A damage rheology model applied to analysis of splitting failure in underground caverns of Jinping I hydropower station

The dominant geological features of southwest China are high mountains with deep, steep slope valleys. Typically engineering projects constructed in these mountain areas have significant overburden depth with associated high in-situ stresses. Characteristic rheological phenomena in the surrounding rock mass produced by these conditions are observed during, and often after excavation of the underground caverns for a hydropower station. This paper describes one such project, the excavation of the Jinping I hydropower Station, located in Sichuan Province. Other than the rheological characteristics, spalling, splitting (observed in local sections), bending and heaving are prominent in the surrounding rock mass of these underground caverns during and after excavation. Coupled damage and rheology models were adopted in numerical analysis for stability evaluation. In addition, a splitting failure criterion and a prediction method for incremental deformation due to crack opening were incorporated in the analysis to estimate the splitting failure zones in the rock surrounding the underground caverns produced by excavation stress release. A block model test was carried out to formulate a method to estimate the incremental deformation due to the opening of cracks. Subsequently, the results were employed to modify the displacements obtained by the damage rheology model. Finally, the displacements, stresses and damage zones in the surrounding rock mass of the underground caverns for the project were predicted and analyzed. The computation results presented herein were found to compare favorably with measurements obtained from the field monitoring.