Rapid growth in urban areas sometimes requires the construction of tall buildings close to existing shield-driven tunnels. The convergence, displacement, and bending moment change of the tunnel lining due to adjacent deep excavations could be significant. The design and construction of a deep excavation must meet the stringent requirements for the stability of the existing tunnels....[ Read more ]

Rapid growth in urban areas sometimes requires the construction of tall buildings close to existing shield-driven tunnels. The convergence, displacement, and bending moment change of the tunnel lining due to adjacent deep excavations could be significant. The design and construction of a deep excavation must meet the stringent requirements for the stability of the existing tunnels.

In this thesis, firstly, the responses of a jointed shield-driven tunnel in-situ are briefly introduced. An analytical approach and a computer program for the prediction of internal forces and displacements of a jointed shield-driven tunnel are proposed. This analytical approach is justified by field observations, numerical verifications and laboratory model tests. The effects of joint stiffness, soil resistance, joint distribution and number of joints on the tunnel response are outlined. A simplified solution of the relationship of maximum bending moment and horizontal diameter change during adjacent excavation is proposed. Secondly, a new method to determine the equivalent factors for approximating a jointed shield-driven tunnel lining as a continuous ring structure under a 2D condition is introduced in order to facilitate the numerical simulations and preliminary design of jointed tunnels. Simplified equations for the estimation of the equivalence factors are also proposed for typical tunnel geometry. Thirdly, a detailed field instrumentation program conducted in a deep excavation site, Wanxiang International Square, Shanghai, where Shanghai Metro Line 2 uptrack tunnel was constructed with the closest clearance of 3.2m to the excavation pit, is introduced. The field data relevant to the behaviors of soil and earth retaining structures, which are in the vicinity of the uptrack tunnel, and the performance of the uptrack tunnel are critically interpreted and evaluated. Preliminary mechanism analyses of the tunnel response to the adjacent deep excavation is discussed and the influence factors are summarized based on the field instrumentation data. The deflection of the tunnel is a combination of several kinds of movements, such as translation, slippage, rotation and squash deformation (distortion). Factors that affect the tunnel response during excavation include horizontal clearance of the tunnel and the wall, embeddment depth of the tunnel, three dimensional and arching effect, bottom slab construction and compensation grouting, consolidation properties of the soil and adjacent existing buildings, etc. Finally, comprehensive fully coupled numerical simulations are employed to further examine the tunnel response and the complicated soil-tunnel interaction behaviors. Stress and strain paths of 10 critical points around the tunnel and the pit are plotted to understand the stress and strain changes along the tunnel lining and around the pit during excavation; strain distribution, pore water pressure distribution, and displacement fields around the site during the excavation are examined. Shoulder regions and left heel region are found to experience significant volumetric and deviatoric strain during adjacent excavation. Pure seepage flow has less effect on tunnel response. The squash deformation of the tunnel is found to be the most critical item among all kinds of movement. The change of maximum bending moment of the tunnel caused by the adjacent excavation can be correlated to the change of horizontal diameter change by the proposed analytical approach.