Study on the lateral deformation mechanism of a sandstone-mudstone interbedded tunnel under heavy rainfall conditions

Abstract

[Objective] The water conservancy project in the north bank irrigation area of Xiaolangdi was taken as the research object, aiming to explore the large deformation phenomenon after excavation and support of local tunnel section, analyze the lateral deformation mechanism of surrounding rock of sand-mudstone interbedded tunnel under heavy rainfall conditions, and put forward reasonable tunnel excavation and support measures. [Methods] By means of field investigation, field monitoring and numerical simulation, the lateral deformation of tunnel surrounding rock, the characteristics of plastic zone and the stress state of supporting unit under different working conditions were studied. [Results] The results show that the maximum displacement of the side wall of the tunnel is relatively small under the initial condition, and the surrounding rock is basically stable. Under the condition of rainfall, the lateral deformation of the tunnel foot is large, and the supporting equipment such as steel arch is destroyed. Under the condition of rainfall and support, the maximum lateral displacement of the side wall can be almost ignored, and the support effect is good. [Conclusion] The lateral deformation of the tunnel is a gradual process. The lateral deformation mechanism of surrounding rock of 9~# tunnel is as follows: the lens of local weak rock layer affects the stability; heavy rainfall infiltration and agricultural irrigation caused the rise of groundwater level, increased pore water pressure and reduced the strength of surrounding rock, [Results] ing in insufficient bearing capacity of the original supporting structure, which could not limit the development of deformation and cause large deformation. Adding transverse support at the bottom can significantly inhibit the lateral deformation of surrounding rock, and the effect is obvious at the bottom feet on both sides. The support optimization scheme of ‘adding transverse steel support at the bottom + grouting reinforcement along 2 m around the hole' is better.

Keywords

soft rock interbedded / tunnel / lateral deformation / failure mechanism / support optimization / monitoring simulation