The morphology of the contact surface between cast-in-place engineering structures and soil is generally random. Previous research focusing on the shear mechanical properties of soil–concrete interfaces has predominantly concentrated on the role of interface roughness by constructing regular concrete surface types, largely neglecting the potential impact of the roughness morphology (i.e., the morphology of the concrete surface). In this study, concrete blocks with the same interface roughness and different roughness morphologies were constructed based on the sand-cone method, including random rough surface, triangular groove surface, rectangular groove surface, trapezoid groove surface, and semicircular groove surface. A series of direct shear tests were conducted on the rough and smooth sand–concrete interfaces, as well as on natural sand. Through these tests, we examined the shear mechanical behavior and strength of the sand–concrete interfaces, and analyzed the underlying shear mechanisms. The results showed that: (i) the interface morphology had little effect on the variation in the shear stress–displacement curve of sand–concrete interfaces, and it had a significant influence on the shear strength of the interfaces; (ii) under the same normal stress, the shear strength of the sand–concrete interfaces with a random rough surface was the greatest, followed by the triangular groove surface, while the shear strength of the rectangular groove surface proved the lowest; (iii) the shear strength of the sand–concrete interfaces with the same roughness was affected by the size of the contact area between the concrete plane and the sand, that is, a larger contact area correlated with a decrease in shear strength. It can be concluded that the shear strength value of a sand–concrete surface with the triangular groove is the closest to the shear strength of a random rough interface. By gaining a deep understanding of the effects of different contact surface morphologies on shear strength and shear behavior, significant insights can be provided for optimizing engineering design and enhancing engineering performance.

Accurately predicting the unconfined compressive strength (UCS) of microsilica-lime stabilized sulfate sand (MSLSS) is critical for the safe and efficient design of infrastructure in arid regions, yet it remains challenging due to the highly nonlinear relationships among influencing factors. This study pioneers the development of hybrid machine learning (ML) models, integrating the Sparrow Search Algorithm (SSA) with XGBoost (XGB), Random Forest, and Decision Tree, for predicting UCS of MSLSS. These models were trained and tested on experimental datasets incorporating input variables: lime content, microsilica content, curing days, curing condition, optimum moisture content (OMC), and maximum dry density. Comprehensive performance evaluation using metrics such as R², MAE, MSE, and MRE demonstrated that SSA optimization markedly enhanced the predictive accuracy and generalization capability of all base models, with the RF model exhibiting the most substantial improvement. The hybrid XGB-SSA model achieved the highest overall predictive accuracy, yielding excellent performance on the testing set (R² = 0.982, MAE = 1.358). The standard XGB model also displayed competitive results, presenting a practical alternative when model complexity is a concern. SHAP-based interpretability analysis revealed OMC and microsilica content as the most influential input variables. This study provides valuable support for geotechnical design and engineering applications in relevant contexts.

A method for computing slip-line fields in the case of cohesionless backfills with stress discontinuity was proposed. The potential failure zone is divided into the Rankine zone and the transition zone, and the Rankine zone is rigorously determined using the theory of plastic mechanics. The potential failure zone and the Rankine zone are then further divided into a series of triangular slices. On the basis of the force and moment equilibrium conditions of a typical triangular slice, the recurrence equation of the lateral force is established. Furthermore, the relationship between the failure surface inclination angle and the interslice force inclination angle is established by satisfying the Mohr–Coulomb criterion. An iterative procedure for calculating the lateral force of the triangular slices by changing the failure surface inclination in the transition zone is performed until the interslice force satisfies the stress condition of the transition zone boundary, resulting in a stress discontinuity line if the Rankine zone and the transition zone intersect and the intersection line satisfies the stress characteristics of stress discontinuity. Example studies are performed to verify the present method, which shows that the soil–wall interface friction has the most significant effect on stress discontinuity, and the location of the stress discontinuity line gradually approaches the backfill surface with an increase in retaining wall inclination.