Equivalent continuous numerical simulation of a large-scale underground powerhouse excavation considering the size effect of the jointed rock mass

For the stability analysis of the surrounding rock mass of an underground powerhouse, reliable mechanical parameters of the rock mass and appropriate analysis methods are highly important. This paper discusses the rationality of using the mechanical parameters of the representative volume element (RVE) of a jointed rock mass as equivalent mechanical parameters and using the equivalent continuity method to simulate the excavation of a large underground powerhouse in a jointed rock mass, with the underground powerhouse of the Wuyue pumped storage power station as an example. Initially, the discrete fracture network (DFN) and synthetic rock mass (SRM) of the jointed rock mass were established. The size of the RVE of the rock mass was determined to be 23 m × 23 m × 23 m through numerical tests. The mechanical parameters of the RVE were used as the equivalent mechanical parameters of the rock mass. Then, the two-dimensional numerical calculation of the excavation of the main powerhouse was carried out using the equivalent continuous method and the discontinuous method. The mean relative error between the deformation of the surrounding rock calculated by the two methods is 8.24 %, which shows that the equivalent continuous method can calculate the overall deformation after excavation of a large underground powerhouse in a jointed rock mass. Furthermore, the three-dimensional equivalent continuous numerical calculation of underground powerhouse excavation is carried out by using the equivalent mechanical parameters determined by the RVE and Hoek–Brown criterion. Compared with the actual measurement results of the multipoint displacement meter, the mean relative error of the calculation result based on the RVE is 12.37 %, and the mean relative error of the calculation result using the Hoek–Brown criterion is 20.37 %, indicating that the numerical calculation using the mechanical parameters of the RVE of the jointed rock mass as equivalent mechanical parameters can consider the size effect of the jointed rock mass and reduce the error of the numerical calculation. Our results are expected to provide guidance for evaluating the stability of an underground powerhouse.