Study On The Dynamic Response Of The Silty Clay Layer Around The Tunnel Under The Operating Load Of The Subway Train

With the continuous expansion of urban underground transportation projects,the problem of uneven settlement of foundation silt caused by subway traffic loads has occurred from time to time.How to effectively control and predict the settlement and ensure the safe operation of subways has become an important issue to be solved urgently in urban underground engineering construction.Based on the silt soil in a section of Xuzhou Metro Line 1,the empirical analysis method is used to study the vibration mechanism of the train load,the dynamic characteristics of saturated silt soil are studied through indoor dynamic triaxial tests,and the three-dimensional finite element numerical model is used to explore the subway tunnel.Based on the dynamic response law of silt foundation,a prediction method for the long-term settlement of saturated foundation silt is proposed.The main conclusions of this paper are as follows:(1)The empirical formula is used to calculate the vibration load of the Xuzhou Metro Line 1 train under different operating conditions,and it is found that the operating speed and operating load have a greater impact on the vibration load characteristics of the train.The operating speed mainly affects the amplitude and period of the vibration load,and the operating load mainly affects the reference value of the vibration load.(2)The dynamic characteristics of the silt in the section of Xuzhou Metro Line 1 are studied through indoor dynamic triaxial tests.When the CSR of the test silt exceeds the critical CSR,it will be destroyed.The critical CSR of the silt under different stress conditions is not necessarily the same.Under isobaric conditions,when the effective confining pressure is 100kPa,the critical CSR of saturated silt is 0.1～0.15;when the effective confining pressure is 250kPa,the critical CSR of saturated silt is 0.06～0.1,and the dynamic stress amplitude is relatively saturated The destruction of silt soil plays a leading role.The hysteresis curve is used to obtain the dynamic shear modulus and dynamic damping ratio of saturated silt under different test schemes with the cumulative strain,and the hyperbolic model is used to derive the dynamic constitutive relationship of the silt in the section of Xuzhou Metro Line 1.Calculate the dynamic shear modulus attenuation model with cumulative strain G/G0=1/(1+13.85771γ0.77892)and the model of sum dynamic damping ratio increasing with cumulative strain D=0.24474(G/G0)2-0.47443(G/G0)+0.25207.(3)A three-dimensional finite element model of the train-tunnel-foundation of Xuzhou Metro Line 1 is established to explore the vibration load generated under different train operating conditions and the dynamic response law of the silt with different buried depths of the tunnel base.The energy dissipation of dynamic stress is the largest when the dynamic stress is transmitted on the rail and the floating slab,and the attenuation exceeds 80%.The attenuation law in the process of spreading in the silt layer shows an exponential trend.The dynamic stress attenuation speed is faster within the buried depth of the tunnel base of 2m.fast.When the train speed is 80km/h,the dynamic stress distribution range of the silt of the tunnel base is 18.088kPa～30.882kPa;the dynamic displacement distribution range of the tunnel base is 0.4849mm～0.828mm during the process from empty to full load.When the train is fully loaded and the train speed increases from 20km/h to 80km/h,the dynamic stress distribution range of the tunnel base silt is 25.927kPa～30.882kPa;the tunnel base silt dynamic displacement distribution range is 0.6518mm～0.828mm.(4)According to the dynamic triaxial test,the undrained cumulative deformation characteristics and pore pressure development characteristics of the silt were obtained,and the cumulative plastic deformation model of the silt in the section of Xuzhou Metro Line 1 was derived εi=2.02(qd/qf)1.303(1+qs/qf)1.083(N)0.196 and silt cumulative pore pressure model u/pc=4.122(qd/qf)1.805(1+qs/qf)4.307(N)0.225,Combined with the analysis of the three-dimensional finite element model,the stress state of the silt at different buried depths of the tunnel foundation under static and dynamic conditions,and the layered sum method is used to analyze the different buried depths of the tunnel base during the 10-year operation period of Xuzhou Metro Line 1.The silt settlement value is predicted and calculated,and the total settlement value is 28.39mm.This article has 91 pictures,23 tables,and 110 references.