A modified initial in-situ Stress Inversion Method based onFLAC3D with an engineering application

Abstract

Abstract:To improve the accuracy of an initial in-situ stress eld determined by inversion, we describe a modi ed initial in-situ stress inversion method that uses partial least-squares regression based on FLAC3D. First, each stress component is regressed to improve the tting accuracy of locally abnormal stress regions, and then the relationship between element stress and unbalanced node force is analyzed according to the computational principles of FLAC3D. The initial in-situ stresses obtained from these regression calculations are added to a numerical model, and the unbalanced node forces are recalculated. An external force equal to the recalculated unbalanced node force is then exerted on the node in the direction opposing the original unbalanced node force to satisfy the equilibrium condition. For the in-situ stresses of elements that do not satisfy the strength conditions, they are modi ed by assuming the average stress is constant and reducing the partial stress to satisfy the equilibrium and strength conditions, which also resolves the unreasonable distribution of the boundary nodal forces and results in good regression estimates. A three-dimensional hypersurface spline interpolation method is developed to calculate the in-situ stress tensor at arbitrary coordinates. Finally, we apply this method to an underground engineering project, and the results are shown to agree well with those obtained from eld monitoring. Therefore, it is concluded that this modi ed in-situ stress inversion method could e ectively improve the tting accuracy of locally abnormal stress regions.

In situ stress distribution law of fault zone in tunnel site area based on the inversion method with optimized fitting conditions

“…However, due to the failure to strictly adhere to the boundary requirements of the linear superposition principle, the error of the multiple linear regression method will increase in practical applications. Specifically, the boundary conditions in Figure 6 were transformed into those in Figure 7A (Li et al, 2015). It can be seen from Figure 7A that the displacement constraints under each calculation condition are different.…”

“…Figueiredo et al (2014) used the multiple linear regression method to reveal that the in situ stress of the granite formation of a hydropower station in northern Portugal was controlled by self-weight stress and shear stress. Li et al (2015) proposed the local least squares regression measure to improve the inversion accuracy based on the multiple linear regression method and applied it to a dam project. Meng et al (2020) adopted the multiple linear regression method to put forward the idea of in situ stress inversion for high geotemperature tunnels considering the temperature stress component.…”

Inversion Method of In-situ Stress and Rock Damage Characteristics in Dam Site Using Neural Network and Numerical Simulation—A Case Study

“…The complex boundary conditions are generated based on the data of the rare samples on the spot, and the nonlinear expressions of boundary loads are fitted. Li et al [19] established a numerical model reflecting the complex geological conditions, and established a regression analysis method to improve the accuracy of the abnormal points. At the same time, it put forward that through rewriting the stress variable of the element and applying the balance node force to complete the in-situ stress loading directly, and solved the singularity problem of the boundary node force.…”

Jointed Surrounding Rock Mass Stability Analysis on an Underground Cavern in a Hydropower Station Based on the Extended Key Block Theory

“…The natural rock mass is always split into different types of blocks with varying sizes by numerous discontinuities [1][2][3][4][5][6][7][8][9][10][11]. When the spatial states of the blocks satisfy certain conditions, the blocks are apt to slide and incur instability, which can be named as key blocks [12].…”