Case Study of Innovative Top-Down Construction Method with Channel-Type Excavation

Although the conventional top-down construction method is widely used in deep excavation, it has the drawback of low efficiency attributable to the long hauling distance and the possibility of the occurrence of excessive excavation deformation and construction risk. This paper introduces a case of deep metro station excavation at West Shanghai Railway Station. The top-down construction method must be used because the excavation is located under a running high-speed railway, and an innovative excavation scheme is proposed to improve construction efficiency and to control excavation deformation. In this method, an operation channel for earth hauling is first excavated in the middle of the excavation. With the available operation channel, the soil on both sides of the channel is excavated simultaneously in a segment pattern, and the required strut systems are subsequently constructed. Both the excavated soil and the construction materials are transported through the channel. This channel-type construction method that resolves the conflict between soil excavation and substructure construction allows for continuous excavation and, thus, reduces construction time and decreases excavation deformation. The case study demonstrates that the presented channel-type excavation is very effective in shortening construction time and reducing both construction cost and excavation deformation.