Surface Settlement Characteristics Of Shield Tunnel In Silty Clay Of Shenyang Metro Line 4

With the acceleration of urbanization,the construction of urban economy,and the focus of the national "14th Five-Year Plan" on underground space development,China will further improve urban rail transit and continue to increase infrastructure construction,which provides an unprecedented opportunity for the development of underground engineering and tunnels in China.In recent years,with the development of science and technology and the progress of shield excavation equipment,shield machine excavation method has become unique in the field of urban tunnel excavation.The complexity of shield machine construction,the difference of specific engineering geological conditions and the accuracy of surface settlement control are the keys to the success or failure of shield tunnel.In this paper,relying on the silty clay shield construction project of Shenyang Metro Line 4 in three stations and two sections,and taking the surface settlement in EPB construction as the research object,the characteristics of surface settlement caused by Shenyang silty clay shield construction are studied by means of indoor test,field measured data analysis,theoretical analysis of surface settlement and numerical simulation,which is of great significance to similar subway shield tunnels in the future.(1)The physical and mechanical properties of water content of silty clay in Shenyang Metro Line 4 are defined according to laboratory tests.It is found that with the increase of water content of silty clay,the internal friction angle,cohesion and deformation modulus decrease;With the increase of confining pressure,the internal friction angle,cohesion and deformation modulus increase.(2)On the basis of stratum loss in Sagaseta,considering the effect of supporting force,the theoretical formula of total surface settlement is obtained by using this formula,combining with soil parameters,soil cabin pressure and friction between soil and shield machine.It is concluded that the transverse and longitudinal surface settlement curves are symmetrical distribution and V-shaped curve respectively during the silty clay shield construction of Shenyang Metro Line 4,with the maximum cross-sectional settlement of 1.7 mm,the maximum uplift of 15 m in front of the excavation face of 1.7 mm,and the distance from excavation.(3)The correctness of the theoretical formula is verified by comparing the field monitoring data,FLAC3D numerical simulation results and theoretical results.The comparison results show that the lateral surface settlement is Gaussian distribution,the maximum settlement is 1.5～2.0 mm,the longitudinal surface settlement is a S curve,the front surface uplift is 1.4～1.8 mm,and the maximum surface settlement behind the excavation face is 2.0～2.3 mm.The influence of water content,soil cabin pressure,supporting force and other parameters on land subsidence is studied by using the control variable method.(4)Finally,the numerical simulation shows that the cross-sectional surface settlement of shield construction of double-track tunnel in Lexia stage presents a V curve,and the maximum settlement is about 2.2～2.5 mm between the two tunnels.The closer the distance between the two tunnels is,the greater the surface settlement and the more obvious the mutual influence.