Study on shaking table test about seismic liquefaction characteristics of sandy soil covered with frozen soil layer
Earthquake-induced liquefaction occurs frequently in frozen soil regions.Taking the earthquake re-cords in China as an example,the earthquake in Bachu County,Xinjiang in 2003,the Ms7.1 earthquake in Yushu,Qinghai in 2010,the Mw6.6 Akto earthquake in the northwest Pamir Plateau in 2016,and the Menyuan 6.9 earthquake in Qinghai in 2022 all showed seismic liquefaction.At the same time,there are 5～10 m thick silt soil layer,fine sandy soil layer,medium-coarse sandy soil layer and other soil layers in the alluvial areas in the eastern part of the river valley around the Qinghai-Xizang Plateau and some debris flow accumulation areas in the middle and western ends of the Qinghai-Xizang Plateau.The perennial saturated area is also in the high-inci-dence area of earthquakes,and the possibility of liquefaction damage is extremely high,which needs urgent at-tention from researchers.The influence of overlying frozen soil on sand liquefaction characteristics is complex.The soil temperature,moisture content,confining pressure,loading frequency and the coupling of various fac-tors will affect the dynamic performance of frozen soil.Freeze-thaw cycles,the content and type of fine-grained sand,poor drainage before freezing and other factors will affect the liquefaction resistance of sandy soil.In or-der to study the seismic liquefaction characteristics of sandy soil covered with frozen soil layer and clarify the variation law of dynamic parameters of frozen soil and sandy soil under different seismic waves,a shear model box of soil freezing system was designed and shaking table test of seismic liquefaction characteristics of sandy soil covered by frozen soil layer was carried out.The variation of acceleration,pore water pressure,soil pres-sure,interlayer and top displacement of the model under different seismic waves was analyzed.The results show that under the condition of frozen soil coverage,the sandy soil layer will begin to liquefy locally from the bot-tom,and the liquefaction height will gradually increase with the increase of the peak value of the input ground motion.The variation law of acceleration amplification coefficient after liquefaction of sandy soil layer is consis-tent with that of frozen soil layer,which increases first and then decreases with the increase of peak value of in-put ground motion.However,the amplification effect of sandy soil layer on input seismic wave is greater than that of frozen soil layer,and different soil layers have different amplification sensitivity to ground motion.When the sandy soil layer is partially liquefied,the peak horizontal displacement increases with the increase of the height of the soil below the liquefaction surface.However,because the friction between the particles of the san-dy soil layer above the liquefaction surface is higher than that of the liquefiable soil layer,the peak horizontal dis-placement will decrease abruptly after exceeding the liquefaction surface.The maximum vibration subsidence value at the top of the model soil reaches 5.16 mm.In addition,the seismic subsidence and slip phenomenon ap-pear in the frozen soil layer.The upward migration of water caused by seismic liquefaction gathers at the frozen-sandy soil interface,which aggravates the slip of the frozen soil layer.The friction between the soil layers is re-duced,and the sliding displacement is related to the degree of liquefaction.It reaches the maximum when the sandy soil layer is completely in the critical state of liquefaction.After the soil is completely liquefied,the slip value of the frozen soil layer relative to the sandy soil layer will decrease.Therefore,the seismic checking of the structure in the liquefiable site of the overlying frozen soil layer should focus on the frozen soil-sandy soil inter-face and the liquefaction height.This study can provide data support for the changes in mechanical behavior of soil in liquefiable sites overlying frozen soil layer.
万方数据
维普
