Study on Construction Mechanical Response and Excavation Sequence of Large Span Asymmetric Small Spacing Tunnel
Based on the large-span asymmetric small-spacing tunnel project of Pingnan Road in Longgang District of Shenzhen,the internal force changes of tunnel lining are analyzed through on-site monitoring results.A finite element model is established to com-pare the arch settlement,the stability of the middle rock pillar and the lining stress of the tunnel under different construction se-quences.The results show that,the side arch waist and arch foot near the middle rock pillar are the structural instability points during the construction of large span asymmetric small spacing tunnel,and reinforcement treatment is needed in the construction.Compared with the large section first,when the small section of the tunnel is first,the arch settlement,lining bending moment and axial force of the large and small sections are reduced by up to 16.1%,10.6%and 12.5%,respectively,and the stability of the middle rock pillar is improved.The horizontal stress and vertical displacement are reduced by up to 16.7%and 28.3%,respectively,which is benefi-cial to the overall safety of the structure.Combined with the comparative analysis of field monitoring data and numerical results,the maximum errors of axial force and bending moment are controlled within 12.5%and 16.5%,respectively.The overall trend of nu-merical results is basically consistent with the field monitoring results,which verifies the accuracy and feasibility of the calculation model.Therefore,it is reasonable to follow the principle of'small section first,large section backward,and backward hole far away from the middle rock pillar area first'in the construction of large span asymmetric small spacing tunnel.
Large span asymmetric small spacing tunnelnumerical calculationfield monitoringexcavation sequencestability
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