【作者】 黄涛；

【导师】 丁明涛；

【作者基本信息】 西南交通大学 ， 地质资源与地质工程， 2023， 博士

【摘要】 在全球气候变暖加速演进的环境下,位于青藏高原东南缘的岷江上游地区同样面临着极端暖湿化的挑战与问题,该地区的极端降水事件也显著增多。相应地,这种极端暖湿天气变化也造就了岷江上游地区泥石流灾害广发、频发和重发的格局。本文将相对高差大（>1000m）沟道纵比降大（≥150‰）,山坡坡度大（25°以上面积>50%）的泥石流定义为高势能泥石流。高势能泥石流因其成灾规模大、致灾范围广以及易形成灾害链等特征,已成为重大危害类泥石流研究的热点和难点。目前,针对广义的暴雨型泥石流早期判识及形成-运动-致灾机理等方面的研究较多,但对于其中危害较大的高势能泥石流识别、沟床启动以及岸坡侵蚀等研究相对匮乏。另外,高势能泥石流防治工程缺乏准确的参数确定方法。因此,本文选取岷江上游流域作为研究区,以岷江上游锄头沟泥石流作为高势能泥石流典型研究案例,综合应用现场调查、室内模型实验、PFC^3D-CFD流固耦合模拟、有限元模拟、GIS分析、无人机测绘和理论分析等方法或手段,对高势能泥石流的判识、沟道侵蚀启动、岸坡侵蚀与防治工程设计关键参数进行系统研究,重点分析了高势能泥石流在不同坡度大径流条件下的启动过程,揭示了岸坡侵蚀启动、滑动、堆积和汇流机制以及高势能泥石流沿程放大效应,提出了两项防治工程设计关键参数的确定方法。本文的研究成果对于深入揭示高势能泥石流形成-演进机理具有重要指导意义,为高势能泥石流防治工程设计关键参数的确定提供了新的思路。本文获得的主要研究成果如下:（1）基于岷江上游地区泥石流灾害调查,共筛选出212处高势能泥石流,分析了212处泥石流的空间分布特征和物源特征。本文对锄头沟泥石流物源变化的研究表明,锄头沟形成区主要以崩滑侵蚀和沟道侵蚀为主;形成流通区表现出以侵蚀冲刷为主的特点,主沟下段冲淤特征表现为以淤积为主的特点,而各支沟普遍表现为以侵蚀冲刷为主的特点;流通堆积区在2013年防治工程修建之前以淤积为主,修建防治工程后细分为沟道堆积区、沟道侵蚀区和堆积扇。通过机器学习混合模型对岷江上游潜在高势能泥石流进行识别,识别结果表明有635处,主要分布在岷江上游地区中部及西北部。随后,对635处潜在高势能泥石流的指标进行统计与分析,从相对高差、纵坡坡降、Melton指数、流域坡度和流域面积等五个指标进一步定义了高势能泥石流。（2）以锄头沟作为典型研究案例,基于室内模型实验揭示高势能泥石流的沟道侵蚀启动过程。实验结果表明,高势能泥石流启动过程主要分为超渗产流、坍塌溜滑和冲刷启动三个阶段。大径流条件下沟道物源以径流侵蚀为主,因此沟道松散堆积体主要受径流剪切力,据此构建了高势能泥石流沟道堆积体稳定性系数计算方法,发现坡度和流量越大,其稳定系系数越低。（3）以锄头沟中下游岸坡发育的H1滑坡体为例,采用PFC^3D-CFD流固耦合分析了锄头沟岸坡H1滑坡体在泥石流侵蚀启动、滑动、堆积和汇流等各阶段的变化特征。根据滑坡启动汇流过程中的位移、速度变化特征,可将其分为6个阶段:（1）启动阶段:滑坡失稳启动阶段;（2）滑动阶段:滑坡颗粒加速运动阶段;（3）入流堆积阶段:滑坡颗粒进入沟道泥石流中暂时堆积阶段;（4）汇流启动阶段:颗粒堆积后重新启动跟随泥石流向下游流动;（5）快速汇流阶段:滑坡颗粒启动后加速跟随泥石流向下游流动;（6）汇流放大阶段:全部或大部分滑坡颗粒跟随泥石流向下游流动,放大了泥石流流量和规模。同时,还讨论了不同流深流速对岸坡侵蚀启动汇流过程的影响,以及高势能泥石流沿程侵蚀放大效应。（4）以锄头沟防治工程为研究对象,基于野外调查和无人机航拍,根据拦沙坝的坝后回淤特征,建立了拦沙坝库容确定方法。将实测库容与计算库容进行比较,计算结果的误差较小,本文建立的库容确定方法具有操作简便、计算结果可视化、效率高和精度高等特点。另外,还提出了防治工程高度参数优化设计方法,先构建不同高度防治工程模型,然后采用RAMMS方法分别模拟分析不同高度防治工程下“8.20”泥石流的冲出特征。模拟结果表明,GD2工况下的防治工程组合可有效防治锄头沟泥石流。更多还原

【Abstract】 Under the environment of accelerated global warming,the extreme warming and humidification are also faced by the upper reaches of Min River located on the southeastern edge of the Qinghai–Tibet Plateau,in which the extreme temperature and precipitation events in the region significantly grow.Correspondingly,a pattern of widespread,frequent,and recurrent debris flow disasters in the upper reaches of Min River is caused by this extreme warm and humid weather change.In this thesis,the debris flow with a large relative height difference（>1000m）,a large longitudinal slope of the ditch（≥150‰）,and a large slope of the mountain slope（>50%of the area above 25°）is defined as the debris flow of high potential energy.Due to the large scale,wide range of disasters,and easy formation of disaster chains,the debris flow of high potential energy have become a hot and difficult topic in the study of major hazardous debris flow.At present,many studies have been conducted on the early identification and formation-movement-disaster causing mechanism of generalized rainstorm-type debris flow,while the relatively few researches have been conducted on the identification,ditch bed startup and bank slope erosion of the debris flow of high potential energy being more harmful.What’s more,the accurate parameter determination methods for the prevention and control projects of the debris flow of high potential energy are absent.Therefore,the upper reaches of Min River are selected as the research area for the debris flow of high potential energy,and the Chutou Gully debris flow in the upper reaches of Min River is taken as a typical case study for the debris flow of high potential energy.The methods or means such as on-site investigation,indoor model experiments,PFC^3D-CFD fluid solid coupling simulation,finite element simulation,GIS analysis,drone mapping,and theoretical analysis are comprehensively applied to carry out a systematic research on the key parameters of ditch erosion initiation,bank slope erosion,and prevention and control engineering design for the debris flow of high potential energy.The initiation process of the debris flow of high potential energy under different slope and large runoff conditions is mainly analyzed,the mechanisms of bank slope erosion initiation,sliding,accumulation,and convergence,as well as the amplification effect of the debris flow of high potential energy along the route are revealed.The proposal of two key parameter determination methods for prevention and control engineering design is conducted.Based on the research results,the important guiding significance for deeply revealing the formation and evolution mechanism of the debris flow of high potential energy is embodied,and the new technical route is provided for determining the key parameters of the prevention and control engineering design for the debris flow of high potential energy.The following is the main research results obtained in this thesis:（1）In accordance with the investigation of debris flow disasters in the upper reaches of Min River,it selects 212 debris flows of high potential energy in total,in which 81 are distributed on both sides of the main stream of the Min River.Under the impact of the spatiotemporal distribution of rainfall,it is found that the debris flows of high potential energy are concentrated and developed in the southwest of the region.The debris flows of high potential energy in this region generally spans three vertical zones of mountain climate,with a maximum of seven climate vertical zones being spanned.From the analysis on the material source of 212 debris flows of high potential energy,the debris flow sources in the watershed are found to be extremely abundant,in which the landslide source mainly constitutes it,and it is mainly distributed in the upstream of the ditch.In particular,in line with the study and analysis of the source changes of debris flow in the Chutou Gully,the formation area of the Chutou Gully is indicated to be mainly characterized by landslide erosion and ditch erosion.The formed circulation area shows the main feature of erosion scouring,while the erosion and sedimentation features in the lower section of the main ditch are mainly characterized by sedimentation,while the erosion scouring features are generally present in each branch ditch.The circulation accumulation area was mainly characterized by sedimentation before the construction of the prevention and control project in 2013.Besides,different sections showed different erosion and sedimentation features after the construction of the prevention and control project,in which the ditch accumulation area,ditch erosion area,and accumulation fan can be subdivided.Finally,in terms of the identification of the debris flow of high potential energy,it firstly adopts Arc GIS to divide small watersheds in the upper reaches of Min River,and obtains 1647 small watersheds after manual correction.Then,the hybrid model of machine learning is used to make the identification,and the results show that there are 635 potential debris flows of potential high energy in the upper reaches of Min River,which are mainly distributed in the central and northwest regions of Min River.After that,the statistics and analysis on the indicators of 635 debris flows of high potential energy are carried out,in which the five indicators of relative height difference,longitudinal slope gradient,Melton index,watershed slope,and watershed area are taken as the starting points to select the final debris flows of high potential energy.（2）The Chutou Gully is taken as a typical research case,and the initiation process of ditch erosion in debris flow of high potential energy is revealed based on indoor model experiments.According to the experimental results,three stages of runoff yield in excess of infiltration,collapse and sliding,and scouring initiation are mainly divided for the initiation process of the debris flow of high potential energy.Under the condition of large runoff,the runoff yield in excess of infiltration quickly occurs in the ditch,and surface flow scours the soil,causing the erosion and downward movement of fine particles of the soil.With surface coarsening and its acceleration into saturation state,the strength of the accumulated soil decreases significantly after saturation,which gradually loses stability under the interference and action of external forces,and then enters the second stage of collapse and sliding.Under the erosion effect of continuous runoff,it causes the gradual loss of the soil particles at the bottom of the slope,the shear strength of soil decreases accordingly,the soil accelerates creep,the local soil gradually loses stability,and the phenomena of cracks,creep and collapse appear.Finally,areas with weak erosion resistance will firstly form multiple rills in the third stage of erosion initiation,and the gradual enhancement of the erosion ability of rill water flow is also shown,With the expansion of the downward erosion and lateral erosion,the size and scale gradually extend to form gullies,which are further expanded to the entire ditch.Due to the instability of most soil at the top and foot of the slope downstream of the accumulation,the phenomenon of collapse occurs,and the debris flow starts,in which the headward erosion and undercutting erosion mainly occur in this stage.In addition,runoff erosion mainly happens under the condition of large runoff,so loose accumulation is mainly affected by runoff shear force.Meanwhile,the frictional force generated on the slope and the cohesive force between soil particles constitute the anti-sliding force of the accumulated soil,while the shear force of runoff,the component force of gravity along the slope direction,and the frictional resistance of movement constitute the sliding force.On this basis,a calculation method for the stability coefficient of ditch deposits for the debris flow of high potential energy is derived and constructed,in which it is found that the larger the slope and flow rate,the lower the stability coefficient.（3）The H1 landslide developed on the middle and lower reaches of the Chutou Gully bank slope is taken as an example.In line with PFC^3D-CFD fluid solid coupling analysis,it carries out the analysis on the entire process change features of the H1 landslide on the Chutou Gully bank slope during the initiation,sliding,accumulation,and convergence of debris flow erosion.Considering the features of displacement and velocity changes during the initiation and convergence process of landslides,six stages are divided as follows:（1）Initiation stage:The initiation stage of landslide instability;（2）The stage of sliding:The accelerated movement stage of landslide particles;（3）The stage of inflow accumulation:The temporary accumulation stage of landslide particles entering the debris flow of ditch;（4）The initiation stage of confluence:After the accumulation of particles,the restarting is triggered to follow the debris flow to move downstream;（5）The stage of rapid confluence:After the starting of the landslide particles,the acceleration is realized to follow the debris flow to move downstream;（6）The stage of concentration amplification:Since all or most of the landslide particles follow the debris flow to move downstream,the flow and scale of the debris flow are amplified.Meanwhile,it conducts the discussion on the impact of different flow depths and velocities on the initiation and convergence process of bank slope erosion,as well as the erosion amplification effect of debris flow of high potential energy along the way.（4）The prevention and control engineering of Chutou Gully is taken as the research object.Based on field investigation and drone aerial photography,the characteristics of sediments of check dam are considered to establish a more accurate method for determining the storage capacity of sand barriers.Through the contrast of the measured data with the analysis results,the error between the design of the sedimentation surface of the check dam and the measured elevation is found to be-1.16-2.96m,with an RMSE of 0.93m.The designed storage capacity of the check dam is 33.6×10⁴m³,in which the measured storage capacity is 36.7×10⁴m³,so the relative error of the designed storage capacity is 8.44%,and the calculation result has a small error.In contrast with traditional methods for the calculation of the storage capacity of check dam,the features of the new method such as simple operation,visualization of calculation results,high efficiency,and high accuracy are embodied.What’s more,a new optimization design method for height parameters of prevention and control engineering is put forward Firstly,it draws the contour lines of prevention and control engineering in CAD in the proposed engineering area.Then,the assignment of contour values in Arc GIS is conducted.Finally,prevention and control engineering models of different height are obtained through the terrain transformation function of Arc GIS together with contour elevation points in non-engineering areas.The RAMMS method is adopted to simulate and analyze the erosion features of the“8.20”debris flow under prevention and control engineering of different heights respectively.In accordance with the simulation results,the combination of prevention and control engineering under GD2 working conditions is indicated to be able to effectively prevent and control the debris flow in Chutou Gully.更多还原