IMHE OpenIR  > 山地灾害与地表过程重点实验室
汶川震区泥石流坝形成机理
Alternative TitleThe mechanism of debris-flow dam formation in Wenchuan-earthquake zone
Language中文
刘晶晶
Thesis Advisor程尊兰
2013
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Name博士
Degree Discipline岩土工程
Keyword泥石流坝 形成机理 汶川震区 影响因素 形态参数
Abstract

泥石流堵塞河流形成泥石流坝,是泥石流造成的常规危害外最严重的次生灾害。泥石流坝体的形成,导致其上游淹没农田、铁路、公路等沿江建筑物,而当坝体溃决时,又会产生大规模的溃决洪水,造成下游长距离超常冲刷,冲毁下游农田和沿江建筑物,形成二次灾害。而5.12 震后山体稳定性降低且松散物质增加,为泥石流的形成提供了大量的物质来源,导致震后的汛期,震区内频繁发生泥石流坝堵河事件,严重阻碍了震区的重建和经济的发展,所以对汶川震区泥石流坝形成机理开展研究与山区人民生产生活、经济建设和生命财产安全息息相关,具有重要的应用价值。
同时,泥石流与主河交汇属于复杂的非牛顿体与牛顿体相互作用的问题。大容重、高流速、大流量和强摧毁力为特征的泥石流骤然间将大量包含各种粒径(尤其是大尺寸颗粒)的泥沙输入主河,堵断主河形成泥石流坝体,在短时间内改变主河水沙组成及局部边界条件,对主河水沙运动特性及演变规律等都带来重要的影响。所以对于泥石流入汇主河形成坝体开展研究,对于认知在交汇区复杂水沙及边界条件下主河水流和泥石流之间相互作用机制以及交汇区的水沙运动特性等又具有重要的理论意义。
本文首先考察和分析了5.12 震区内近年发生的典型泥石流坝堵河事件,研究泥石流堵塞主河的原因和整个过程,讨论并统计了导致泥石流堵河成坝的主要影响参数。其次,选择支沟泥石流入汇平均速度(vd)和平均流量(QB)、泥石流密度( d  )和屈服应力( d  )、主河来流平均流速(vw)和平均流量(QM)、以及泥石流总量(Vd)作为主要变化参数,设计42 组次主河无来流和主要有来流的入汇对比室内实验和6 组屈服应力测定实验。通过野外考察、室内实验和理论分析相结合的方法,探讨各单因素对于泥石流坝体形成的影响,分析泥石流入汇主河的系列典型现象,并且最终建立泥石流坝体主河无水堆积和主河有水堆积的形态参数计算公式,提出泥石流堵河坝体形成的判定条件。目前,初步得到如下结论:
1. 通过对泥石流入汇主河试验现象的描述和分析,探讨各参数对于泥石流坝的单一影响,归纳为:
Ⅰ)入汇速度和平均流量对于泥石流坝体的形成有着积极影响,其中入汇速度越大,则坝体形成长度和最终堆积的体积调整比例越大,而入汇流量越大则最终坝体堆积量越大。同时入汇速度还影响着坝体形成角度,其随着入汇速度的增加而减小。
Ⅱ)不同改变方法的屈服应力(τd)对坝体形成的影响并不一致,不能以屈服应力(τd),作为衡量泥石流坝体形成参数的唯一因素,必须全面的考虑泥石流本身的物性,尤其大粒径颗粒对于坝体形成参数的影响作用不可忽视。
Ⅲ)一定泥石流总量对于泥石流坝体的形成长度和形成高度有着积极影响。但是泥石流参与体积到达一定程度后,由于后续来流在前期堆积上的叠加,使得其对泥石流坝体形成长度和高度的影响就并不显著了。参与试验的泥石流样品总量越少,其后的体积调整比例越大,而泥石流总量越多,体积调整比例越小。
Ⅳ)支主沟的流量比表征了支沟泥石流与主河水流相互作用的强度,流量比越大,无论坝体的形成长度参数和高度参数都是增大的,即流量比越大,越容易堵塞主河,形成泥石流坝。
2. 泥石流入汇后,尤其是在相对于支沟泥石流流量较大而主河流量较小的情况下,主河水流提供的润滑和扩散作用使得泥石流龙头进入主河后的加速现象十分明显。本文采用能量分析和量纲分析的方法,结合20 组主河来流试验的试验数据,建立主河水流对于入汇泥石流的加速作用公式F阻。
3. 采用能量分析的方法,我们通过19 组主河来流试验中测定的最大冲击高,计算其回弹掺混的速度的垂直分量。并且探讨了各因素,包括屈服应力d  、流量比Q R 、泥石流总量Vd、泥石流密度d  、主河来流水深HM 和和主支水深比RH 对最大冲击高和回弹速度可能的影响,依据各单一因素的影响分析和量纲分析,建立最大冲击高I h 和回弹速度垂直分量' I v 的公式。并且采用动量和冲量守恒的法则,最终建立了最大冲击力I max F( )的计算公式。
4. 建立主河来流影响下的泥石流掺混密度计算公式和屈服应力计算公式。
5. 基于连续体假设,汇流龙头部动量守恒和泥石流堆积形态静力学分析,建立了主河无来流时和主河有来流时的泥石流坝体堆积长度计算公式,并将40组试验数据进行验证,发现建立的公式准确性较高。
6. 提出泥石流堆积坝体高度计算应针对不同的堆积方法(一次性堆积和累次堆积)采用不同的计算方法。假定泥石流坝的纵断面形状为梯形断面,建立判断堆积方法种类的泥石流最小参与量计算公式。建立主河无来流与主河有来流时的一次性堆积泥石流坝体高度计算公式和累次堆积泥石流坝体高度计算公式,并将40 组试验数据进行验证。

Other Abstract

The debris-flow dam is caused by debris flow, which carries a great amount of
sediment into the main river. It is the most serious secondary disasters caused by
debris flow. After the Ms 8.0 Wenchuan Earthquake, many debris flows have occurred
in the quake-stricken area and more than 10 dams formed and blocked the mainstream
rivers, resulted in great disasters and greatly influenced the reconstruction and
economic development of the area.
Field surveys of three typical cases indicate that the velocity (vd), discharge (QB),
density ( d  ), yield stress ( d  ) and total volume (Vd) of debris flow, and flow velocity
(vw) and discharge (QM) of main river, are the major factors controlling the dam
formation. In the following, we conducted 42 groups of experiments simulating the
dam formation by debris flow and 6 groups of experiments measuring the yield stress.
The influence of each single factor on debris-flow dam formation and typical
phenomenon of deposit in confluence are explored. In the finally, the formulas of
morphological parameters of the debris-flow dam are established and determination
conditions are proposed. In this paper, it was found that:
1. We analyze the influence of each single factor on debris-flow dam formation
Ⅰ)the velocity and average discharge of debirs flow have a positive effect on
the debris-flow dam formation. But the angle of dam decreases with the increase in
debris-flow velocity.
Ⅱ)because the influence of yield stress, which changes in diffierent way , on the
debris-flow dam isn’t consistent, the yield stress dosen’t used to be only parameter for
the dam-formation measurement and the influence of maxium-size particles in
composition can not be ignored.
Ⅲ)the total volume of debris flow has a positive impact on morphological
parameters including length and height of dam. But when the total volume reaches a
certain level, this influence is not significant.
Ⅳ)the ratio of debris flow in tributary to water in main river characterize their
interactions. The more ratios lead to the more prone to block the main river.
2. The changes of surface resistance, are caused by water in the main river, are so
important. By the way of energy and dimensional analysis, combining with the data of
the 20 experiments, the formula of debris-flow acceleration force (F阻) by water is
established.
3. Using energy analysis, the law of conservation of momentum and the
information of indoor experiments, the formulas of maximum impact height ( I h ) and
maximum wallop( I max F( )) are established.
4. The formulas of the mixing density ( (d w)   ) of debris flow and yield stress
( c d  ) are established.

5. The formulas of length of debris-flow dam are established. And it is found that
the formula has a higher accuracy to verify data of 40 experiments.

6. Debris-flow dam height depends on the processes of deposition, i.e., the
deposition en masse, or deposition by multi-surge accumulation. The formulas of
debris-flow dam height are established and verified by information of 40 experiments.

7. It is proposed that three determination conditions whether the debris-flow dam
form.

Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/7072
Collection山地灾害与地表过程重点实验室
Recommended Citation
GB/T 7714
刘晶晶. 汶川震区泥石流坝形成机理[D]. 北京. 中国科学院研究生院,2013.
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