Abstract
The in situ stress field is the fundamental factor causing deformation and damage in geotechnical engineering, so it is the main basis for underground engineering design and excavation. However, it is difficult to accurately obtain the in situ stress through most existing inversion methods in areas with complex geological conditions. For the problem of a relatively discrete and nonlinear relationship of measured stress in the Yebatan Hydropower Station area, a new in situ stress inversion method called the local stress field correction (LSFC) method combining a genetic algorithm (GA), backpropagation (BP) neural network, and submodel method is proposed. The inverted in situ stress results produced by this method show that the distribution of in situ stress is greatly influenced by tectonic movements in the Yebatan area, there is no obvious linear relationship with depth, and the stress release phenomenon occurs at the faults. By comparison with the multiple regression method, it is found that the method still has high inversion accuracy under complex geological conditions, and the average relative error of LSFC inversion results is 17.05%, which is much lower than the value of 43.58% via the multiple regression method. Therefore, the LSFC method can be used for the inversion of in situ stress in complex geological regions and provide a reference for engineering design and construction.
Highlights
In situ stress is the most basic engineering load in geotechnical engineering and is the main basis for underground engineering design, excavation, and stability analysis [1, 2]: this stress exerts a great influence on the failure and deformation of the rock mass [3]. erefore, it is essential to simulate the distribution of the in situ stress field, which is influenced by a number of factors, including topography, lithology, geologic structure, gravity, and groundwater [4, 5]
Based on the genetic algorithm, BP neural network, and FLAC3D, an LSFC method was proposed for in situ stress field inversion. e effect of the fault on the stress field in the key area has been analyzed by means of the submodel secondary inversion method. e following conclusions can be drawn: (1) e proposed local stress field correction method (LSFC) can effectively set up the mapping relationship between the stress components and the relative positions
By a refined submodel with faults, the influence of faults is considered, and the relative errors of the inversion results are further decreased versus those of the large model without faults. e final errors of Yebatan in situ stress are in the range of 10.44%–25.99%, which is less than the measurement error, indicating that the above method is feasible and can satisfy the inversion requirement of the in situ stress field
Summary
In situ stress is the most basic engineering load in geotechnical engineering and is the main basis for underground engineering design, excavation, and stability analysis [1, 2]: this stress exerts a great influence on the failure and deformation of the rock mass [3]. erefore, it is essential to simulate the distribution of the in situ stress field, which is influenced by a number of factors, including topography, lithology, geologic structure, gravity, and groundwater [4, 5]. Erefore, this paper proposes a new method called the local stress field correction (LSFC) method to solve the problem of in situ stress inversion in complex geological conditions such as the Yebatan area. E results obtained from equation (2) can approximately show the distribution of the stress field, but there is still a difference between the calculated stress and the actual stress values at the measurement points. The ground stress calculated by equation (2) is often very coarse and cannot be used for further excavation analysis, so a method called local stress field correction (LSFC) has been proposed to correct the stress according to the measured values. E stress component values calculated by Step 1 are applied to the numerical model built in FLAC3D and the program is run to equilibrate the stress field. Step 5. e corrected stress components are applied to the numerical model, the FLAC3D program is run again to equilibrate the stress field, and the output stress field is taken as the final inverted stress field of the submodel with faults
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