Inversion analysis of the Three Dimension Geostress Field in A Tunnel

The initial geostress field is an important basis for the design and stability analysis of geotechnical engineering. The geostress field of the whole engineering area must be calculated by inversion analysis with the limited geostress data, because there are few measured geostress points. Based on the geological background of a tunnel in northern Hebei province and considering the influence of regional highly weathered, moderately weathered and slightly weathered stratum on the stress field, the 3D finite difference method and multiple linear regression method were used to calculate the three-dimensional geological model of the study region to get the optimal regression coefficient. It is found by comparing the regression value with the field measured value that the two values are equal in magnitude and close in direction, indicating that the geostress field calculated by regression is reasonable, then the distribution law of the geostress field in the study area is further analyzed on this basis. The results show that there is a stress concentration in the tunnel center, z peaking at 50m below the center, and decreasing in the left and right direction with a large stress gradient then getting out of the area of stress concentration and tending to be stable. The study area is a medium geostress area, based on gravity stress, the control effect of gravity stress field is gradually enhanced with the increase of buried depth. The research results have important value in the design and construction of tunnel in special geological conditions.