黄河下游冲积粉土地震液化机理及其判别

在粉土或砂土分布广泛的地区，地震液化是导致地基失稳和上部结构受损的直接原因之一.基于大量的现场调查,分析了黄河下游冲积粉土的成因及土体组成，在该区域粉土组成中粒径为0.005~0.020 mm的粉粒已经具备黏性，明显影响到粉土的工程性质.在动三轴试验基础上阐述了该区域粉土的动力特性和液化机理.最后结合该区域粉土土质特点和工程实例比较了现有的地震液化判别方法，指出该区域粉土液化判别应考虑黏性粉粒的影响，并依此利用塑性指数对液化判据进行了改进.对于该区域粉土，可将现行抗震规范中“黏粒含量10、13、16对应地震烈度7度、8度、9度判别为不液化”的规定，改为“塑性指数7.0、8.5、10.0对应地震烈度7度、8度、9度判别为不液化”.

Mechanism and assessment of earthquake liquefaction of alluvial silt in lower reaches of Yellow River

The soil liquefaction caused by earthquake is one of the direct reasons for the foundation invalidation and the structure collapse in the area where the saturated sand or silt distributes widely. The formation and composition of the alluvial silt in the lower reaches of Yellow River were investigated based on the practical investigation. The silt whose grain diameter lies in the range of 0.005 mm to 0. 020 mm has possessed viscosity and obviously affects the engineering property of soil. Then the dynamic properties and liquefaction mechanism of the silt were illuminated on the basis of dynamic triaxial test. And a comparison was presented between the existed earthquake liquefaction assessment methods combined with the silt properties and several engineering examples. Analysis suggests that the influence of cohesive silt should be taken into account in the liquefaction assessment, which can be realized with plasticity index. According to the characteristics of the silt in this area, the statement in the code for seismic design that according to the seisimic fortification intensity 7, 8, 9, the situations of cohesive grain content 10,13,16 should be as no liquefaction, should be replaced with the statement that according to the seisimic fortification assessed intensity 7, 8, 9, the situations of plastic index 7.0, 8.5, 10.0 should be assessed as no liquefaction.