Study On Long-term Settlement Prediction Of Silty Strata In Curved Metro Tunnel Under Train Load

(1)The cumulative deformation test and liquefaction test of silty sand under half sine cyclic load in Zhengzhou area were carried out.The cumulative deformation law and liquefaction characteristics under different frequency,effective consolidation stress,dynamic stress amplitude and consolidation ratio were analyzed.The results show that the range of influencing factors in this paper,the smaller vibration frequency of 0.5 Hz and the larger dynamic stress amplitude of 40 k Pa have more obvious effects on the cumulative deformation of silty sand.The increase of consolidation ratio significantly improved the liquefaction resistance of silty sand.when Kc=1.4,the corresponding failure cycle is 9.35 times that when Kc=1.0 and its critical dynamic stress ratio(CSR)is 1.5 times when other conditions are the same.(2)A three-dimensional numerical model of the roadbed-tunnel-soil is established,and the dynamic response of the tunnel and the surrounding soil is analyzed in the range of the tunnel curvature radius of 250 m-350 m and the train speed of 20-160 km/h.The results show that the bottom and lateral displacement responses of the curved tunnel are 7.4% and6.9% larger than those of the straight tunnel,respectively.In this paper,the surface displacement of the curved tunnel increases by 18.2% compared with that of the straight tunnel when the minimum curvature is 250 m.The influence range of horizontal and vertical direction in the foundation soil of train load curve tunnel is larger than that of straight tunnel.(3)Combined with cumulative deformation test and numerical simulation proposed the long-term settlement prediction formula of silty soil foundation in the Zhengzhou area under different curvature and train speed.The liquefaction possibility of foundation soil was analyzed using the UBC sand constitutive method.The results show that the cumulative deformation mainly occurs in the first 3 years,and the settlement predicted in this paper is in good agreement with the measured settlement.Using the above settlement prediction formula,the cumulative settlement of the tunnel in 30 years is predicted to be 19.35 mm.Under normal operating conditions,the excess pore water pressure around the tunnel under each train load is about 3-5 k Pa,and then all dissipates.Under the simulated train speed and tunnel curvature radius in this paper,the tunnel foundation liquefaction will not be caused.