The Study Of Dynamic Characteristics On Silty Clay And Dynamic Response Analysis On Metro Tunnel Structure In Qingdao Area

With the speeding up of urbanization process,the urban population, urban trafficregional planning and urban ecological environment are suffered from great pressure inthe last ten years.The development and utilization of urban underground space hasbecome the focus which everyone concerned with ground transportation been greatlyimproved. This paper takes Qingdao subway which is being built as the study subject.Different geological layers are crossed by Qingdao subway in the ground. The partialsections of the proposed Qingdao metro line no.1cross the quaternary pleistocene seriesalluvial deposition of silty clay layer Q3al+plin Chengyang district. We do the indoordynamic triaxial test on Qingdao quaternary pleistocene series alluvial deposition ofsilty clay and study its dynamic characteristics. On the basis of getting some dynamicparameters of quaternary pleistocene series alluvial deposition of silty clay, the dynamicresponse on three kinds shapes of subway tunnels crossing the quaternary pleistoceneseries alluvial deposition of silty clay layer is analyzed by ANSYS. The main studycontents and results are as follows.1.The study of the dynamic characteristics on the quaternary pleistocene seriesalluvial deposition of silty clay in Qingdao area. The indoor dynamic triaxial test onQingdao quaternary pleistocene series alluvial deposition of silty clay under Qingdaosubway lines is done. A series of dynamic properties are gotten, including the dynamicstress-strain relationship of soil, the relationship between dynamic elastic modulus andconfining pressure,the relationship between dynamic shear modulus and dynamic shearstrain, the value range of initial elastic modulus Ed0, the relationship between initialdynamic shear modulus Gd0, the maximum dynamic shear stressyand the axialconsolidation stress, the relationship between damping ratio and the axial consolidationstress and the value range of damping ratio and so on. The specific study results are asfollows.(1)The dynamic stress-strain relationship on Qingdao standard sequence eleventhlayer quaternary pleistocene series alluvial deposition of silty clay is in line withhyperbolic model. The inverse of dynamic elastic modulus1/Edand dynamic straind approximate to linear relationship.The fitting linear relation is gotten between1/Edanddunder different confining pressure.(2)The dynamic elastic modulus of soil decreases with increasing of dynamic strainand increases with the increase of confining pressure.The dynamic shear modulus ofsoil decreases with the increase of dynamic shear strain.The the initial dynamic elasticmodulus range is between31MPa to48MPa.(3)We find that it has a good power function relationship between the initialdynamic shear modulus of soil Gd0,the maximum dynamic shear stressyand the axialconsolidation stress.Power function equation obtained by experimental data fitting isGd0=1.19(Kc3c)0.483，y=1.304(Kc3c)0.582.(4)Consolidation confining pressure3and consolidation ratio Kchas little effecton damping ratio.Damping ratio decreases with the increase of shear strain γd.When theshear strain γdis close to0.002,damping ratio tends to be stable at0.01.2.Dynamic finite element theory which is applied to the analysis of undergroundstructure dynamic problem,elastic-plastic DP model in ANSYS and the steps ofsimulation computing are introduced.3.The train vibration load is determined.According to the predecessors’ experienceand the existing study results，we simulated the train vibration load with artificialexcitation function and get the time history curve of load changing with time.4.Three kinds shapes of tunnel structures dynamic finite element models areestablished on ANSYS which is a kind of large general finite element software. Based onthe dynamic characteristics of silty clay test results and Qingdao metro line no.1surveydatum, we do a numerical simulation of tunnel system from excavation to loadingvehicle vibration load and get the internal force and dynamic response of tunnelstructure. Through the analysis of the tunnel internal force and dynamic response,thefollowing conclusions are gotten.(1) The most reasonable structure in silty clay layer is circular tunnel. We suggestthat the circular lining tunnel is used on the proposed metro line no.1crossing silty claylayer.Technology of shield driving is used on circular tunnel.(2)By comparing,the change of the internal force and dynamic response of the linings of different shapes is small with loading vehicle vibration load. So the trainvibration load is not the main influencing factors on the stability and safety of tunnelstructure.