非塑性细粒粒径与含量对饱和砂类土强度的影响

Effects of Non-plastic Fines Size and Content on Strength of Saturated Sandy Soils

松散状态下的饱和砂类土受剪切后出现静态液化现象,且受到细粒含量、颗粒级配、固结围压等因素的影响。而目前对于中密状态下砂类土的相关研究鲜有报道,特别对于细粒粒径的影响研究尚少。采用福建标准砂与三种不同粒径的石英粉进行混合,开展了一系列三轴不排水压缩试验。试验中保持所有土样的相对密度相同,相对密度控制为50%,同时还考虑了细粒含量(FC=10%,20%,30%)、围压(50,100,200 kPa)等因素的影响。试验结果表明:相同细粒含量下随着标准砂平均粒径与石英粉平均粒径比Rd的增大(Rd=10~65.76),最大孔隙比和最小孔隙比均有增大趋势;在细粒含量较低时(FC=10%和20%),峰值偏应力随着Rd的增大呈现近似线性递减关系,而在细粒含量较高时(FC=30%),峰值偏应力在Rd达到某个临界值迅速下降,而后基本保持不变或者缓慢下降;中等密实状态的砂类土在高细粒含量的情况下可发生静态液化,且平均粒径比Rd越大静态液化越容易发生,因此,评估饱和砂类土的强度需要考虑非塑性细粒粒径的不利影响。

Saturated loose sand containing low non-plastic fines is prone to static liquefaction subjected to undrained monotonic loading;this phenomenon is normally termed as static liquefaction,which is affected by various factors,such as non-plastic fines content,particle gradation and confining pressure. However,limited work focused on sandy soils in medium-dense state and especially the effect of silt size on the liquefaction potential of the sandy soils;thus,in this study,a series of strain-controlled monotonic undrained triaxial compression tests are conducted on a single base sand mixed with three different essentially non-plastic silts at three different fines content(FC = 10%,20%,30%)and three different confining pressure(50 kPa,100 kPa,200 kPa). The relative density of all soil samples was the same and has a value of 50%. The results show that:(1)Under otherwise identical conditions,the maximum porosity ratio and the maximum porosity ratio increase with the increase in the average particle size ratio Rdin the range of 10~65.76,where Rdis defined as the ratio of the average particle diameter of the base sand to the non-plastic silts;(2)the peak deviatoric stress of sandy soils tends to decrease nearly linearly with the increase in Rdwhen FC = 10% and 20%;however when FC = 30%,the peak deviatoric stress rapidly decreases as Rdreaches a critical value and then remains unchanged or slightly decreases with the further increase in the Rd;and(3)complete static liquefaction of sandy soils could occur at medium dense state at high fines contents. In addition,static liquefaction is more likely to occur when the Rdbecome larger. Therefore,it is necessary to consider the adverse effect of not only the content of low-plastic fines but also the size of low-plastic fines on undrained strength of sandy soils.