Seismic Response Study Of Liquefied Interlayer Foundation-raft Type Shallow Foundation-superstructure

Earthquake-induced soil foundation liquefaction is one of the most destructive natural disasters and has received great attention from scholars and engineering circles at home and abroad over the years.Liquefaction of sandy soil can lead to damage to the superstructure,but it can also have a damping effect on the superstructure.At the same time,the structure-soilstructure interaction generated during the seismic process will also affect the seismic performance of the structure when there are adjacent structures on the liquefied foundation.And most of the current studies ignore the seismic isolation effect of the liquefied layer and only consider the seismic hazard of adjacent structures on non-liquefied sites and independent structures on liquefied sites.Therefore,in this paper,based on the Biot two-phase saturated porous medium dynamic coupling theory,a finite element-finite difference coupled numerical method is used.To study the effect of seismic isolation of liquefied layer on the seismic response of independent raft-type shallow foundation structures,to compare and analyze the difference of seismic response between adjacent structures on liquefied interlayer foundation and independent structures,to find out the law of seismic response of different factors on liquefied interlayer foundation-adjacent structure system,and to provide reference and guidance significance for seismic design of adjacent shallow foundation structures in the liquefied foundation.The main research of this paper is as follows:(1)Based on the finite-element-finite difference coupled numerical method,the effect of seismic isolation of liquefied layer on the seismic response of independent shallow foundation structure is analyzed,and the results show that increasing the compactness or seismic intensity of liquefied layer will weaken the seismic isolation effect of liquefied layer on the superstructure.In addition,the existence of the interval of liquefied layer thickness-to-depth ratio K(thickness of liquefied layer compared with the sum of overburden and liquefied layer thickness)can both enhance the seismic isolation effect of liquefied layer and reduce the settlement and tilt hazard of the superstructure.(2)By comparing the differences in floor acceleration,column bending moment,and tilt angle,as well as structural settlement and super porous pressure response of the foundation between independent structures and different adjacent structural models,the results show that the structure-soil-structure interaction causes the peak acceleration response and a structural bending moment of shallow foundation structures to show different degrees of decrease compared with independent structures.The degree of influence is related to the spectral characteristics of seismic waves and the size of the structure itself.In addition,the adjacent higher structure will drop the structured settlement,increase the structure tilt,and suppress the growth of the super porous pressure ratio in the soil layer below the adjacent structure.(3)A numerical analysis model of liquefied foundation-adjacent structure under different working conditions was established to investigate the influence of six factors on the seismic response of structure-liquefied foundation-structure system,namely,dense area of the cover layer,the thickness of the double liquefied layer,the height difference of adjacent structure,burial depth difference of adjacent structure,density ratio of the cover layer and liquefied layer,height difference,and spacing ratio F.The results show that the increase of the dense area of the cover layer,burial depth and height difference of foundation,and density ratio of the cover layer and liquefied layer can effectively reduce the settlement and tilt of adjacent structures.The results show that the increase of cover layer density,foundation depth,and height difference,and the ratio of the cover layer to liquefied layer density can effectively reduce the settlement and tilt of adjacent structures,but will increase the acceleration response of structures;The increase of double liquefaction layer thickness will intensify the settlement of the upper adjacent structures and reduce the acceleration response;when the adjacent structure spacing is less than the foundation width,the increase of F,can reduce the acceleration and settlement of the structure.