Abstract
Great attention must be paid to the safety and serviceability of existing tunnels when new tunnels are constructed nearby in soft soils. In this study, the influence of pipe-jacking construction on the Ningbo Metro Line 3 was investigated by field monitoring and numerical analysis. A Burger-creep visco-plastic (CVISC) model was used in the numerical analysis to examine the long-term deformation of the existing tunnels. The effectiveness of protection measures and improvement parameters were investigated. The monitoring results show that the deformation of existing tunnels caused by the jacking can be divided into four stages: (I) initial subsidence; (II) rapid rise; (III) deformation fluctuation, and (IV) slow rise. Compared with the Mohr-Coulomb model, the results of the CVISC model are more close to the monitored data. The numerical simulation shows that the maximum deformation of the existing tunnel is reduced by 11.66 and 8.07 mm under the protection measure of ground improvement and surcharge loading, respectively. The deformation of existing tunnel decreases as the elastic modulus and area of ground improvement increase. This study has reference value for the protection of existing tunnels in soft soils during adjacent construction.
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