含黏粒砂土场地液化离心机振动台试验研究

提出了含黏粒砂土模型地基制备、饱和与均匀性监测技术，利用ZJU-400土工离心机振动台开展了相同相对密度含黏粒砂土（黏粒含量10%）和洁净砂的地震液化模型试验，再现了水平场地地震液化现象，揭示了含黏粒砂土场地液化灾变特点。弯曲元波速监测表明，模型制备均匀性良好，相同条件下含黏粒砂土剪切波速比洁净砂低。而根据超静孔压消散与固结沉降观测分析发现，含黏粒砂土渗透系数比洁净砂低一个数量级，从而影响其液化前后超静孔压响应和应力应变行为。渗透性差异导致模型内超静孔压产生模式和消散速率显著不同，振动时含黏粒砂土模型浅层超静孔压累积比洁净砂慢，而深层则相反；震后含黏粒砂土孔压消散时间是洁净砂的15倍。液化过程中含黏粒砂土剪应力应变响应比相同深度处的洁净砂更显著，液化后其滞回圈应变较大、割线模量较小且阻尼比较大。土体液化沉降主要发生在液化后超静孔压消散过程，含黏粒砂土模型超静孔压消散时间更长，沉降量更大。上述成果为进一步研究含黏粒砂土地震响应分析及其液化判别提供了科学依据。

Dynamic centrifuge tests on liquefaction of clayey sand ground

The preparation, saturation and uniformity checking methods for clayey sand ground model are proposed. Then liquefaction model tests on clayey sand with clay content of 10% are performed by means of ZJU-400 geotechnical centrifuge shaking table, and the other model for clean sand with the same relative density is also performed for comparison. Seismic liquefaction phenomena of level ground are reproduced and the liquefaction characteristics of clayey sand ground are revealed. Measuring of bender elements shows that both models are uniformly prepared, and the shear wave velocity of the clayey sand is lower than that of the clean sand under the same condition. The permeability coefficient of the clayey sand is nearly an order of magnitude lower than that of the clean sand according to the test observations, which affects the responses of the excess pore water pressure (PWP) and stress-strain relationship during liquefaction. The difference of permeability results in slower buildup of PWP in the clayey sand at shallow depth but faster one at deep depth, while the post-liquefaction dissipation is 15 times longer than that of the clean sand. Response of shear stress-strain of the clayey sand is more pronounced than that of the clean sand at the liquefaction stage, and its secant modulus is smaller and the damping ratio is larger under post-liquefaction cyclic loadings. Model settlement mainly occurs during the process of PWP dissipation, and the clayey sand has longer dissipation time and doubles the settlement of the clean sand. This study presents scientific evidence for seismic response analysis and liquefaction evaluation of clayey sand ground.