Abstract:

It is difficult to bring the ground surface settlement under control when the shield is boring in ③1 silty sand strata. The paper is based on the shield boring of XiGu running tunnel on Line 1 of Ningbo Metro. In the paper, the mechanical properties of the strata and the shield boring are analyzed, the rule of the ground surface settlement is summarized, the mechanism of the abrupt ground surface settlement when the shield is boring in ③1 strata is obtained, and countermeasures are proposed. In the end, the ground surface settlement has been brought under effective control and the risks of shield tunneling have been minimized. Furthermore, the measures to be taken when shield is boring in silty sand strata in this area are summarized. 

Key words: Ningbo Metro, silty sand strata, running tunnel, shield, settlement