Effects of surrounding rock surface morphology in hard rock tunnels on adhesion strength and failure characteristics of fiber-reinforced shotcrete-rock interfaces

The interface failure between shotcrete and rock is a critical defect in underground construction. However, the macroscopic undulating morphology of the hard surrounding rock surface formed by tunnel blasting significantly affects the interfacial adhesion performance. Previous studies have primarily focused on interfaces with regular morphologies, which fundamentally differ from the surface morphology of hard rock surrounding tunnels formed by blasting. To address this gap, this study proposes a three-dimensional point cloud-based characterization metric (PZD) to quantify the macroscopic undulation features of surrounding rock surfaces after blasting. Based on actual tunnel data, rock-fiber shotcrete composite specimens simulating the random undulating characteristics of surrounding rock surfaces were prepared. The experimental results demonstrated a non-monotonic relationship between interfacial adhesion performance and PZD variations. The adhesion strength of the composites initially increased and subsequently decreased with increasing PZD values, reaching a peak of 1.834 MPa at PZD = 4–5. The study identifies an optimal PZD range of 2 to 5 for hard surrounding rock and characterizes three corresponding failure modes. This discovery provides an experimental foundation for enhancing the integrity and stability of tunnel support systems.