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1.
We investigate experimentally the depositions of two contiguous debris flows flowing into a main river reach.The aim of the present experimental research is to analyze the geometry and the mutual interactions of debris flow deposits conveyed by these tributaries in the main channel.A set of 19 experiments has been conducted considering three values of the confluence angle,two slopes of the tributary,and three different triggering conditions（debris flows occurring simultaneously in the tributaries,or occurring first either in the upstream or in the downstream tributary）.The flow rate along the main channel was always kept constant.During each experiment the two tributaries had the same slope and confluence angle.The analysis of the data collected during the experimental tests indicates that the volume of the debris fan is mainly controlled by the slope angle,as expected,while the shape of the debris deposit is strongly influenced by the confluence angle.Moreover,in the case of multiple debris flows,the deposit shape is sensitive to the triggering conditions.Critical index for damming formation available in literature has been considered and applied to the present case,and,on the basis of the collected data,considerations about possible extension of such indexes to the case of multiple confluences are finally proposed.  相似文献   

2.
The frequency and extent of debris flows have increased tremendously due to the extreme weather and the Wenchuan earthquake on May 12, 2008. Previous studies focused on the debris flow from gullies damming the mountain streams. In this paper, an equation for the run-out distance of debris flow in the main river is proposed based on the dynamic equation of debris flow at different slopes given by Takahashi. By undertaking field investigations and flume experiments, a new calculation method of the volume of debris flow damming large river is obtained. Using the percolation theory and the renormalization group theory it was deduced that the large particles should comprise more than 50% for forming a stable debris flow dam. Hence, the criteria of damming large river by debris flow is presented in terms of run-out distance and grain composition which was then validated through the event of damming river by debris flow at Gaojia gully, the upper reaches of the Minjiang River, Sichuan, China, on July 3, 2011.  相似文献   

3.
The quadratic rheology model considers the yield stress, viscous stress, turbulent stress and disperse stress, so it is used in this study to derive the velocity profile of debris flows. The quadratic model with the parabolic eddy viscosity was numerically solved, and an analytical solution was derived for the quadratic model with a constant eddy viscosity. These two solutions were compared with the Arai-Takahashi model that excluded the viscous stress and the yield stress. The three models were tested by using 17 experiment cases of debris flows over rigid beds. The results prove that the quadratic model with parabolic and constant eddy viscosities is applicable to muddy and granular flows, whereas the Arai-Takahashi model tends to overestimate the flow velocity near the water surface if a plug-like layer exists. In addition, the von Karman constant and the zero-velocity elevation in the three models are related to sediment concentration. The von Karman constant decreases first and then increases as the sediment concentration increases. The zero-velocity elevation is below the bed surface, likely due to the invalidity of the non-slip boundary condition for the debris flows over fixed beds.  相似文献   

4.
Debris flows have caused serious human casualties and economic losses in the regions strongly affected by the Ms8.0 Wenchuan earthquake of 2008. Debris flow mitigation and risk assessment is a key issue for reconstruction.The existing methods of inundation simulation are based on historical disasters and have no power of prediction.The rain-flood method can not yield detailed flow hydrograph and does not meet the need of inundation simulation. In this paper,the process of water flow was studied by using the Arc-SCS model combined with hydraulic method,and then the debris flow runoff process was calculated using the empirical formula combining the result from Arc-SCS.The peak discharge and runoff duration served as input of inundation simulation. Then,the dangerous area is predicted using kinematic wave method and Manning equation.Taking the debris flow in Huashiban gully in Beichuan County,Sichuan Province,China on 24 Sep.2008 as example,the peak discharge of water flow and debris flow were calculated as 35.52 m3·s-1 and 215.66 m3·s-,with error of 4.15%compared to the measured values.The simulated area of debris-flow deposition was 161,500 m2,vs.the measured area of 144,097 m2,in error of 81.75%.The simulated maximum depth was 12.3 m,consistent with the real maximum depth between 10 and 15 m according to the field survey.The minor error is mainly due to the flow impact on buildings and variations in cross-section configuration.The present methodology can be applied to predict debris flow magnitude and evaluate its risk in other watersheds inthe earthquake area.  相似文献   

5.
Debris flows form deposits when they reach an alluvial fan until they eventually stop.However,houses located in the alluvial fan might affect the debris flow flooding and deposition processes.Few previous studies have considered the effects of houses on debris flow flooding and deposition.This study conducted model experiments and numerical simulations using the Kanako2D debris flow simulator to determine the influence of houses on debris flow flooding and deposition.The model experiments showed that when houses are present,the debris flow spreads widely in the cross direction immediately upstream of the houses,especially when the flow discharge is large or the grain size is small.Houses located in the alluvial fan also influence the deposition area.The presence of houses led to flooding and deposition damage in some places and reduced the damage in others.The simulation also demonstrated the influence of houses.Both the model experiment and the simulation showed that houses change the flooding and deposition areas.  相似文献   

6.
Debris flow often causes enormous loss to life and property,especially on alluvial fans.Engineering structures such as retention check dams are essential to reduce the damage.In hazard mitigation evaluation and planning it is of significance to determine the location,size and type of dam and the effects of damage mitigation.We present a numerical simulation method using Kanako simulator for hazard mitigation planning of debris flow disaster in Tanjutani Gully,Kyoto City,Japan.The simulations were carried out for three situations:1) the simulations of erosion,deposition,hydrograph changing and inundation when there were no mitigation measures;2) the simulations of check dams in four locations(470 m,810 m,1,210 m and 1,610 m from the upstream end) to identify the best location;3) the simulations of check dams of three types(closed,slit and grid) to analyze their effects on sediment trapping and discharge reduction.Based on the simulations,it was concluded that two closed check dams(located at 470 m and 1,610 m from the upstream end) in the channel and a drainage channel on the alluvial fan can reduce the risk on the alluvial fan to an acceptable level.  相似文献   

7.
A pair of flumes with variable inclinations were employed to investigate the entrainment mechanics and dynamical evolution of a debris avalanche/flow. A fixed quantity of solid and water mixture was released from a constant elevation and accelerated along a higher chute to impact substrate materials with different water contents and particle size distributions in the lower chute. Two high-speed cameras, pore and earth pressure detecting devices, were placed in the substrate materials where severe scouring occurs in order to collect multiple measurements of dynamical and mechanical parameters. The entrainment dynamics were verified by geometrical analysis and quasi-static simulation. The results show that wet and fine materials that are placed in the lower chute with steeper slopes are easily entrained during debris flow initiation, the pattern of which can be described by Coulomb friction and the Mohr-Coulomb law. Elaborate measurements of dynamical parameters enable the results of an elementary computational framework to predict the time-dependent scouring depth ht, which provides insight into rapidly determining debris flow propagation. Finally, the post-entrainment dynamics were studied. The results indicate that the propagation and the amplification of debris flows along erodible beds are dominated by the velocity and the solid volume fraction of the mixed substrate, and the coarse particle group of the substrate is a key feature affected by momentum changes.  相似文献   

8.
鄂尔多斯盆地南部彬长区块的延长组长6-长7段发育厚层无沉积构造的块状砂岩,具有良好的油气显示和开发效益,然而关于该套砂岩的形成机制尚不清晰。确定长6-长7段砂岩的沉积相及沉积模式,对于该套低渗砂岩储层"甜点"形成机制的理解,"甜点"分布模式的预测,以及后续勘探开发都具有重要的指导意义。对彬长区块36口取心井的长6-长7段1 024 m长的岩心进行了沉积学特征描述,结合粒度分析资料及地质制图分析,确定了该套厚层砂岩的沉积相及沉积模式。结果表明:鄂尔多斯盆地南部彬长区块的延长组长6-长7段砂岩共发育15种岩相和3种主要沉积微相类型,即:砂质碎屑流、浊积岩和震积滑塌岩微相,以及它们在空间上的3类组合关系。其深水重力流沉积模式可以概括为扇根（坡折带斜坡上半部分）的震积滑塌相-砂质碎屑流亚相（沉积组合）、扇中（斜坡中下部位-坡脚）的砂质碎屑流-浊积岩沉积亚相（沉积组合）和扇端（坡脚-盆底）浊积砂等亚相（沉积组合）。通过对彬长区块延长组长6-长7段发育的致密砂岩沉积特征的分析与讨论,确定了该厚层块状砂岩的主要沉积相及沉积微相的特征及分布,为致密砂岩储层的高效开发及"甜点"预测提供了科学依据与良好借鉴。   相似文献   

9.
Debris flows are recurrent natural hazards in many mountainous regions.This paper presents a numerical study on the propagation of debris flows in natural erodible open channels,in which the bed erosion and sedimentation processes are important.Based on the Bingham fluid theory,a mathematical model of the two-dimensional non-constant debris flow is developed.The governing equations include the continuity and momentum conservation equations of debris flow,the sediment convection-diffusion equation,the bed erosion-deposition equation and the bed-sediment size gradation adjustment equation.The yield stress and shear stress components are included to describe the dynamic rheological properties.The upwind control-volume Finite Volume Method (FVM) is applied to discretize the convection terms.The improved SIMPLE algorithm with velocity-free-surface coupled correction is developed to solve the equations on non-orthogonal,quadrilateral grids.The model is applied to simulate a debris flow event in Jiangjia Gully,Yunnan Province and to predict the flow pattern and bed erosion-deposition processes.The results show the effectiveness of the proposed numercial model in debris flow simulation and potential hazard analysis.  相似文献   

10.
《山地科学学报》2020,17(1):156-172
Loose deposits, rainfall and topography are three key factors that triggering debris flows.However, few studies have investigated the effects of loose deposits on the whole debris flow process.On June 28, 2012, a catastrophic debris flow occurred in the Aizi Valley, resulting in 40 deaths.The Aizi Valley is located in the Lower Jinsha River,southwestern Sichuan Province, China. The Aizi Valley debris flow has been selected as a case for addressing loose deposits effects on the whole debris flow process through remote sensing, field investigation and field experiments. Remote sensing interpretation and laboratory experiments were used to obtain the distribution and characteristics of the loose deposits, respectively. A field experiment was conducted to explore the mechanics of slope debris flows, and another field investigation was conducted to obtain the processes of debris flow formation, movement and amplification. The results showed that loose deposits preparation, slope debris flow initiation,gully debris flow confluence and valley debris flow amplification were dominated by the loose deposits.Antecedent droughts and earthquake activities may have increased the potential for loose soil sources in the Aizi Valley, which laid the foundation for debris flow formation. Slope debris flow initiated under rainfall, and the increase in the water content as well as the pore water pressure of the loose deposits were the key factors affecting slope failure. The nine gully debris flows converged in the valley, and the peak discharge was amplified 3.3 times due to a blockage and outburst caused by a large boulder. The results may help in predicting and assessing regional debris flows in dry-hot and seismic-prone areas based on loose deposits, especially considering large boulders.  相似文献   

11.
随着勘探程度的提高,深水重力流成因的浊积岩储层已成为我国东部断陷湖盆油气勘探开发的重要目标之一。因为沉积分异不足和成岩破坏,重力流砂岩的储层质量通常整体较差,优质储层的预测成为制约其有效油气勘探的关键地质因素。利用岩心、测井资料及储层物性、岩石薄片分析结果,研究了南堡凹陷东北部东营组二段重力流砂岩的岩相特征、成因类型、储层特征,以探索优质储层的控制因素和发育规律。研究表明,区内重力流沉积可细分为8种岩相,解释为滑动滑塌、砂质碎屑流、泥质碎屑流、浊流4类成因。储层物性参数统计分析证实,本区重力流砂岩储层非均质性强,储层质量受控于砂岩成因、砂-泥结构及其影响的溶蚀强度。从成因看,砂质碎屑流和浊流对重力流砂岩优质储层的发育贡献最大。砂质碎屑流成因的块状砂岩厚度较大、泥岩夹层较少、钙质胶结物的溶蚀程度高,储层质量最好;而浊流成因的砂岩厚度较薄,与泥岩呈互层或夹层产出,成岩环境封闭、钙质胶结物溶蚀程度低,储层质量较差。本研究为湖盆深水重力流砂岩油气的高效勘探开发提供了一种基于成因和结构的储层预测思路。  相似文献   

12.
Slope debris flows in the Wenchuan Earthquake area   总被引：1，自引：0，他引：1  
Avalanches and landslides, induced by the Wenchuan Earthquake on May 12, 2008, resulted in a lot of disaggregated, solid material on slopes that could be readily mobilized as source material for debris flows. Rainstorms triggered numerous slope debris flows with great damage to highways and rivers over the subsequent two years. Slope debris flows (as opposed to channelized debris flows) are defined as phenomena in which high-concentration mixtures of debris and water flow down slopes for short distances to highways and river banks. Based on field investigations and measurements of 19 slope debris flows, their main characteristics and potential mitigation strategies were studied. High rainfall intensity is the main triggering factor. Critical rainfall intensities for simultaneous occurrence of single, several and numerous slope debris flow events were 20 mm/day, 30mm/day, and 90 mm/day, respectively. Field investigations also revealed that slope debris flows consist of high concentrations of cobbles, boulders and gravel. They are two-phase debris flows. The liquid phase plays the role of lubrication instead of transporting medium. Solid particles collide with each other and consume a lot of energy. The velocities of slope debris flows are very low, and their transport distances are only several tens of meters. Slope debris flows may be controlled by construction of drainage systems and by reforestation.  相似文献   

13.
According to the observational data of viscous debris flows with hyper-concentration, debris flows can be classified into three types： high-viscous, viscous, and sub-viscous debris flows. Distinct formation mechanism of different graded bedding structures in deposits of viscous debris flows was analyzed in this paper by using their yield-stress ratio and flow plug ratio. This paper specially analyzed the effect of Weissenberg which the gravels in squirm condition of hyper-concentration viscous flows would tend to move vertically, and the formation mechanism of the gravels accumulated at surface was also studied. The analysis in this paper can establish a foundation for the studies on differentiation of bedding structures of debris flow deposits and studies on dynamic parameters of debris flows.  相似文献   

14.
Debris flows consist of grains of various sizes ranging from 10~(-6) m ～1 m. Field observations in the Jiangjia Gully (JJG) and other sites throughout China indicate that the grain size distribution of sediment in debris flows can be characterized by an exponential function fit to the cumulative distribution. The exponent value for the function varies by location and may be useful in distinguishing between debris flows from different valleys. For example, minimum values and ranges of the exponent are associated with the high frequency of debris flows in the JJG. Furthermore, the distribution presents piecewise fractality (i.e. scaling laws hold in various ranges of the grain size) and we propose that the fractal structure determines the matrix and that the fractal dimension plays a crucial role in material exchange between a debris flow and the substrate it flows over. Finally, the empirical data support an exponential relation between grain composition and non-dimensional shear stress for the critical state of the channel. Overall we propose a material-determinism approach to studying debris flows which contrasts with the enviro-determinism that has dominated much recent work in this field.  相似文献   

15.
The upper Yangtze River region is one of the most frequent debris flow areas in China. The study area contains a cascade of six large hydropower stations located along the river with total capacity of more than 70 million kilowatts. The purpose of the study was to determine potential and dynamic differences in debris flow susceptibility and intensity with regard to seasonal monsoon events. We analyzed this region’s debris flow history by examining the effective peak acceleration of antecedent earthquakes, the impacts of antecedent droughts, the combined effects of earthquakes and droughts, with regard to topography, precipitation, and loose solid material conditions. Based on these factors, we developed a debris flow susceptibility map. Results indicate that the entire debris flow susceptibility area is 167,500 km2, of which 26,800 km2 falls within the high susceptibility area, with 60,900 km2 in medium and 79,800 km2 are in low susceptibility areas. Three of the six large hydropower stations are located within the areas with high risk of debris flows. The synthetic zonation map of debris flow susceptibility for the study area corresponds with both the investigation data and actual distribution of debris flows. The results of debris flow susceptibility provide base-line data for mitigating, assessing, controlling and monitoring of debris flows hazards.  相似文献   

16.
Non-homogeneous two-phase debris flows are widely found in the western mountainous regions of China. To investigate the characteristics of the debris flow deposition process related to the morphology and extent of the debris fan, a series of physical experiments were carried out using an experimental flume. Some useful relationships were obtained to link the flow velocity with the geometric characteristics of deposition morphology and the corresponding area or volume. Based on these, some expressions about energy dissipation process in both the transport-deposition zone and deposition zone are presented, and improved equations describing solidliquid two-phase energy transformations in the specific deposition zone are also established. These results provide a basis for further investigating the underlying mechanisms of non-homogeneous debris flows, based upon which effective disaster control measures can be undertaken.  相似文献   

17.
降雨过程中降雨强度的变化会影响土体渗透率及饱和过程, 从而改变土体的力学性质, 影响泥石流起动模式及破坏规模。为探究不同降雨模式对震后泥石流起动机制的影响, 自制了小比例模型槽, 结合可控雨型的降雨模拟系统, 进行了人工降雨诱发泥石流的室内模型试验; 基于不同降雨模式下泥石流的起动过程分析, 对坡体内部含水率和孔隙水压力的变化规律进行了研究。研究结果表明: 递增型降雨模式下泥石流发生突然, 呈整体滑坡转化为泥石流起动模式, 坡体破坏规模最大; 递减型降雨模式下表现为后退式溃散失稳起动模式; 均匀型降雨模式下则表现为溯源侵蚀起动模式; 中峰型降雨模式下以局部滑坡转化为泥石流起动模式; Ⅴ型降雨模式下则由坡面侵蚀加剧转化为泥石流启动模式, 破坏规模最小。研究结果可以为九寨沟地区泥石流的预报预警提供参考。   相似文献   

18.
Natural dams are formed when landslides are triggered by heavy rainfall during extreme weather events in the mountainous areas of Taiwan.During landslide debris movement, two processes occur simultaneously: the movement of landslide debris from a slope onto the riverbed and the erosion of the debris under the action of high-velocity river flow. When the rate of landslide deposition in a river channel is higher than the rate of landslide debris erosion by the river flow, the landslide forms a natural dam by blocking the river channel. In this study, the effects of the rates of river flow erosion and landslide deposition(termed the erosive capacity and depositional capacity, respectively) on the formation of natural dams are quantified using a physics-based approach and are tested using a scaled physical model.We define a dimensionless velocity index vde as the ratio between the depositional capacity of landslide debris(vd) and the erosive capacity of water flow(ve).The experimental test results show that a landslidedam forms when landslide debris moves at high velocity into a river channel where the river-flow velocity is low, that is, the dimensionless velocity index vde 54. Landslide debris will not have sufficient depositional capacity to block stream flow when the dimensionless velocity index vde 47. The depositional capacity of a landslide can be determined from the slope angle and the friction of the sliding surface, while the erosive capacity of a dam can be determined using river flow velocity and rainfall conditions. The methodology described in this paper was applied to seven landslide dams that formed in Taiwan on 8 August 2009 during Typhoon Morakot,the Tangjiashan landslide dam case, and the YingxiuWolong highway K24 landslide case. The dimensionless velocity index presented in this paper can be used before a rainstorm event occurs to determine if the formation of a landslide dam is possible.  相似文献   

19.
Debris flows and landslides, extensively developing and frequently occurring along Parlung Zangbo, seriously damage the Highway from Sichuan to Tiebt(G318) at Bomi County. The disastrous debris flows of the Tianmo Watershed on Sept. 4, 2007, July 25, 2010 and Sept. 4, 2010, blocked Parlung Zangbo River and produced dammed lakes, whose outburst flow made 50 m high terrace collapse at the opposite bank due to intense scouring on the foot of the terrace. As a result, the traffic was interrupted for 16 days in 2010 because that 900 m highway base was destructed and 430 m ruined. These debris flows were initiated by the glacial melting which was induced by continuous higher temperature and the following intensive rainfall, and expanded by moraines along channels and then blocked Parlung Zangbo. At the outlet of watershed,the density, velocity and peak discharge of debris flow was 2.06 t/m3, 12.7 m/s and 3334 m3/s, respectively. When the discharge at the outlet and the deposition volume into river exceeds 2125 m3/s and 126×103 m3, respectively, debris flow will completely blocked Parlung Zangbo. Moreover,if the shear stress of river flow on the foot of terrace and the inclination angel of terrace overruns 0. 377 N/m2 and 26°, respectively, the unconsolidated terrace will be eroded by outburst flow and collapse. It was strongly recommended for mitigation that identify and evade disastrous debris flows, reduce the junction angel of channels between river and watershed, build protecting wall for highway base and keep appropriate distance between highway and the edge of unconsolidated terrace.  相似文献   

20.
On 13 August 2010, a catastrophic debris flow with a volume of 1.17 million m3 occurred in Xiaojiagou Ravine near Yingxiu town of Wenchuan county in Sichuan Province, China. The main source material was the landslide deposits retained in the ravine during the 2008 Wenchuan earthquake. This paper describes a two-dimensional hybrid numerical method that simulates the entire process of the debris flow from initiation to transportation and finally to deposition. The study area is discretized into a grid of square zones. A two dimensional finite difference method is then applied to simulate the rainfall-runoff and debris flow runout processes. The analysis is divided into three steps; namely, rainfall-runoff simulation, mixing water and solid materials, and debris flow runout simulation. The rainfall-runoff simulation is firstly conducted to obtain the cumulative runoff near the location of main source material and at the outlet of the first branch. The water and solid materials are then mixed to create an inflow hydrograph for the debris flow runout simulation. The occurrence time and volume of the debris flow can be estimated in this step. Finally the runout process of the debris flow is simulated. When the yield stress is high, it controls the deposition zone. When the yield stress is medium or low, both yield stress and viscosity influence the deposition zone. The flow velocity is largely influenced by the viscosity. The estimated yield stress by the equation, τ y = ρghsin θ, and the estimated viscosity by the equation established by Bisantino et al. (2010) provide good estimates of the area of the debris flow fan and the distribution of deposition depth.  相似文献   

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