatures. However, relevant researches are scarce currently. This study conducts a series of large-scale interface shear tests on coral sand with three PSD ranges (0.25 similar to 1mm, 1 similar to 2mm, and 2 similar to 4mm) at varying temperatures (5 degrees C similar to 80 degrees C). Experimental results demonstrate that the IB value at the CS-GG interface ascends and then descends with the increase of PSD from 20 degrees C to 40 degrees C. The IB value at the interface descends and then ascends with the increase of PSD from 60 degrees C to 80 degrees C; The PSD curves at the interface indicate that the particle breakage degree of coral sand increases with rising temperature (5 degrees C similar to 40 degrees C); The larger PSD of coral sand, the smaller fractal dimensions (D) of the interface; A mathematical formulation of the relationship between the relative breakage rate (Br) and the D value at interfaces is presented, which considers temperature effects; The relationship between the total input energy (E) and the Br value has been expressed by empirical formulations with different PSD ranges, where the fitting curve for 2 similar to 4 mm coral sand exhibits a hyperbolic pattern.

Bearing capacity of a pile foundation depends mainly on the magnitude of the pile-side freezing force. The magnitude of the pile-side freezing force is affected by a variety of factors, among which the roughness of the pile body is an important influencing factor. In this paper, the freezing strength problem of the pilesoil contact surface is transformed into the shearing strength problem of the frozen soil-concrete contact surface. The shear characteristics of the permafrost-concrete contact surface are investigated by a large-scale straight shear test. The results show that the peak shear strength at the contact surface increases with increasing roughness. The increase in contact surface roughness has a more pronounced effect on cohesion, while the effect on the angle of internal friction is relatively small.