Analysis of Buoyancy Force on Segments During Metro Shield Tunnel Construction.

A large number of shield tunnel construction practices have shown that the assembled tunnel segments just detached from the tail of the shield machine are prone to various defects such as ring displacement, crack propagation, and local damage. The reason for these defects is that the tunnel segments tend to float locally or as a whole during the construction process between the connecting rings. To investigate the reasons for the floating of tunnel segments during the construction period, a combination of theoretical derivation, numerical simulation, and on-site monitoring were used to roughly divide the floating force into two parts: "static floating force" and "dynamic floating force" for different strata and stages. The study focused on the theoretical derivation and analysis of the dynamic floating force magnitude and distribution during the grouting process at different stages. With the support of numerical simulation and on-site monitoring of the tunnel segment floating condition in the shield tunnel section from Sanyuanqiao station to Taiping Temple station of Chengdu metro line 9, the correctness of the formula and distribution pattern of the dynamic floating force calculation were verified for the poorly permeable and weathered mudstone stratum. [ABSTRACT FROM AUTHOR]