Mechanical Analysis of Construction Process for Shallow Weaking Surrounding Rock Multi-Arch Tunnel

Based on a practical engineering, considering the characteristics such as shallow,weaking surrounding rock, large span, double-arch of the tunnel, the stress and strain of surrounding rocks, support structure and mid-wall were analyzed by FEM for different excavating procedure. The simulation results were compared with in-situ monitoring results. The crown settlement and convergence displacement are divided two obvious increasing stages. Surrounding rock upper and under the mid-wall generate bigger plastic strain and should be strengthened. Temporary support of the pilot bears bigger load and should be reinforced. Bearing bigger horizontal direction tensile stress and uneven load, the bottom of mid-wall must have enough reinforcing steel bar or employ augment foundation. The analysis results provide a scientific basis and technical guidance for the construction optimization of the tunnel constructed by three-pilot excavation method.