Deformation failure characteristics and control measures of a shallow loess tunnel in water-rich strata

Abstract

Abstract With the acceleration of tunnel construction, it is inevitable to cross the collapsible loess region. The engineering properties of loess are very poor in the water-rich environment. Additionally, if the buried depth is shallow, the load bearing capacity is further weakened, which can increase the difficulty of tunnel construction. Therefore, this paper provides a case study on the Pangwan Tunnel based on a geological survey, numerical simulation, and on-site monitoring. The failure characteristics of the studied area under the original support scheme are analyzed in detail, and the extreme deformation mechanism is discussed combining the geological conditions and surrounding rock properties. The results show that there are five main reasons resulting in the extreme deformation of the Pangwan Tunnel, which are: abundant groundwater, low strength of surrounding rock, disintegration of loess after water immersion, depth of tunnel is shallow, and unreasonable original support scheme with low bearing capacity. Then, the corresponding countermeasures are proposed, which are advance drainage, large arch foot and foot-lock bolt, sealing tunnel face and grouting timely, as well as advance pipe shed and small pipe grouting. Finally, from the feedbacks of numerical analysis and field application results, extreme deformation of the Pangwan Tunnel is effectively controlled. This work can provide some helpful guidance for similar projects.