토석류 충격력에 의한 유도벽 영향성 검토

Flume investigation of debris flow entrained boulders with cylindrical baffles and a rigid barrier

Debris flow is a huge hazard to downstream lives and property, which must be controlled by engineering. The construction of gravity sand retaining dams (hereinafter referred to as sand retaining dams) from the formation area to the circulation area is one of the quick and effective measures. Prevention and control projects often play a role in controlling the development trend of debris flow and reducing the size and frequency of debris flow. Debris flow will cause erosion and impact damage to the dam foundation of sand retaining dams. For the debris flow impact force, the most dangerous part is usually designed based on the largest impact force, while all parts of the dam body are designed according to the most dangerous part, which wastes materials. It's not economical. In this study, a debris flow gully is selected as the research model. Considering the interaction between debris flow and sand retaining dam, the impact simulation of debris flow on sand retaining dam was carried out. The research results show that the existence of the sand retaining dam hinders the movement process of debris flow, changes its speed and direction of movement, and in addition, the impact force varies at different places of upstream face of sand retaining dam. Research results provide a scientific and reasonable theoretical basis and design reference for the stability of sand retaining dam under debris flow impact impact. This will, to a certain extent, have important social needs and practical significance for disaster reduction to improve the technical level of debris flow prevention projects.

Debris flow is one of the catastrophic geohazard, poses significant threat to all system of infrastructure including buildings, bridges, pipelines and retaining walls. For the sustainable design of oil and gas pipeline prone to debris flow hazard, It is crucial to consider the expected debris flow impact forces to ensure the safe and effective performance of pipeline. This study numerically investigates the dynamic impact of viscous debris flow on exposed pipeline. Altair Hyperwork CFD software was utilized to perform numerical investigation in CFD environment, simulating two-phase debris flow. Hershel Bulkley rheology and Spalart-Allmaras turbulence model was adopted to simulate the complex interaction of debris flow on pipeline. The results revealed that debris flow dynamics are highly dependent on sediment composition, fine content, and flow volume. These factors significantly influence the flow behavior and its potential impact on pipeline infrastructure. Furthermore, this study highlights the critical role of impact forces due to debris flow in pipeline design to enhance the safe and longevity of pipeline system in alpine terrain. The findings underscore the need for comprehensive approach of pipeline design that integrate the advanced numerical techniques with thorough understanding of local geological conditions.

Debris flows are one of the most hazardous and frequent landslides in mountainous regions. In this research, we apply dendrogeomorphological techniques to analyze the debris flow that occurred in February 2010 in the Monarch Butterfly Biosphere Reserve in central Mexico. Firstly, analyzed precipitation data from two nearby meteorological stations has indicated that an extraordinary precipitation event accumulated 236.4 mm of rainfall over a 5-day period, from January 31st to February 4th, 2010. In addition, we generated a geomorphological cartography of the area at 1:600 scale by interpreting the images obtained using an Unmanned Aerial Vehicle. Subsequently, we carried out dendrochronological sampling on 98 Abies religiosa trees (125 cores); the cores were dated using cross-dating and the ring width was measured for generating a chronology, in which the years with growth disturbances as a result of the debris flow could be identified and characterized. We identified three types of growth anomalies in the tree ring series: (a) traumatic resin ducts, (b) growth suppression, and (c) growth releases, related to the 2010 debris flow event. We also estimated the debris flow intensity through the scar heights recorded in the trees, which allowed us to identify that the intensity of the debris flow was greater in the transport zone. These results highlight the benefit of the dendrogeomorphological technique used in the collection of spatio-temporal information on debris flow activity in intertropical montane environments, especially where information about mass movement processes is limited. Therefore, we demonstrate that dendrogeomorphological techniques, in combination with other parameters such as scar height on the trees, as well as a detailed geomorphological survey, allows for an understanding of the dynamics of debris flows, which, in the case of Mexico have not been previously evaluated using this approach.

Mining-induced geo-hazards have caused enormous destruction and threat to mines. Known as the "kingdom of nonferrous metals" and located in Southwest China, Yunnan Province developed mining-induced geo-hazards well with characteristics of multiple types, widespread distribution and serious damage. Landslides and debris flows are two common sub-types of geohazards causing most serious damage in Yunnan, and some of them were very representative in the world. Two landslides and two debris flows were chosen to analyze deeply. Both Laojinshan Landslide and Sunjiaqing Landslide possess the characteristic of rock avalanches. The high sliding speed and long distance made the landslides translate into clastic flows with impact force and caused enormous destruction. Rainstorm and mining waste rock were two main factors to induce debris flows in Yunnan mines. Heishan valley debris flow of Dongchuan copper mine was a super large rainstorm type viscose debris flow with very low frequency, which brought a good caution to utilize valleys which looked an unlikely debris flow. Nandagou Valley of Jinding lead-zinc mine in Lanping County was a rainstorm stimulating, gully-type, high frequency and large scale debris flow, which was induced by mining activities. Many countermeasures have been used for Yunnan mines, including engineering treatment technology and ecological remediation, monitoring and forecasting, relocation and public administration.

Landslide barrier structures are a useful mitigation tool for managing debris flow risks, working to slow their momentum or alter their course to avoid damage to downslope inhabitants or infrastructure. Their design is typically governed by the expected impact force, which is predicted using analytical models or numerical simulations. These methods only provide estimates of the peak force and require detailed information about the flow at impact that can be difficult to accurately predict. In this experimental study, we use the large Queen’s University Landslide Flume to explore the relative contributions of the fluid and solid phases of a multi-phase flow on the structural demand on a barrier. Impact forces following dam break experiments of up to 0.4 m3 of material, released from the top of a 6.5 m long slope inclined at 30 degrees are explored for material releases of pure water, dry granular particles (3 mm diameter), and fully saturated water-grain mixtures. Temporal impact behaviour captured using ultrahigh speed imaging (7500 fps) is correlated with the time series of impact load measured at the barrier. The addition of the fluid phase was found to significantly increase the impact force and the maximum run-up height along the barrier. Further tests are performed using single-graded particles ranging in diameter from 3-25 mm. Over this range, the dilatancy of the flow increased with increasing particle size, leading to reduced influence of the fluid phase on the flow dynamics and decreased impact force, despite similar flow velocities (4-5 m/s).To explore the performance of an alternate barrier type, impact tests were conducted using a single-slit barrier with varying slit size (30-240 mm) and grain diameter (3-25 mm), providing a wide range of relative slit sizes. A benefit of the slit barrier design is its ability to ‘self-clean,’ letting material slowly release through the slit following an impact event. This allows the barrier to remain effective in halting a secondary debris flow without maintenance clearing between impacts. To explore the dynamics of this subsequent event, secondary releases were performed for both solid and slit barrier designs. Barrier performance is investigated using load measurement, LiDAR imaging, and PIV analysis. The solid barrier experienced overtopping under the second release. The addition of the slit alters the deposit geometry, generating two slopes on either slide of the slit which act as redirection berms, altering the flow behaviour and reducing the runup height and force of the second impact. The results of this large-scale experimental study provide detailed data on the flow behaviour, impact mechanics, and barrier efficiency for a range of debris flow compositions, particle sizes, and slit sizes under single and sequential impacts, suitable for numerical model benchmark tests that may lead to improved barrier design.

The impacts of logging on landslide activity at Clayoquot Sound, British Columbia

Landslides and debris flows that occur around residential areas are considered, globally, as significant disasters that cause damage to human life and property. With terrain slope defining the flow characteristics of debris flows, flow depth, flow velocity, and impact force vary by time and distance. In particular, when a structure is located in the flow path of debris flows, the flow characteristics of debris flows vary by terrain slope and direction angle. To simulate the flow characteristics of these debris flows, the simulation results obtained by FLO-2D were analyzed with six-stage conditions for the research area. In the analysis, the flow depth, flow velocity, and impact force were estimated on the basis of the outlet of the research area in the presence and absence of structure(s) at certain distances. With this, the variation of the impact force in accordance with the variation of the flow depth of the debris flows was highly similar to the simulation results obtained by FLO-2D, when the correction index (α) of the suggested dynamic impact force equation was 0.3–0.4. There were sections where the estimated value of the impact force was overestimated near the outlet, and it was judged that the fixed values of the terrain factors (width, roughness coefficient, slope, etc.) caused the impact force to be overestimated. However, the correlation analysis showed that the correlation index was above the normal ranges in the suggested dynamic impact force equation for debris flows with the application of the terrain factors.

<p>For the design of mitigation measures knowledge of debris-flow impact forces, usually estimated based on hydrostatic, hydrodynamic, or combined approaches, is essential. As these approaches are based on Newtonian fluids, they must be adjusted by empirical correction factors to account for the solid-fluid nature of debris flows. The values for the correction factors shown in the literature vary over a wide range and several studies showed a clear dependence with the Froude regime of debris flows.</p><p>To better understand the correction factors and to be able to calculate them using parameters that describe the flow behaviour a total of 32 experiments were conducted in the course of the project “Debris flow impact forces on bridge super structures (DEFSUP)”, funded by the Austrian Science Fund (FWF). Two different material compositions, different water contents as well as a total impact and a bypassing of the measuring block were tested.</p><p>The experimental setup designed within the project consists of a 4 m long semi-circular channel with a diameter of 300 mm and an inclination of 20°. The material is released from a rectangular reservoir in a dam-break scenario and accelerated with zero roughness on a length of 1.2 m and transferred to the semi-circle profile. The subsequently introduced roughness with a grain diameter of 1-2 mm generates a stationary phenomenological debris flow until it hits the measuring setup. With a starting volume of 50 kg, flow heights between 8 and 12 cm and velocities from 0.8 to 2.2 m/s were achieved according to the material composition and different water content. With these different mixtures a Froude-range from 0.6 to 3.6 was covered. In addition, normal stresses and pore water pressures were measured at the exact same point.</p><p>A detailed analysis of the measured impact forces together with the above mentioned measured parameters showed that the hydrodynamic correction factor is a constant mainly corresponding to the liquification ratio of the debris-flow mixture. Hence, the hydrodynamic correction factor can be regarded as a drag coefficient and seems to depend mainly on the internal friction of the flowing medium. At low Froude numbers measured impact forces exceed even a full momentum transfer if the mean bulk density is used for the calculation. This indicates that the impact forces can no longer be described by the hydrodynamic approach alone. For this reason, an additional pressure term based on a hydrostatic approach is considered in the combined concept. This additional pressure term depends on the dynamics of flow (Froude number) and can be modelled via a dynamic earth pressure coefficient.</p><p>The findings from these experiments contribute to a better prediction of debris-flows impact forces in terms of their material composition and flow behaviour.</p>

Abstract. On 10 January 2003, a rockfall of approximately 10 m3 affected a cliff some 25 m high located along the northern slopes of Mt. St. Angelo (Nocera Inferiore, province of Salerno) in the southern Italian region of Campania. The impact of boulders on the lower sector of the slope, along which detrital-pyroclastic soils outcrop, triggered a small channelled debris flow of about 500 m3. Fortunately, no damage nor victims resulted from the landslide. Several marks of the impacts were observed at the cliff toe and outside the collapsed area, and the volumes of some fallen boulders were subsequently measured. By means of in-situ surveys, it was possible to reconstruct the cliff's geo-structural layout in detail. A rockfall back-analysis was subsequently performed along seven critical profiles of the entire slope (surface area of about 4000 m2). The results of this numerical modelling using the lumped-mass method were then used to map the kinetic iso-energy curves. In the triggering area of the debris flow, for a falling boulder of 1 m3, the mean kinetic energy was estimated at 120 kJ, this value being equivalent to an impact force, on an inclined surface, of some 800 kN. After landing, due to the locally high slope gradient (about 45°), and low angle of trajectory at impact (about 23°), some boulders slid down the slope as far as the endpoints. The maximum depth of penetration into the ground by a sliding block was estimated at about 16 cm. Very likely, owing to the high impact force of boulders on the saturated soil slope outcropping at the cliff base, the debris flow was triggered under undrained loading conditions. Initial failure was characterized by a translational slide involving a limited, almost elliptical area where the pyroclastic cover shows greater thickness in comparison with the surrounding areas.

BackgroundUncertainties exist in the magnitude and outbreak of debris flow disasters, resulting in significant loss of lives and property to human society. Improved identification of debris flow susceptibility areas can help to predict the location and sphere of influence of debris flow disaster, thus accurately assessing the risk of debris flow disaster and reducing losses caused by such a disaster. The dry-hot valleys of Basu County in the Eastern Qinghai-Tibet Plateau are typical areas of high debris flow incidence, mapping of debris flow susceptibility identification and regional risk assessment is needed in this area.ResultsThe parameters improved Flow-R model was first applied to identify debris flow susceptibility areas in Basu county using the digital elevation model, flow accumulation, slope, plan curvature, and land use data, followed by debris flow risk assessment. The Flow-R model can output high result accuracy of high-resolution susceptibility to debris flow identification on a regional scale with less data, and its accuracy value is 87.6%, indicating that the susceptibility to regional debris flow disaster is credible. This study provides a useful basis for effective prevention of regional debris flow disasters in the future, and provides a useful method for effectively identifying the debris flow susceptibility areas and assessing the related risk in large-scale areas.Conclusions(1) The debris flow susceptibility areas in Basu County covered 97.04 km2 (0.79% of the study area), distributed mainly in the Nujiang River Valley, Lengqu tributaries, and both sides of National Highway 318. (2) The debris flow susceptibility areas were dominant in zones characterized by an altitude range of 3000–4000 m, a plane curvature of − 2/100 m−1 to 1/100 m−1, and a low slope of 20°–40°. In addition, the susceptibility areas were dominant in the unused land and less prevalent in the water area. The highest and lowest susceptibility values were observed for cultivated and unused lands, respectively. (3) The debris flow risk in the study areas accounted for 0.82 km2 and revealed a distribution of high-risk debris flow along roads. The areas with a high debris flow risk were mainly distributed along the mainstream of the Nujiang River, which is the main future protected area.

Debris flow is a typical natural disaster in the middle reaches of the Dadu River, which seriously threatens the safety of life and property of local residents. However, there is currently a lack of a comprehensive analysis methods applicable to the blockage of river channels by debris flow in the Dadu River basin, limiting disaster prevention and mitigation in this area. Based on previous large-scale model tests carried out in the middle reaches of the Dadu River, the debris flows are divided into dam-type debris flows and submerged debris flows. The calculation formulas for the maximum travel distance of the two kinds of debris flows entering the river are obtained via theoretical derivation. The formulas for calculating the length and volume of debris flow accumulation are derived, and the relationship between the debris flow loss coefficient and river blocking degree in the middle part of the Dadu River is analyzed. An identification method of river blocking by debris flow is put forward in this study. By calculating the maximum blocking degree, S (the ratio of the maximum driving distance of the debris flow to the width of the river), and the volume of the source materials needed to form a debris flow dam under the conditions that the debris flow does not reach the opposite bank (V1), reaches the opposite bank but does not block the river (V2), and reaches the opposite bank (V3), the form of debris flow blocking the river is distinguished. When S = 1, V > V3, complete blockage occurs; when S = 1, V > V2, the river is mostly blocked; when S < 1, V > V1, the river is half-blocked. This study established an identification method of river blocking by debris flow, providing a basis for early warning for river blocking and disaster prevention in the middle reaches of the Dadu River.

It is quite common in highway engineering that building a bridge across a debris flow gully to prevent roadbed from damage by strike of debris flows. As bridges are designed with the purpose to protect their piers against debris flows, it is crucially important for engineers to determine the magnitude of the Impact Force Exerted by Boulders Transported (IFEBT) in rush torrents. In view of the theory of energy conservation, a formula is introduced in this paper to calculate the IFEBT with appreciable improvement compared to the commonly used equations, in which only the two types of structures (cantilever and simply supported) are taken into account in modelling. The Thornton elastoplastic contact criterion is included in the formula in consideration of buffer effect of two-phase debris flow on bridge piers and dynamic responses of bridge upper-structure. Comparisons on calculation accuracy are elaborately made between our improved formula and previous methods in a case study of Den Jigou Bridge. It is found that according to our proposed method the values of IFEBT obtained in circumstances of varied velocity and boulders sizes are lower than the ones calculated by previous methods. Providing the depth of debris flow body in the two-phase condition is up to 2.4 cm, there is a considerable decrease of 21% in the value of IFEBT. In the meantime, a decrease of 1.4% in the IFEBT value is attained in consideration of the inertia force of the bridge's upper-structure. In addition, it is feasible to dissipate impact energy of IFEBT when low elasticity modulus and high decrement material are used in practical engineering.

Evaluating the flood discharge and deposition process of a debris flow is important for risk assessment, management, and design of possible supporting works for geo-hazard mitigation. The movement and deposition process of a typical debris flow gully in southern Gansu province, China, was simulated using the Soil Conservation Service-curve number (SCS-CN) approach and a two-dimensional finite model (FLO-2D PRO model) coupled with geographic information systems. Runoff volumes and depths were obtained by the use of the SCS-CN model using different precipitations and different intervals. The deposition, velocity, impact force, and influence zone of the debris flow were simulated with the FLO-2D PRO model based on the results of the SCS-CN method. Simulation results for a storm that occurred on 12 October 2010 suggest a maximum flow velocity of 23.1 m/s, a maximum deposition depth of 27.9 m, and a hazard zone of about 0.414 km2. These results were consistent with measured results from the documented debris flow. Verification demonstrated that model results could be used to help predict disaster-causing debris flows, thus helping to protect the lives, property, and economy of the local population.

Debris flow normally occurs after heavy rains in mountainous regions with multiple surges. Flexible barriers are installed in torrents to intercept debris flows in an early stage. For the safer design of a flexible barrier installed in the upstream, the forces on the barrier invaded by debris flows should be taken into consideration. An outdoor physical modelling facility was utilized to study the interaction between debris flows and a flexible barrier. Three continuous debris flow impact tests were conducted to investigate the performance of a flexible barrier affected and overflowed by multiple surges of debris flow. A parameter named Initial Block Ratio (IBR) is introduced in this study to describe the initial condition of a flexible barrier filled by the earlier debris flow surges. By analysing the results of these tests, the dynamic response of a flexible barrier under the impact of multiple surges of debris flow is studied, and the influence of IBR on the interaction of debris flow with the flexible barrier is investigated. Based on the findings of the experimental study, a new simple method is proposed to calculate the loads on a filled flexible barrier overflowed by debris flow. By comparing with the measured impact force in the overflow test, this method has a good performance and can be utilized in design analysis with further calibration.