Fracture patterns induced by deep underground excavation based on a crack propagation model

A two-dimensional model is established considering the heterogeneity and the existence of initial cracks of rock materials based on a two dimensional finite difference code. Using the inherent compiling language,the different distributions of the initial cracks’ lengths and orientations are implemented in each zone of the numerical model. The crack propagation rate is described by the subcritical crack growth theory,thus allowing for the analysis of the time effect of the crack propagation and lifetime prediction of the model. It is assumed in the model that the crack propa- gates forming wing crack. And a simplified wing crack model is adopted for the calculation of the crack length and tress intensity factors. In each calculation step,the crack propagation direction is influenced by the stress condition the zone is subjected to,and the stress intensity factor of the crack is controlled by the stresses and the length of the simplified wing crack. The model is used to simulate the failure process of surrounding rock under unloading of high geo-stress due to excavations. The fracture pattern in the surrounding rock due to excavations is analyzed,and the in- fluence of different shape of the excavation and initial crack distributions is also discussed. The simulation results pres- ent the relation between the formation of non-continuous disintegration and the initial crack orientation distributions. The fracture pattern is affected by the angle between the initial crack and the maximum compressive stress. The frac- ture time of surrounding rock is also influenced by the mean value of initial crack orientations. The fracture patterns and failure time of surrounding rock with different excavation shapes are studied using the numerical model. According to the model with the different shapes of the excavation,within the same calculation stages,the most failure zones are found around square shaped excavations and the lease failure zones are found around circle excavations. The calcula- tion result verified the influence of the distribution of the initial cracks on the fracture patterns of the surrounding rock of excavations,and the time effect in the crack propagation process can allow for the prediction of the extend and scope of failure of the surrounding rock. The results can provide information and guide the applications of the induced fractu- ring and non-explosive continuous mining in deep excavation sites under high geo-stresses.