Discharge evolution law of debris flow based on a sharp bend physical modeling test

For the basins with debris flow development,its channel terrain exhibits a tortuous shape,which significantly restricts the movement of debris flows and leads to severe erosion effects on the concave bank.Therefore,this study aims to analyze the shear force of debris flows within the bend channel.We established the relationship between the shear force and bend curvature through laboratory experiments.Under the long-term erosion by debris flows,the curvature radius of bends gradually increases,however,when this increasing trend reaches an equilibrium state with the intensity of debris flow discharge,there will be no significant change in curvature radius.In general,the activity pattern and discharges of debris flows would remain relatively stable.Hence,we can infer the magnitude of debris flow discharges from the terrain parameters of the bend channel.

Types and Causes of Debris Flow Damage to Drainage Channels in the Wenchuan Earthquake Area

Debris flows are among the most common geological disasters in China,and have been particularly frequent in Sichuan Province since the Wenchuan earthquake on 12 May 2008.The construction of debris flow drainage channels is a countermeasure used to distribute debris flow fans,and these channels play a critical role in the mitigation and prevention of damage resulting from debris flows.Under field conditions,the useful life of drainage channels can be greatly shortened as a result of strong abrasions to the drainage structure caused by the debris flow.Field investigations have shown that the types of damage to drainage channels include(a) erosion caused by hyper-concentrated silt flow,(b) impact fractures and foundation scour at the groundsills of the drainage channel,(c) destruction of the drainage channel outlet,and(d) destruction of the drainage channel caused by debris flow abrasion.In addition,based on the destruction of the drainage channel during the debris flow drainage process,a new type of drainage channel with energy dissipation components was proposed and applied in a steep,narrow gully for debris flow mitigation.Moreover,design and engineering repair recommendations for drainage channels are provided as a reference for repairing the damage to the channel.The results can provide an important reference for the effective repair and optimal design of drainage channels.

The properties of dilute debris flow and hyper-concentrated flow in different flow regimes in open channels

Particle Image Velocimetry(PIV) technique was used to test the analogues of hyperconcentrated flow and dilute debris flow in an open flume. Flow fields, velocity profiles and turbulent parameters were obtained under different conditions. Results show that the flow regime depends on coarse grain concentration. Slurry with high fine grain concentration but lacking of coarse grains behaves as a laminar flow. Dilute debris flows containing coarse grains are generally turbulent flows. Streamlines are parallel and velocity values are large in laminar flows. However, in turbulent flows the velocity diminishes in line with the intense mixing of liquid and eddies occurring. The velocity profiles of laminar flow accord with the parabolic distribution law. When the flow is in a transitional regime, velocity profiles deviate slightly from the parabolic law. Turbulent flow has an approximately uniform distribution of velocity and turbulent kinetic energy. The ratio of turbulent kinetic energy to the kinetic energy of time-averaged flow is the internal cause determining the flow regime: laminar flow(k/K<0.1); transitional flow(0.1< k/K<1); and turbulent flow(k/K>1). Turbulent kinetic energy firstly increases with increasing coarse grain concentration and then decreases owing to the suppression of turbulence by the high concentration of coarse grains. This variation is also influenced by coarse grain size and channel slope. The results contribute to the modeling of debris flow and hyperconcentrated flow.

Geomorphic Characteristics of Hillslope and Channelized Debris Flows: A Case Study in the Shitou Area of Central Taiwan

The data on the hillslope and channelized debris flows in the Shitou area of central Taiwan occurred during Typhoons Toraji and Nali in 2001 were applied in this paper. The geomorphic parameters, including the flow length, gully gradient, drainage area and form factor of the debris flows were determined by spatial analysis using a Geographic Information System (GIS) based on the data derived from field investigation, aerial photographs, and topographical maps. According to such determined geomorphic parameters, the threshold conditions and empirical equations, such as the relationship between the gully gradient and drainage area and that between gully length and drainage area and topographic parameter, are presented and used to distinguish the geomorphic characteristics between the channelized and hillslope debris flows.

Characteristics of a Drainage Channel with Staggered Indented Sills for Controlling Debris Flows

The characteristics of a new type of drainage channel with staggered indented sills for controlling debris flows were studied. The intermediate fluid in the non-viscous debris flow exhibited a helical movement, whereas the fluid near the sidewall had a stop-start movement pattern; the viscous debris flow exhibited a stable structure between the indented sills. The experimental results indicate that the mean velocity of the debris flow increased with increasing channel gradients, and the debris flow velocity was slightly affected by the angle of the sills. The average velocity of the non-viscous debris flow increased in the range of(0.5–1.5) interval between the indented sills, whereas the average velocity of the viscous debris flow increased initially and then decreased in the range of(0.75–1.25) interval between the indented sills. The depth of the non-viscous debris flow tended to gradually increase as the channel gradients increased, whereas the depth of the viscous debris flow gradually decreased as the channel gradients increased. When the discharge of the debris flow was constant, the angle and the interval between the indented sills had a slight effect on the depth of the viscous debris flow, whereas the depth of the non-viscous debris flow exhibited a different trend, as the sill angles and intervals were varied.

Characteristics of viscous debris flow in a drainage channel with an energy dissipation structure

A new type of drainage channel with an energy dissipation structure has been proposed based on previous engineering experiences and practical requirements for hazard mitigation in earthquakeaffected areas.Experimental studies were performed to determine the characteristics of viscous debris flow in a drainage channel of this type with a slope of 15%.The velocity and depth of the viscous debris flow were measured,processed,and subsequently used to characterize the viscous debris flow in the drainage channel.Observations of this experiment showed that the surface of the viscous debris flow in a smooth drainage channel was smoother than that of a similar debris flow passing through the energy dissipation section in a channel of the new type studied here.However,the flow patterns in the two types of channels were similar at other points.These experimental results show that the depth of the viscous debris flow downstream of the energy dissipation structure increased gradually with the length of the energy dissipation structure.In addition,in the smooth channel,the viscous debris-flow velocity downstream of the energy dissipation structure decreased gradually with the length of the energy dissipation structure.Furthermore,theviscous debris-flow depth and velocity were slightly affected by variations in the width of the energy dissipation structure when the channel slope was 15%.Finally,the energy dissipation ratio increased gradually as the length and width of the energy dissipation structure increased;the maximum energy dissipation ratio observed was 62.9%(where B = 0.6m and L/w = 6.0).

Experimental study on the energy dissipation characteristics of debris flow deceleration baffles

Debris flow can cause serious damages to roads, bridges, buildings and other infrastructures.Arranging several rows of deceleration baffles in the significant influence on the mobility and deposition characteristic of debris flow. The deposit amount first increased then decreased when the flow density rises,flow path can reduce the flow velocity and ensure better protection of life and property. In debris flow prevention projects, deceleration baffles can effectively reduce the erosion of the debris flow and prolong the running time of the drainage channel.This study investigated the degree to which a 6 m long flume and three rows of deceleration baffles reduce the debris flow velocity and affect the energy dissipation characteristics. The influential variables include channel slope, debris flow density, and spacing between baffle rows. The experimental results demonstrated that the typical flow pattern was a sudden increase in flow depth and vertical proliferation when debris flow flows through the baffles. Strong turbulence between debris flow and baffles can contribute to energy dissipation and decrease the kinematic velocity considerably. The results showed that the reduction ratio of velocity increased with the increase in debris flow density,channel slope and spacing between rows. Tests phenomena also indicated that debris flow density hasand the deposit amount of debris flow density of 1500kg/m^3 reached the maximum when the experimental flume slope is 12°.

Influence of Fine Sediment on the Fluidity of Debris Flows

Debris flows include a great diversity of grain sizes with inherent features such as inverse grading,particle size segregation,and liquefaction of fine sediment.The liquefaction of fine sediment affects the fluidity of debris flows,although the behavior and influence of fine sediment in debris flows have not been examined sufficiently.This study used flume tests to detect the effect of fine sediment on the fluidity of laboratory debris flows consisting of particles with various diameters.From the experiments,the greatest sediment concentration and flow depth were observed in the debris flows mixed with fine sediment indicating increased flow resistance.The experimental friction coefficient was then compared with the theoretical friction coefficient derived by substituting the experimental values into the constitutive equations for debris flow.The theoretical friction coefficient was obtained from two models with different fine-sediment treatments:assuming that all of the fine sediments were solid particles or that the particles consisted of a fluid phase involving pore water liquefaction.From the comparison of the friction coefficients,a fully liquefaction state was detected for the fine particle mixture.When the mixing ratio and particle size of the fine sediment were different,some other cases were considered to be in a partially liquefied transition state.These results imply that the liquefaction of fine sediment in debris flows was induced not only by the geometric conditions such as particle sizes,but also by the flow conditions.

基于多源遥感技术的泥石流小流域及沟道侵蚀特征分析

本文主要探究了多源遥感技术在泥石流小流域及沟道侵蚀特征分析中的应用。分别从卫星雷达影像、航空遥感影响、大比例数字地形图和野外调查数据获取研究区数据,使用二轨法和偏移量跟踪技术进行形变信息提取,并建立了“坡面-流域-沟道”数字系统。利用该系统提取研究区内的坡体侵蚀产沙特征,分别选取沟道高差、沟道长度、流域面积、植被覆盖率4项因素,探究各项因素对侵蚀速率的影响。结果表明,减小沟道高差,延长沟道长度,能降低沟道侵蚀速率;减小流域面积,提高植被覆盖率,能降低小流域侵蚀速率。

基于Flow-R模型的八一沟泥石流危险性评价

目前泥石流危险性评价方法通常是一条泥石流沟对应一个危险等级。Flow-R模型将泥石流源区识别与泥石流运动相结合计算泥石流的危险概率,能够评价一条泥石流沟内不同部位的危险性。为丰富泥石流评价方法的应用研究及探究单沟内泥石流危险分布特征,以八一沟为研究区,在确定八一沟泥石流源区识别阈值和运动参数的基础上,用Flow-R模型对泥石流可能的危害范围进行模拟计算,并用混淆矩阵对模拟结果进行评估,最后对八一沟流域不同部位进行了泥石流危险性评价。结果表明:(1)泥石流源区主要分布于沟道20°～50°坡度范围和1 400～1 600 m高程范围内,沟顶细小汇水沟道为泥石流提供了丰富的活动物质;(2)泥石流危险区域大致分布在沟道左右40 m范围,占整个研究区域的20.06%;极高危险区分布于沟道中心,危险性由沟道中心向两边逐渐降低;(3)Flow-R应用于研究区的正确率为84.18%,给出的泥石流危险区图合理,能够反映研究区泥石流的基本危险特征。

成昆铁路K295泥石流灾害特征分析及治理对策研究

为消除山区铁路泥石流灾害威胁,确保铁路长期运营安全,结合成昆铁路峨攀段K295泥石流灾害整治工程,分析泥石流灾害情况、规模、分区、成因、危害程度及发展趋势等。基于“以疏为主、兼顾防护”的整治思路,采用“基底注浆加固+导流式渡槽明洞+隧底泄水涵+导流槽+急流槽”的综合处治方案。为避免明洞现浇造成既有铁路运营中断,综合考虑现场地形、结构安全及施工工期,创新地在既有运营铁路上采用明洞拱圈预制拼装技术方案,减小了施工作业与铁路运输的相互干扰,大幅缩短了工期。

四川木里“7·5”黄泥巴沟泥石流灾害过程及防治措施建议

2021年7月5日项脚沟七条支沟在连日降雨的情况下相继暴发泥石流灾害,因群测群防体系的高效运转,避免了20户118人因灾伤亡和1421万元的经济损失,实现了成功避险。黄泥巴沟是暴发泥石流的支沟之一,流域面积14.47 km^(2),此次灾害中冲出物规模12×10^(4)m^(3),损毁房屋数间。黄泥巴沟在2020年“3·28”森林火灾中地表植被焚毁严重,导致其泥石流孕灾环境发生剧烈变化,在鲜有泥石流活动的背景下,于2020年和2021年数次暴发泥石流灾害。通过实地调查,得出发生剧烈变化的泥石流孕灾环境和沟口外村寨旧有布局格式之间的矛盾是导致下坪子村受灾严重的关键原因,然后推断整个灾害过程:先前暴发的泥石流冲出物堵塞村寨中部沟渠,随后流出的山洪因无法顺畅排泄而发生大面积漫流,导致村寨所受损失倍增。首要的治理措施是修建一条连接沟口与主河的排导槽并重新规划村寨布局,使泥石流可以顺畅的排泄到主河之中并且使村寨建筑远离泥石流的直进范围。最后分析了此次群防群测体系的成功实践,总结经验以供参考。

青海省化隆县德恒隆乡牙曲滩村山尕滩社泥石流形成条件及治理措施

为减少青海省化隆县德恒隆乡牙曲滩村山尕滩社泥石流频发造成的地质灾害,在研究区开展了一定工作量的地形测量、工程地质测绘、山地工程、钻探工程以及现场试验等工作的基础上,从地形地貌、气象、物源等方面分析了区内泥石流的形成条件、泥石流的基本特征及控制因素。综合区内地质环境背景、泥石流形成条件、运动堆积特点及其对区内居民、村道的危害特征,经详细勘查工作提出了“拦挡坝+排导渠”工程治理措施,改变了以往该区泥石流治理措施的盲目性和随意性,从而减少泥石流灾害的发生。对山尕滩社泥石流的形成条件及其治理进行分析研究具有重要意义。

沟道松散物质起动形成泥石流实验研究

为研究震后环境突变条件下的泥石流形成模式和机理,开展震后泥石流防治和预测,根据震后泥石流形成环境特点,设计泥石流起动装置,开展震后泥石流形成模式和机理试验。本研究共进行了25组试验,主要研究了泥石流在不同坡度情况下的泥石流形成模式和机理,结果表明:1)在坡度8°～12.5°情况下,泥石流的形成模式是冲蚀→冲沟→崩塌→堵塞→溃决→泥石流的模式;2)在坡度12.5°～17.5°情况下,泥石流的形成模式是逐渐侵蚀加剧(朔源侵蚀、下切侵蚀和侧蚀),容重逐渐增加形成泥石流的模式;3)在坡度17.5°～25°情况下,泥石流的形成模式是坡面流水→入渗→失稳→下滑→流态化的模式;4)根据孔隙水压力变化特征,不同的起动模式下的土体内部孔隙水压力变化特征不同,孔隙水压力的变化可以解释不同泥石流起动模式的机理特征。根据研究结果,可以对不同起动下的泥石流模式进行不同的防治规划,同时结合泥石流起动过程中孔隙水压力的变化,可以解释泥石流起动的模式,对开展震后泥石流预报提供了参考。

沟床起动型泥石流预报研究

贵州省望谟县2011年6月6日暴发了特大山洪泥石流,其中暴雨中心所在的打易镇多处暴发泥石流。短历时强降雨激发了沟床起动类型的泥石流。本文通过对贵州望谟河流域群发泥石流的调查,得出该流域的66条沟中,22条沟无沟床起动类型泥石流暴发,25条沟暴发沟床起动类型泥石流,还有19条沟无法确定是否有沟床起动类型泥石流暴发。在前期工作基础上,提出了地质条件和降水条件因子的改进方法;并在前期工作的3大条件(地形条件、地质条件和降水条件)之间的关系基础上,由贵州望谟群发泥石流数据得出改进沟床起动类型泥石流的临界值,提出了泥石流的预报模型。本文模型在我国西南地区的泥石流验证中非常成功,为泥石流的预报提供了一个新方法。预报模型中的地形因子和地质因子还可以判断泥石流流域的暴发频率,为正确地判断泥石流流域的特征打下了基础。预报模型也可以估算泥石流的暴发规模,为定量地预测泥石流危害范围提供了依据。

谷坊在泥石流防治中的作用——以云南蒋家沟2条支沟的对比为例

泥石流灾害严重威胁其影响区人民的生命和财产安全,但是泥石流灾害可以通过诸如控制侵蚀等工程措施来预防或者减轻。谷坊正是能够在泥石流形成区对泥石流灾害进行有效防治的工程措施之一。在野外实地调查的基础上,运用构造地质、工程地质、岩土力学等理论和方法,对比云南蒋家沟泥石流的2个主要支沟——门前沟(有谷坊布设)和多照沟(没有谷坊布设)在沟床纵坡降、沟谷两侧斜坡稳定性及泥石流侵蚀速率等3个方面的差异,来说明谷坊工程能够有效抬高泥石流侵蚀基准面,降低泥石流沟谷回淤段沟床纵坡及由此带来的泥石流流速的降低和能量的耗散,固定沟床、稳定岸坡、促进植被生长,最终达到防治泥石流的目的。此外,还讨论了谷坊设计时需要注意的几点问题。

珠江口盆地荔湾井区珠江组深水扇沉积特征

珠江口盆地白云凹陷荔湾深水区为油气勘探有利区域,通过岩石学和古生物组合特征研究,认为该区珠江组下部属于典型的深水扇沉积,可划分为早期盆地扇和晚期斜坡扇两种类型,两类深水扇都以发育颗粒流、砂质碎屑流及低密度浊流等顺坡重力流沉积为主,同时夹有少量内波和等深流等深水牵引流改造沉积。砂质碎屑流为两类深水扇水道砂体的主要沉积类型,发育有逆-正粒序层理、平行层理和水平层理,粒序层内可见各种丰富的液化变形和生物逃逸构造,而水平层内发育有更多的生物钻孔和扰动现象。两类深水扇的沉积构造和古生物特征有明显差异,其中盆地扇水道砂岩中普遍含硅质小砾石,水道间泥岩中含有较多保存完好的抱球虫化石,斜坡扇水道砂岩以富含炭泥屑为典型特征,水道间泥岩含有更丰富的颗石藻和抱球虫化石,其中部分抱球虫和颗石具有遭受海底溶蚀作用的现象,指示斜坡扇相对盆地扇有更大的水体深度。平面上两类深水扇具有相似的重力流沉积的分带性,都具有自陆架坡折向盆地方向由颗粒流沉积逐渐向砂质碎屑流和近源高密度浊流、远源低密度浊流等单向演化的特点。

四川德昌茨达“8·24”群发性滑坡型泥石流之地形条件

2004-08-24,四川省德昌县茨达乡暴发了群发性滑坡型泥石流,给当地居民生活和生产造成了严重的损失。此次群发性泥石流范围较小,地质和水文条件比较接近,由此认为地形条件是控制泥石流发育的关键因素。在分析地形条件对滑坡型泥石流形成的影响基础上,从其形成机理出发,选取研究区各沟谷流域面积A,沟床比降J,沟谷两侧斜坡25°~45°坡度所占百分比S等3个重要地形因子进行研究,对比相互关系,建立起此次泥石流暴发的临界曲线和综合地形因子G,G=S×（A/A0）0.15×J0.8,得出在地质和降雨条件都相近似的情况下,地形因子G越大,地形条件越好,越容易暴发泥石流。因此可用G因子划分区域内沟谷泥石流的易发等级,并为滑坡型泥石流的危险性评价和预警预报提供了新的研究思路。

四川西昌邛海的浊流沉积初探

鹅掌河位于邛海南岸,在近15年来泥石流和洪水不断地将泥沙从鹅掌河带入邛海,在邛海底部大量淤积泥沙,形成一由南到北(长2km),由低到高(平均高2m),由窄到宽(南岸宽200m,北岸宽600m)的水下堤,在邛海湖中连接鹅掌河河口堆积扇处还发现了的水下冲沟。湖底扇,水下堤和水下冲沟对于研究湖相和海相浊流沉积有一定的研究和应用价值。浊流特别是高浓度浊流在湖中的沉积模式研究对于湖底和海底地貌的变迁,湖盆和深海油气藏的发现都有一定的价值和意义。

“东川型”排导槽结构对泥石流流速影响的实验研究

消能肋槛和排导槽纵比降是控制"东川型"泥石流排导槽内流体运动的两个关键因素。泥石流流速是反映排导槽工程输移力及对排导槽的冲刷淤积破坏的重要参数之一。通过实验,对固定配比的泥石流流体在不同的肋槛组合下的排导槽中的流速进行了研究,结果表明:(1)肋槛间距从40cm增加至60cm时,泥石流流速先增加后减少,在间距50cm时达到最大值;(2)肋槛高度对泥石流流速的影响非常复杂,在不同的肋槛间距和纵比降下表现不同的相关关系;(3)纵比降对排导槽内的泥石流流体基本呈正相关;(4)得到了肋槛间距与肋槛高度之比值N与泥石流流速V之间关系的数学表达式:V=0.0341N+C,其中C为常量。