IMHE OpenIR  > 山地灾害与地表过程重点实验室
泥石流沟岸堆积体侧蚀破坏过程实验和模拟研究
Alternative TitleExperimental and simulation studies on the lateral bank accumulation under flow erosion on debris flow gully
Language中文
严华
Thesis Advisor葛永刚
2020
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Name硕士
Degree Discipline岩土工程
Keyword泥石流 土体失稳 侧蚀 随机性 离散元
Abstract泥石流是一种由松散土体和水体耦合形成的固液两相流体,是一种常见的山地灾害。汶川地震后,强震区大面积山体震裂,发生数万处崩塌、滑坡,山区沟岸两侧堆积着大量的松散坡积体,极易在径流冲刷作用下发生破坏,是震后灾区沟道泥石流形成的重要方式之一,也是泥石流发展过程中重要的补给源。随着震后时间的推移,山坡的逐渐稳定,沟道内物质的逐渐粗化,大型滑坡发生的概率越来越小,沟道内固体物质直接起动的难度也逐渐增大,这些堆积体对于泥石流物源的补给也越来越重要。本文以泥石流沟沟岸堆积体为研究对象,通过室内水槽实验,考察泥石流沟岸堆积体在径流作用下的土体活动过程,归纳破坏过程中各个阶段的特点,重点揭示沟岸堆积体侧蚀发展过程背后蕴含的随机性规律和侵蚀特性,最后参考物理模型实验,基于CFD-DEM数值模拟手段,实现了对堆积体侧蚀破坏过程的模拟。主要研究成果如下:(1) 根据已有的灾史数据和研究区域的野外调查结果,统计各个泥石流沟岸堆积体和所在沟道断面的几何参数,分析了沟岸堆积体的几何特征和沟道断面形态之间的关系。野外考察数据和灾史数据的分析表明,泥石流沟岸堆积体,多以三角椎体存在。研究提出三个无量纲参数来定义沟岸堆积体和沟道的几何形态,宽高比W/H,表征堆积体在沟道最大压缩断面呈现的坡角;外形系数V1/3/H,表征堆积体可以被径流运移的物质的量;沟道最大进占比W*=W/Wc,表征沟道的堵塞程度(W表示堆积体在沟道断面方向的最大宽度、H表示堆积体的高度、V表示堆积体的体积、Wc表示沟道宽度)。以舟曲三眼裕、罗家裕、汶川县洱沟、牛圈沟、桃关沟、七盘沟、都江堰龙池共计46个不同的泥石流沟岸堆积体为原型,并统计了它们的无量纲参数。结果表明,外形系数V1/3/H和宽高比W/H呈现显著的正相关关系;宽高比W/H主要位于数值1附近;并且数据点相对集中的分布在一个狭窄的带状区域;沟道最大进占比W*=W/Wc的分布则比较离散。(2) 基于室内物理模型实验考察泥石流沟岸堆积体在径流作用下的土体活动过程,归纳破坏过程中各个阶段的特点,通过概率函数描述了沟岸堆积体侧蚀发展过程的随机性规律。泥石流沟岸堆积体的侧蚀破坏过程可以分为坡脚侵蚀阶段和失稳崩滑破坏两个阶段。第一阶段稳定而连续,持续时间通常较短,水力侵蚀起主导作用;第二阶段持续时间比较长,重力侵蚀起主导作用。失稳崩滑破坏阶段的土体活动可看作是一组不连续的土体失稳序列,土体失稳活动是间歇性的,形式和规模都在不断发生着变化。具体来讲,土体失稳序列在间歇时间上服从参数为λ的Poisson分布,在规模上服从Pareto分布。底床坡度、流量和细颗粒含量对土体失稳间歇时间(即失稳频率)影响显著,土体失稳规模具有较强的随机性,受实验条件的影响变化不大。参数λ的变化可以反映出不同实验条件下土体失稳频率的差异性,参数λ越大,土体的失稳频率越高。参数λ随着底床坡度和流量的增大而增大;在底床坡度较小时(3o),参数λ随着细颗粒含量的增多而增大;随着底床坡度的增大(7o),参数λ随着细颗粒含量的增多先增大后减小;在底床坡度较大时(11o),参数λ随着细颗粒含量的增多而减小。(3) 通过实验数据分析了堆积体侧向侵蚀速率随影响因素的变化规律;并且考虑堆积体的三维特性,分析了侵蚀速率随时间和空间的变化规律。底床坡度为7o是堆积体侵蚀速率的临界坡度,底床坡度小于7o时,平均侵蚀速率随着细颗粒含量的增加而增大;底床坡度大于7o时,平均侵蚀速率随着细颗粒含量的增加而减小。平均侵蚀速率随着密实度的增加显著减小。平均侵蚀速率随着底床坡度的增加而增大。平均侵蚀速率随着上游来流流量的增加而增加。各个影响因素权重排序为:密实度大于流量大于坡度大于细颗粒含量。堆积体任意一点侧向侵蚀速率的大小与该点床面切应力的分布具有一致性。不同时间点上,侵蚀速率随着观测断面相对位置x/L数值的增大均存在先增大后减小的趋势,最大侵蚀速率点通常出现在堆积体的中轴线略偏左的位置,并且随着时间的变化逐渐向下游移动,同时,随着侧蚀展宽过程的发展,平均侵蚀速率整体呈现下降趋势。沟岸堆积体的侧向展宽过程可以概括为:沟岸堆积体初始状态→堆积体本体进入冲刷→崩体下落淤积→崩滑体进入冲刷状态→崩滑体冲刷结束→进入下一个冲刷循环过程。一次完整的侧向展宽过程所需要的总时间为: (4) 基于颗粒离散元方法,通过CFD-DEM流固耦合的方式实现径流条件下沟岸堆积体侧蚀破坏过程的模拟,对堆积体起动运移过程的关键参数进行了监测。通过程序内置的粗网格流固耦合方法进行径流条件的模拟,以获得堆积体的侧蚀破坏过程,并与真实物理模型实验进行对比。结果表明,模拟结果与实际模型实验中堆积体侧蚀破坏过程和现象基本相符,堆积体在侧蚀破坏过程中,物源冲出量随着时间的变化逐渐增长,但增量值逐渐减小;堆积体不同部位的孔隙率的变化在侧蚀过程中存在较大差异,堆积体上层土体的孔隙率的变化具有滞后性。
Other AbstractDebris flow is a solid-liquid two-phase fluid formed by the coupling of loose soil and water, and is a common mountain hazard. After the Wenchuan earthquake, a large area of the mountain in the strong earthquake area was cracked, tens of thousands of collapses and landslides occurred, and a large number of loose slope accumulations were accumulated on both sides of the mountain bank, which was easy to be damaged under the effect of runoff erosion. The important way of debris flow formation is also an important source of supply in the development of debris flow. And with the passage of time after the earthquake, the slope of the hill is gradually stable, the material in the channel is gradually thickened, the probability of large landslides is getting smaller and smaller, and the difficulty of directly starting the material in the channel is gradually increasing. These accumulations are The supply of sources is also increasingly important. This article takes debris flow gully bank deposits as the research object, through the indoor flume experiment, investigates the soil body movement process of debris flow gull bank deposits under the action of runoff, summarizes the characteristics of each stage in the destruction process, and focuses on revealing the side erosion of the trench bank deposits The random law and erosion characteristics behind the development process, finally referring to the physical model experiment, based on the CFD-DEM numerical simulation method, to achieve the simulation of the accumulation body side corrosion failure process. The main research results are as follows:(1) Based on the existing disaster history data and the field investigation results of the research area, the geometric parameters of each debris flow gully bank accumulation body and the channel cross section are counted, and the relationship between the geometric characteristics of the gully bank accumulation body and the channel cross section shape is analyzed.The analysis of field investigation data and disaster history data shows that the accumulation bodies of debris flow gully banks mostly exist as triangular vertebral bodies. The study proposes three dimensionless parameters to define the geometry of trench deposits and trenches. The aspect ratio W/H represents the slope angle of the deposits at the maximum compression section of the trench; the shape factor V1/3/H represents The amount of material that can be transported by the runoff; the maximum channel occupation ratioW*=W/Wc, which indicates the degree of blockage of the channel (W represents the maximum width of the deposit in the channel cross section, H represents the height of the deposit, and V represents the volume of the deposit , Wc represents the channel width). A total of 46 different debris flow gully bank accumulations in Zhouqu Sanyanyu, Luojiayu, Ergou, Niuquangou, Taoguangou, Qipangou and Dujiangyan Longchi were used as prototypes, and their dimensionless parameters were counted , The results show that the shape factor V1/3/H and the aspect ratio W/H have a significant positive correlation; the aspect ratio W/H is mainly located near the value 1; and the data points are relatively concentrated and distributed in a narrow band Area; the distribution of the maximum channel advancement ratioW*=W/Wc is more discrete.(2) Based on the indoor physical model experiment, the soil movement process of the debris flow gully bank deposits under the action of runoff was investigated. The characteristics of each stage in the destruction process were summarized. The randomness law of the development process of the side erosion of the gully bank deposits was described by the probability function.The process of lateral erosion and destruction of debris flow gully bank deposits can be divided into two stages: slope foot erosion stage and instability collapse failure. The first phase is stable and continuous, and the duration is usually short, and hydraulic erosion plays a leading role; the second phase has a relatively long duration, and gravity erosion plays a dominant role. The soil activity in the stage of instability, collapse and failure can be regarded as a set of discontinuous soil instability sequences. The soil instability activity is intermittent, and the form and scale are constantly changing. Specifically, the sequence of soil instability follows the Poisson distribution with parameter λ in the intermittent time, and the Pareto distribution in scale.The bed slope, flow rate and fine particle content have a significant effect on the instability interval time of the soil, that is, the frequency of instability. The scale of the soil instability has a strong randomness and is not affected by the experimental conditions. The change of parameter λ can reflect the difference of the frequency of soil instability under different experimental conditions. The larger the parameter λ, the higher the frequency of soil instability. The parameter λ increases with the increase of the bottom bed slope and flow; when the bottom bed slope is small (3o), the parameter λ increases with the increase of fine particle content; with the increase of the bottom bed slope (7o) The parameter λ increases first and then decreases as the fine particle content increases; when the bed slope is large (11o), the parameter λ decreases as the fine particle content increases.(3) Through the experimental data, the variation law of the lateral erosion rate of the accumulation body with the influencing factors was analyzed; and considering the three-dimensional characteristics of the accumulation body, the variation law of the erosion rate with time and space was analyzed.The bed slope of 7o is the critical slope of the accumulation body erosion rate. When the bed slope is less than 7o, the average erosion rate increases with the increase of fine particle content; when the bed slope is greater than 7o, the average erosion rate increases with the fine particle content Increase and decrease. The average erosion rate decreases significantly with increasing density. The average erosion rate increases with the slope of the bed. The average erosion rate increases with the increase of upstream flow. The order of weight of each influencing factor is as follows: density is greater than flow, slope is greater than fine particle content. The size of the lateral erosion rate at any point of the accumulation body is consistent with the distribution of the bed shear stress at that point. At different time points, the erosion rate tends to increase first and then decrease with the increase in the relative position x/L value of the observation section. The maximum erosion rate point usually appears at a position slightly to the left of the central axis of the accumulation body, and With the change of time, it gradually moved downstream. At the same time, with the development of the lateral erosion broadening process, the average erosion rate showed a downward trend overall.The lateral broadening process of trench bank deposits can be summarized as follows: initial state of trench bank deposits → deposit body enters scouring → collapsing body falling sedimentation → collapsing body enters scouring state → collapsing body erosion ends → enters the next scouring cycle process . The total time required for a complete lateral widening process is: (4) Based on the particle discrete element method, the CFD-DEM fluid-solid coupling method was used to simulate the process of lateral erosion of trench deposits under runoff conditions, and the key parameters of the deposit migration process were monitored.The runoff conditions were simulated by the coarse mesh fluid-structure coupling method built in the program to obtain the side erosion failure process of the accumulation body, and compared with the real physical model experiment. The simulation results are consistent with the actual side model erosion failure process and The phenomenon is basically consistent. During the process of lateral erosion and destruction of the accumulation body, the amount of source erosion gradually increases with time, but the incremental value gradually decreases. There is a big difference, the change of the porosity of the upper soil body of the accumulation body has hysteresi
Pages104
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/54987
Collection山地灾害与地表过程重点实验室
Affiliation中国科学院成都山地灾害与环境研究所
Recommended Citation
GB/T 7714
严华. 泥石流沟岸堆积体侧蚀破坏过程实验和模拟研究[D]. 北京. 中国科学院大学,2020.
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