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1.
Debris flows are typical two-phase flows, which commonly accompany erosion in mountainous areas, and may destroy bridge engineering by scouring. In this study, a physically-based two-phase model is applied for the simulation of debris flow scouring of bridge pier. In this model, the shear stress of debris flow on an erodible bed is considered to be a function of the solid shear stress, fluid shear stress, and volume fraction; accordingly, the erosion is incorporated into the two-phase model. Using a highaccuracy computational scheme based on the finite volume method, the model is employed for simulating a dynamic debris flow over an erodible bed. The numerical results are consistent with the experimental data, and verify the feasibility of the two-phase model. Moreover, a simple numerical test is performed to exhibit the fundamental behaviour of debris flow scouring of bridge pier, which shows that the degree of erosion on each side of the pier is higher compared to other areas. The scouring depth is influenced by the variations of solid volume fraction and velocity of debris flow and pier width.  相似文献   

2.
Debris flow fan affects the river profile and landscape evolution.The propagation of multiple debris flows along a river can cause inundation and breaching risk,which can be exemplified by the Min River after the Wenchuan earthquake,Sichuan province,China.In this work,large flume tests were conducted to examine the interactions between debris flows and water current with the fan geometry,momentum,runout distance,deposited width,the relative water level upstream and dominated stress.The results reveal that stony flow commonly travels at a high speed and forms a long rectangle shape fan,while the muddy flow generally travels at a low speed and forms a fan-shaped depositional area.The stony flow can block a river even when the momentum is close to the water current;the muddy flow can block a river when the momentum is lower than that of water current.In case of complete river damming,the relative water level upstream indicates that the inundation risk from the muddy flow damming river would be higher than the inundation risk of stony flow.The diversion ratio of muddy flow decreases as damming ratio.Comparison of dimensionless numbers reveals that stony flow is dominated by grain collision stress combined with turbulent mixing stress,while the muddy flow is dominated by viscous shear stress over friction stress.The fan geometry,damming ratio,diversion ratio,and the dominated stress all together indicate that stony flow strongly interacts with water current while the muddy flow does not.The results can be helpful for understanding the physical interactions between water current and various debris flows,and debris flow dynamics at the channel confluence area.  相似文献   

3.
The phenomenon of debris flow is intermediate between mass movement and solid transport. Flows can be sudden, severe and destructive. Understanding debris flow erosion processes is the key to providing geomorphic explanations, but progress has been limited because the physical-mechanical properties, movement laws and erosion characteristics are different from those of sediment-laden flow. Using infinite slope theory, this research examines the process and mechanism of downcutting erosion over a moveable bed in a viscous debris flow gully. It focuses specifically on the scour depth and the critical slope for viscous debris flow,and formulas for both calculations are presented.Both scour depth and the critical conditions of downcutting erosion are related to debris flow properties(sand volume concentration and flow depth) and gully properties(longitudinal slope,viscous and internal friction angle of gully materials,and coefficient of kinetic friction). In addition, a series of flume experiments was carried out to characterize the scouring process of debris flows with different properties. The calculated values agreed well with the experimental data. These theoretical formulas are reasonable, and using infinite slope theory to analyze down cutting erosion from viscous debris flow is feasible.  相似文献   

4.
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.  相似文献   

5.
In order to evaluate the danger of debris flow properly, eight factors were selected as the risk assessment indexes of the debris flow, namely the vertical slope, valley relative difference, hillside slope, area of basin, loose solid material reserves, the path length of sediment supply probability, silting and scouring derricking and vegetation coverage. The improved Analytic Hierarchy Process (AHP) method was used to obtain the weights of the factors; and the efficacy coefficient method was adopted to evaluate the risks of six typical debris flow gullies. According to the research, the improved AHP method not only avoids the subjectivity in the individual factor valuation by comparing two factors of each layer, but also makes the subsequent consistency check unnecessary.  相似文献   

6.
Debris flows can be extremely destructive because they can increase in magnitude via progressive entrainment. In this paper, a total of 18 landslide-type debris flows and 268 channelized debris flows in Wenchuan earthquake and Taiwan region, as well as other regions were collected to analyze the entrainment rate of debris flows in each triggering condition. Results show that there is a power relationship between volume of initial triggered mass and final deposited debris for landslide type debris flow. The debris flows during 2008 and 2013 in Wenchuan earthquake-region have smaller entrainment rate than that from 2001 t0 2009 in Taiwan. The entrainment rate of debris flow events from 2001 to 2009 in Taiwan shows a decaying tendency as elapsed time. Comparison of the entrainment rate in the two earthquake-hit regions with other regions proves that entrainment rate has a close relation with major sediment availability and secondary rainstorm conditions.  相似文献   

7.
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   

8.
The erosion shape and the law of development of debris flow sabo dam downstream is a weak part in the study on debris flow erosion. The shape and development of scour pit have an important effect on the stability and safety of debris flow sabo dam, which determines the foundational depth of the dam and the design of protective measures downstream. Study on the scouring law of sabo dam downstream can evaluate the erosion range and reasonably arrange auxiliary protective engineering. Therefore, a series of flume experiments are carried out including different debris flow characteristics （density is varying from 1.5 t/m3 to 2.1 t/m~） and different gully longitudinal slopes. The result shows that the scour pit appears as an oval shape in a plane and deep in the middle while superficial at the ends in the longitudinal section, the position of the maximum depth point moves towards downstream with an increase of flume slope angle. The maximum depth of scour pit is mainly affected by the longitudinal slope of gully, density of debris flow, and the characteristics of gully composition （particle size and the viscosity of soil）. The result also indicates that the viscosity of soil will weaken the erosion extent. The interior slopes of scour pit are different between the upstream and the downstream, and the downstream slope is smaller than the upper one. For the viscous and non-viscous sands with the same distribution of gradation, the interior slope of non- viscous sand is smaller than the viscous sand.According to tbe regression analysis on the experimental data, the quantitative relationship between the interior slope of scour pit, slope of repose under water and the longitudinal slope of gully is established and it can be used to calculate the interior slope of scour pit. The results can provide the basis for the parameter design of the debris flow control engineering foundation.  相似文献   

9.
The initiation mechanism of debris flow is regarded as the key step in understanding the debris-flow processes of occurrence, development and damage. Moreover, migration, accumulation and blocking effects of fine particles in soil will lead to soil failure and then develop into debris flow. Based on this hypothesis and considering the three factors of slope gradient, rainfall duration and rainfall intensity, 16 flume experiments were designed using the method of orthogonal design and completed in a laboratory. Particle composition changes in slope toe, volumetric water content, fine particle movement characteristics and soil failure mechanism were analyzed and understood as follows: the soil has complex, random and unstable structures, which causes remarkable pore characteristics of poor connectivity, non-uniformity and easy variation. The major factors that influence fine particle migration are rainfall intensity and slope. Rainfall intensity dominates particle movement, whereby high intensity rainfall induces a large number of mass movement and sharp fluctuation, causing more fine particles to accumulate at the steep slope toe. The slope toe plays an important role in water collection and fine particle accumulation. Both fine particle migration and coarse particle movement appears similar fluctuation. Fine particle migration is interrupted in unconnected pores, causing pore blockage and fine particle accumulation, which then leads to the formation of a weak layer and further soil failure or collapses. Fine particle movement also causes debris flow formation in two ways: movement on the soil surface and migration inside the soil. The results verify the hypothesis that the function of fine particle migration in soil failure process is conducive for further understanding the formation mechanism of soil failure and debris flow initiation.  相似文献   

10.
On-spot observation and field reconnaissance of debris flows have revealed that inflexion points in the longitudinal profile of a movable channel may easily become unstable points that significantly affect their entrainment behavior. In this study, small-scale flume experiments were performed to investigate the entrainment characteristics of debris flows over two types of inflexion points, namely, a convex point, which has an upslope gradient that is less than the downslope gradient; and a concave point, which has an upslope gradient that is greater than the downslope gradient. It was observed that when debris flowed over a convex point, the entrainment developed gradually and progressively from the convex point in the downstream direction, and the primary control factors were the slope gradient and friction angle. Conversely, when debris flowed over a concave point, the entrainment was characterized by impacting and impinging erosion rather than traditional hydraulic erosion, and the impingement angle of the flow significantly determined the maximum erosion depth and outflow exit angle. An empirical relationship between the topography change and the control factors was obtained from the experimental data.  相似文献   

11.
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   

12.
On 4th November 2010, a debris flow detached from a large debris cover accumulated above the lowermost portion of the Rotolon landslide (Vicentine Pre-Alps, NE Italy) and channelized in the valley below within the Rotolon Creek riverbed. Such event evolved into a highly mobile and sudden debris flow, damaging some hydraulic works and putting at high risk four villages located along the creek banks. A monitoring campaign was carried out by means of a ground based radar interferometer (GB-InSAR) to evaluate any residual displacement risk in the affected area and in the undisturbed neighbouring materials. Moreover, starting from the current slope condition, a landslide runout numerical modelling was performed by means of DAN-3D code to assess the impacted areas, flow velocity, and deposit distribution of the simulated events. The rheological parameters necessary for an accurate modelling were obtained through the back analysis of the 2010 debris flow event. Back analysis was calibrated with all of the available terrain data coming from field surveys and ancillary documents, such as topographic, geomorphological and geological maps, with pre- and post-event LiDAR derived DTMs, and with orthophotos. Finally, to identify new possible future debris flow source areas as input data for the new modelling, all the obtained terrain data were reanalysed and integrated with the GB-InSAR displacement maps; consequently, new simulations were made to forecast future events. The results show that the integration of the selected modelling technique with ancillary data and radar displacement maps can be a very useful tool for managing problems related to debris flow events in the examined area.  相似文献   

13.
Debris flow is a common natural hazard in the mountain areas of Western China due to favorable natural conditions,and also exacerbated by mountainous exploitation activities.This paper concentrated on the characteristics,causes and mitigation of a catastrophic mine debris flow hazard at Longda Watershed in Songpan County,Sichuan Province,on 21 July 2011.This debris flow deposited in the front of the No.1 dam,silted the drainage channel for flood and then rushed into tailing sediment reservoir in the main channel and made the No.2 dam breached.The outburst debris flow blocked Fu River,formed dammed lake and generated outburst flood,which delivered heavy metals into the lower reaches of Fu River,polluted the drink water source of the population of over 1 million.The debris flow was characterized with a density of 1.87~2.15 t/m 3 and a clay content of less than 1.63%.The peak velocity and flux at Longda Gully was over 10.0~10.9 m/s and 429.0~446.0 m 3 /s,respectively,and the flux was about 700 m 3 /s in main channel,equaling to the flux of the probability of 1%.About 330,000m 3 solid materials was transported by debris flow and deposited in the drainage tunnel(120,000~130,000 m 3),the front of No.1 dam(100,000 m 3) and the mouth of the watershed(100,000~110,000 m 3),respectively.When the peak flux and magnitude of debris flow was more than 462 m 3 /s and 7,423 m 3,respectively,it would block Fu River and produce a hazard chain which was composed of debris flow,dammed lake and outburst flood.Furthermore,the 21 July large-scale debris flow was triggered by rainstorm with an intensity of 21.2 mm/0.5 h and the solid materials of debris flow were provided by landslides,slope deposits,mining wastes and tailing sediments.The property losses were mainly originated from the silting of the drainage tunnel for flash flood but not for debris flow and the irrational location of tailing sediment reservoir.Therefore,the mitigation measures for mine debris flows were presented:(1) The disastrous debris flow watershed should be identified in planning period and prohibited from being taken as the site of mining factories;(2) The mining facilities are constructed at the safe areas or watersheds;(3) Scoria plots,concentrator factory and tailing sediment reservoir are constructed in safe areas where the protection measures be easily made against debris flows;(4) The appropriate system and plan of debris flow mitigation including monitoring,remote monitoring and early-warning and emergency plan is established;(5) The stability of waste dump and tailing sediment reservoir are monitored continuously to prevent mining debris flows.  相似文献   

14.
四川省小流域泥石流危险性评价   总被引：1，自引：0，他引：1  
泥石流危险性评价是泥石流防灾减灾的重要内容。本文以四川省为研究区,以DEM为数据源,通过提取水流方向,计算汇流累积量,实现四川省小流域划分。基于收集的已查明泥石流流域资料,分析了泥石流孕灾环境与成灾特点,选择流域高差、流域面积为指标,建立基于能量条件的潜势泥石流流域判识模型,对划分的小流域进行判识,识别出7798个小流域具备泥石流发生所需能量条件,面积为31.1×104 km2,占四川省总面积的64.18 %。进而建立了泥石流危险性评价指标体系和可拓物元模型,开展了小流域泥石流危险性评价,划分了危险度等级,得到中度、高度、极高危险区的小流域个数分别为1946、1725和1002个,面积分别为9.1×104、7.7×104和3.4×104 km2,中度以上危险区面积共20.2×104 km2,占四川省总面积的41.67%。最后对评价结果可靠性和各等级泥石流危险区在各地市级行政区、各大流域的分布进行了分析。其结果对促进泥石流判识与危险性评价理论,区域泥石流防灾减灾与山区可持续发展等具有重要的理论和现实意义。  相似文献   

15.
The objective of this study is to incorporate a numerical model with GIS to simulate the movement, erosion and deposition of debris flow across the three dimensional complex terrain. In light of the importance of erosion and deposition processes during debris flow movement, no entrainment assumption is unreasonable. The numerical model considering these processes is used for simulating debris flow. Raster grid networks of a digital elevation model in GIS provide a uniform grid system to describe complex topography. As the raster grid can be used as the finite difference mesh, the numerical model is solved numerically using the Leap-frog finite difference method. Finally, the simulation results can be displayed by GIS easily and used to debris flow evaluation. To illustrate this approach, the proposed methodology is applied to the Yohutagawa debris flow that occurred on 20th October 2010, in Amami- Oshima area, Japan. The simulation results that reproduced the movement, erosion and deposition are in good agreement with the field investigation. The effectiveness of the dam in this real-case is also verified by this approach. Comparison with the results were simulated by other models, shows that the present coupled model is more rational and effective.  相似文献   

16.
Jiangjia Ravine is a world-famous debris flow valley in Dongchuan,Yunnan Province,China.Every year large numbers of landslides and collapses happened and caused enormous damages to people’s properties and lives.With longtime observation and testing in Jiangjia Ravine we had found out one kind of special landslide which had the characteristics of landslide and collapse.Landslide and collapse supplied sufficient materials for debris flow.When a debris flow broke out,some kind of intergrowth existed among rainfall,landslide and debris flow.In order to study the intergrowth and some key parameters,we carried out artificial rainfall landslide tests and model experiments to observe the phenomena such as collapse,surface slide and surface flow.By observing the experimental phenomena and monitoring water contents,the transformation process among landslide deposits and debris flow under the condition of rainfall had been analyzed.Research results revealed the relationship of this kind of intergrowth among rainfall,landslide and debris flow in Jiangjia Ravine.Meanwhile,it was found that this kind of intergrowth relationship existed only when the moisture content was in a certain range.That is,the critical state seemed to be existed in the transformation process.  相似文献   

17.
Measuring the internal velocity of debris flows is very important for debris flow dynamics research and designing debris flow control works. However, there is no appropriate method for measuring the internal velocity because of the destructive power of debris flow process. In this paper, we address this problem by using the relationship between velocity and kinetic pressure, as described by surface velocity and surface kinetic pressure data. Kinetic pressure is the difference of impact pressure and static pressure. The former is detected by force sensors installed in the flow direction at the sampling section. Observations show that static pressure can be computed using the formula for static water pressure by simply substituting water density for debris flow density. We describe the relationship between surface velocity and surface kinetic pressure using data from seven laboratory flume experiments. It is consistent with the relationship for single phase flow, which is the measurement principle of the Pitot tube.  相似文献   

18.
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   

19.
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   

20.
Large spoil tips from reconstruction works as a result of the Wenchuan Earthquake in China are new debris flow hazards to the human society. However, there is a lack of detailed comparative study on debris flow initiation in different spoil materials. This paper describes a series of tests and analyses on debris flow characteristics (initiation, scale and mechanism) at six sites with limestone and sandstone materials near the Dujiangyan area. Research shows the limestone spoil contains debris flow prone clay content with high concentration of montmorillonite (highly expandable). In addition, limestone spoil is of such a low permeability that water mainly concentrates in the upper surface layer. Those factors make it easy for the increase of pore water pressure, decline of internal friction and conhesion force, leading to the occurence of large debris flows. In contrast, the sandstone spoil is less problematic and causes no major debris flow threats. Based on our research on the mechanism, the“stereometric drainage”method is sucessfully applied to control limestone spoil debris flows.  相似文献   

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