The Chengnan Expressway is a 215-kilometer highway connecting Chengdu and Nanchong. It starts from the Nanchong Dongguan interchange, passing through Hanjiawan, Gaoping, Jialing, Pengxi, Tangjia, Daying, Cangshan, Huaikou, Qingquan, and finally connecting to the Chengdu Ring Expressway at the Luosiban interchange. The entire road is constructed according to highway standards, including two 1482-meter twin-tube tunnels and three extra-large bridges totaling 4344 meters in length.

　　The Songjiagou Tunnel is located in Qinglian Village, Dangliang Street Office, Bazhou District, with a total length of 815 meters. It passes through various formations such as mudstone and sandstone, presenting complex geological conditions. The tunnel mainly passes through alternating layers of mudstone and sandstone in the Lower Cretaceous Bai Long Formation, with nearly horizontal bedding and relatively tight structure.

　　LanHi's LG312M intelligent arch integrated trolley integrates multiple processes such as measurement point setting, under-excavation operation, arch installation, welding mesh, and connecting bars. It can complete the excavation and arch installation of a double-track tunnel without moving. The entire vehicle adopts an engineering chassis, with a dual-power system of diesel and electricity, a bidirectional cab structure, good driving performance, and adaptation to various complex tunnel road conditions. The arm uses wireless remote control and manual control operation, making it easy to control the movement of the mechanical arm, with features such as speed, efficiency, and energy saving.

　　The Chengnan Expressway expansion project started in September 2022 and is expected to be completed and opened to traffic by 2025.