Deformation and Damage Characteristics of a Newly Operated Tunnel Caused by above Foundation Pit Construction
The construction of foundation pits in granite residual soil layers is prone to causing upheaval deformation and structural damage in shield tunnels below.Based on the engineering case of a newly operated metro tunnel collinear with the above long-distance deep foundation pit in Shenzhen,a three-dimensional finite element model was established to investigate the variation law of the heave and horizontal convergence of the shield tunnel caused by the deep foundation pit excavation.The correlation between the longitudinal stress of the lining structure and the damage was analyzed.The results indicate that the tunnel deformation caused by foundation pit unloading is primarily vertical heave,accompanied by slight section deformation.After adopting the jump excavation method and the stripped soil reinforcement above the tunnel crown,the average tunnel heave is reduced by 14.4%,and the lateral displacement of the envelop enclosure is reduced by 49.1%.The shield tunnel damage caused by the above unloading is mainly the spalling at the circumferential joints of the tunnel crown.The reason is that the compressive shear cracks occur and expand on the intrados of the circumferential joints of the tunnel crown under the combined action of bending moment and shear.
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