Analysis of large deformation of deep-buried brittle rock tunnel in strong tectonic active area based on macro and microcrack evolution

Abstract

The large deformation is a common engineering problem during tunnel excavation. For brittle rock tunnels, the large deformation is closely related to the rock mass structure. In this study, taking the Guanshan tunnel as an example, large deformation of a deep-buried brittle rock tunnel in a strong tectonic active area was analyzed. The large deformation was explained in terms of the surrounding rock (diorite) mechanical properties and the development and evolution of macro and microcracks. The results showed that the diorite in the Guanshan mountain is characterized by high strength and brittleness. However, numerous microcracks are developed in the diorite, which can easily induce a cataclastic brittle failure of the surrounding rock by the transformation of the stress field. In terms of the spatial distribution, the macro and microcracks in the surrounding rock have a good unified relationship, whose development mechanism is related to strong tectonic activity. The stress environment of the surrounding rock changed during the tunnel excavation. A borehole camera revealed that the large deformation of the Guanshan tunnel is synthetically influenced by the macro and microcracks in the surrounding rock. The deformation includes the relaxation of the original macrocracks, fracture of the microcracks, and rock dilatation caused by the opening of the microcracks, among which the fracture of microcracks is the dominance. This study provides a new concept for analyzing large deformation in brittle rock tunnels, indicating that the negative effects on the stability of the surrounding rock induced by the development and evolution of microcracks should be fully considered in strong tectonic active areas.