Study On Surface Subsidence And Environmental Impact Caused By Small Radius Curved Tunnel Under Buildings

City metro is an effective way to alleviate the pressure of urban traffic congestion,which improves people's livelihood and improve land use rate.In addition to the developed cities that have opened metro,most regions in China have also included it in the future urban development planning.However,due to the restriction of urban planning or the influence of existing buildings,the small radius curve mode has to be applied to shield tunneling route when the metro is built in some sections.Compared with the linear tunneling mode,the small radius curve tunnel is more affected by the existing buildings,groundwater seepage,geotechnical media and other surrounding environmental factors,and the corresponding research data on structural stress,surface settlement,propulsion speed and other aspects are relatively limited,which brings some problems to the engineering design,construction technology,safety operation and maintenance of metro shield tunnel.In order to solve the above problems and reveal the influence of shield construction process of small radius curved tunnel on the surrounding environment,this paper takes the shield project of tj02 bid section of Changzhou Metro Line-2 as a case study,through theoretical analysis and numerical simulation,and combined with the field monitoring data of the project case,This paper analyzes the ground surface and building settlement caused by the shield construction of small radius curve tunnel,and puts forward the corresponding construction technical measures,which provides a certain reference for the construction of shield passing through buildings with small radius curve,and has a certain practical significance for the optimization of construction technology of small radius curve tunnel and the maintenance and guarantee of surrounding environment.The main research contents and achievements are as follows:(1)Based on Mindlin's solution,the calculation formula of surface deformation caused by non-uniform additional thrust of shield face,non-uniform friction of shield shell and difference of shield tail gap on both sides of the line are derived by using the piecewise integration method.The formula is verified by the engineering example of Changzhou Metro Line 2and the numerical simulation results,and the difference coefficient of unbalanced force,the difference coefficient of shield shell and the difference coefficient of shield tail gap on both sides of the line are discussed.The influence law of formation loss on surface deformation.(2)The main disturbance factors of small radius curve shield construction to surrounding strata are friction of shield side wall and ground loss,in which ground loss is the decisive factor of ground settlement.The relationship between the center offset of surface settlement trough and the difference coefficient of unbalanced force on both sides of the line is analyzed.(3)This paper analyzes and discusses the influence of vertical,horizontal and curvature deformation of ground surface on buildings when small radius curve tunnel passes under buildings.Combined with the actual engineering case of Changzhou Metro Line 2,through numerical simulation,this paper analyzes the stability of the building structure disturbed when the small radius curve tunnel passes through the building,and puts forward the corresponding safety control measures.(4)Seepage has an important influence on the long-term settlement of small radius curved tunnel.According to the characteristics of small radius curved shield tunnel,based on the mapping transformation of complex function,the analytical expressions of pore water pressure distribution,stratum and long-term settlement of shallow buried curved tunnel surrounding soil under stable seepage are derived,and applied to the small half diameter curved shield tunnel of Changzhou Metro Line 2 for verification and analysis.(5)The pore water pressure distribution and long-term settlement development law of small radius curved tunnel under different seepage conditions are analyzed.The influence of key factors,such as the ratio of cover to diameter,the relative permeability coefficient between soil and lining,and the radius of curve,on pore pressure and ground settlement are discussed.(6)Due to the variability of the stratum environment,it is necessary to replace high-quality soil timely during the construction process,strengthen the monitoring of the surrounding environment,set reasonable tunneling parameters according to the geological exploration and environment on the spot,correct the deviation accurately and quickly,and minimize the impact of small radius curved shield construction on the environment.