Timeliness of collinear crack propagation in rock mass

There are a large number of non-penetrating collinear cracks in the rock slope of an open-pit mine. The timeliness of cracks in the rock mass is a problem that cannot be ignored in terms of slope engineering safety. Based on the superposition principle and fracture mechanics, the stress intensity factor of the rock mass crack tip with collinear fractures under biaxial compression was calculated in this study. A mechanical model of rock mass crack propagation with collinear fractures under constant load was established according to the Charles equation. The effects of loading time, crack penetration rate, and crack dip angle on crack propagation along the direction of the rock bridge were analyzed theoretically. The variations in crack propagation with time in the rock mass were examined using a LS-DYNA creep numerical model. The results show that the fracture growth rate changes in three stages over time, progressing through a stable stage, a decreasing stage, and an abrupt stage. A higher crack penetration rate and a larger crack inclination angle cause a higher rock bridge penetration rate in the rock mass. When the crack penetration rate exceeds 74% or the fracture inclination angle is about 60°, the crack expansion directly enters the abrupt stage, and the rock bridge is penetrated. The theoretical analysis results are in close agreement with the numerical results of this work, which validates the proposed age expansion mechanical model for rock masses with non-penetrating collinear fractures.