【作者】 李宁；

【导师】 唐川；

【作者基本信息】 成都理工大学 ， 地质工程， 2020， 博士

【摘要】 2008年汶川“5.12”大地震对地质环境的强烈扰动,使得震区地形发生了剧烈变化,导致震后泥石流异常活跃。时至今日,震区每年雨季仍在爆发规模不等的泥石流灾害,给当地生产生活造成了极大的损失,而急陡沟道泥石流便是当前强震区泥石流灾害研究中的薄弱环节,也是该地区地质灾害预警及防治的难点之一。然而当前由于资料有限,重视程度不够,研究程度不足等问题,导致对该类泥石流的致灾机制与过程的认识和研究工作还存在很大的不足。为此,本文重点研究了急陡沟道泥石流的发育与活动特征、起动模式与判别式的建立、侵蚀机理与侵蚀模型的研究、冲出特征的研究和冲出量的计算模型。基于国内外大量泥石流研究成果,本文针对急陡沟道泥石流大纵比降、物源低黏粒含量等特征,选取震区急陡沟道泥石流沟为研究对象,通过大量现场调查、资料收集、文献调研、模型实验、数值模拟等途径,探讨了急陡沟道条件下的泥石流起动-侵蚀-冲出的动力过程及机理。本文的研究内容和主要研究成果包括以下几个方面:(1)归纳总结汶川强震区急陡沟道泥石流总体特征:(1)沟床平均纵比降大于等于400‰,流域面积大于1km~2小于3.5km~2,相对高差在767～2238m之间,沟道呈深“V”型;(2)主沟两侧斜坡为泥石流物源的主要补给区,且单位物源量大;(3)急陡沟道泥石流的沟谷目前正处于强烈侵蚀的初期,地貌阶段处于幼年期,切割较轻,易发生泥石流,但规模小;(4)形成区不明显,流通区较长且支沟发育较少,主沟纵坡降随流域面积的增加呈现减小的趋势;(5)单位物源密度大,且多发育有大-巨型崩滑体;(6)急陡沟道泥石流活动性高,以暴雨型—黏性—中频泥石流为主。(2)通过室内物理模拟实验,揭示了在急陡沟道条件下泥石流起动模式为消防管效应起动型;在急陡坡度条件下,径流形成时间过快,导致径流对泥石流起动的作用较渗透作用更大。而在坡度相同时,清水流量越大,预饱水时间越短。急陡沟道条件下的泥石流爆发时间远小于一般情况,而此时径流量越大,其泥石流持续时间也越长;得出在30°坡度条件下,起动流速V_q(m/s)与冲水流量V_c(ml/s)的关系式为:V_s=0.0036V_c-0.1152,R~2=0.98。文中还通过对泥石流形成临界状态的力学分析,建立了急陡沟泥石流单颗粒及沟床堆积物起动判别式。(3)基于野外调查和实验现象,发现急陡沟道泥石流的侵蚀特征介于切沟和冲沟之间,主要以下蚀作用为主,并出现于径流的峰值阶段,与此同时常伴有侧蚀与铲蚀。基于对侵蚀特征的分析,通过对急陡沟道泥石流沟床侵蚀过程进行受力分析,构建了在泥石流自重静压、流动剪切以及孔压共同作用下,泥石流沟床侵蚀深度的计算模型。通过野外实验分析急陡沟道泥石流侵蚀特征的同时,利用三维激光扫描仪获取泥石流过程中的地形侵蚀变化特征,进而验证了侵蚀模型的可靠性。(4)基于野外调查和数值模拟,发现急陡沟道泥石流冲出运动过程表现出以下特点:(1)急陡沟道泥石流冲出沟口的流速快、堆积过程快速,运动时间较常规泥石流更短;(2)泥石流过程表现出大冲大淤的过程,沟口堆积扇表现出范围小、厚度大的特点;(3)由于沟道窄、纵坡降陡,泥石流体运动势能高,滞留在沟道内的堆积物较少,大部分泥石流体都被冲出沟口,物源转化率更高。为实现急陡沟道泥石流威胁范围定量评价,本文通过对流域特征、沟道特征、物源特征、地形特征等因素与该类泥石流冲出量单因子相关性评价及回归分析,建立了急陡沟道泥石流冲出量模型。此外,使用Flow-3d模拟了典型急陡沟道泥石流的运动堆积过程,增加了对该类泥石流冲出过程一定的认识。受研究资料的地域性限制,本文所得结论与研究成果可应用于汶川强震区急陡沟道型泥石流,对在此范围外的泥石流是否适用还需要论证。由于调查数据难免的不全面性和研究能力的有限,本文所得急陡沟道型泥石流起动-侵蚀-冲出特征及模型成果,在实际工程应用和科研研究中可能会因各种基本条件的差异性而存在不可避免的误差。但仍期望本文可以进一步揭示了该类泥石流的起动-侵蚀-冲出特征与机制,以提高对其致灾机制的认识,以期为该类泥石流的预警防治提供理论支撑,为该类泥石流进一步的研究提供一定的参考和研究基础。更多还原

【Abstract】 The 2008 Wenchuan "5.12" earthquake severely disturbed the geological environment,causing drastic changes in the topography of the earthquake area,resulting in unusually active debris flows after the earthquake.Today,debris flow disasters of varying scales are still erupting in the earthquake area during the rainy season each year,causing great losses to local production and life.The rapid and steep channel debris flow is the weak link in the current research on debris flow disasters in strong earthquake areas.One of the difficulties in the early warning and prevention of geological disasters in this area.However,due to the limited data,insufficient attention and insufficient research level,the understanding and research work on the disaster mechanism and process of this type of debris flow are still very insufficient.To this end,this paper focuses on the development and activity characteristics of the steep channel debris flow,the establishment of starting modes and discriminants,the study of erosion mechanisms and erosion models,the study of outburst characteristics,and the calculation model of outburst.Based on the research of debris flow at home and abroad,this paper selects the debris flow gully of the steep gully in the earthquake area as the research object in view of the characteristics of large longitudinal drop and low clay content of the debris flow in the steep gully.Through a large number of field investigations and data collection,Literature investigation,model experiment,numerical simulation,etc.,to explore the dynamic process and mechanism of debris flow initiation-erosion-out under steep channel conditions.The research content and main research results of this article include the following aspects.(1)Summarize the general characteristics of the rapid and steep channel debris flow in the Wenchuan meizoseismal area as follows:(1)The average longitudinal gradient of the gully bed is greater than or equal to 400‰,the drainage area is greater than 1km2 and less than 3.5km~2,and the relative elevation difference is between767-2238 m.Deep "V" shape;(2)The slopes on both sides of the main ditch are the main replenishment areas for debris flow sources,and the unit source volume is large;(3)The gully of the steep channel debris flow is currently in the early stage of strong erosion,and the landform stage is in its infancy.The cutting is lighter,and debris flow is prone to occur,but the scale is small;(4)The formation area is not obvious,the circulation area is longer and the branch ditch is less developed.The longitudinal slope of the main ditch decreases with the increase of the watershed area;(5)The unit source density Large,and mostly large-giant avalanche landslides are developed;(6)The rapid and steep channel debris flow is highly active,mainly rainstorm-viscous-medium-frequency debris flow.(2)Through indoor physical simulation tests,it is revealed that the start-up mode of debris flow under steep trench conditions is the fire pipe effect start-up type;under steep slope conditions,runoff formation time is too fast,resulting in a more permeable effect of runoff on debris flow initiation.The effect is greater.When the slope is the same,the greater the clear water flow,the shorter the pre-saturation time.The eruption time of debris flow under steep channel conditions is much shorter than the general situation.At this time,the larger the runoff,the longer the debris flow duration.It is concluded that under the condition of 30° slope,the initial velocity Vq(m/s)and the impact The relational formula of water flow Vc(ml/s)is: Vs=0.0036Vc-0.1152,R2=0.98.In this paper,through the mechanical analysis of the critical state of the debris flow,a discriminant formula for the initiation of the single particle of the debris flow and the accumulation of the ditch bed is established.(3)In view of field investigations and experimental phenomena,it is found that the erosion characteristics of the steep channel debris flow are between the trench and the gully,and the main erosion is the main effect,which occurs in the peak stage of runoff,and is often accompanied by Side erosion and erosion.Based on the analysis of the erosion characteristics,through the force analysis of the erosion process of the debris flow gully bed in the steep gully,a calculation model of the erosion depth of the debris flow gully bed under the combined action of the debris flow’s dead weight static pressure,flow shear and pore pressure is constructed.While analyzing the erosion characteristics of the steep channel debris flow through field experiments,the three-dimensional laser scanner was used to obtain the terrain erosion characteristics during the debris flow process,which verified the reliability of the erosion model.(4)Based on field investigations and numerical simulations,it is found that the rushing process of the debris flow in the steep channel shows the following characteristics:(1)The debris flow in the steep channel rushes out of the ditch with a fast flow rate,a rapid accumulation process,and the movement time is shorter than that of the conventional debris flow.(2)The debris flow process shows the process of large erosion and large siltation,and the ditch accumulation fan shows the characteristics of small range and large thickness;(3)Because the channel is narrow,the vertical slope is steep,the potential energy of debris fluid movement is high,and the accumulation stays in the channel The material is less,most of the mud and rock fluid is washed out of the ditch,and the material source conversion rate is higher.In order to realize the quantitative evaluation of the threat range of the debris flow in the steep channel,this paper establishes the steep and steep channel by evaluating the single-factor correlation and regression analysis of watershed characteristics,channel characteristics,provenance characteristics,topographic characteristics and other factors of the debris flow.Model of the amount of debris flow out of the channel.In addition,Flow-3d is used to simulate the movement and accumulation process of a typical steep channel debris flow,which increases the understanding of the process of this type of debris flow.Due to the regional limitations of the research data,the conclusions and research results obtained in this paper can be applied to the steep channel debris flow in the Wenchuan strong earthquake area.Whether it is applicable to debris flow outside this range needs to be demonstrated.Due to the inevitable incompleteness of the survey data and the limited research capabilities,the initiation-erosion-outlet characteristics and model results of the steep trench-type debris flow obtained in this article may differ due to various basic conditions in actual engineering applications and scientific research.There are unavoidable errors.However,it is still hoped that this article can further reveal the characteristics and mechanism of the initiation-erosion-out of this type of debris flow,in order to improve the understanding of its disaster mechanism,in order to provide theoretical support for the early warning and prevention of this type of debris flow,and to further improve this type of debris flow.Research provides a certain reference and research basis.更多还原