落石堆积的结构特征与斜坡破坏型式之转换

Structural characteristics of rock-drop accumulations and transformation type of slopes failure

在基岩山区和丘陵区,落石堆积的分布非常广泛,并可经长期积累而形成巨大规模。然而,因缺乏研究,它们(尤其是规模较大者)经常被误定成滑坡或崩塌堆积。为此,作者结合长江三峡工程和西部大开发的需要,采用天然模型勘测和岩相分析等多种方法对其进行了长期研究。结果认为:1 落石堆积(累积体)通常是在扩离-落石发育而崩塌、滑坡不发育的陡崖(坡)下形成,同时还需有较平坡面,便于落石停积而不易被重力和流水搬走的堆积场所;2 落石堆积的结构特征为:(1)前缘土体较密实且粒(块)径较小,后缘多大块石并常具架空结构;(2)不等粒系数普遍较大;(3)常有淤泥质和砂、卵石夹层或透镜体;(4)前缘可具向外陡倾的加积层理。基于此,水的潜蚀作用和地表水对前缘的集中冲刷常成为落石堆积变形破坏的主因;3 落石堆积的破坏型式为滑坡、泥石流或碎屑流;4 落石堆积的勘查应特别注意查明环境水文地质条件、储水结构及相关参数;其稳定性评价应首先分析不同工程活动影响下产生潜蚀的可能性;5 为防治斜坡失稳,首先应保护落石堆积的自稳结构和选用有防潜蚀功能的开放型措施;6 深入研究落石堆积,对沉积学和工程地质学也具有理论意义和实用价值。

At rocky mountains and hills,rock-drop accumulations are widely distributed and can become giant bodies through long periods.However,as lack of study,they,especially those giant bodies,are usually mistaken as the accumulations of landslides or rock falls.For this reason,the authors of this paper have been engaged in this research for a long time for the needs of the three Gorges Project in Yangtze River and the Western Development Project of China,based on lithofacies analysis,natural model survey etc.,and following knowledge is resulted:\;1\^The rock-drop accumulation bodies commonly occurred under scarps(or steep slopes) where leaving-rockdropping is developed while landslides and rock falls are not developed.Meanwhile,a relatively flat top surface is needed for the accumulating material of the rock-drops and keep out of further thansport by running water and gravity.\;2\^The rock-drop accumulations are of typical textural characteristics as following:(1)the front soil has finer grain and denser texture but the back soil is coarser and loser and rich in pore space.(2)The inequigranular coefficient(the ratio of macrograined diameter to fine-grained diameter) is generally great much more.(3)There generally are intercalations or lenticels of sludge,sand and gravel.(4)The steep inclined accretion bedding may exist near front margin.Therefore,the suffosion and surface flows of scouring the front soil are usually the main causes for the destruction of the slopes.\;3\^The destructive types(transform types of the slope failure) are landslides,debris flow or debris-rock flow.\;4\^More attention must be paid to the identification of the environmental hydrogeologic condition,water-bearing structure and correlative parameter through the exploration of rock-drop accumulations;the suffosion calculating(with influence of various engineering) is most important task for stability evaluation.\;5\^For preventing destabilization of the slopes,the original stable structures must be protected and the open form measures with function of the preventing suffosion should be selected.\;6\^Penetrated study about the rock-drop accumulations will have obtained a lot of theoretical and practical worth for sedimentology and engineering geology(example,explorations of harbor and wharfs).