Multiscale numerical approach to assess impact forces on cylindrical barriers by debris flows

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 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.

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.

Owing to a recent abnormal weather, landslide and debris flow`s occurrence causes that damage of the urban increases rapidly. Therefore, when the disaster occurres, the disaster prevention method should be required. So, utilization of inactive space, such as a park, retarding basin, reservation area, the ground and parking lot when the urban forms reduces the damage of sediment disaster. It needs development of induction technology. Furthermore, it is necessary to review the induction wall influence by debris flow`s impact force. This study accomplishes about induction wall influence review by debris flow`s impact force. Now facilities and the technology guiding control to landslide and debris flow do not exist. In Japan training wall about reduction method from the damage of lava flow is being installed, but that kind of facilities does not exist in Korea. However, a scale and frequency of landslide and debris flow increases year after year. In the case that the urban forms near mountainous district, technical development of guide control should be needed for reducing damages from landslide and debris flow.

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.

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

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 flows are one of the perilous landslide-related hazards due to their fast flow velocity, large impact force, and long runout, in association with poor predictability. Debris-flow barriers that can minimize the energy of debris flows have been widely constructed to mitigate potential damages. However, the interactions between debris flows and barriers remain poorly understood, which hampers the optimal barrier installation against debris flows. Therefore, this study examined the effect of barrier locations, in particular source-to-barrier distance, on velocity and volume of debris flows via the numerical approach based on smoothed particle hydrodynamics (SPH). A debris-flow event was simulated on a 3D terrain, in which a closed-type barrier was numerically created at predetermined locations along a debris-flow channel, varying the source-to-barrier distance from the initiation point. In all cases, the closed-type barrier significantly reduced the velocity and volume of the debris flows, compared to the cases without a barrier. When the initial volume of source debris was small, or when the flow path was short, the barriers effectively blocked the debris flow regardless of the source-to-barrier distance. However, with a long flow path, installation of the barrier closer to the initiation location appeared more effective by preventing the debris volume from growing by entrainment. Our results contribute to a better understanding of how source-to-barrier distance influences debris-flow behavior, and show that the methodology presented herein can be further used to determine optimum and efficient designs for debris-flow barriers.

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.

In order to effectively prevent and control debris flow disasters, it is one of the most effective engineering measures to construct a blocking project in the valley section of the circulation section to actively reduce the flow and velocity of debris flow. The check dams is taken as a control structure to intercept the solid materials of flush flood and debris flow in the channel, which play an important role in debris flow prevention and control project. However, the huge impact force of debris flow often causes the check dam to be destroyed. Based on the theory of fluid–solid coupling, by means of structural dynamics simulation software, fluid dynamics simulation software and coupling plane data transfer software, numerical simulation of the interaction between debris flow and the check dam has been carried out. Research results indicate that (1) the overflow section is subjected to the impact of the debris flow greater than the abutment; (2) debris flow impact only has a greater impact on a certain depth of the check dam, and the impact beyond this range is less. The numerical simulation results can provide data support for the design and optimization of the check dam.

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.

Impact of debris flow consists of two distinctive phases due to its physical composition. One is the dynamic impact from fluid phase, and the other is collision from the solid phase. At present, there is no effective way to differentiate these two phases of impact. An empirical mode decomposition (EMD)-based signal process method was proposed in this paper to extract fluid and solid impact force of debris flow from the mixed signal. Miniaturized flume tests have been carried out with 14 work conditions, and the impact signals were captured by a digital logger. From the experiment, frequencies of fluid phase and solid phase impact signals were identified in the range of 0.05–2 Hz and 300–600 Hz, respectively. The impact signals from solid and liquid phases were reconstructed using the proposed method. In addition, the impact force of fluid phase that measured directly from the flume tests and calculated from isolated signals showed good agreement and the average difference was about 10%. However, large deviation of solid phase impact was observed especially when this method was applied to the full-scale debris flow events and the difference ranged from 26.33 to 61.47%. This proposed method provided an alternative approach to study the debris flow impact force in terms of slurry and large particles separately.

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.

ABSTRACTConcrete piers located in steep mountainous regions are highly susceptible to damage from debris flows. Existing studies often oversimplify debris flows as particle flows or equivalent fluids, neglecting their multiphase characteristics. In this paper, a three‐dimensional numerical model of debris flow‐bridge piers interaction is established based on the coupled CFD‐DEM approach. The Hertz–Mindlin (no‐slip) model and the Navier–Stokes equations are employed to describe the behavior of particle contacts and the fluid phase, respectively. An interface program compiled using user‐defined functions (UDFs) facilitates the transfer of information (drag, buoyancy, and viscous forces) between the fluid and particles. The accuracy of the model is validated by the simulation results of single‐particle settlement and underwater granular collapse. This study conducts a detailed investigation into the interaction mechanisms between the debris flow—bridge piers, considering the cross‐sectional shape of the piers and the solid volume fraction. It has been discovered that the shape of the bridge piers significantly influences the behavior of debris flows and the separation points. A power function effectively describes the relationship between the solid volume fraction and the peak impact force coefficient, Cd. Simplifying debris flows to dry granular flows or equivalent fluids may lead to an underestimation of the impact pressure.