Debris Flow Velocity Research Articles

Substantiation of debris flow velocity from super-elevation: a numerical approach

The use of super-elevations that a forced vortex flow leaves on the valley walls of a curved flume is a plausible approach toward estimating debris flow velocities in earthquake-induced geo-hazard studies. The centrifugal force of a speeding flow is responsible for a higher flow depth on the outer bend. However, in reality, a flow is not steady, and only the highest flow-marks are left at the outer and inner bends of the flow, which can lead to an inaccurate estimation of the actual velocity. Seeing the real scenario of the field, a series of numerical flume tests using smoothed particle hydrodynamics (SPH) is conducted to validate the estimation of debris flow velocities from flow-marks. Velocities estimated from flow-marks are lower than real velocities near the source region, but they converge to real velocities as the distance to the source increases. Based on several simulations, a best-fit line is proposed for adjusting debris flow velocity from mud-marks, and it is used to estimate flow velocities of the well-documented debris event called “Shiraito river debris flow,” which happened near the rim of the Hakone Crater, Kanagawa Prefecture, Japan, ensuing from the 1923 Great Kanto earthquake.

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, the viscous 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 = 0.6 m and L/w = 6.0).

Comparison of measurement methods of the front velocity of small-scale debris flows

Debris flow is a gravity-driven process, which is characterized by a travelling dense surge including large boulders, and it is followed by a more fluid tail. These characteristics make difficult the measurement of the mean flow velocity by means of common hydraulic techniques. Different methods can be used at real scale and small-scale to measure the front velocity but a dedicate comparison between available methods is still lacking. This research aims to compare the front velocity measurements in the transport zone of a miniature debris flow using three devices: i) a common digital video camera (29 frames per second); ii) a high speed thermo camera (60 fps); and iii) a laser photoelectric sensors system. The statistical analysis of data has highlighted no significant differences exist between front velocities obtained by means of the video camera and the thermo camera, whereas photocells data statistically differ from those achieved via the other systems. Some lack of data recorded by photocell was documented, while the thermo camera technique did not show significant loss of information being also helpful to detect the kinematic behaviour of single particles. Finally, the tests confirmed the influence of the solid volumetric concentration in the debris-flow mechanics, which promotes, <em>ceteris</em> <em>paribus</em>, the debris-flow slowing down.

전파면의 경사에 따른 토석류 흐름양상에 대한 연구

As sudden rainfall has happened, the debris flow has occurred in the mountain area. Recently sudden rainfall occurred so frequently caused by abnormal climate. Thus debris flow hazard had consecutively increased damage because of debris flow. Recently, Enormous damage due to debris flow have occurred in Korea. Various studies have been conducted to prevent search debris flow hazard. This study was carried out for debris flow behavior according to the land slope on propagation. It is the important one among factors that are related to the propagation over the city with respect to debris flow discharge and depth. For the numerical simulations in this study, the land slope was varied of 5, 0, <TEX>$-5^{\circ}$</TEX> to investigate the debris flow behavior with the FLO-2D, often recommended by FEMA to simulate debris flow. To verify the performance of FLO-2D, comparison with the USGS experiments (Iverson et al, 2010) was conducted. From numerical results the propagation length of the debris flow was found the most sensitive one. Maximum of debris flow thickness and velocity and structural vulnerabilities were investigated to the effect of land slope. They was became smaller according to land slope of 5, -5, <TEX>$0^{\circ}$</TEX> in the order. As a result, debris flow behavior analysis about the effect of the land slope could contribute to understand the vulnerability of city for debris flow hazards.

Reconstruction of a destructive debris‐flow event via numerical modeling: the role of valley geometry on flow dynamics

AbstractDebris‐flows are widespread natural phenomena characterized by high mobility (high velocity and long runout distance) and impact forces, which frequently cause human casualties and significant damage to infrastructure. To better understand the dynamics of such events, analyzing in particular the effect induced by the valley geometry on flow velocity, runout and mobilized volumes, in this work we reconstruct a real debris‐flow event through numerical modeling. Specifically, we used a modified version of the BING model, a fluid‐dynamic depth‐integrated numerical model for debris flows, which has been properly modified to account for width changes along the valley. The studied event, which occurred in Scaletta Zanclea (Messina, north‐eastern Sicily, Italy) on October 1, 2009, is exceptionally well constrained by field and topographic information. In this respect the flow velocity, estimated from two specific locations on the basis of field evidence, the distribution of erosional and depositional areas along the Racinazzo valley, based on the comparison of pre‐ and post‐event digital elevation models (DEMs), and the runout distance were used as constraints to calibrate the model. Furthermore, we report a detailed description of the main event characteristics based on hydrological records and witness reports. The numerical modeling results are consistent with witness reports and the severe damage recorded in the Scaletta Marina village, and highlight the effect of the valley geometry on both the debris flow velocity and the erosion/deposition processes. The effect of changing valley width has been also quantified, resulting in accelerations of the debris in correspondence of the valley narrowing and stagnations at the plateaus. Copyright © 2015 John Wiley &amp; Sons, Ltd.

An experimental study of dilute debris flow characteristics in a drainage channel with an energy dissipation structure

An experimental study was performed to determine the characteristics of a dilute debris flow in a drainage channel with an energy dissipation structure and a channel slope i of 15%. Flow pattern, debris flow depth, and velocity downstream of the energy dissipation structure were investigated along with the energy dissipation characteristics. Dilute debris flow velocity and depth were measured, analyzed, and subsequently used to characterize the dilute debris flow. The flow pattern in the drainage channel indicated that the dilute debris flow was highly turbulent and that flow depth initially increased. However, this increase was followed by a noticeable decrease after passing through the energy dissipation structure. The experimental results also indicated that the debris flow velocity gradually decreased as the length of the energy dissipation structure increased, whereas flow depth gradually increased with increasing length of the energy dissipation structure. Velocity characteristics and depths of the dilute debris flow downstream of the energy dissipation structure were also affected to some extent by variations in the width of the energy dissipation structure. The energy dissipation ratio gradually increased with increasing length and width of the energy dissipation structure for i=15%, and the maximum energy dissipation ratio was approximately 58.69%. These experimental results provide a theoretical foundation for optimal design of drainage channels with energy dissipation structures.

2011년 용인시 토석류 피해지역에 대한 리스크 평가

In this study, risk assessment for the debris-flow hazard which caused casualties and property loss in the area of Neungwon-ri, Yongin in July, 2011 was performed. Considering the return period of rainfall, debris flow volume was estimated. Dynamics of debris flow and impact range was also simulated by numerical approach. Based on the result of numerical analysis, impact pressure and vulnerability of building was calculated according to flow depth and velocity of debris flow. Finally risk assessment was performed based on the economic value of each building. Risk assessment showed that the longer the return period induced the high impact pressure and vulnerability regardless of a structure type. In addition, under a similar hazard situation, non-concrete frame building was more vulnerable than the reinforced concrete frame building.

Exploring the velocity distribution of debris flows: An iteration algorithm based approach for complex cross-sections

The estimation of debris-flow velocity in a cross-section is of primary importance due to its correlation to impact force, run up and superelevation. However, previous methods sometimes neglect the observed asymmetric velocity distribution, and consequently underestimate the debris-flow velocity. This paper presents a new approach for exploring the debris-flow velocity distribution in a cross-section. The presented approach uses an iteration algorithm based on the Riemann integral method to search an approximate solution to the unknown flow surface. The established laws for vertical velocity profile are compared and subsequently integrated to analyze the velocity distribution in the cross-section. The major benefit of the presented approach is that natural channels typically with irregular beds and superelevations can be taken into account, and the resulting approximation by the approach well replicates the direct integral solution. The approach is programmed in MATLAB environment, and the code is open to the public. A well-documented debris-flow event in Sichuan Province, China, is used to demonstrate the presented approach. Results show that the solutions of the flow surface and the mean velocity well reproduce the investigated results. Discussion regarding the model sensitivity and the source of errors concludes the paper.

Debris-flow velocities and superelevation in a curved laboratory channel

The vortex equation is often used to estimate the front velocity of debris flows using the lateral slope of the flow surface through a channel bend of a given radius. Here we report on laboratory experiments evaluating the application of the vortex equation to channelized debris flows. Systematic laboratory experiments were conducted in a 8 m long laboratory flume with a roughened bed, semi-circular cross section (top width 17 cm), and two different bend radii (1.0 and 1.5 m) with a common bend angle of 60°, and two channel inclinations (15° and 20°). Four sediment mixtures were used with systematic variations in the amount of fine sediment. In the experiments, 12 kg of water-saturated debris were released in a dam-break fashion, and multiple experiments were conducted to verify the repeatability for a given sediment mixture. Data are available for 69 experimental releases at a channel inclination of 20° and 16 releases at an inclination of 15°. Flow velocity was determined with high-speed video, and flow depth and the lateral inclination of the flow surface (superelevation) were measured using laser sensors. In general, the results from an individual sediment mixture are repeatable. We found that the channel slope as well as centerline radius have a significant influence on the correction factor k used in the vortex equation. Relatively coarse-grained sediment mixtures have larger superelevation angles than finer-grained mixtures. We found a statistically significant relation between the correction factor and Froude number. Correction factors of 1 &lt; k &lt; 5 were found for supercritical flow conditions. However, for subcritical flow conditions the correction factor shows a larger value as a function of the Froude number, which leads to an adaption of the forced vortex formula considering active and passive earth pressures. Finally, based on our experimental results, we present a forced vortex equation for debris-flow velocity estimation without a correction factor.

Calculation of the separation grid design length in a new water–sediment separation structure for debris flow defense

A new water–sediment separation structure with a herringbone separation grid has been developed for debris flow defense. Previous model experiments showed that, compared to existing structures, this structure can continuously maintain its water–sediment separation function. However, in the structure design, the length of the separation grid is key to its success in separating water and sediment. This paper presents a theoretical formula for calculating the design length of the grid. The theoretical formula shows that the grid length relates to the debris flow velocity v x, the grid width B, and the grid incline angle θ. A series of model experiments were conducted in the laboratory to test the accuracy of the formula. The results show that the experimental value and the theoretical value for grid length form a linear relationship and the design length of the grid may be corrected by a coefficient. Further analysis indicates that the correction coefficient changes with the bulk density of debris flow. Finally, a formula for determining the grid design length is derived from the theoretical formula, corrected using a coefficient related to the bulk density of a debris flow.

The formation and development of debris flows in large watersheds after the 2008 Wenchuan Earthquake

The Wenchuan earthquake has caused abundance of loose materials supplies for debris flows. Many debris flows have occurred in watersheds in area beyond 20 km(2), presenting characteristics differing from those in small watersheds. The debris flows yearly frequency decreases exponentially, and the average debris flow magnitude increases linearly with watershed size. The rainfall thresholds for debris flows in large watersheds were expressed as I = 14.7 D (-0.79) (2 h < D < 56 h), which is considerably higher than those in small watersheds as I = 4.4 D (-0.70) (2 h < D < 37 h). A case study is conducted in Ergou, 39.4 km(2) in area, to illustrate the formation and development processes of debris flows in large watersheds. A debris flow develops in a large watershed only when the rainfall was high enough to trigger the wide-spread failures and erosions on slope and realize the confluence in the watershed. The debris flow was supplied by the widely distributed failures dominated by rill erosions (14 in 22 sources in this case). The intermittent supplying increased the size and duration of debris flow. While the landslide dam failures provided most amounts for debris flows (57 % of the total amount), and amplified the discharge suddenly. During these processes, the debris flow velocity and density increased as well. The similar processes were observed in other large watersheds, indicating this case is representative.

Velocity and runout determination of a debris flow based on energy conservation: the Dongwopu debris flow in Tianjin, China

This paper focuses on a model that predicts the runout and velocity of the Dongwopu debris flow in Tianjin, China. Based on the law of energy-conservation, the established model primarily considers potential energy and energy loss in debris-flow movement. The present study discusses several stresses that could cause energy loss for debris flows, and the friction energy loss is emphasized. Ultimately, the analytical expressions of runout and velocity are established. The calculation results show that the velocity of the Dongwopu debris flow is 14 m s -1 . At this velocity, the runout distance will not cause a threat to residents and engineering facilities in the area.

토석류에 의한 건물의 물리적 취약함수 특성

2011년 7월과 8월 사이에 발생한 총 8개 토석류 재해 지역에 대한 재해이력 사례를 분석하여 각 재해지역의 토석류 물리적 특성을 파악하였다. 또한 각 재해지역에서 피해를 입은 15개 건물에 대한 손상 특성 분석을 수행하였다. 토석류의 물리적 특성과 건물 손상정도를 바탕으로 토석류의 높이, 속도 및 충격압력으로 구성된 취약함수를 구하였다. 또한 보강 콘크리트 구조와 비 콘크리트 구조와 같은 건물의 구조 형식에 따른 취약함수를 각각 산출하였다. 비 콘크리트 건물의 경우 토석류 충격압이 30 kpa 이상일 때 완전 파괴, 15~30 kPa일 때 심각한 손상, 0~15 kPa일 때 경미한 손상이 발생하는 것으로 분석되었다. 이에 비해 보강 콘크리트 건물의 경우 100 kPa 이상에서 심각한 손상, 35~100 kpa일 때 보통 손상, 0~35 kPa일 때 경미한 손상을 입는 것으로 파악되었다. 콘크리트 건물의 경미한 손상에 대응하는 토석류 충격압은 비 콘크리트 건물에서는 완전 파괴에 해당되는 손상을 가져다 줄 수 있음을 의미한다. 건물 구조형식과 토석류 물리적 특성에 따른 취약곡선을 비선형 회귀분석을 수행하여 함수형태로 나타내었다. 이러한 토석류 취약함수는 토석류 재해로 피해가 발생할 가능성이 있는 지역의 건물손상 정도를 정량적으로 평가하는 방법으로 이용할 수 있다. The physical characteristics of debris flows were analyzed from a total of 8 cases of debris flow disasters occurred in between July and August, 2011. 15 buildings damaged in these events were also investigated in detail to study the characteristics and patterns of building damages by debris flows. Physical vulnerability was obtained from the relationship of the degree of building damage and the physical characteristics of debris flow. Three different empirical vulnerability curves were obtained, which were functions of debris flow height, flow velocity and impact pressure, respectively. Furthermore, the vulnerability function was characterized according to the structural types of the building. In the case of non-concrete building, a complete destruction occurred at the impact pressure of more than 30 kPa, an extensive damage at the impact pressure between 15 and 30 kPa, a slight damage at the impact pressure below 15 kPa. In the case of reinforced-concrete buildings, an extensive damage occurred at the impact pressure of more than 100 kPa, a moderate damage at the impact pressure between 35 and 100 kPa, a slight damage at the impact pressure below 35 kPa. The impact pressure of debris flow corresponding to a slight damage to the reinforced-concrete building produced a complete damage for the case of non-concrete building, Nonlinear regression analysis was performed according to the physical characteristics of debris flow and the building structural type. The proposed physical vulnerability curves could be used as a quantitative assessment of the structural resistance of buildings affected by a debris flow event.

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.

Case history of the disastrous debris flows of Tianmo Watershed in Bomi County, Tibet, China: Some mitigation suggestions

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.

Mean velocity estimation of viscous debris flows

The mean velocity estimation of debris flows, especially viscous debris flows, is an important part in the debris flow dynamics research and in the design of control structures. In this study, theoretical equations for computing debris flow velocity with the one-phase flow assumption were reviewed and used to analyze field data of viscous debris flows. Results show that the viscous debris flow is difficult to be classified as a Newtonian laminar flow, a Newtonian turbulent flow, a Bingham fluid, or a dilatant fluid in the strict sense. However, we can establish empirical formulas to compute its mean velocity following equations for Newtonian turbulent flows, because most viscous debris flows are turbulent. Factors that potentially influence debris flow velocity were chosen according to two-phase flow theories. Through correlation analysis and data fitting, two empirical formulas were proposed. In the first one, velocity is expressed as a function of clay content, flow depth and channel slope. In the second one, a coefficient representing the grain size nonuniformity is used instead of clay content. Both formulas can give reasonable estimate of the mean velocity of the viscous debris flow.

A new approach for analyzing the velocity distribution of debris flows at typical cross-sections

The asymmetrical distribution of debris-flow velocity in a cross-section has long been observed and is currently regarded as one of the most essential issues in debris-flow research. Due to a lack of quantitative models for the velocity distributions of debris flows, most studies consider only the mean velocity. However, to optimize countermeasure structures, to estimate the erosion rate, or to evaluate the constitutive equations for shear behavior, it is beneficial to know the velocity profile in a cross-section. In this paper, a generalized model of typical channel geometries (e.g., rectangular, trapezoid, or V-shape) is proposed. A description of the velocity distribution that optimizes the Manning–Strickler velocity equation for transverse distribution and Egashira’s velocity equation for vertical distribution is presented; thus, the debris-flow velocity at any point in the cross-section can be calculated and the distribution profile therefore obtained. A well-documented debris-flow reference case and the Jiasikou debris flow in the high-seismic-intensity zone of the Wenchuan earthquake are selected as case studies to demonstrate the model. Analyses of both cases confirm the asymmetrical distribution of debris-flow velocity in cross-section, as originally expected. This shows that the velocity at the top surface in the middle of the channel is much larger than that at each sidewall and than the mean value calculated by former equations. The obtained velocity distribution profile is a better approximation of the observed field profiles.

Failure modes of reinforced concrete columns of buildings under debris flow impact

Buildings are the element of greatest concern with regard to debris flow hazard risk, and their destruction is mainly caused by the collapse of walls and reinforced concrete (RC) columns. This research classifies the failure modes of the columns in a typical beam–column-framed building based on field investigations and historical data. It also proposes the collapse mechanism for columns damaged by debris flow, with reference to their failure modes. Based on the collapse mechanism, three typical types of RC columns with different strengths, which are usually used in many mountainous areas of Western China, were selected for the damage analysis. The critical velocity of debris flow and the diameter of particles were obtained using theories of material and structural mechanics. The results showed that the critical bearing condition of columns can be indicated by the formation of plastic hinges along columns and by the shear damage in the column section. The development of plastic hinges was mainly determined by the debris flow velocity and diameter and the impact location of large boulders. The energy of viscous debris flow is much larger than that of the dilute flow, and there will be more severe damage for columns under viscous flow impact. The critical velocities for three plastic hinge collapses are about twice those of two plastic hinge collapses. If the diameter of the boulders is larger than 0.5 m, the impact force of the large boulders plays a major role in the column collapse. Otherwise, both the dynamic pressure of debris flow and the impact force of boulders are responsible for column failure. Finally, the critical condition of column failure was applied to Zhouqu’s debris flow hazard. The calculated critical velocity is consistent with the value given by field investigation, which implies that this study can be used for risk analysis and damage estimation in a debris-flow-prone area.

Rheological Characteristics and Debris Flow Simulation of Waste Materials

휴 폐광산지역은 복합지질재해지역으로 집중호우에 의해 토사재해와 산성광산배수를 발생시킨다. 본 연구는 폐석적치장 전반에 걸쳐 토사재해가 관측된 임기광산에 대해 지반공학적 유변학적 시험을 수행하고 얻어진 시험결과를 토대로 1-D 토석류 수치해석을 수행함으로써 토석류의 확산성을 조사하였다. 모래와 자갈로 구성된 광산폐석 시료의 유변학적 특성을 조사하기 위해 베인관입형 레오미터(Vane-penetrated rheometer)를 사용하였으며, 전단응력 제어를 통한 전단응력(<TEX>${\tau}$</TEX>)-전단속도(<TEX>${\dot{\gamma}}$</TEX>)와 점도(<TEX>${\eta}$</TEX>)-전단속도(<TEX>${\dot{\gamma}}$</TEX>) 간의 상관관계를 얻었다. 또한 광산폐석 시료에 대해 잘 알려진 유변학적 모델들(Bingham, Herschel-Bulkley, Power-law, bilinear 및 Papanastasiou 모델)을 적용함으로써 수치해석에 필요한 유변학적 매개변수(항복응력과 소성점도)를 결정하였다. 실험결과에 따르면, 체적농도에 무관하게 전형적인 전단담화(shear thinning) 거동이 관측되었으며, 함수비가 증가할수록 Bingham 유체처럼 거동하는 것으로 나타났다. 또한 사용된 모든 유변학적 모델들은 파괴 후 거동에 적합한 모델들로 밝혀졌다. 토석류 흐름특성을 조사하기 위해 실험결과를 토대로 토석류 크기(5 m, 10 m 및 15 m)와 항복응력(100 Pa, 200 Pa, 300 Pa 및 500 Pa)을 선정하여 1-D BING을 통해 수치해석을 수행하였다. 그 결과, 토석류 이동거리와 이동속도는 항복응력의 크기에 반비례한 것으로 나타났으며, 토석류 항복응력이 500 Pa 이하인 경우 대부분의 토사는 계곡부까지 흘러갈 수 있는 것으로 나타났다. 따라서 집중호우 기간에 산악지역에 방치된 광산폐석은 토사재해에 취약하고 2차적으로 인근 수계로 유입되어 환경적 문제를 야기시킬 수 있는 것으로 나타났다. Abandoned mines often cause environmental problems, such as alteration of landscape, metal contamination, and landslides due to a heavy rainfall. Geotechnical and rheological tests were performed on waste materials corrected from Imgi waste rock dump, located in Busan Metropolitan City. Debris flow mobility was examined with the help of 1-D BING model which was often simulated in both subaerial and subaqueous environments. To determine flow curve, we used a vane-penetrated rheometer. The shear stress (<TEX>${\tau}$</TEX>)-shear rate (<TEX>${\dot{\gamma}}$</TEX>) and viscosity(<TEX>${\eta}$</TEX>)-shear rate (<TEX>${\dot{\gamma}}$</TEX>) relationships were plotted using a shear stress control mode. Well-known rheological models, such as Bingham, bilinear, Herschel-Bulkley, Power-law, and Papanastasiou concepts, were compared to the rheological data. From the test results, we found that the tested waste materials exhibited a typical shear shinning behavior in <TEX>${\tau}$</TEX>-<TEX>${\dot{\gamma}}$</TEX> and and <TEX>${\eta}$</TEX>-<TEX>${\dot{\gamma}}$</TEX> plots, but the Bingham behavior is often observed when the water contents increased. The test results show that experimental data are in good agreement with rheological models in the post-failure stage during shearing. Based on the rheological properties (i.e., Bingham yield stress and viscosity as a function of the volumetric concentration of sediment) of waste materials, initial flowing shape (5 m, 10 m, and 15 m) and yield stress (100 Pa, 200 Pa, 300 Pa, and 500 Pa) were input to simulate the debris flow motion. As a result, the runout distance and front velocity of debris flow are in inverse propositional to yield stress. In particular, when the yield stress is less than 500 Pa, most of failed masses can flow into the stream, resulting in a water contamination.

Post Seismic Debris Flow Modelling Using Flo-2D; Case Study of Yingxiu, Sichuan Pronvince, China

In many parts of the world debris flows are one of the most dangerous of all mass wasting events. Mountainous areas with high slope instability, high seismic activities and extreme rainfall condition are the main triggering factors. The Monday, May 12, 2008, mega-earthquake of magnitude 8.0 that struck the Wenchuan area, Northwestern Sichuan province in China was catastrophic. This event, led to co-seismic landslides and subsequent rainfall induced debris flow in Yingxiu catchment on August 14th, 2010. The catchment has a very steep topography, an area of 5.35 km2 and a channel length of 3.55 km. The aim of this research is to model the post seismic debris flow, Parameterize and calibrate the event. Two main initiation zones were identified based on susceptibility assessed from geomorhological mapping and formed the bases for input in the FLO-2D model. 161, 350 m3 (64.54%) of the debris flow volume was modeled with FLO-2D in a manner consistent within the limit of the data available. FLO-2D model do not incorporate entrainment of materials in the transport zone. Thus, limitation to the production of the total deposits volume on the debris flow fan. The model was parameterized and the result shows that, Sediment concentration and the coefficient of friction were the two main parameters that affected the velocity of debris flow, area of inundation and the impact force respectively. Finally, the debris flow was calibrated using a back analysis of the debris flow event of 2010.