Simulation of a New Construction Method in a Shallow-Buried Weak Tunnel

The double down-side drifts construction method was put forward in a shallow-buried weak tunnel. Its construction behavior was studied by numerical simulation using MIDAS. Results show: (1) this method can improve tunnel load, the key construction step is arch ring excavation and core soil is good to tunnel steady; (2) weak parts mainly locate wall foot and crown foot of drifts, crown foot of tunnel and the connections; (3) reinforcement of soil under the drifts has no apparent effect on improving rock deformation and support load. From an economical and safety point of view, main parts to be reinforced are drifts (its foot depth, connection parts with tunnel, and its corners); core soil should be kept if rock is unsteady and needs reinforcing.