黄河三角洲粉质土硬壳层特征及成因研究

Study of characters and formation mechanism of hard crust on tidal flat of Yellow River estuary

在黄河三角洲选择硬壳层发育的典型研究区,用人工振动模拟波浪荷载,通过孔隙水压力的监测和强度的原位测试研究了1 m范围内粉土硬壳层的重复液化和强度变化规律。结果表明,硬壳层动态响应沿深度存在较大差异,经过重复液化后强度总体是升高的,上层土体强度提高相对显著。采集荷载施加前后的原状样品进行SEM图像定量分析,得到了微结构的变化规律,如不均匀系数变小,粒度分维值升高,孔隙比显著减小,定向性增强等,但各项指标的变化程度不同,沿深度存在着显著的差异,主要变化集中在上部土层。讨论了硬壳层的动态响应特征与微结构调整的对应耦合关系,初步了解了循环荷载作用下粉土硬壳层的特征及成因的微结构控制规律。

The typical area was chosen on the tidal flat of the Yellow River estuary where hard crust develop, simulating wave load test with a light compactor was carried out to study the repeat liquefaction and change law of crust layer within one meter through the monitoring of pore water pressure and in-situ soil strength measure. The results revealed that the dynamic response varies a lot along depth and the strength of silt increases after repeat liquefaction; the upper crust layer increases more obviously than the down. The undisturbed samples were taken before and after vibrating; and quantitative analyzing of SEM structure images is carried out on the samples of different depths. The results revealed that some indexes of microstructure change evidently; such as asymmetry coefficient descended, granularity direction strengthed, granulometric fractal dimensions improved and figure coefficient improved and ratio of pore will descended etc. The transformation varied a lot along depth with the range mainly concentrated above the upper site. The relation between the dynamic response character and their microstructure changes has been discussed; and the character and formation mechanism of hard crust under the control law of microstructure are grasped primarily on this base.