Construction Sequence Optimization of Overlap Shield Tunnel Beneath Water Supply Pipe in Close Distance

Based on the overlap shield tunnel beneath the water supply pipe between Xiandaidadao Station and Loujiangdadao Station of Suzhou Metro Line 3, numerical method was used to analyze the mechanical properties of new structure-existing structure-earth’s surface under different construction sequences ("first lower then upper" or "first upper then lower"). And the better construction sequence was recommended considering the earth’s surface settlement, the water supply pipe deformation and the shield lining deformation. Combined with site monitor results, the influence of construction on water supply pipe was analyzed. Through the above research, the following conclusions were obtained: 1) constructions of overlapping tunnels caused two disturbances to the water supply pipe, and the adverse effects gradually increased; 2) the influence of lower tunnel construction on earth’s surface settlement and water supply pipe deformation was less than that of upper tunnel construction; 3) the construction sequence "first lower then upper" should be recommended; 4) the deformation of the water supply pipe caused by the construction of overlapping tunnels could meet the requirements of normal use of the water supply pipe.