Time-dependent crack development processes around underground excavations

Abstract The time-dependence of rock strength is an issue that cannot be ignored in the rock engineering field. This paper summarizes previous study results on the degradation of the uniaxial compressive strength of rock (including component cohesion and internal friction angle), tensile strength and Young's modulus over time. Based on previous studies, the degeneracy formulas of intact rock cohesion and internal friction angle are derived. Taking circular tunnel excavation under hydrostatic pressure as an example, the surrounding rock response is studied under different degradation degrees of rock strength and stiffness, including the radius of the excavation damage zone, damage degree of surrounding rock, lining support pressure and tunnel boundary displacement. The results show that with the increasing degree of degradation of the surrounding rock compressive strength, the above four parameters increase in the form of an exponential function and that weakening of the tensile strength had little effect on the surrounding rock response. In addition, as the degradation degree of rock stiffness increases, the radius of the excavation damage zone remains unchanged, whereas the other three parameters values are reduced. An actual engineering case simulation using the combined finite-discrete element method shows that results consistent with field observations can be obtained if the rock strength degradation law proposed in this paper is adopted.