Abstract:

BeiPing running tunnel of Line 14 of Beijing Metro, which is excavated by mining method, crosses underneath the piles of an existing bridge. However, dewatering cannot be made to facilitate the excavation of the tunnel. In the paper, 2D finite element model is established and analysis is made on the structural deformation of the bridge, so as to study the influence of the tunneling on the existing bridge and to determine the design and construction scheme of the tunneling. The following countermeasures are taken according to the analysis results: temporary invert is installed for the mined tunnel; fullface deephole grouting is made to consolidate the ground in advance and to seal the ground water; fullcourse monitoring is made for the bridge piles during the tunneling, and the monitoring results are compared with the results calculated by finite element model. So far, the tunnel has passed the asbuilt acceptance, and the bridge keeps stable. Conclusions drawn are as follows: 1) The tunneling can cross underneath the existing bridges successfully after temporary invert is installed and grouting is performed; 2) The settlement of the existing piles can be predicted by means of finite element model.

Key words: mined tunnel, tunneling underneath existing piles, deformation, finite element model, Metro