A screw pile is a special-shaped pile with several advantages, including good bearing capacity, economy, and rapid construction. The calculation of the screw piles’ ultimate bearing capacity in the individual bearing failure state remains controversial. To address the problems of an unclear failure mechanism and the pile–soil contact relationship in screw piles, we conducted large-scale direct shear tests using a partial amplification method. The variation law for soil stress and the failure pattern of soil around the screw teeth were analyzed. The bearing capacity of the screw shear plate with screw teeth was found to be significantly higher than that of the plane shear plate, while that of the screw pile first increased and then decreased with an increase in the screw pitch. The optimal screw pitch allowed the determination of the maximum bearing capacity. Furthermore, the optimal screw pitch was generally equal to the critical screw pitch, which distinguished the individual bearing failure from the cylindrical shearing failure. A new calculation method for the critical screw pitch and ultimate bearing capacity in the individual bearing failure state was presented, and its rationality was proved using the direct shear test results. The calculation of the critical screw pitch considers the shear strength of soil and the geometric parameters of the screw teeth, making it more widely applicable. These results can provide a theoretical basis for the subsequent design of screw piles.

The anti-slide pile is a primary method of landslide control. The effect of the passive soil arch in front of the embedded section of piles has a significant effect on the anti-slide pile’s bearing capacity. The upgraded model test scheme was used to conduct model tests with a pile spacing four times the width of the pile and a geometric scale ratio of 1:15. The anti-slide pile stress, pile bending strain, and soil stress in front of the pile were all studied in relation to the loading amount. In addition to the model test, the numerical simulation method was utilized to investigate the three-dimensional morphological change of the passive soil arch in front of the pile. The results indicated that: clearly, the side piles can eliminate the border effect. The distribution of pile bending strain along the pile after loading is referred to as a parabola. Bending failure occurred at a depth of 40 mm, approximately 0.9 m from the pile top. Under the condition that the pile spacing is four times the pile width, a passive soil arch occurs in front of the anti-slide pile’s fixed part, and its development can be split into four stages: formation, development, completion, and destruction. The passive soil arches in front of the piles are generated and destroyed gradually along the buried depth, and the three-dimensional surface of the space drops gradually along the buried depth with the loading amount and advances toward the loading direction until the anti-slide pile system fails. The research findings and experiences can serve as a basis for future research.

Soil-rock mixture, as a multiphase heterogeneous material composed of soil and rock blocks, is widely applied in subgrade, dam, and slope engineering. To elucidate the mesoscopic mechanical mechanisms of soil-rock mixtures during vibratory compaction, this study employs discrete element software to investigate the behavior of soil-rock mixtures under vibration, using the Ling-Sui high-speed railway high embankment subgrade as the engineering background. Macroscopic mechanical parameters of the material were obtained through uniaxial compression tests on rock blocks and direct shear tests on soil. Mesoscopic parameters between particles were determined based on numerical inversion. By integrating PFC with MATLAB digital image processing techniques to reconstruct the realistic morphology of rock blocks, a simulation model of the soil-rock mixture is developed. This model enables the investigation of particle porosity variation, crack propagation, force chain evolution, and the influence of vibratory force on rock block breakage during the vibratory compaction process. The results indicate that the vibratory compaction process of the soil-rock mixture can be divided into three stages: initial compaction, rapid compaction, and steady state, with the porosity variation exhibiting a significant negative correlation with the number of rock block cracks. Shear failure predominantly occurs in the upper rock blocks, while tensile failure is the primary mode of failure in the middle and lower layers. The vertical stress of particles rapidly increases to a peak during the initial compaction stage, then gradually decreases and stabilizes. The force chain undergoes a top-down reorganization and evolution throughout the compaction process, accompanied by an increase in heterogeneity. Increasing the vibratory force significantly enhances both the rock block breakage rate and the degree of compaction, with the breakage rate exhibiting an accelerating growth trend, particularly beyond 600 kN. The study aims to deepen the understanding of the vibratory compaction mechanism of soil-rock mixtures at the particle scale, providing mesoscopic mechanical insights for engineering applications.