Shear behavior of grouted rock joints under a cyclic normal load

Abstract

In underground engineering, the surrounding rock is susceptible to instability and failure under dynamic disturbance loads. To investigate this issue, cyclic shear tests were conducted on grouted rough rock joints under a dynamic normal load. The effects of the initial normal load (\(\:{F}_{\text{n}\text{s}}\)), dynamic normal load amplitude (\(\:{F}_{\text{A}}\)), and dynamic normal load frequency (\(\:{f}_{\text{n}}\)) on the shear behavior of the grouted joints were systematically investigated. The shear stress–shear displacement curves exhibited clear two-stage behavior. In the first cycle, influenced by grouting reinforcement, the curves exhibited fluctuating peak values. As \(\:{F}_{\text{n}\text{s}}\) increased from 20 kN to 100 kN, the peak shear strength increased by approximately 125.66%. In subsequent cycles, owing to the shearing of the rock-grout bonding interface and cement asperities, the curves transitioned to a fluctuation-dominated slip mode governed by steady-state friction. The normal displacement–shear displacement curves consistently exhibited a fluctuating “V”-shaped pattern across all cycles. The average dilation angle exhibited a decreasing-then-increasing trend with an increasing number of load cycles. The magnitude of the phase shift increased linearly with \(\:{F}_{\text{A}}\) but decreased exponentially with \(\:{f}_{\text{n}}\). The phase shift proportion of the grouted joint reached its maximum in the frequency range of 0.5–1 Hz. The failure characteristics of the joint surface were the fracture of the rock–grout bonding interface and the continuous abrasion of the cemented grout body by the joint surface. These findings provide valuable insights for evaluating the stability of grouted surrounding rock under dynamic disturbances.