Study on ecological restoration in engineering construction: Analysis of soil rock interface coupling characteristics of slope surface

In engineering construction, rock slopes often require stabilization due to the exposure of rock during excavation. External soil spray seeding (ESSS) is a widely used method for this purpose, but the shear performance at the interface between soil and rock can lead to external soil slippage. This study investigates the effects of polymer content and rock surface undulation angle on the shear strength of the soil-rock interface. Hydroxypropyl high-molecular polymer is used as a soil-strengthening agent, and various undulation angles of simulated rock surfaces (0°–50°) are tested using indoor direct shear tests. The results show that increasing the polymer content significantly enhances the shear strength. Under consistent undulation angle, the addition of 2 % polymer can lead to an increase in shear strength of up to approximately two times. The polymer primarily improves shear strength by increasing cohesion, although its effect on the internal friction angle is minimal. Increasing the undulation angle of the rock surface further improves shear strength, with a 50° angle providing a 0.9-fold increase in shear strength. Both polymer content and surface undulation angle improve the shear performance by increasing cohesion and internal friction. Mechanistically, the polymer formed hydrogen bonds and spatial networks to stabilize clay particles, while undulated interfaces promoted mechanical interlocking and soil-concrete contact area. These findings provide insight into the mechanisms by which polymer content and surface undulation angle enhance the shear strength of the soil-rock interface, contributing to more effective slope stabilization in ecological restoration projects.