Back Analysis Of Initial Stress Field And Stabilization Analysis Of Surrounding Rock In Underground Power House

The development and utilization of underground space is a new development trend in 21st century and more and more large-scale hydraulic underground caverns were built in high-mountain gorge areas. The stability or not of underground caverns would directly affect the success or failure and operation benefits of engineering constructions. The stability of underground engineering was closely related to the initial ground stress state of rock body, which would directly affect the engineering design and construction safety and reliability. In addition, rock-blot crane beams were commonly adopted in underground power house, which was also an important factor to the stability of underground caverns. Thus, thinking from the safety and economy of underground construction, it was necessary to back analyze the initial stress field and analyze the stability of surrounding rock before underground engineering construction.A numerical model was built and meshed generation by use of the finite element software ANASYS in this paper. Then the meshed model was introduced into finite difference software FLAC3D by use of interface program and the software was taken as platform to calculate numerically. Same hydropower station was used as engineering example in this paper in which the excavation of underground caverns was simulated and the stability of underground caverns during excavation process was analyzed. The main content as follows:(1) Based on the practically measured ground stresses, we built the three-dimensional nonlinear finite element model and then we obtained the calculated in-situ stress measurements of test points by use of the FLAC3D program, by which we could establish the learning and training samples of neural network. The calculated in-situ stress measurements were taken as input vectors and the boundary condition was taken as output vectors to train the neural network. After we obtained a mature network structure and training time, we input the practically observed values of ground stress of test points to obtain the output vectors and adoptable boundary condition. At last, we induced the obtained boundary condition to numerical calculation software to do feed forward calculation for one time then we could obtain the needed initial ground stress field.(2) Applied the inversed initial ground stress field to the three-dimensional nonlinear finite element model and then we determined parameters of surrounding rock and supports and so on. We temporarily not considered the pouring effect of the rock bolt crane girder and used the finite difference software to simulate the excavation of underground cavern group. At last, we analyzed the distribution of stress, displacement and plastic failure zone.(3) To the stability analysis of the rock bolt crane girder after its excavation and pouring, whether it was safe or not of the contact position between the beam and surrounding rock had become a key factor. The paper used weaken element and interface element respectively to simulate the mechanical characteristics of the contact position to analyze the stability of the rock bolt crane girder and compared the applicability of the two methods.