Asymmetric large deformation of tunnel induced by groundwater in carbonaceous shale

摘要

The Xinhua Mountain Tunnel, which belongs to Zhangjiajie-Jishou-Huaihua Highspeed Railway, encounters asymmetric large deformation when tunnelling through carbonaceous shale stratum, accompanied with groundwater inflow. To reveal the mechanism of large deformation, the mechanical properties of carbonaceous shale are investigated by laboratory tests, and a numerical model is established to analyze tunnel deformation considering different bedding angles, bedding spaces, and water contents. Finally, countermeasures for large deformation are put forward. It is found that the significant strength reduction of carbonaceous shale under the action of groundwater is the main reason for tunnel asymmetric large deformation. The carbonaceous shale has obvious anisotropic characteristics. Its uniaxial compressive strength is 44.63-159.52 MPa and is in U-shaped distribution with the increase of bedding angle. While, that reduces sharply to 15.56 MPa under saturation. The tunnel deformation changes in the exponential form as the bedding space or groundwater content increases. The difference exists in that the tunnel deformation is positively correlated with the change of bedding space, but negatively correlated with water content. From the feedback, the combined countermeasures, i.e., surface sleeve valve pipe grouting reinforcement, backfilling, advanced pipe shed, arch foot reinforcement and arch replacement, can effectively deal with tunnel asymmetric large deformation, indicating that the proposed countermeasures are reliable.