Back Analysis of Initial Geostress Field in Tunnel Site of Granitic Intrusive Rock Stratum

The stratum of the Huoshan tunnel mainly distributes sandstone and mudstone intrusive by granodiorite. The tunnel axis passes through the granitic intrusive rock area where the lithology changes drastically, and the distribution of initial geostress is complicated. Back analysis the characteristics of the initial geostress field in the intrusive rock mass area based on the measured geostress data can further guide the design and construction. A three-dimensional numerical model is established depending on the geological survey data of the Huoshan tunnel. The initial geostress data of borehole is measured by the hydraulic fracturing method, multivariate linear regression method is used to obtain the initial geostress field in engineering area. The distribution of initial geostress near the granodiorite intrusion surface is discussed. The results show that the distribution of the initial geostress field in granitic intrusive rock is very complicated. Both the magnitude of the principal stresses and the direction of the horizontal principal stresses inside and outside the intrusive bodies have changed dramatically (the change range of the principal stress magnitude is about 2.0−5.3 MPa, and that of the principal stress angle is about 50.7°−178.8°). Burial depth and distribution of intrusive body have become important factors affecting the distribution of initial geostress field, and the larger the burial depth or the smaller the cross section of the intrusive rock body, the larger the initial geostress value; At the same time, the front area of the intrusive body was significantly impacted by compressive tectonics, and stress concentration is more obvious. Copyright ©2022 JOURNAL OF SOUTHWEST JIAOTONG UNIVERSITY. All rights reserved.