抄録
The inevitable influence of large excavation in soft soils on adjacent tunnel is greatly concerned in practice. A case in Ningbo Metro Line 1 in China is presented in this paper. The constructed metro line of which axes were at a depth of 12 m to 18 m was almost parallel to the excavation. The minimum horizontal distance between the metro line and the retaining structures was 7.2 m. Field montoring indicated that the left tunnel suffered considerable deformation during the 3rd excavation step of the adjacent excavation, and the maximum increment of horizontal displacement of left tunnel reached 33.5 mm. From the completion of left tunnel to the completion of the excavation, the maximum increments of settlement and convergence of left tunnel reached 33.6 mm and 28 mm, respectively. As a result, these deformations caused the appearance of visible cracks and leakages of linings and threatened left tunnel severely. Numerical simulation was conducted with Plaxis 3D. The performance of surrounding soils and structures due to the nearby excavation, especially of left tunnel, are investigated. It is found that displacement growth of left tunnel and surrounding soils caused by adjacent excavation has intense correlation. In addition, the effects of divided excavation on alleviating the displacements and internal forces of left tunnel during the 3rd excavation step are also discussed. The above problems and findings should be paid more attention to to ensure the safety of the nearby twin tunnels.
