Mechanical Properties of Strongly Weathered Rock–Soil Mixtures with Different Rock Block Contents

Abstract

Although soil–rock mixtures (S-RMs) exist extensively on Earth’s surface, their mechanical behaviors remain elusive. In this study, a series of large-scale direct-shear tests was conducted to investigate the mechanical behaviors of S-RMs composed of weathered basalt with different rock block contents, including stress–strain relationship, dilatancy, particle breakage, and shear strength. The results indicate that the S-RM shows more and more pronounced strain-hardening behavior as its rock block content increases. For S-RMs with different rock block contents, there is a power law relationship between the stress ratio and the displacement-increment ratio before the peak shear strength is reached. The horizontal shear stress depends strongly on the volumetric strain of the S-RM. Namely, volume compression results in closer contacts among particles, enhancing the strength and strain-hardening behavior of the S-RM, whereas volume expansion disperses particles, reducing the strength and enhancing the strain-softening behavior. It is also shown that particle breakage can exert significant control over the mechanical properties of the S-RM. Particle breakage becomes more and more severe as the rock block content and the normal stress increase, and then it reaches a critical state. In addition, it is remarkable that the relationship between the shear strength and the normal stress follows a power law instead of a linear one.