# Inversion and Analysis of the Initial Ground Stress Field of the Deep-Buried Tunnel Area
## 1 Introduction  
Ground stress is the inherent force that causes deformation and even breaking of surrounding rock during tunnel construction without proper design. It seriously affects the regional stability of strata. Many engineering geological disasters, such as large deformation of soft rock section and rockburst of hard rock section, are related to the initial ground stress of stratum rock mass [1]. Therefore, to ensure the safe construction of the tunnel, it is necessary to test the initial ground stress in the construction area before the construction of large-scale projects such as the tunnel. In most cases, on-site measuring methods, such as the mechanical and vibrating wire load sensors, the hydraulic fracturing and so on, are one of the most advanced and effective methods to obtain the initial ground stress [2, 3, 4, 5, 6, 7, 8, 9, 10]. Considering the input cost of economy and manpower, it is generally impossible to set up boreholes with sufficient density to fully determine the ground stress in the tunnel area, and the data of the measuring points are discrete and lack representativeness, so there are many limitations in the measurement of ground stress [11, 12, 13, 14, 15]. Therefore, under the limited on-site measuring data, through effective calculation and analysis methods, a more accurate ground stress and a wide range of ground stress distribution laws can be obtained, which plays an important guiding role in tunnel route selection, excavation, and construction. For the limitations of in-situ initial ground stress measurement, many theoretical analysis methods have obtained good results of ground stress inversion. To date, the most widely used ground stress inversion calculation methods [16; 17; 18] are the lateral pressure coefficient method, neural network method, regression analysis method, and so on. The lateral pressure coefficient method is mainly suitable for areas where the geological tectonism is weak and the terrain is flat [19; 20; 21]. The neural network method is mainly used to solve nonlinear problems, which is in development. Some scholars have shown the feasibility of its application. [PERSON] and [PERSON] [22] proposed a new type of evolutionary neural network that the rock mass parameters and the initial ground stress can be determined at the same time. The on-site measuring data of the ground stress around the Longtan Tunnel in China were inversely analyzed. The stability of surrounding rock around the tunnel and the accuracy of the initial ground stress calculated by back analysis are verified by numerical calculation. [PERSON] et al. [23; 24] inversed the parameters of rock mass and the initial ground stress field in the calculated area with a radial basis function network and improved backpropagation network with a model under a finite difference software. [PERSON] et al. [25] established a three-dimensional model of the underground powerhouse. The factors affecting the initial ground stress field are analyzed, and the results of numerical simulation are used as test set for training in the network model with radial basis function. Finally, the inversion results of the ground stress field in this area are obtained. In the above-mentioned practical application, the neural network inverse analysis method shows some shortcomings, such as overtraining, slow convergence, and so on [26]. Therefore, the overall maneuverability of it is weak. The regression analysis method is a calculation method, that is, based on numerical analysis, according to existing data, the regression relationship between independent variables and dependent variables is established [27; 28]. Combined with the principle of finite element method and regression analysis method, the rationality and accuracy of ground stress analysis are better. It has been widely used in the study of the initial ground stress field.