Study on Mechanical Effects of Strength Characteristics of Soil–Rock Mixture Based on Field Tests

The structure of soil–rock mixture (S-RM) is hierarchical, ranging from rock-block structures at the meter scale to centimeter-scale soil–rock structures. At different scales, these structures exert varying degrees of control over the physico-mechanical properties of S-RMs and the deformation–failure behavior of slopes. To further investigate the mechanical strength characteristics of S-RMs, in situ large-scale horizontal push-shear tests were carried out at six test points. The results show that the shear-stress–displacement curves of S-RMs clearly present three stages: elastic deformation, yield, and strain hardening, and that obvious stress jumps are observed in some curves. The relationships between fitted internal friction angle φ, cohesion c and rock-block proportion (RBP) reveal that the internal friction angle shows low dispersion with changing RBP. whereas cohesion exhibits considerable dispersion. The internal friction angle increases rapidly with rising RBP, increasing from 21.07° (RBP = 54%) to 60.93° (RBP = 61%); by contrast, cohesion decreases sharply as RBP grows. The internal friction angles derived from in situ horizontal push-shear tests are generally higher than those obtained from laboratory tests, while the effective cohesion values are lower, and this discrepancy is presumably related to specimen size effects. The findings offer reliable guidance for the in situ strength parameter selection and engineering design of S-RM structures.