Triaxial creep test and PFC numerical simulation of rock-like materials with cracks

In order to study the triaxial compression creep characteristics of rock samples containing cracks, indoor triaxial compression creep tests of intact rock-like specimens and rock-like specimens with cracks were carried out. Accordingly, the effects of confining pressure, axial stress level, and the inclined angle of prefabricated cracks on the axial creep strain, axial strain rate, long-term strength, and fracture morphology of the specimens were analyzed. Based on the soft element proposed by others according to the fractional derivative theory, the nonlinear rheological model of rock-like specimens with a crack was obtained by combining it with the existing element models. The PFC 2D program was developed again, and a new nonlinear rheological model was put into the PFC 2D program. The PFC 2D program was used to perform the numerical tests of triaxial compression creep characteristics of intact rock-like samples and rock-like samples with cracks. Based on the laboratory test, the effects of crack length on the axial instantaneous strain, axial creep strain, axial strain rate, long-term strength, and fracture morphology of specimens were further analyzed. The results showed that when the applied axial stress was the same, the average axial strain rate of the specimen first increased and then decreased with the dip angle β of the crack. In addition, the long-term strength of the sample increased with the increase of the dip angle β of the crack. The new nonlinear viscoelastic plastic creep model was used to fit and analyze the uniaxial creep test curves of intact specimens. The theoretical results agreed with the test results, showing that the model was reasonable. When the crack length and axial stress level were the same, with the confining stress increase, the axial instantaneous strain and creep strain decreased, and the long-term strength increased. When the confining stress and axial stress levels were the same, with the crack length increase, the axial instantaneous strain and creep strain would increase, and the long-term strength would decrease. The main research achievement of this study is to obtain the variation of triaxial compression creep characteristics of rocks containing cracks with influencing factors. This research predominantly furnishes theoretical backing for the design of support systems for deep underground tunnels being constructed in western China.