| Tunneling in watery soft,especially underwater strata with high water pressure by earth pressure balance shield machines brings large construction risk,and the probable accidents may cause great economic losses and casualties,and therefore,it is indispensable to focus on the effect induced by shield tunneling on the surrounding environment.Based on the engineering practice of a river-crossing tunnel of the Hangzhou Metro Line 6,combined with field measurement,theoretical calculation and numerical analysis methods,this paper studied the response of shield tunneling.The main contents include:(1)The analysis of the shield tunneling parameters and their influence on the soil of the cross-river tunnel.According to the record data of the excavation parameters of the earth pressure balance shield machine across the land section and the river section,the calculation method of the excavation parameters was analyzed,and the laws and relationship of the parameters were discussed.On the basis of the Mindlin theory and the closed solution under the concentrated force in saturated soil,the calculation methods of soil settlement and excess pore water pressure caused by grouting pressure and cutterhead friction,etc.during construction were deduced.According to the engineering parameters of the river-crossing tunnel,the law of soil settlement and excess pore water pressure was studied,and the settlement calculation results of the two methods were compared,and the influence of soil layer,tunnel diameter,tunnel depth,etc.on ground settlement were researched.The results indicated that the cutter head torque increased significantly when the machine passed through the round gravel layer under water,and the shield construction parameters were prone to large fluctuations.Controlling the chamber earth pressure at a stable level on account of on the static earth pressure value of the excavation face helped to maintain the cutter head torque,which could reduce the wear of the cutter head and increase the advancing speed;and there were weak positive correlations among the cutter head torque,shield thrust,grouting pressure,and chamber earth pressure during construction;and the friction of the shield shell and the grouting pressure had a greater influence on the settlement and pore water pressure,while the friction of the cutter head almost had no influence on the formation.(2)The analysis of the influence of the shield construction on the strata deformation.According to the measured data,the distribution law of the ground settlement,the soil volume loss rate,the settlement trough width,etc.are analyzed.The maximum ground settlement value decreased linearly with the increase of the buried depth of the tunnel,and there was a certain linear correlation between the settlement trough width parameter and soil loss rate.By Flac3 d software,on account of the fluid-solid coupling theory,a three-dimensional numerical model considering various construction factors was established,and the changes of soil displacement and pore water pressure during excavation were researched and compared with the measured values.The width of the settlement trough decreased as the depth of the soil layer increased,and the excess pore water pressure caused by shield tunneling is basically distributed in the range of 2D(D is the tunnel diameter)from the excavation face.(3)The analysis of the influence of the shield construction on the surrounding building and the pipeline.Considering the shearing stiffness of the ground and the angle between the tunnel and the pipeline,a Pasternak foundation beam analysis method for the vertical displacement of the pipeline caused by the twin-tunnel excavation was established,and the calculation results were compared and verified with DCM numerical simulation and field measurements.The influence of factors such as angle,tunnel axis distance,stratum loss rate,and relative bending stiffness on pipeline settlement was analyzed.Finally,the influence of pipeline shearing stiffness was considered based on the Timoshenko beam model.As to the calculation of the settlement value caused by tunnel excavation,the error without considering the shearing stiffness didn’t exceed 1%,indicating that the Euler-Bernoulli beam model was reasonable.On account of the Gaussian distribution law of the ground and the equivalent beam method,considering the bending and shearing effects of the building,considering the interaction between the building and the soil,the double foundation coefficients are applied,and the building settlement curve caused by the tunnel construction was obtained by the method of differential equilibrium.The analysis considered the potential gap between the building and the soil,and the influence of the each parameter was obtained.It indicated that there may be gaps at the bottom of low-rise buildings,and if there is no gap,the building load has no effect on the settlement of the building.(4)The simulation analysis of the influence of underwater shield construction on the strata.Based on the numerical simulation method of the land section,a three-dimensional numerical analysis model of the deepwater zone under river was established,and the change law of soil displacement and pore pressure caused by the construction of the underwater tunnel was studied.Considering the risk of tunnel leakage,the changes of the ground caused by the seepage of the excavation face and the seepage of the lining in the clay,silt,and gravel soil layers were compared and analyzed,and the influence of water level changes on the ground was discussed.Compared with the impact of tunnel construction in the land zone,the soil loss rate under river was slightly higher,and the soil settlement troughs at various depths caused by the construction under river at the same tunnel depth are wider. |
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