震后沟道泥石流启动条件——松散堆积体雨中失稳的水力学机制分析
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摘要
5.12地震导致大规模的松散崩滑物质堆积于沟道,极大的增加了震后降雨型沟道泥石流爆发的概率。然而,灾后特殊的物源条件和成灾环境改变了传统沟道泥石流的形成机制,给震后沟道泥石流的防治工作带来了巨大的困难。为此,以水文学为基础,在构建松散堆积体潜水位变化水文学模型的前提下,借助水力学理论,分析了沟道堆积体内水力随潜水位变化的规律和特征,研究作用在单元条块堆积体上静水压力和动水压力的计算方法。在合理分段沟道松散堆积体的前提下,基于无限边坡理论完成了对各段堆积体下滑力、基底抗滑力及剩余下滑力的表达构建。结合算例解析了震后降雨条件下堆积体失稳的力学机制。分析表明,震后沟道松散堆积体失稳启动并泥石流化是流域降雨作用下堆积体内潜水位不断抬升、水力环境不断劣化的结果。流域大、沟道窄、堆积深、导水系数小、沟床缓的堆积体因较高的潜水位更易在降雨中失稳,且失稳模式因条块间剩余下滑力差异而分为整体推移启动及解体牵引启动两类。
Because large quantities of loose deposits were accumulated in gully after "5.12" Earthquake,the occurrence probability of gully debris flow is enhanced greatly in rainfall.However,due to the special conditions of provenance and disaster environment,the traditional theory cannot be used to expound the mechanism of gully debris flow and prevent the disaster effectively as ever after the event.Here,based on hydrology,the hydrological model of ground water table in loose deposits is established first.Then by aid of hydraulic theory,the change of hydraulic characteristics and the variation of hydraulic power with the rising of groundwater level are analyzed.Furthermore,the calculation formulas of hydrodynamic and hydrostatic pressure are also proposed.Finally,by applying infinite slope theory in calculation of sliding force,anti-sliding force and residual sliding force acting on each segment,the failure mechanism of accumulation body is illustrated clearly with an example.The result indicates the failure of loose deposits in rainfall is the result of increase of the hydraulic power with the rising of groundwater level.Those deposits which have small coefficient,gentle slope,narrow-deep gully and large basin would be easy to fail because of its high hydraulic pressure generating in rainstorm,and the failure modes can be divided into two types according to residual sliding force as pushing failure and hauling failure.
Because large quantities of loose deposits were accumulated in gully after "5.12" Earthquake,the occurrence probability of gully debris flow is enhanced greatly in rainfall.However,due to the special conditions of provenance and disaster environment,the traditional theory cannot be used to expound the mechanism of gully debris flow and prevent the disaster effectively as ever after the event.Here,based on hydrology,the hydrological model of ground water table in loose deposits is established first.Then by aid of hydraulic theory,the change of hydraulic characteristics and the variation of hydraulic power with the rising of groundwater level are analyzed.Furthermore,the calculation formulas of hydrodynamic and hydrostatic pressure are also proposed.Finally,by applying infinite slope theory in calculation of sliding force,anti-sliding force and residual sliding force acting on each segment,the failure mechanism of accumulation body is illustrated clearly with an example.The result indicates the failure of loose deposits in rainfall is the result of increase of the hydraulic power with the rising of groundwater level.Those deposits which have small coefficient,gentle slope,narrow-deep gully and large basin would be easy to fail because of its high hydraulic pressure generating in rainstorm,and the failure modes can be divided into two types according to residual sliding force as pushing failure and hauling failure.
引文
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[19]柴军瑞,仵彦卿.作用在裂隙中的渗透力分析[J].工程地质学报,2001,9(1):29-31.CHAI Jun-rui,WU Yan-qing.Analysis of seepage forcesacting on single fissure walls[J].Journal of EngineeringGeology,2001,9(1):29-31.
[2]唐川,陈永波.汶川震区北川县城魏家沟暴雨泥石流灾害调查分析[J].山地学报,2009,27(5):625-630.TANG Chuan,CHEN Yong-bo.Reconnaissance andanalysis on the rainstorm induced debris flow inWeijiagou valley of Beichuan city after the Wenchuanearthquake[J].Journal of Mountain Research,2009,27(5):625-630.
[3]IVERSON R M.The physics of debris-flows[J].Reviewsof Geophysics,1997,35(3):245-296.
[4]IVERSON R M.Dynamic pore-pressure fluctuations inrapidly shearing granular materials[J].Science,1989,246(4931):796-799.
[5]MAJOR J J,IVERSON R.M.Debris-flow deposition:Effects of pore-fluid pressure and friction concentrated atflow margins[J].Geological Society of America Bulletin,1999,11(10):1424-1434.
[6]崔鹏.泥石流启动条件及机理的实验研究[J].科学通报,1991,36(21):1650-1652.CUI Peng.Experiment study on the mechanism andcondition of starting up of debris flow[J].ChineseScience Bulletin,1991,36(21):1650-1652.
[7]欧国强.关于泥石流发生规模之研究[D].东京:京都大学,1992.
[8]胡明鉴.蒋家沟流域暴雨滑坡泥石流共生关系研究[D].武汉:中国科学院武汉岩土力学研究所,2001.
[9]陈晓清.滑坡转化泥石流启动机理试验研究[D].成都:西南交通大学,2006.
[10]张万顺,乔飞,崔鹏,等.坡面泥石流起动模型研究[J].水土保持研究,2006,13(4):146-149.ZHANG Wan-shun,QIAO Fei,CUI Peng,et al.Thestudy on the numerical model of debris flow on theslope[J].Research of Soil and Water Conservation,2006,13(4):146-149.
[11]HUTCHINSON J N,BHANDARI R K.Undrainedloading,a fundamental mechanism of mudslide and othermass movements[J].Geotechnique,1971,21(4):353-358.
[12]徐永年,匡尚富,黄永键,等.泥石流入汇的危险性判别指标[J].自然灾害学报,2002,11(3):33-38.XU Yong-nian,KUANG Shang-fu,HUANG Yong-jian,et al.Hazard-deciding indices for convergence of debrisflow[J].Journal of Natural Disaster,2002,11(3):33-38.
[13]胡明鉴.泥石流崩滑堆积体自组织临界性及灾变机理[D].武汉:中国科学院武汉岩土力学研究所,2008.
[14]徐友宁,曹淡波,张江华,等.基于人工模拟试验的小秦岭金矿区矿渣型泥石流启动研究[J].岩石力学与工程学报,2009,28(7):1388-1395.XU You-ning,CAO Dan-bo,ZHANG Jiang-hua,et al.Research on starting of mine debris flow based onartificial simulation experiment in Xiaoqinling gold orearea[J].Chinese Journal of Rock Mechanics andEngineering,2009,28(7):1388-1395.
[15]MONTGOMERY D R,DIETRICH W E.A physicallybased model for the topographic control on shallowlandsliding[J].Water Resources Research,1994,30(4),1153-1171.
[16]WILKINSON P L,ANDERSON M G,LLOYD D M,et al.Landslide hazard and bioengineering:Towardsproviding improved decision support through integratednumerical model development[J].EnvironmentalModeling and Software,2002,17(4):333-344.
[17]张电吉,白世伟.渗透水压力对节理裂隙岩质边坡的影响[J].西部探矿工程,2003,2:4-6.ZHANG Dian-ji,BAI Shi-wei.Influence of seepageforces on fractured rock slope[J].West ChinaExploration Engineering,2003,2:4-6.
[18]李峰,郭院成.降雨入渗对边坡稳定性作用机理分析[J].人民黄河,2007,29(06):44-48.LI Feng,GUO Yuan-cheng.Analysis of mechanism ofrainfall infiltration to slope stability[J].Yellow River,2007,29(06):44-48.
[19]柴军瑞,仵彦卿.作用在裂隙中的渗透力分析[J].工程地质学报,2001,9(1):29-31.CHAI Jun-rui,WU Yan-qing.Analysis of seepage forcesacting on single fissure walls[J].Journal of EngineeringGeology,2001,9(1):29-31.
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