Numerical Simulation Of Influence Of Shield Tunneling In Closely Overlapped Tunnel

With the rapid development of subway construction and the constantly improving of the urban rail network, more and more complicated construction situation would inevitably arise on the network nodes'constructions, such as parallel tunnels, overlapped tunnels and crossing tunnels. When the distance between the two tunnels is getting smaller and smaller, the influence on construction in the process of coverlapped tunnels becomes increasingly evident. So it needs to know the influence on the existing shield tunnel and on ground surface settlement induced by building overlapped tunnels.There is a section of overlapped shield tunnels between LaoJie station and Dongmen station of Shenzhen No.3 subway. Because of 1.6m interval in the two tunnels, it is extremely difficult to tunnel. Under the condition of grouting reinforcement, 3-D elastic-plastic numerical simulations were conducted on the two overlapped tunnels by using the general finite element analyze software ABAQUS.Up-to-down and down-to-up tunneling procedures were taken into account. In the process of new tunnel construction, the influence on ground surface settlement was analysed, and the influence on rock stress and displacement of the existing shield tunnel was analysed, the influence on lining circumferential axial force of the existing shield tunnel was ananlysed. By the numerical simulation study, some useful conclusions are as follows:①The secondary disturbance of ground surface settlement and rock displacement of the existing shield tunnel was smaller, which caused by tunneling new shield tunnel in the down-to-up tunneling procedure. Judging from the affected area of ground surface settlement and rock displacement of the existing shield tunnel,which caused by excavating face of new shield tunnel, the affected area of the down-to-up tunneling procedure was less than the affected area of the up-to-down tunneling procedure.The former was about 15m, and the latter was greater than 15m.②The rock displacement of the existing shield tunnel was increased, which caused by tunneling new shield tunnel in the up-to-down tunneling procedure. The rock of the existing shield tunnel was floated, which caused by tunneling new shield tunnel in the down-to-up tunneling procedure. ③The secondary disturbance of arch bottom vertical stress of the existing shield tunnel's surrounding rock was bigger, which caused by tunneling new shield tunnel in the up-to-down tunneling procedure. The secondary disturbance of tunnel vault vertical stress of the existing shield tunnel's surrounding rock was bigger, which caused by tunneling new shield tunnel in the down-to-up tunneling procedure.④The secondary disturbance of arch bottom and hance circumferential axial force of the existing shield tunnel's lining was bigger, which caused by tunneling new shield tunnel in the up-to-down tunneling procedure. The secondary disturbance of tunnel vault circumferential axial force of the existing shield tunnel's lining was bigger, which caused by tunneling new shield tunnel in the down-to-up tunneling procedure.⑤Considering thesee factors comprehensively, the secondary disturbance of ground surface settlement and the existing shield tunnel was smaller, which caused by tunneling new shield tunnel in the down-to-up tunneling procedure.