黄河下游泺口边滩大型环状滑塌构造研究

黄河下游泺口浮桥北岸的泺口边滩中后部发育了两个大型环状滑塌构造，小者长42.54 m，宽31.55 m，高0.63 m；大者长58.30 m，宽46.24 m，高0.76 m。根据几何学特征及运动要素，可以将大型环状滑塌构造分为三个部分：主体带、过渡带和消失带。主体带以规模较大的滑塌块体为主，滑塌块体宽20～30 cm，长2～3 m，高40～60 cm，呈弧片形；滑塌缝开放或被淤泥充填，此带长宽十余米；过渡带以规模中等的滑塌块体为主，滑塌块体宽5～20 cm，长0.5～2 m，高20～40 cm，也呈弧片形，滑塌缝半开放或紧闭，滑塌块体的相对运动方向在此带发生转变，由单向运动转变为相对运动；次级侵蚀沟槽在此带汇合，形成了一个放射状的大“空腔”，滑塌以此“空腔”为圆心相对滑动，并由此形成环状滑塌构造，此带长10～20 m。在过渡带之外为消失带，总体特征是滑塌块体及滑塌位移量逐渐由大到小，直至消失，此带长15～30 m。黄河泺口大型环状滑塌构造是在一种近水平条件下形成的，滑塌坡度为0.745°，滑塌是以“多米勒”骨牌方式实现和完成的。泺口边滩是以粉砂和泥质粉砂为主的易于液化的细粒物质，其滑塌构造的形成与黄河暴涨暴落导致的孔隙水过饱和及泺口边滩的特殊结构造成的渗水有关。

Study on large-scale circular slump structures on Luokou point bar in downstream of Yellow River

Two large-scale circular slump structures are well developed on the middle-rear Luokou point bar of the downstream of Yellow River. The smaller one is 42.54 m long, 31.55 m wide and 0.63 m high and the larger one is 58.30 m long, 46.24 m wide and 0.16 m high. These structures can be divided into three parts: the main body belt, the transitional belt and the vanishing belt accord- ing to the geometrical characters and the kinematical elements. Some larger collapsed blocks, which are 20 - 30 cm wide, 2-3 m long and 40 - 60 cm high and with the shape of arc-slice, dominate in the main body belt whose length is 8 - 15 m, what is more, the collapsed slots are open or filled with the silt in the main body of these structures.The 10-20 m long transitional belt, with the character of moderate collapsed blocks whose dimensions are 5 - 20 cm wide, 0.5 - 2m long and 20 - 40 cm high has the same shape of arc-slice as the main body belt, but the slots are somehow different because some are half-open and others are stuffed with the silt. It is important that the relative movement directions of the collapsed blocks have a change here, i.e. from the sere one-way movement to the relative movement. The relative glides with the circle center of a big radial cavity, which are formed by the associate erosive grooves' gathering, contribute to this kind of ring-like collapsed and slippery structures. The 15 - 30 m long vanishing belt which is located beyond the area of the transitional belt, is characterized by the decreasing of the block' s dimension as well as the displacement space of the slide of blocks.The structures studied here are developed in a horizontal surface with the collapse gradient of 0.745 degree, and they are developed and accomplished in a "domino" manner. Some factors such as the liability to liquefaction of the fine sediments made up of silts and muddy-silts, the supersaturated pore water due to sudden and sharp rising or falling level of the Yellow River and the seepage water formed by the special configurations of the Luokou point bar, all contributed to the development of the slump structures.