Failure Mechanism and Countermeasures of an Operational Railway Tunnel Invert in Horizontally Stratified Rock Masses

Invert anomaly has become a typical problem of railway tunnels in stratified rock during operations, which seriously affects the transportation capacity of railroad lines. This paper will study the failure mechanism and deformation behavior of an operational railway tunnel in horizontally stratified rock masses. Borehole investigations and in situ stress tests will be conducted to real the properties and stress state of the surrounding rock, and the characteristics of the structural distress will be detected via a structural inspection. A numerical analysis that considers the stratigraphic geological information and field structure state will be performed to study the structural stress and deformation response under different conditions of stratigraphic lateral pressure coefficient (K0) and thickness of the stratified rock layer (L). The results demonstrate that the warping deformation of horizontally stratified rock masses below the tunnel invert was the main cause of the invert anomalies; however, when K0 ≤ 1.0 or K0 ≥ 2.0, and when L was in the range of thin-thick thickness to medium-thick thickness, there was a high risk of instability and cracking in the tunnel invert. In addition, the numerical analysis demonstrated that the rock reinforcement scheme could deweaken the layer effect of the rock masses and suppress the uplift deformation, which is recommended for practical projects.