Analysis On Stability Of Surrounding Rock And Reliability Of Hydraulic Tunnel Of Yangjiang Nuclear Power Station

The stability of hydraulic tunnel is being concerned more and more, which is closely related to the initial ground stress state of rock. So the reliability of initial ground stress field being used will directly influence the security of design and construction of underground works. Meanwhile, there are many uncertainties in tunnel project. If we can not reasonably quantify the randomness of the impact to the project structure, a greater risk of structural safety will be certainly brought out. In this paper, linear regression, artificial neural network, and finite element method were used, relying on the drainage tunnel project of Yangjiang nuclear power plant, to carry out the research of ground stress field inversion method, for stable simulation of tunnel excavation and reliability calculation of lining structure. The main contents and results of this paper are as follows:(1) Based on the analysis of ground stress composition and influencing factors, and given the fact that linear regression ignores the nonlinear physical and mechanical properties of rock and soil and neural network has problems that samples construction is blind and the training result is possibly a non-global optimal solution, a ground stress inversion method combining linear regression with GA-ANN is proposed in this paper. Considering the difficulty of building terrain model in finite element software, a stratum modeling method based on NURBS technology was introduced in the paper. Then, the precise topographical, geological finite element model within the project area was built, providing an effective method of ensuring ground stress inversion effect. Finally, ground stress inversion was carried out in the study area, combined with orthogonal design principle of statistics. Compared with inversion result obtained from traditional method, this method is proved more accurate.(2) The engineering ground stress distribution is analyzed in this paper. The traditional rock burst prediction to judge the possibility of the tunnel rock burst by a small quantity of actual measurement point was bounded. In order to predict the possibility of rock burst during the excavation of all drainage tunnels. This paper obtained the stress field of the entire engineering field by inversion and the tangential stress criterion. Through the finite element method, the secondary stress fields, deformation field, plastic zone distribution of surrounding rock are worked out, which can provide support on construction safety.(3) The stress distribution of tunnel lining structure under different conditions is calculated in order to obtain the worst condition. Considering the fact that there are many uncertain factors in tunnel project, and factors are looked as deterministic parameters in the traditional safety analysis whose result is one-sidedness and subjective, this paper introduces the stochastic finite element method in stability analysis of tunnel lining structure. Using Monte-Carlo method, the reliability of the tunnel structure is calculated. At the same time, the sensitivity analysis is carried out, and the most unfavorable factors for the construction process is presented, which provides effective support to timely adjustment to the lining structure according to the actual geological structure.