Study On Deformation Characteristics Of Shield Tunnel During Construction And Operation Period Based On Water-Soil Coupling

With the increasing shortage of urban land area and the saturation of ground traffic construction,underground traffic construction is the best choice to solve the above problems.Shield tunnel engineering plays an important role in the field of underground traffic construction,and it is inevitable that the shield tunnel will cross rivers,lakes,seas or water rich strata in the process of construction,resulting in the problem of fluid structure coupling of shield tunnel.In the shield tunnel construction period,the original balance state of the stratum stress field and seepage field is destroyed due to the unloading effect.In order to realize the new balance,the fluid-solid coupling problem occurs during the shield tunnel construction period.During the operation period of shield tunnel,the change of seepage field of surrounding rock results in the deformation of surrounding rock mass caused by seepage volume force,which leads to the hidden danger of safety of operation tunnel caused by stratum settlement,resulting in the problem of fluid-solid coupling during the operation period of shield tunnel.This paper is based on the key research and development project of Shandong Province(2018GSF120010)"study on the longitudinal deformation characteristics and design mode of the shield tunnel in the changeable composite stratum based on water and soil coupling".By means of numerical simulation,the three-dimensional numerical model of soil and water coupling during shield tunnel construction is established,and the fluid structure coupling research is carried out during the shield tunnel construction in silty clay and sand pebble composite stratum.By means of numerical simulation and model test,the fluid-solid coupling of shield tunnel in composite stratum under local seepage and ground infiltration is studied.This paper mainly carried out the following work:(1)The reason why different rock and soil have different fluid-solid coupling characteristics,different rock and soil have different permeability characteristics and different mechanical response to seepage is explored.The calculation process of seepage pressure and stress of surrounding rock during the construction of shield tunnel,the calculation model of fluid-solid coupling during the construction of shield tunnel and the analysis process of stratum displacement caused by seepage during the operation of shield tunnel are explored.(2)By using Midas GTS NX finite element analysis software,a three-dimensional numerical model of fluid-solid coupling in the construction period of shield tunnel in composite stratum is established,and the variation laws of displacement field,stress field and seepage field of surrounding rock and lining in the construction process of shield tunnel in composite stratum are studied.It can be concluded that:(1)the head loss of the current section caused by each construction step on the gravel side is about 14% more than that caused by the silty clay side.(2)Compared with horizontal displacement,the influence of tunnel excavation and seepage on the vertical displacement of surrounding rock is more obvious.(3)During the construction period,under the condition of fluid-solid coupling,the surrounding rock pressure value and the shear stress value of segment structure at the boundary of soil layer are relatively large,so the tunnel structure is at the most unfavorable position at the boundary of soil layer.(3)By means of numerical simulation and model test,the displacement and deformation characteristics of segment structure and the change characteristics of water and soil pressure around segment during the operation period of shield tunnel in composite stratum under the condition of local leakage and ground infiltration are studied.It can be concluded that:(1)with the downward movement of the leakage part,the influence of leakage on the pore water pressure and vertical displacement of each part gradually increases on both the silty clay side and the sandy pebble side.(2)Under the local leakage condition of silty clay side and sand pebble side,the vertical displacement of segment structure is more affected by local leakage than that of horizontal displacement.(3)Under the condition of ground infiltration,the settling time of the tunnel on the gravel side is shorter than that on the silty clay side,and the settling time of the tunnel is inversely proportional to the permeability coefficient of the soil layer.(4)Under the condition of ground infiltration,the segment structure of the model tunnel is characterized by compression on the top and bottom of the arch and tension on the waist of the arch.During the operation period,the cross section of the segment of the model tunnel is transformed from a circular section to an elliptical section with a long axis transverse.(5)Under the condition of ground infiltration,the change time of pore water pressure around the model tunnel during the operation period is earlier than that of soil pressure,and the change time of water and soil pressure on the sandy pebble side is earlier than that on the silty clayside,and the time when the water and soil pressure on the sandy pebble side tends to be stable is shorter than that on the silty clay side.