Research On Deformation And Control Technology For Shield Tunnel In Rich Water Sand Stratum

Shield construction in rich water sand stratum can cause soil liquefaction,surface subsidence,horizontal displacement,etc.,and even damage the above and adjacent underground pipelines.Based on the example of shield tunnel excavation in rich water sand stratum,the spatial distribution patterns and parameters of surface settlement above the tunnel are confirmed by the actual tracking and monitoring in the field.The causal analysis diagram and arrangement diagram are used to study the deformation influencing factors and control methods,and evaluate the control effect.The main research results are as follows:(1)The settlement above the tunnel in rich water sand stratum basically shows "U" type with small amount of settlement on both sides and large amount of intermediate settlement.The cumulative settlement near the center of the shield tunnel approaches the maximum settlement of the section.(2)The influence range of shield tunnel on the surrounding soil layer is generally within 6 ~ 35 m on both sides of the tunnel axis,of which the main affected area is about 10 m on both sides of the tunnel and the maximum settlement is about 40mm;The surface subsidence of the secondary influence area outside the axis 15 m is generally less than 10 mm.(3)Statistical analysis of the monitoring data shows that the accumulative settlement of the measuring points along the longitudinal axis of the shield tunnel is basically uniform and the number is concentrated in the range of-20 to-25 mm.During the process of shield tunnel,the deformation of the tunnel is stable and concentrated at-6mm ~ 6mm,and the tunnel tends to be stable after one week of completion.(4)By causal analysis diagram and permutation diagram,the main influencing factors of surface settlement caused by shield construction in rich water sand stratum are obtained,such as synchronous grouting amount,grouting pressure and grouting timing.The corresponding control measures grouting pressure,ensure the amount of synchronous grouting,reduce the construction of the proposed disturbance.(5)It is verified by examples that it is necessary to pre-reinforce the strata of rich water sand stratum,especially under the existing strata.It is appropriate to pre-reinforce the strata outside the existing strata and test the stratum reinforcement effect when the new strata is put into operation.Control shield tunnel parameters to ensure the stability of the work surface and the existing line of safety operation.