Interfacial bonding and erosion resistance mechanisms of EICP-treated sand layers for rock slope protection under rainfall and seepage

Exposed rock slopes are prone to interfacial instability and erosion under heavy rainfall and seepage, severely compromising the integrity of hydroseeded restoration layers. To enhance the bonding performance between the restoration layer and the rock surface, this study employed the enzyme-induced carbonate precipitation (EICP) technique to reinforce sand layers placed on tuff slabs to simulate hydroseeding substrate layers on exposed rock slopes. Tilting, rainfall, and seepage tests were conducted, complemented by electrical resistivity tomography (ERT) and ultrasonic pulse velocity (UPV) measurements to quantitatively characterize structural degradation. Under tilting tests, EICP treatment improved sand–rock interfacial bonding, with the critical sliding angle increasing from 58° to 80° as CaCO₃ content rose. Under rainfall tests, cumulative erosion mass decreased with higher CaCO₃ content, and the reduction ratio of UPV showed an exponential correlation with erosion mass. Under seepage tests, specimens with low CaCO₃ content exhibited higher resistivity and greater UPV attenuation, whereas those with higher CaCO₃ content displayed lower, more homogeneous resistivity and smaller UPV variation. An empirical relationship between CaCO₃ content and electrical resistivity was established based on a modified Archie model. Three-dimensional scanning and microscopic analyses further revealed that increased CaCO₃ content produced thicker and more continuous cemented layers, where interparticle CaCO₃ bridges enhanced resistance to sliding, erosion, and seepage. The combined use of ERT and UPV provides an effective means to quantitatively evaluate interfacial and internal deterioration in EICP-cemented sand-rock systems, offering theoretical support for the evaluation and monitoring of restoration layers on exposed rock slopes.