Large Deformation Control and Structural Optimization of Tunnels in Shallow Fractured and Expansive Formations Based on Discrete Element Simulation

Tunnel construction in shallow-buried fractured and swelling schistose rock formations is highly prone to large structural deformation issues. Taking the context of a tunnel located on the Xi’an–Ankang high-speed railway as background, thorough investigations were conducted into the arch crown subsidence, horizontal convergence, initial support cracking, and spalling, as well as ground deformation. Subsequently, an optimization of the original support scheme was carried out using the Universal Distinct Element Code (UDEC) software. The results revealed that large deformation is more likely to occur at the top and foot of the arch in the shallow-buried fractured and swelling schistose rock, characterized by phenomena such as cracking and spalling of sprayed concrete, longitudinal cracks in the arch crown, bending of steel arches, and substantial convergence and deformation of the arch crown. Through comparative analysis using UDEC modeling it was determined that among all the optimized schemes the most effective measure for controlling large deformation in shallow-buried fractured schistose rock is the addition of lock foot anchor rods, which resulted in reductions of over 50% in arch crown subsidence and horizontal convergence compared with the original design, while the plastic zone range decreased by 80%.