Structural Response of Large Span Underground Spaces Due to Adjacent Excavation

Underground structures such as tunnels, powerhouse caverns and subway stations, as a main structure, have different side structures that are considered for utility and access. Side structures have usually been constructed adjacent to the main structure in the form of gallery and shaft. The study focuses on the influence of construction of a nearby link tunnel between line 6 and 7 of Tehran metro in Iran, as a side structure, on existing F6G7 exchange subway station as a main structure using 3D numerical model, analytical and observational method. When a structural element is deformed, the internal forces are induced within it, therefore the host ground deformation due to adjacent excavation is known as a controlling factor to ensure the structural adequacy of existed underground structure. This goal will not be achieved unless the adjacent structure construction process is selected with proper staged construction and accepted ground deformation. Eight different schemes for excavation of link tunnel adjacent to F6 station were evaluated. The state of stress surrounding non-circular link tunnel, induced internal forces and structural design of F6 station were assessed based on eight construction schemes for link tunnel. The results show that partial excavation, using invert in initial support system, using pre-supporting system in link tunnel staged construction process have significant effect to reduce the host ground deformation and structural responses of F6 subway station consequently.