Study On Construction Stability Of Shield Tunneling Through South-to-North Water Transfer Channel In Weak Collapsible Strata

Shield underpass and sidepass construction will lead to differential settlement or horizontal deformation of existing structures owing to formation disturbance,besides,the prediction and control of this part has become the focus and difficulty of the tunnel project.For the clay and silty clay strata of the South-to-North water diversion in Zhengzhou,they have some weak collapsibility in addition to the general stratigraphic characteristics.When the shield crosses such bad stratum under the comprehensive effects of surface overload,long-term water load,push stress disturbance of shield cutter head and other factors,it is easy to cause the tunnel stratum loss to increase,the shield cutter head excavation pressure imbalance,and then the stratum deformation and surface settlement are too large,which seriously endangers the safety of existing structures.Based on the engineering background of shield tunneling through the main channel of the South-to-North water diversion in Zhengzhou Metro Line 14 civic culture area,the mechanism of the weakly collapsible stratum under the canal and the side-crossing of the highway bridge and the deformation law of the structure are studied.Through the theoretical analysis of the surface settlement caused by the under-passing construction and the force and deformation of the highway bridge piles with the correction and optimization of the tunneling parameters,new inert grouting materials,secondary grouting stratum reinforcement and strengthened pipe segments are used to control the deformation of adjacent structures,and the stability control system of the main channel for water supply from south to north through the shield tunnel of weak collapsible stratum is established.The main work and conclusions are as follows:(1)Analysis of construction mechanism and structure deformation law of weak collapsible stratum shield tunneling through the main channel of South-to-North Water Transfer Project.Combined with the engineering geology,hydrological conditions and construction difficulties of the civic culture section of Zhengzhou metro line 14,construction mechanics behavior of shield tunneling under(Side)through structures is studied,and the mechanical model for shield tunneling is established.Based on Mindlin’s basic solution,the formula of ground settlement and deformation caused by shield construction is deduced,and the stress and deformation of shield side-crossing highway bridge piles are calculated theoretically with the basic assumption theory of foundation beam.(2)Modification of shield tunneling parameters.Theoretical calculation combined with the Acquisition of relevant tunneling parameters of shield 100 ring test tunneling segment are used to modify and optimize the tunneling parameters of the main channel of South-To-North water diversion under shield tunneling of weak collapsible strata.(3)High precision numerical models are established.Relevant measures such as using new inert grouting materials,secondary grouting stratum reinforcement and strengthened pipe segments are proposed.Formation deformation caused by shield tunneling construction before and after reinforcement,settlement of main channel of South-to-North water diversion and deformation of highway bridge piles are predicted by simulation.The results show that considering the water pressure of 7m(designed water depth)in the trunk canal,the maximum settlement of the trunk canal is 10.5mm,which meets the requirements of the specification.Meanwhile,the maximum horizontal deformation of bridge pile occurs at the position of pile cap,which is about 2 mm,and the maximum settlement deformation of bridge pile is 4.7 mm,which are less than the standard warning value.(4)Different monitoring techniques are used to monitor the surface deformation of the main canal,the bridleway settlement,the road bridge pile and the bridge deck deformation during the shield tunneling process,and the monitoring data is statistically analyzed and compared with the simulation prediction results.The results show that the monitoring and simulation calculation results are in good agreement,and the all of the relevant deformation meet the standard warning value,which verifies the feasibility of the above construction method and the accuracy of the numerical simulation.Therefore,the effect of the undercut reinforcement control measures is significant,which can provide theoretical basis and technical guidance for the construction of the main channel of the South-To-North water diversion under the shield tunneling of weak collapsible stratum.