贵州关岭大寨高速远程滑坡碎屑流研究
INVESTIGATION OF A HIGH SPEED AND LONG RUNOUT ROCKSLIDEDEBRIS FLOW AT DAZHAI IN GUANLING OF GUIZHOU PROVINCE
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摘要: 2010年6月28日，贵州关岭因突降暴雨发生高速远程滑坡，滑程约1.5km，体积约174.9万m3，两个村组被毁，99人遇难。滑坡区位于西南地区常见的煤系地层区，上部为灰岩、白云岩，中部为相对较缓的砂岩地层，下部为页岩、泥岩地层，局部含煤，具有上硬下软的山体地质结构和上部富水下部隔水的水文地质结构，极易形成滑坡地质灾害。从地形上看，斜坡上陡下缓，形似靴状地形，上部陡峭地形导致山体易于失稳，而中下部开阔伸展良好的沟谷提供了远程的运动条件，较大的势能向动能的转化，容易形成高速远程滑坡碎屑流。6月27日和28日的降雨是触发此起特大灾害的主要原因，其24h降雨量达310mm，超过了当地近60a来的气象记录，分析表明，降雨产生的沟谷径流量是平时强降雨(100～150mmd-1)的沟谷径流的2倍之上，一是在滑源区砂岩裂隙岩体中形成静水压力和渗透压力，触使滑坡的失稳下滑； 二是在沟谷中产生地表径流，为碎屑流远程流动形成饱水下垫面，导致了碎屑流流动距离和速度的显著增加。近年来随着极端强降雨等灾害性天气的重现期缩短，高速远程滑坡造成的群死群伤特大地质灾害在我国呈逐渐增加趋势，应加强对这种灾害类型的调查与防范，特别是要进行滑坡安全避让范围和逃逸速度的研究。Abstract: On June 28， 2010，due to sudden heavy rainfall，a high speed and long runout rockslidedebris flow occurred at Dazhai in Guanling of Guizhou Province. Its runout distance was about 1.5km.Its rock debris volume was about 174.9 M m3.Its destroyed two villages and resulted 99 fatalities.The landslide was located at the coalrelated sedimentary rock strata area.This rock system commonly presents in southwestern China.The upper strata are limestone and dolomite.The middle strata are sandstone with gentle dipangles.The lower strata are mainly shale and mudstone and have coal seams in local regions.The strata forming the mountains have a special geological structure with hard rocks at upper portion and soft rocks at lower portion and a hydrogeological structure with upper rich groundwater aquifer and lower impermeable beds，which can easily form landslide hazards.From the site topography，the hillside slopes are steeper at the upper portion and gentler in the lower portion.The topography looks like a shoeshaped geometry. The upper steep slopes can easily occur slope instability and the middle and lower gentle and wide slope valleys offer the kinematic conditions for landslide debris to flow long distance. Transformation of the larger potential energy into kinetic energy can easily form rockslidedebris flows with high speed and long runout distance. The heavy rainfall on June 27and 28 were the main factor triggering the major disaster.The rainfall was up to 310mm and exceeded the records over the last 60 years.Analysis indicates that the runoff in valley streams were two times more than those during usual rainfall at the region.The large runoff water formed static groundwater pressure and seepage pressure in joints and fossils of the sandstones at the landslide source zone，which led the landslide to occur.Secondly，the runoff was formed in stream valleys，which became a layer of saturated water bed for the rock debris to flow long distance.As a result，the runout distance and speed of the rock debris flow was evidently increased. The findings of this investigation are useful to reduce and mitigate the disasters of such high speed and long runout rockslides and debris flows，the occurrences of which seem to have been increasing in recent years in China due to extremely heavy rainfall events.
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