Characterization of the High Geostress Field in Deep-Buried Diversion Tunnels and its Inversion Analysis

The distribution characteristics and evolution law of initial in-situ stress field in deep tunnel are the important basis for the stability analysis of surrounding rock and the design of support and reinforcement scheme. Taking a deep-buried high geostress diversion tunnel as the study object, this study used the hydraulic fracturing method to measure the geostress and explore the distribution law of the geostress field in the deep-buried diversion tunnel area. Based on the measured data, we constructed a geological model of the tunnel area, and employed the finite element regression calculation analysis theory to run the initial inversion calculation of the geostress field in the deep-buried diversion tunnel area. The results showed that the average stress at the tunnel axis was around 23 MPa, and the maximum horizontal principal stress was 46.32 MPa, which belongs to a high geostress tunnel. The triaxial principal stresses can be ordered as
$\sigma \mathrm{H} > \sigma \mathrm{z} > \sigma \mathrm{h}$
, indicating that the initial geostress field was a
$\sigma \text{Hz}$
type and dominated by the horizontal tectonic stress. The difference between the maximum and minimum principal stresses at the tunnel axis was significant. According to the Mohr-Coulomb criterion, there is large shear stress at the critical surface of the tunnel excavation, which is likely to cause rock explosions in the tunnel. The inversion results of the initial geostress field were basically consistent with the measured results. Therefore, this study can provide a theoretical basis for the characterization of the geostress field in similar deep-buried high geostress tunnel projects, as well as the design and construction of the cavern.