黄河水下三角洲塌陷凹坑构造形成的水槽试验研究

FLUME TEST FORMED BY COLLAPSE IN THE YELLOW RIVER SUBAQUEOUS DELTA

黄河三角洲沉积物以粉土为主,在黄河水下三角洲发现大量的塌陷凹坑微地貌,平面形态以封闭的圆形或椭圆形为主,直径为10～30m,凹坑内扰动土体与下部稳定土体界面呈向上凹的圆弧面。通过室内波浪对粉土底床作用的水槽试验,发现波浪可以使粉土底床浅表部分土体振荡运动,底床发生振荡运动土体处形成凹坑,凹坑内土体表层为落淤黏土,下部为粗化粉土。据此分析黄河水下三角洲塌陷凹坑构造形成的一种模式是:在风暴浪侵蚀作用阶段,局部浅表土体发生振荡运动从而产生凹坑,凹坑内扰动土体因波浪的振荡作用而离析溢出细粒黏土成分,从而形成比周围物质成分粗的土体;在静水状态下,凹坑内表层落淤细粒黏土,形成下粗上细的二元结构,凹坑内沉积物呈透镜体状。黄河水下三角洲塌陷凹坑的形态规模对研究风暴作用具有很好的指示意义。

In the Yellow River submarine delta mainly consisting of silt, there is a physiognomy with a great number of small-scale collapse pits whose planar shape is almost closed-circle or elliptical with the diameter of 10～30 cm, and in which the interface between the disturbed soil and the underlying steady soil-body is concave camber opening upwards. Through the indoor flume experiment simulating the influence of the wave on the silt-bed, we can observe the to-and-fro vibration of shallow-surface soil due to the wave and the vibration leads to the collapses in which the surface is clayey silt and the underlying is coarse silt. So in the Yellow River submarine delta, during the period when the storm wave erodes the soil-body, the vibration of shallow-surface soil leads to the collapses and in these collapses the clay is separated from the disturbed soil-body due to the vibration and the coarse grains remains; and in the static state, the clay is falling to the surface of the seabed. Thus the two-unit structure of fine grains in the upper and coarse ones in the lower is formed in the collapses. The shape and scale of this sedimentary lentoid body is significant to the research of the storm tide in the history.