In this paper

based on the combined point estimation method and finite element method (i.e. PEM/FEM) for the spatial variability of geotechnical mechanical parameters

the application of PEM/FEM was extended to study the spatial variability of joint distribution through the geometric models and meshing characteristics of joints. A pumped-storage hydropower station in China was adopted as a case to verify the accuracy and rationality of the expanded PEM/FEM by analyzing the influence of spatial variability of joint distribution on the deformation and plastic zones of the surrounding rock mass in the underground caverns. A finite element analysis model for spatial variability of joint distribution was established through the probabilistic statistics of more than 1

400 joints in the underground caverns. The effects of spatial variability of joint distribution on the stability of the surrounding rock mass was comprehensively studied through the expanded PEM/FEM probability analysis method. Results show that: (1) The comparative analysis of the deformation probability distribution of the surrounding rock mass obtained by the expanded PEM/FEM and on-site monitoring shows that after removing some abnormal values

most of the monitoring deformation values are within the range of the displacement probability distribution

indicating that the spatial variability of joint distribution is the main factor that cause the fluctuation of the monitoring deformation. (2) The probabilistic distribution of the standard deviation of the deformation can be adopted to identify the incidences of the spatial variability of joint distribution on the deformation. For the studied case

the influence of the spatial variability of joint distribution on the deformation is the most significant in places near the floorsand least near the top arches. (3) The probabilistic zoning of the plastic zones of surrounding rock mass can reasonably determine the areas and ranges that are greatly affected by the joints during the excavation of the underground caverns

which provides a support for the design of engineering construction.