Design for a Super-Shallow Large-Section Double-Level Tunnel in Complex Conditions Underneath Sensitive Buildings

In light of the Gongbei tunnel in the Hong Kong-Zhuhai-Macao Bridge,which is a current worldclass project in China,this paper introduces a new construction method: shallow mined excavation with a combination pipe roof and supporting structure system for the construction of a super-shallow large-section tunnel with six lanes and two levels underneath sensitive buildings in water-rich soft ground.In this method,the pipe-roof advance support and the supporting structure as the primary support are combined and connected to form an integrated circumferential and longitudinal load system with great stiffness,which can effectively control surface deformation during tunnel construction and operation and significantly reduce construction risks.Using this method,a waterproof curtain is formed by freezing soil between the pipes to avoid the surface deformation caused by loss of groundwater and the water- and mud-bursting that occurs during excavation,as well as to ensure excavation in a water-tight underground space.Pipe-jacking and ground freezing,which are rarely used in tunnel construction,have been combined reasonably with the supporting structure,successfully solving the technical problems of constructing a super-shallow large-section tunnel underneath sensitive buildings in complex geological and environmental conditions.A new concept and method for tunnel construction has been developed.