黄河水下三角洲粉质土扰动土层特征及成因探析

Analysis of characteristics and formation of disturbed soil on subaqueous delta of Yellow River

黄河水下三角洲上分布着大量的扰动土层,其性质与周围未扰动土相比有很大的差异。在老黄河口区选择扰动土层的典型分布区,利用工程地质钻探取样、原位静力触探试验和浅地层剖面探测对海底扰动土层的厚度及工程地质特征进行了调查分析。结果表明,与未扰动土相比,扰动土的重度较大、孔隙比较小、含水率较低、强度有一定程度的提高。同时,分别对风暴潮作用下黄河水下三角洲粉质土的瞬时液化极限深度和残余液化极限深度进行了计算。计算结果表明,残余液化极限深度较大。将残余液化极限深度、通过浅地层剖面探测结果所得的扰动土层厚度以及通过土工试验统计结果所得的扰动土层厚度进行了对比,发现三者对应很好。对黄河水下三角洲粉质土中扰动土层的形成机制进行了探讨,认为风暴潮作用过程中产生的土体液化是其主要诱因。

Disturbed soil is widely spreaded on the subaqueous delta of the Yellow River.It is different from the ambient undisturbed soil in many aspects.A sea area in the old Yellow River estuary is chosen as the study area.Geotechnical drilling and geophysical prospecting is processed to get the stratification and the geotechnical characteristics of the soil in this area.It turns out that compared with the undisturbed soil,the bulk density of disturbed is bigger,the void ratio is smaller,the water content is lower,and the shear resistence is higher.The limit liquefaction depth is calculated.The depth is coincident with the maximum thickness of the disturbed soil;and according to the statistics of the geotechnical factors,the abnormity of the soil is more or less limited in this very depth.The forming mechanism of the disturbed soil is discussed;and liquefaction during storm time is believed to be the controlling factor.