Influence of normal stress on the shear failure mechanisms of cement-rock composites

Abstract

Cement is a widely used grouting material in geotechnical engineering, and the bonding properties of cement-rock interfaces play a crucial role in the stability analysis of engineering structures. In this study, laboratory direct shear tests were performed on standard cube cement-rock composite specimens under varying normal stress. The shear failure mechanisms of the cement-rock composite were investigated using Acoustic Emission (AE) and Digital Image Correlation (DIC) techniques. The results show that increased normal stress enhances peak shear stress, residual shear stress, and the shear displacement corresponding to peak shear stress. The values of peak AE energy and ringing count at peak stress are significantly higher than those at other stages, indicating brittleness at the cement-rock interface. The evolution of the b-value and AE amplitude suggests that interface failure results from the repeated formation of large- and small-scale microcracks. The distribution of AE frequency and RA-AF values reveals the influence of normal stress on the types of cracks generated at the interface. Under normal stress conditions, cement-rock composites exhibit shear fractures, while tensile failure occurs in the absence of normal stress. The DIC analysis supports the efficacy of AE analysis in detailing the failure process. The scanning electron microscope results suggest that the interface cracks primarily originate from the fracture of hydration products.