Experimental Study On Anti-liquefaction Performance Of Aeolian Sand Foundation Reinforced By Different Piles In Valley Area

In recent years,with the continuous development of China ’s western transportation construction,the line project will inevitably cross the aeolian sand valley area.Due to the rich groundwater provided by rivers and the frequent earthquakes in western China,these strata are facing serious liquefaction risks.For example,the Lhasa-Linzhi section of the SichuanTibet Railway is closely built along the Yarlung Zangbo River and passes through many aeolian sand valleys.The roadbed project will face the problem of foundation liquefaction.Therefore,the reinforcement and seismic design of the aeolian sand foundation in the valley area need to be optimized to promote the realization of the strategy of building a strong transportation country.In this paper,the aeolian sand stratum in the valley area of Lhasa to Linzhi of Sichuan-Tibet Railway is taken as the research object,and the liquefaction performance test of aeolian sand foundation reinforced by gravel pile,prefabricated cement pile and screw pile is carried out by using one-way horizontal seismic simulation shaking table.The anti-liquefaction effect and reinforcement mechanism of aeolian sand foundation reinforced by three pile types are analyzed.The dynamic response of aeolian sand foundation reinforced by different pile types before and after liquefaction is analyzed from the perspectives of elevation peak change,main frequency change,main frequency band migration,time-frequency change and energy transfer.At the same time,a method for judging the liquefaction damage of aeolian sand pile-soil composite foundation based on energy variation index is established.The research results of this paper are as follows :(1)Under the action of earthquake,gravel pile,precast cement pile and screw pile can effectively resist the settlement of aeolian sand foundation.(2)Because the gravel pile body and the prefabricated cement pile surface can act as a good drainage path,it can effectively dissipate the excess pore water pressure inside the foundation,so as to improve the liquefaction resistance of the foundation,and the gravel pile and the prefabricated cement pile have the best anti-liquefaction effect on the shallow and middle parts of the aeolian sand foundation respectively.The threaded pile will change the stress field of the aeolian sand foundation under the action of earthquake,and increase the vertical effective stress between or around the piles,thus offsetting some of the excess pore pressure and reducing the liquefaction potential of the aeolian sand foundation.(3)Based on the correlation analysis of pore pressure growth at different buried depths in the vertical direction,it is found that when the seismic intensity is low,the seepage phenomenon mostly occurs in the soil between piles.When the seismic intensity increases,the seepage phenomenon of foundation pore water transfers to the drainage path of gravel piles.(4)When the El Centro seismic wave propagates from bottom to top,the main frequency band of the response of the gravel pile foundation will expand and migrate to high frequency(≥ 22 Hz),and the liquefied soil layer has high frequency filtering effect.As the loading seismic intensity gradually increases,the lower limit of the main frequency band of the response of different parts of the aeolian sand foundation reinforced by precast cement piles will gradually migrate to the low frequency,and after liquefaction,the lower limit of the main frequency band will reverse to the high frequency migration.The threaded pile reinforced aeolian sand foundation is dominated by discrete instantaneous strong earthquake response,and the response frequency band correlation and elevation of different elevation parts are not strong,and the independent response is dominant.(5)Through wavelet packet transform,the anti-liquefaction performance of aeolian sand foundation reinforced by different pile types is studied from the perspective of energy variation,which overcomes the difficulty of defining foundation liquefaction due to the complex mechanical characteristics of pile-soil interaction under earthquake.