Initial Support Failure Mechanisms and Control Techniques for Tunnel in Silty Clay Stratum

When a tunnel passes through the silty clay stratum, disasters such as initial support failure and sudden instability of the face are prone to occur, which seriously affects construction safety and geo-ecology. To find the causes of tunnel deformation failure and propose effective solution measures, this study takes a highway tunnel crossing a powdery clay stratum as the research object. Firstly, the tunnel disaster characteristics were scrutinized through comprehensive on-site research. Subsequently, soil specimens were subjected to triaxial testing and microscopic analysis to discern the underlying causes of initial support damage. Furthermore, various reinforcement strategies were evaluated via numerical simulations. Subsequent to this, the identified reinforcement measures were implemented in the field, and their efficacy was assessed through on-site deformation and force monitoring. The findings reveal that the increased water content of the silty clay and its accumulation at the foot of the arch leads to a lack of load-bearing capacity, while the earth in the arch appears to slip and cut, which is the main cause of the initial support misalignment disaster. After optimization, a reinforcement solution of “advanced large pipe shed +1.0 m large arch foot + 6 m of double feet-lock anchor pipes at 70° and 0°” is determined. Site deformation and stress tests demonstrated maximum deformation of 13.4 cm, maximum surrounding rock pressure of 164 kPa, and maximum stress in the steel frame of 28.31 MPa, validating the effectiveness of the reinforcement solution.