Numerical Simulation On Excavation Process Of Large-scale Underground Powerhouses With FEM

The geomechanics environment conditions of the Baishan Hydropower Station powerhouse are analyzed based on the local geology research and the analysis of geologic prospecting data. A mechanical model is developed to depict the actual conditions of the research area. The excavation and support processes are simulated by the ANSYS.The main problems of simulation on excavation of powerhouse are the evaluation and control of deformations and stability of excavation front, loads and stress in the lining. In order to investigate stability of surrounding rock of cavern, finite element model and sequential excavation procedures were proposed. The excavation process is simulated step by step.The numerical modeling relies on a two-dimensional analysis, implementing elastic constitutive model. The excavation process is divided into six loading steps for simulation of the stress redistribution due to excavation.The variation due to the excavation of the stress state in the rock mass can be evaluated through a finite element analysis in which equivalent nodal forces, corresponding to the release of the initial stress, are applied to the contour of the cavern. Stresses in the excavated elements are converted into forces along the excavation boundary at each stage representing the construction advance. The numerical simulation results show that the lining has obvious influence on the distribution of displacement and first principal stress of surrounding rock and makes the tensile stress zones decrease.The main objectives of in-situ monitoring include: to control the deformations of the cavern, to verify that the appropriate excavation method was selected, to measure the development of stresses in the structural members, and to indicate progressive deformations, which require support strengthening. In monitoring the stability of cavern, the displacements of surrounding rock were measured during excavation. The field measurement results show that the surrounding rock of cavern is stable while the shotcrete was designed as the supporting structures. By comparing the numerical deformations with measured ones, the numerical simulated results agreed well with in-situ measured values. The simulation of excavation is carried out by using the numerical method. The internal force and safety factor of the lining are calculated to evaluate structure security. The effect of thickness changing on lining safety factor and structure stability is discussed.