摘要
滑坡是一种全球性的自然灾害,危害性仅次于地震和洪水。雅砻江流域作为一个梯级开发的重点区域,已建、在建、规划的大型水库有12个,这些水库大多修建在地质条件非常复杂的高山峡谷地区。对于某些已经趋于稳定的老滑坡,由于水库修建将改变其原来赋存的地质环境,导致发生库岸再造,甚至使库岸发生变形乃至再次失稳滑动,给大坝、库岸堤防以及下游地区造成严重灾害。库岸失稳后果严重,轻者淤积库坝,使水库的库容减少,严重的甚至能摧毁大坝,涂炭生灵。巨型老滑坡由于其特殊的工程地质条件,对于坝址的选择会有重要的影响,甚至有时会起到决定性的作用。
卡拉水电站位于雅砻江中游,拟建混凝土重力坝,拟装机105万kW,初选上、中、下三个坝址进行比选。由于近坝址区发育5个巨型滑坡,滑坡体规模巨大,一旦失稳,不仅会造成水库淤积而且将危及大坝及其它枢纽建筑的安全。本文依托于《雅砻江卡拉水电站近坝址区(下游河段)滑坡成因机制及稳定性研究》科研项目,对位于坝址区的田三滑坡进行了深入细致研究。
田三滑坡为一巨型老滑坡,C区目前发育多条长大拉裂缝,变形迹象较明显,其稳定性对坝址的选择有重要影响。本文基于野外地质调查和翔实的勘探资料,对田三滑坡赋存的环境地质条件进行了深入分析,探讨滑坡基本特征,研究滑坡成因机制。采用定量计算,结合定性分析和数值模拟等方法,综合评价其稳定性状况,预测其发展趋势,并对影响滑坡稳定性的敏感性因素进行分析。对滑坡发生后的涌浪高度和是否堵江两个问题进行计算分析,在此基础上进行危害性分析,并综合评价其工程效应。取得的主要成果如下:
(1)田三滑坡是一巨型老滑坡,为两期形成。滑坡边界较清晰,地形上总体前陡后缓。滑体物质组成分为三层:表层的坡积物及残坡积物(Q_4~(el+dl))、中部滑坡堆积(Q_3~(del))和底部滑带。田三滑坡根据工程地质条件不同,分为A、B、C三个区。A、B区目前稳定性较好,C区中前部目前发育多条长大拉裂缝,变形迹象较明显,结合变形观测资料分析,其安全储备不高。
(2)根据田三滑坡赋存的环境地质条件分析,田三滑坡成因机制为滑移～拉裂。是雅砻江右岸边坡在长期的内外营力作用下,发生顺层滑动而形成的。二维离散元动态模拟结果验证了其变形机制。
(3)滑坡稳定性分析:
1)定性分析表明:田三滑坡A、B区目前稳定性较好。C区变形迹象较明显,目前处于蠕变阶段,若C区失稳,有可能形成牵引式滑动,导致更大规模的滑体失稳。
2)对滑坡Ⅳ—Ⅳ′剖面所确定的计算模型的整体稳定性进行验算,然后对各期滑坡的整体稳定性分别进行校核,计算结果表明:水库正常运营期间,C区处于极限平衡状态;水库非常运营期间,滑坡不能满足安全标准,尤其稳定性较差的C区。
3)局部稳定性计算分析表明:在1986m蓄水位正常运营状况下,Ⅳ—Ⅳ′剖面局部出现4次滑动达到整体和局部的稳定。滑坡失稳方式为逐级解体:首先是C区出现失稳,然后B区出现渐进式破坏,最终滑坡形成新的平衡体而不再解体破坏。
4)数值模拟的分析结果总体上符合边坡应力场分布的一般规律,且与极限平衡分析法的分析结果是基本一致的,即田三滑体中前部处于临界状态或蠕滑变形状态,而且变形主要产生在中前部滑带附近。
(4)危害性分析及工程影响评价:
田三滑坡的危害性主要为淤积、涌浪和堵江,通过计算分析:
1)蓄水或地震工况下,田三滑坡淤积方量为110×10~4m~3,相对于卡拉水电站的库容,其影响较小。但是,滑坡区距水库大坝最近仅1km,大量的松散岩土体堆积于坝前,对安全行洪、水库清淤及发电设施的维护仍有不可忽视的影响。
2)田三滑坡在蓄水工况下,存在C区失稳的危险性,若C区全部失稳,则在入水点最高可引起73m的涌浪,传递至下坝址处最大涌浪高度达5.9m,超过1991m坝顶高程,存在翻坝的可能性;传递至中坝址处高达11m,超出坝顶8～11m,存在翻坝的危险性。
3)如果田三滑坡前部C区失稳,将在雅砻江段形成高约34m的天然堆积土石坝,堆积坝坝顶高程约1930m,略高于地下厂房出水口设计洪水位(1929.37m),并对施工期上坝址下游围堰等建筑有一定影响。
The landslide is one kind of global natural disaster, the hazardous nature is only inferior to the earthquake and the flood. The Yalong River basin took a stave development the key region, has constructed, is constructing, the plan large-scale reservoir has 12, these reservoirs mostly construct in the geological condition extremely complex mountain canyon area.Regarding certain already tended to the stable old landslide, because the reservoir construction will change the geological environment which its original tax saved, caused to have the storehouse shore restoration, even caused the storehouse shore to have the distortion and even once more the jitter glide, for the dam, the storehouse shore embankment as well as the down stream area created the major disaster.The storehouse shore jitter consequence is serious, the light siltation storehouse dam, causes the reservoir the storage capacity reduction, serious even can destroy the dam, spreads the coal life.
The giant old landslide as a result of its special engineering geology condition, can have the important influence regarding the dam site choice, even sometimes can play the decisive role.
The Kara Hydroelectric power station is located the Yalong River middle reaches, plans to construct the concrete gravity dam, plans to install equipment 1,050,000 kW, the primary election upper, middle and lower three dam sites carries on the ratio to elect. Because the near dam site area will grow 5 giant landslides, the landside mass scale is huge, once jitter, not only will be able to create the reservoir siltation moreover to endanger the dam and other key position construction security.
This article depends on " Kara Hydroelectric Power Station in Yalong River Near Dam Site Area (Downstream Water) Landslide Formation Mechanism And Stability Study" the scientific research item, to was located the dam site area the Tiansan landslides to conduct the thorough careful research.
The Tiansan landslide is a giant old landslide, the C area grow at present the multi-strip coarsening tension fracture seam, the distortion sign are obvious, its stability has the important influence to the dam site choice.This article based on the open country geological investigation and the full and accurate exploration material, the environment geological condition which saved to the Tiansan landslide taxes has carried on the thorough analysis, the discussion landslide basic characteristic, the research landslide origin mechanism.Uses the quantitative evaluation, methods and so on union qualitative analysis and value simulation, quality synthetic evaluation its stable condition, forecast its trend of development, and to affects the landslide stable sensitive factor to carry on the analysis.Has after swell to the landslide highly and whether the river two questions do carry on the computation analysis, carries on the hazardous analysis in this foundation, and quality synthetic evaluation its project effect.Obtains the main achievement is as follows:
(1) Tiansan landslides as a giant old landslide, is two issue of formations.The landslide boundary is clear, after in terrain in front of overall steep slow.The slippery body material composition divides into three: The surface layer slope sediment and the remnant slope sediment (Q_4~(el+dl)), middle the landslide piles up (Q_3~(de)l) and the base slippery belt.The Tiansan landslide basis engineering geology condition is different, divides into A, B, the C three areas.A, the B area the stability is at present good, in the C area the front part grows at present the multi-strip coarsening tension fracture seam, the distortion sign is obvious, the union distortion observed data analysis, its safety margin is not high.
(2) the environment geological condition analysis which saves according to the Tiansan landslide taxes, the Tiansan landslide cause mechanism is slip ~ drawing breakage.Is the Yalong River right bank side slope under a long-term inside and outside battalion of action of force, has the bedding slip to form.The two-dimensional Discrete element calculation result has confirmed its cause mechanism.
(3) landslide stability analysis:
1) the analysis indicated that, Tiansan landslide A, the B area the stability is at present good.The C area distortion sign is obvious, at present is at the slow change stage, if the C area jitter, has the possibility to form the towable glide, causes the large-scale slippery body jitter.
2) Select IV -IV' plane as the computation model overall stability carries on the checking calculation, then carries on the examination separately to various issue of landslide overall stability, the computed result indicated: Reservoir normal operation period, the C area is at the limiting equilibrium condition; Reservoir unusual operation period, the landslide cannot satisfy the standard of security, especially C area.
3) the partial stable computation analysis indicated that,Under 1986m store water level normal operation condition, IV—IV The section appears 4 glides to achieve the whole and the partial stability partially.The landslide jitter way is the progressive disintegration: First is the C area appears the jitter, then the B area appears the evolution type to destroy, but the final landslide forms the new balanced body no longer to disintegrate the destruction.
4) the value simulation analysis result as a whole conforms to the side slope stress field distribution general rule, also with the limiting equilibrium analytic method analysis result is basic consistent, namely in the Tiansan slippery bodies the front part is at the critical state or the creep strained condition, moreover distorts mainly produces nearby the front part slippery belt.
(4) hazardous analysis and project influence appraisal:
The Tiansan landslide hazardous natures mainly for the deposition, surge and stream jam, through computation analysis:
1) stores water or under the earthquake operating mode, the Tiansan landslides silt up 110×10~4m~3, is opposite in the Kara hydroelectric power station storage capacity, its influence is small.But, the landslide area was apart from reservoir dam recently only 1 km, the massive loose gneiss stack in front of the dam, to safe line of Hong, the reservoir clear silt and the electricity generation facility maintenance still had the noticeable influence.
2) the Tiansan landslides under the inpoundment operating mode, have the C area jitter the risk, if C area complete jitter, then in enters the water drop to be highest may cause the 73m surge, transmits reaches 5.9m highly to the under dam site place biggest surge, surpasses the 1991m top of dam elevation, the existence turns the dam the possibility.
3) if the Tiansan landslide front part C area jitter, will form high approximately 34m in the Yalong River section the natural pile of fill stone dam, stack dam top of dam elevation 1930m, slightly will be higher than the underground workshop water outlet design flood level approximately (1929.37m), and to the construction period in constructions and so on dam site downstream coffer dam will have certain influence.
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