长江上游川峡二江续接地段岸坡演变过程探讨

The study on development process of slope in the connected part between Chuan and Xia rivers in Changjiang river

长江三峡工程库首区地质问题的复杂性及其认识程度是已困扰奉节、巫山和巴东等县城移民工程建设多年的大难题。本文从地质历史分析角度 ,提出长江的川峡二江续接贯通这一重大地质事件及其伴生的三种强烈地质作用 ,即“水锯”下切、溯源侵蚀和暗河垮塌作用 ,使其所在江段在较短的时间内 (约 3 0— 4 0万年 ) ,塑造了高达 3 0 0 m的复杂岸坡。这些作用引发的岸坡演化过程是 ,山体卸荷—松动—开裂—转动—泥化—垮塌—崩滑改造和阶地“超覆”等。目前的斜坡是该过程造就的“复合堆积体”,其主体是垮塌—滑移体。这类斜坡的工程地质环境质量是较差的 ,不同于正常固结的土体或岩体 。

It has been a difficult problem that some counties, such as Fengjie, Wushan and Badong etc, have been hardly pressed by complex geological environment in the front region of the Three Gorges reservoir in Changjiang river since migration engineering beginning(about ten years ago). On the basis of geologic history analysis, it is put forward that the connection action between Chuan and Xia rivers is a basic reason in this paper. As a great geological event, three types of strong hydrodynamics action caused by the connection, i.e.“water saw” undercutting, head ward erosion and collapse, sculptures the complex high slopes for 300 meters or so in the two banks of the Three Gorges. It is these actions that induced a process of bank slope development which includes rockmasses stress relief, relaxation, parting crack, rotating, softening, breakdown, collapse and then sliding in the surface and overlying of terrace from river deposit in the succeeding period. The present slopes are a sort of “compound accumulation” made from above process, especially breakdown, collapse and then sliding of its. So, these slope areas are not good at engineering geological environment properties, which is different from normal solidified rock or soil bodies. Some special research must be arranged on geological conditions above slope areas when overall planning is done for migration engineering construction and protection of reservoir banks.