Stratified rock masses are typically characterized by their structural planes, which have unique mechanical behaviors. Excavation can change the stress field of these stratified rock masses, and result in sliding, separation, and even flexing of the rock mass. While a number of studies have explored safety and stability during stratified rock strata excavation, in reality, the stress balance and structural deformation is a slow and gradual process, not visible until well after tunnel excavation. Railway tunnels in particular require better control of structural stability, and any small displacement of the structure below the track would be disastrous.
A new study published in the International Journal of Geomechanics, “Failure Mechanism and Countermeasures of an Operational Railway Tunnel Invert in Horizontally Stratified Rock Masses”, investigates the failure mechanism and deformation behavior of a real-world railway tunnel in horizontally stratified rock strata.
Using field investigations and numerical simulations, authors Linyi Li, Junsheng Yang, Jian Wu, Shuying Wang, Xinghua Fang, and Cong Zhang surveyed the geological conditions and structural status of the invert uplift sections, seeking patterns in the concrete stress and structural deformations. Learn more about their research in the abstract below, or by reading the full paper in the ASCE Library, https://doi.org/10.1061/(ASCE)GM.1943-5622.0002280.
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.
Read the full paper in the ASCE Library: https://doi.org/10.1061/(ASCE)GM.1943-5622.0002280