Reinforce End Of Shield Construction In Tianjin Soft Soil Area And Effect Of The Influence On Surrounding Environment

With the rapid development of underground utilities in China today, shieldtechnology is more and more widely adopted.Choose a reasonable starting end soilconsolidation scope and accurate grasp of shield construction on the surroundingenvironment influence regularity of shield construction in soft soil is extremelyimportant.Taking Tianjin airport extension of metro line2of shield tunnelconstruction period as the background, combined with the actual measured data, Thispaper using ABAQUS finite element program Calculate the shield originating inTianjin area end reasonable scope of longitudinal reinforcement, the rule of groundsubsidence caused by shield construction and shield nearly meet elevated pilefoundation construction on its influence,Basically have the following conclusion:（1）Compared the theoretical calculation results with the simulation analysisresults,it showed that the theoretical calculation results of reinforcement length is alittle short, and should not be directly used to the engineering design. The comparisonof the displacement and the stress of soils under the conditions of removed the sealeddoor and excavation in different reinforcement lengths indicated that reasonablelongitudinal reinforcement range in the soft soil area of Tianjin is from8.2m to11.5m.If we take the greater safety margin into consideration in our design,we canuse the method of reducing the dosage of cement in the late triaxial mixing pile toachieve the purpose of to be helpful to the shield tunneling control and reducing thecost on the premise of safety.（2）Recognize the surface at any cross section in the shield construction processis going to have a changing settlement process by different relative position to theexcavation face.The same cross section at different depth of soil layer of subsidenceand subsidence scope are different,deep soil by the construction disturbance responseis more sensitive to the surface.Normally,the surface subsidence consistent with thetrend of deep soil settlement,but because of the existence of urban surface crust layer,monitoring data are smaller than the actual value of subsidence. we should take fullyconsider of this phenomenon.（3）As a result of the existence of shade effect, near the tunnel of the single pilein pile group foundation horizontal displacement than from the single pile of thetunnel. The distance between the pile hole will influence of shield construction toadjacent pile the degree of disturbance. The closer distance with tunnel,The greaterthe horizontal and vertical displacement caused by Shield construction.Pile end andthe relative position of the tunnel axis can also affect the horizontal displacement ofthe pile body. When the pile end below the tunnel axis, horizontal displacements ofpile body less than the pile end above the tunnel axis and axis with the usual situation.