Stress-induced collapse in horizontally layered rock and a yielding support strategy: A case study

Abstract

Squeezing problems pose a serious challenge for tunnel engineers because they can slow down a project, increase the project budget, and potentially lead to catastrophic collapse. The choice of an adequate support is also often difficult owing to complex geological environments. Lack of sufficient understanding of geological conditions such as high geostress and horizontal layered rock mass could cause tunnel collapse and further lead to economic loss and endanger human life. In an attempt to deal with in-situ squeezing problem, this paper focus on the investigation of the mechanical behavior of tunneling in horizontal layered rock mass with high geostress and the proposal of proper engineering measures. A tunnel collapse incident occurred in northeastern China is analyzed using comprehensive methods including photographing, laboratory tests, discrete element numerical simulations, and site monitoring. The discrete element method was applied to investigate the tunneling mechanical behavior under high-geostress conditions in a horizontally layered rock mass. Numerical simulations show that the dominant horizontal stress and joints cause the maximum deformation at the corner of the arch region. The effect of horizontal joints and horizontal dominant stress were analyzed and found to be the main causes of the collapse. Based on the simulation results, an innovative, simple and efficient tangential yielding element is developed and implemented to test its applicability in a tunnel engineering scenario. Load-displacement curves of the tangential yielding element were obtained through laboratory tests and introduced to the numerical model using the 3D discrete element method. The performance of the developed tangential yielding element was validated in the simulation. Site monitoring was also conducted to determine the in-situ performance of the yielding support using the tangential yielding element. The monitored settlement at the crown region is in agreement with the simulation. The in-situ tests show that the yielding element was considerably deformed while the tunnel remained stable, which confirms the applicability of this technique. The effectiveness of the yielding element is also confirmed in terms of a comparative cost analysis of the yielding and resistant support schemes.