Experimental Study On Seismic Performance Of Shield Tunnels With Soil-rock Combination Strata In Jinan Area

With the develepment of urban underground engineering construction,shield method,as one of the main construction methods of tunneling,has been widely used in the field of urban underground rail transportation.Therefore,it is of strong scientific significance and engineering application value to explore the mechanism of seismic response and its seismic performance of shield tunnels through complex strata,especially when crossing the soil-rock combination strata with rapid changes in stiffness and shear characteristics.In this paper,the following studies are carried out to study the seismic response of shield tunnel through soil-rock combination strata in the context of the shield tunnel project of Jinan Railway Line 4:(1)the shaking table model test,which mainly includes the derivation of physical parameter similarity ratio,soil-rock combination strata formulation,tunnel modeling,sensor arrangement,seismic wave selection and loading;(2)a single layer of all-powder clay and a sudden change layer of soil-rock combination strata,and to compare and analyze the seismic response law of the two types of free-field models;(3)to establish four groups of ground shaking test models of soil-rock-tunnel structure interaction,and to conduct shaking table test by changing the location of different soil-rock interfaces in the tunnel cross-section,different seismic load levels,different seismic wave types,and to analyze the seismic response law of shield tunnels in soil-rock combination strata based on the test data;(4)numerical calculation and verification analysis of the shaking table test of shield tunnels in soil-rock combination strata by using MIDAS/GTS finite element software.The study shows that:(1)The self-oscillation frequency of the soil-rock site is higher,and the tunnel structure responds more to seismic waves with energy concentrated in the middle and high frequencies;the hard rock side is significantly affected by the high frequency band and the acceleration changes less with the burial depth,and the acceleration increment on the soil side of the partition interface is two times of that on the hard rock side;the pulverized clay enters the damage state before the rock layer,and the site is bimodally controlled by the double main frequency.(2)The tunnel structure is not significantly affected by the earthquake,and the response characteristics mainly depend on the dynamic characteristics of the strata.When the soil-rock partition interface is at the arch waist of the tunnel,the force characteristics of the structure are mainly controlled by the rock and clay,and the structurel dynamic response differs significantly;the peak acceleration response changes less along the height of the tunnel structure,and as the soilrock partition interface rises from the foot of the tunnel arch to the arch shoulder,the acceleration difference between the structures above and below the soil-rock partition interface increases first and then decreases.(3)The bending moment distribution of the structure in the soil-rock combination field tests showed a "four peaks phenomenon",between the soil-rock interface and the top of the arch ±60°,the peak moment gradually shifted toward the top of the arch as the acceleration peak increased;when the soil-rock interface was located at the foot and waist of the arch,the deformation of the model structure obviously tended to the deformation characteristics of cohesive strata,while the soil-rock interface is located at the shoulder of the arch,the sudden change of internal force is located at the side of the surrounding rock;under the same peak acceleration,the internal force generated by the structure is the smallest when the soil-rock interface is located at the shoulder of the arch.(4)The bending moment and shear force mutation of the tunnel structure at the soil-rock interface is significantly larger than the axial force mutation,which is prone to bending and shear damage state;the influence range of structural internal force mutation at the soil-rock interface will gradually increase with the acceleration,and the mutation influence area is between ±10° of the interface.