Estimating the complete in-situ stress tensor along deep tunnels with frequent rockbursts near a steep valley

The intensities and locations of rockbursts directly relate to both the magnitude and direction of the in-situ principal stresses in the rock mass. Therefore, achieving an accurate estimation of the in-situ stresses is essential when making rockburst assessments. Typically, the cases in deep tunnels are located in hard rock in tectonic regions near steep valleys. This study focuses on evaluating the complete in-situ stress tensor in deep tunnels in hard rock starting from the geological structure, topography, and in-situ stresses measured in the tunnel area, using multivariate linear regression. By inverting the three-dimensional (3D) in-situ stress field, a novel criterion was proposed for assessing rockburst potential that takes into account the directions of the in-situ principal stresses with respect to the axis of the tunnel. The new integrated approach is supported by rockburst generation in a tunnel in southwestern China. If the tunneling axis intersects the direction of the major horizontal principal stress at a large inclined angle, the post-excavation maximum stress would increase by some times. Taking into account the Kirsch solution, considerable stress concentrates after the tunnel excavation. Even though the overburden is less than 300 m, rockbursts occur frequently during excavation. The main reason for their occurrence is thought to be the in-situ stress field in the valley. Numerical modeling demonstrates a significant concentration of in-situ stress on both sides of the faults present. Moreover, rockbursts are expected to occur over 63.52% of the total length of the tunnel. Specifically, these rockbursts are expected to be of weak–moderate intensity.