Abstract:

MaizidianSanyuanqiaoLiangmahe shieldbored tunnel on Line 10 of Beijing Metro consists of twin tubes, which go parallel for 235m with only 1.7～3m net spacing. The tunnel crosses underneath close to a 12storey assembled residential building, with the horizontal net distance to the building foundations being 3.7～5m and the vertical net distance to the building foundations being 11.7m. The construction of the shieldbored tunnel is presented in the paper. The theoretical calculation equations and the measurement methods for the comprehensive looseness coefficient “K” are provided. In additional to the conventional construction measures, such as proper use of the articulations and overcutters, proper control of the thrust forces of the shields and timely retightening of the segment bolts, two items of new countermeasures are proposed for the construction of the curved sections of the shieldbored tunnels. The two items of new countermeasures include: 1) Due to the inertia of the shields, the shields start to bore on curved sections 3～5m ahead of the schedule and stop the boring on the curved sections 3～5m ahead of the schedule; 2) Due to the rotation of the shields on the curved sections when the segment rings are released, rotationrectifying measures are taken in advance.

Key words: earth pressure balanced shield, tunnel boring close to existing structure, tunnel boring on curved section, tunnel boring underneath close to assembled residential building, cross shaped steel support, settlement control