Abstract:The total length of Shimentang Mountain Tunnel Extension Project is about 2 km. It is proposed to construct a 720-m long oversized-span single-hole four-lane tunnel, which is the first oversized-span tunnel newly built at the side if the existing multiple arch tunnel in China. After the implementation of the tunnel expansion project, the original two-way four-lane multi-arch tunnel will be combined into a two-way eight-lane section tunnel, which effectively open the traffic bottleneck and alleviate the congestion problem at this place.