Shaking Table Tests Study On The Effects Of Ground Motion Duration On The Seismic Response Of Liquefiable Site

The site failure caused by earthquake liquefaction is one of the main causes of the failure of engineering structures,and it is a hotspot in geotechnical seismic engineering.The site disaster investigation,numerical analysis,and physical model test are three commonly used methods to study the earthquake response and failure process of engineering structure and foundation.However,the field survey data is very limited,and the numerical analysis method is flexible and economical,but it requires higher and stricter conditions in the input ground motion,the dynamic constitutive relation and the boundary condition,now it is still in the developing stage.Therefore the physical model test is still one of the important method to study the seismic damage mechanism of the site and the engineering structure.Shaking table model test is scaled model test,the similarity ratio design of the model system and the input ground motion is the crux to ensure the test object can accurately reflect the seismic response of the prototype system,the time similarity ratio design of the input ground motion is one of the crucial conditions for the success of shaking table test.Ground motion characteristics are changed after compressing the duration of ground motion,which has a noticeable influence to the seismic response of liquefied system.In the past shaking table tests,part of the shaking table test compressed the ground motion duration,Partial shaking table test did not compress the ground motion duration,compressing the ground motion duration or not and ground motion duration compression ratio has been not studied,therefore a series of shaking table tests were performed to study the effects of ground motion duration compression on the seismic response of liquefied system.The performance of model box was examined by the shaking table test of liquefied free field.The results showed that the free shear effects of soil was reflected in the time domain and frequency domain by the model box.The effects of ground motion duration compression on the seismic response of liquefied system was studied by three shaking table tests.Failure mechanism and dynamic response law of liquefied foundation were discussed by macroscopic phenomena,acceleration,pore water pressure,relationship between shear stress and shear strain,settlement of foundation.The law of dynamic interaction between soil and pile was researched by dynamic soil pressure and the coupling relationship between dynamic soil pressure and other physical quantity.The liquefaction of foundation depended on the ground characteristics and seismic energy,which have have important effects on site liquefaction.The greater the compression ratio was,the stronger the ground motion energy was and the larger the deformation of the foundation was.In linear phase,the acceleration of model foundation was stronger to the ground motion which was compressed according to the dominant frequency of model foundation compared to the original ground motion.The effects of high frequency vibration characteristics on the acceleration response should be concerned for the similitude design of system.During nonlinear stage and failure stage of foundation,the effects of original ground motion on the dynamic response,namely acceleration,pore water pressure,foundation deformation,dynamic soil pressure,of liquefied system was stronger than the ground motion compressed according to the predominant frequency of model foundation.It is suggested that original ground motion should be adopted by the shaking table tests regarding foundation liquefaction as research objective.