Dynamic splitting response and mechanical effect of joint angle in sandstone containing various weak-filling joints

Abstract

Weak-filling joints substantially degrade the integrity and load-bearing capacity of rock masses, thus increasing the complexity and unpredictability of their mechanical response behavior. One of the main mechanical properties of jointed rocks is their splitting performance, which heavily influences their failure mode. To study the effects of joint angles on splitting mechanical properties, we conducted dynamic splitting tests on sandstone samples with seven different inclination angles of weak-filling joints. These tests were conducted using the Brazilian disc method and a modified split Hopkinson bar apparatus. The splitting mechanical response, energy rate characteristics, joint angle damage factors, failure modes, micromorphology characteristics, and the mechanical effects of joint angles were systematically analyzed. The findings suggested that varying joint angles led to different initial damage levels in the rock mass, which can be described by a power exponential function. The observed relationship between peak load and joint angle was corroborated by integrating a damage parameter into the theoretical derivation of the mechanical effect of the joint angle. Weak-filling joints reduced the brittle failure characteristics and peak loads of the samples but enhanced their ability to deform. Furthermore, the energy reflection rate exhibited an inverse relationship with the joint angle, which is contrary to the trends observed in energy transmission and absorption rates. Additionally, both macroscopic and microscopic morphology analyses confirmed that the joint angle primarily determined the fracture trajectory of the samples, causing a gradual shift in the failure modes of jointed samples from shear to tensile failure.