Stability Analysis of an Excavation Based on the Regression Analysis of an In Situ Stress Field

The in-situ stress field is one of the most important factors affecting the rock stability in an underground powerhouse excavation, and its distribution directly affects the secondary stress distribution caused by excavation. And the regression analysis is widely used to obtain the in-situ stress field and is the basis of rock stability analysis especially for a high geostress region. The underground powerhouse in the Pubugou Hydropower Station is located in a complex geological environment and rockbursts occur frequently during excavation. The in-situ stress and its regression analysis method are applied to analyze rock stability based on the least squares method, FEM and the measured geostress data, and is accomplished in ANSYS in order to acquire the accurate and actual in-situ stress field. Furthermore, basing on the elastic-plastic constitutive model and Drucker-Prager criterion, a 3D finite element numerical model for the powerhouse excavation is established to analyze the stability of the rock mass during the underground excavation. The results show that the tectonic stress is very significant, and the next excavation has little effect on the former excavation in regard to the displacement. In addition, some sporadic tensile, shear and tensile shear failures may occur on the sidewalls of the main powerhouse, at the vault of the main transformer chamber and at the bottom board of the tailrace surge chamber. Medium-level rockburst can also easily occur, particularly at the vaults of the caverns.