土石坝坝体和地基液化分析方法与评价

Methods for liquefaction potential evaluation of embankment and foundation and discussion on these methods

对应用于土石坝坝体和地基的液化分析方法进行了评述,指出了在应用规范方法和动力反应分析法判断坝体和地基液化时应注意的问题。水工建筑物基础埋深和影响深度比较大,水利水电工程领域不采用上覆非液化土层厚度作为液化初判指标是合适的。采用相对含水率判别少黏性土的液化,对9度区以下(包括9度)区域是有效的,对于9度以上区域,则难以涵盖可能液化的土类。采用动力反应分析进行液化判别时,结果合理与否很大程度上取决于所采用的本构模型,以及本构模型参数的确定是否合理,且不同的分析方法对液化的评价标准不同,可能会得到不同的判别结果,需要进行综合判断。对于坝基覆盖层可能液化土体,由于受试验控制密度、级配和原位结构性等的影响,室内试验准确确定覆盖层静动力计算参数困难很大。此外,试样和试验结果的代表性也是人们关注的问题。因此,对于包括复杂深厚覆盖层地基的土石坝工程,建议同时采用多种方法,在比较分析的基础上综合确定其液化可能性。

This paper presents a discussion on the methods commonly used for liquefaction potential evaluation of dam foundation and embankment,and reveals some issues that need great attention in using these methods specified by the Codes of Engineering Geological Investigation of Water Resources and Hydropower（GB50487-2008） and the methods of dynamic response analysis.The buried depth of hydraulic structures and their influence depth are deep,and thus the thickness of overburden layer should not be taken as a preliminary index for soil liquefaction.Relative moisture content is an effective index for evaluation of soils liquefaction potential in the areas of seismic intensity not higher than 9 degree,while it can not be used for all types of soils in an area above 9 degree.If seismic response analysis is used for the evaluation,two issues should be noticed.（1） The validity of evaluation depends on the constitutive model and its parameters,and（2） a comprehensive judgment is needed as the methods that adopt different liquefaction criteria often lead to different results.Under the influence of density and gradation controls in tests and in-situ soil structure,an accurate determination of static and dynamic parameters of liquefiable soils in the overburden layers is very difficult.Besides,the representativeness of samples and their test results are also a serious issue.In liquefaction potential evaluation of the earth-rockfill dam with deep overburden layer,multiple approaches should be used with a great care.