Study On Dynamic Response Of Liquefiable Soil And Anti-uplift Measures Of Underground Structure Under Earthquake

When underground space is developed in areas where seismic works,it is often faced with the situation of underground structure crossing liquefiable soil.When the earthquake occurs,the soil around the underground structure will liquefy,which causes uplift displacement and damage to the structure.It can be seen that the dynamic response of liquefiable soil under earthquake action is very important to evaluate the structure uplift and its control measures.In this paper,the finite element analysis software DBLEAVES is used to carry out numerical analysis.For liquefiable soil layer and underground structure,free site model,different types of structure-soil model and multi-layer-soil-structure model of practical engineering are established.The response law of excess pore water pressure ratio(EPWPR)etc.under earthquake action is analyzed and the effect of uplift control of underground structure is evaluated.The main research contents and results are as follows:(1)By applying sine wave,natural seismic wave and artificial seismic wave load to the free-field model,the effects of vibration load type,vibration wave amplitude and frequency on soil liquefaction are studied.Change the soil permeability coefficient and soil material Parameters corresponding to the standard penetration test(SPT)number to study the effects of changes in soil properties on liquefaction.The study shows that the high-frequency part of the wave during the propagation of the liquefiable soil layer will be filtered by the soil.The sine wave load with the frequency of 0.5~4Hz is more likely to liquefy the soil.The greater the earthquake intensity,the deeper the liquefaction depth of the soil.Increasing the permeability coefficient will reduce the degree of liquefaction of the soil.When the soil permeability coefficient is greater than a certain value,the soil will no longer liquefy.The higher the SPT number,the lower the degree of liquefaction of the soil.(2)The dynamic response of circular and rectangular underground structures-soil interactions is studied.The effects of changing soil properties on the liquefaction of rectangular structures-soil models and the uplift of structures are explored.It is found that under the action of earthquake,the subsurface floating structure of the liquefiable soil layer will be partially uplifted,the rectangular structure will maintain the displacement consistent with the surrounding soil,and the circular structure will have a great influence on the displacement of the upper layer soil.The smaller the SPT number,the smaller the degree of liquefaction of the soil,and the smaller the floating displacement of the structure.(3)Exploring the dynamic response of the actual engineering multi-soil-underground structure interaction.The effects of different seismic intensities on the floating displacement of the structure were studied,and the effects of different liquefaction prevention measures on the liquefaction of the soil and the uplift of the structure were taken.The results show that the structural uplift displacement caused by seismic liquefaction is caused by soil liquefaction and soil vibration,respectively,and the former is the main cause of structural damage.Underground continuous wall method,uplift pile method and replacement method can improve soil liquefaction and structural uplift.With the increase of uplift pile diameter and pile length,the structural self-weight and pile-soil friction force will increase accordingly.The structure uplift is suppressed,and when the pile spacing is close,the "group pile effect" occur weakening the floating control effect.The deeper the replacement depth,the smaller the uplift on the structure.In the local regulations of Shanghai,the anti-uplift safety check of the underground structure in liquefiable soil can be corrected according to the liquefaction grade determined by the SPT.