河床深厚覆盖层砂土液化判定对比研究

Comparative Study on Sandy Soil Liquefaction Judgment of Deep Overburden in Riverbed

砂土液化会导致地基失稳和上覆建筑物结构受损,是地震区常见的工程地质灾害之一,因此,对拟建场地的液化判别是勘察设计中的重要课题。通过采用粒径法、标准贯入试验法、动三轴试验法及剪切波速法,分别对河床覆盖层中的全新统湖积层进行砂土液化判别。结果表明:各方法对湖积上层的判别结果存在差异,粒径法显示其黏粒含量达50%,且动三轴试验所得破坏强度比计算得土层抗液化剪应力小10 kPa以上,判定为不会发生液化,但土层的标贯基准击数比临界标贯击数小,剪切波速也比上限剪切波速小,判定其存在液化可能;对于湖积下层粉细砂层,各方法判别结果一致,均认为其存在砂土液化问题;综合对比分析4种不同方法的液化判别结果,最终评定为湖积上层淤泥质黏土层不会发生液化,但下层粉细砂层抗液化能力较弱,存在砂土液化问题。研究成果对解决工程区砂土液化问题具有重要实用价值。

Liquefaction of sandwill leadtoinstability of foundation and damage of overlyingbuilding structure,whichisone of the common engineering geological disasters inseismic area.Therefore,the liquefactiondiscrimination of proposedsiteisanimportant issueinsurvey and design.This paper uses the particlesizemethod,standardpenetrationtest method,dynamic triaxial test method and shear wave velocitymethod todiscriminate the sandliquefactionof the Holocene lacustrine deposits inthe riverbedoverburdenof the lower reservoir area.The results showthat:discrepancies exist in the discrimination results of the upper lacustrine deposits among different methods.The particle size analysis reveals a clay content of up to 50%,and the failure strength derived from the dynamic triaxial test is over 10 kPa lower than the calculated liquefaction shear stress of the soil layer,which is judged to be non-liquefaction.However,the standard penetration blow count of the soil layer is smaller than the critical standard penetration blow count,and the shear wave velocity is also below the upper limit,so it is judged that there is a possibility of liquefaction.Regarding the silty fine sand layer in the lower part of the lacustrine deposits,all methods consistently indicate the presence of sand liquefaction issues.Based on the comprehensive comparison and analysis of the liquefaction discrimination results of four different methods,it is finally evaluated that the upper muddy clay layer of the lacustrine will not be liquefied,but the lower silty sand layer has weak liquefaction resistance and has sand liquefaction problems.The study results have significant practical value for the prevention and control of sand liquefaction in engineering area.