Impacts of stress and roughness on steady-state creep of synthetic rock joints under shear

Abstract

This study presents a systematic experimental investigation on the effects of joint roughness on the steady stage creep of rock joints. Multi-stage creep tests were conducted on synthetic rock joints with different roughness characterised by joint roughness coefficient (JRC, 0–2, 6–8 and 18–20) under different normal stress levels (10–30% of the uniaxial compressive strength, σc). Each creep test includes five loading steps at shear stress of 50–90% of the peak shear strength (τp). This study focuses on the steady-state creep rate of rock joints, which is characteristic of the time-dependent deformation behaviour, and stability of rock mass. The experimental results show that steady-state creep rate is highly affected by the magnitude of JRC and normal stress level. The creep rate decreases as the JRC increases and the relationship exhibits an exponential trend. The normal stress level affects heavily the creep rate at low values. The influence diminishes when normalised normal stress exceeds 0·2σc because the influence of joint roughness becomes less important and the creep rate is close to that of intact rock. The experimental results reported herein provide valuable data regarding the time-dependent deformation behaviour of rock joints, which have been rarely reported. This will be of significance to the improvements in theoretical models and engineering design.