Shear mechanical properties and debonding failure mechanisms of bolt-resin-rock anchoring system with anisotropic interfaces

Abstract

This study investigates the shear mechanical responses and debonding failure mechanisms of anchoring systems comprising three anisotropic media and two anisotropic interfaces under controlled boundary conditions of constant normal load (Fs), constant normal stiffness (K), and shear rate (v). A systematic analysis of shear mechanical properties, the evolution of maximum principal strain field, and damage characteristics along shear failure surface is presented. Results from direct shear tests demonstrate that initial shear slip diminishes with increasing Fs and K, attributed to the normal constraint strengthening effect, while an increase in v enhances initial shear slip due to attenuated deformation coordination and stress transfer. As Fs increases from 7.5 to 120 kN, K from 0 to 12 MPa/mm, and v from 0.1 to 2 mm/min, the peak shear load increases by 210.32% and 80.16% with rising Fs and K, respectively, while decreases by 38.57% with increasing v. Correspondingly, the shear modulus exhibits, respectively, a 135.29% and 177.06% increase with rising Fs and K, and a 37.03% decrease with larger v. Initial shear dilation is identified as marking the formation of shear failure surface along anisotropic interfaces, resulting from the combined shear actions at the resin-bolt interface, where resin undergoes shear by bolt surface protrusions, and the resin-rock interface, where mutual shear occurs between resin and rock. With increasing Fs and K and decreasing v, the location of the shear failure surface shifts from the resin-rock interface to the resin-bolt interface, accompanied by a transition in failure mode from tensile rupture of resin to shear off at the resin surface.

1. Introduction

Anchorage support technology has gained prominence due to its superior support strength, convenient installation process, high adaptability, and significant economic benefits, leading to widespread application in geotechnical engineering fields such as mining, tunneling, and slope stabilization [1 −4], as depicted in Figure 1. The load-bearing capacity and long-term stability of anchorage systems during service are outcomes of multiple interacting factors, which primarily include the strength of materials (anchor bolts, bonding agents, and surrounding rock masses), boundary conditions (such as constant normal load, constant normal stiffness, disturbance intensity, and load type), anchorage parameters (including anchorage length, spacing, angle, and preload), and the shear mechanical characteristics and debonding failure mechanisms between anisotropic media [6−10].

The support resistance provided by anchorage systems primarily depends on the shear strength and friction at anisotropic interfaces, with the cumulative progression of damage and degradation potentially leading to system failure [11, 12].