Numerical study on the damage evaluation of a check dam under boulder-enriched debris flow impact

Debris flows cause recurrent interruptions and permanent damages in rural road networks, representing significant economic losses. Embankments are road assets frequently exposed to debris flows, especially in mountainous areas. The potential risk of infrastructure exposed to debris flows can be assessed in terms of the probability of expected damage based on fragility curves. The aim of the study is to develop fragility curves for road embankments exposed to debris flows representative to the expected physical damage and capacity loss. Two conceptual models are proposed to describe the impact and erosion of debris flows that run perpendicularly to road embankments. Probabilistic models are then developed in terms of limit state functions and the simulation of potential scenarios. The resulting models are finally fit to log-normal distributions and compared to historical data. Headcut erosion has higher probabilities of occurrence compared to sliding failure caused by the impact of debris flow. Lower road embankments present higher probabilities of failure to the impact of debris flows, especially for dense flows. Whereas, longer interaction times of less dense flows increase the probability of headcut erosion. Two-lane roads may present 50% more probabilities of headcut erosion compared to multilane roads for similar debris flows intensity.

Provision of mitigative and control measures are necessary for a pipeline to survive in a debris flow event, but the forces in the soil-structure interaction must be estimated for the design. Based on physical experiments in a flume and numerical analyses, this paper presents a method for estimating the impact drag force on laid-on-seafloor and suspended (free-span) pipelines. The method may be applied in practice to a wide range of debris flow impact situations. Two conceptual mitigative and control measures for design against submarine debris flow impact are discussed: the berm-protected laid-on-seafloor pipeline and the cable-controlled pipeline system. The latter may be applied to both the pipeline-on-seafloor and suspended pipeline situations. The observations from a laboratory flume experiment with a model pipe protected by an upstream berm, and complementary Computational Fluid Dynamics (CFD) numerical analyses results are presented. The results from the flume experiment showed that there is a possibility to protect a pipeline provided the protective structure can withstand the basal shear and lift forces induced by the water and debris flows on its surfaces. The results may be used for conceptual and preliminary design purposes, and the analysis methodology may be tailored to other situations or the detailed design. The feasibility of the two conceptual mitigative and control measures is briefly discussed. Introduction Fast moving, flow-like submarine landslides are among the most destructive and frequent occurring geohazards with potential to seriously damage seafloor installations. Estimation of the forces from a submarine debris flow impact is required for the pipeline design and routing. A common practice is to protect the pipelines by burying in areas where it could be affected by debris flow impact. Besides the construction difficulties associated with the burial, a buried pipeline may become exposed during its course of service due to seafloor scour and wave-induced or operational uplift forces. Further, it is likely that a buried pipeline in a debris flow pathway becomes exposed just prior to the impact due to seafloor erosion from the water displaced by the debris front or later by the debris flow itself. Upon impact with a pipeline, the maximum drag force is exerted shortly after the contact, provided that the debris flow is not supplied by consecutive failures upstream trailing at higher velocities. The magnitude of the drag force drops quickly as the upstream debris flow velocity decreases. If a pipeline can withstand the drag forces exerted upon and shortly after the impact, it will most likely survive the entire event. Without provision of protective measures, a pipeline alone cannot withstand the debris flow impact forces. The mitigative and control measures may only be designed once the debris flow impact forces are estimated. For pipelines, the methods available in the literature mainly address the problem of forces on a buried line in an unstable zone as opposed to the debris flow impact[1, 2]. However, as is discussed below recent developments in the field have shed new light on the problem of submarine debris flow impact forces on pipelines[3, 4]. The impact forces on pipelines may be mitigated or controlled by techniques such as constructing protective berms (either on the upstream or both sides of the pipe) or mooring the line to the seafloor using cables and suction caissons. The feasibility and constructability of each technique depends on many factors which have to be evaluated on project basis to a defined set of criteria. This paper briefly outlines a method to estimate the impact forces induced on suspended (free-span) and laid-on-seafloor pipelines. It then discusses two conceptual mitigative and control measures: the berm-protected laid-on-seafloor pipeline and cable-controlled pipeline system. The latter may be adopted for both laid-on-seafloor and suspended pipelines. To that extent, the results from a laboratory experiment and series of CFD simulations for an upstream berm-protected laid-on-seafloor pipeline model are discussed. The analysis results may be used for conceptual and preliminary design purposes. The feasibility of the two conceptual measures is also briefly discussed.

The shale gas well station plays a critical role in the extraction of shale gas, and its safety status exerts significant influence not only on shale gas production but also on the ecological balance of the surrounding environment. To investigate the response characteristics of the shale gas well station under the impact of tailings dam failure debris flow, a comprehensive analysis was conducted using a combination of physical modeling and numerical simulation. The analysis focused on the dynamic inundation process and the impact siltation law caused by the downstream flow of tailings dam failure debris at the shale gas well station. The depth of inundation and the extent of siltation damage were employed as key parameters for characterization. Experimental findings revealed that the downstream mudflow inundation process could be divided into three distinct stages: rapid increase (0–60 s), steady increase (60–106 s), and slow advance (106–250 s). The pattern of mudflow siltation height variation at the well station exhibited an initial rise, followed by a subsequent decline and eventual stabilization. The highest siltation volumes recorded at measurement points A to D were 4.4, 4, 5.2, and 6 m, respectively. Additionally, by employing computational fluid dynamics, numerical calculations were performed under unprotected conditions, with the error between the calculated conclusions and the test results not exceeding 15%. Furthermore, the blocking effect of 8 and 16 m debris flow blocking dam on the debris flow was thoroughly investigated. The study demonstrated that the check dam with a height of 16 m yielded the most effective blockage, resulting in the highest sediment siltation height of 0.4 m. The research results provide some reference for the prevention and control of debris flow disasters.

This paper examines the environmental and economic impact of cloudburst-triggered debris flow and flash flood in four villages of Uttarkashi district, Uttarakhand Himalaya. On 18th July 2021 at 8:30 p.m., a cloudburst took place on the top of the Hari Maharaj Parvat, which triggered a huge debris flows and flash floods, affecting 143 households of four villages of downstream areas. Immediately after the cloudburst occurred, the authors visited four affected villages—Nirakot, Mando, Kankrari, and Siror. A structured questionnaire was constructed and questions were framed and asked from 143 heads of affected households on the impact of debris flows and flash floods on people’s life, settlements, cowsheds, bridges, trees, forests, and arable land in and around the villages. The volume of debris, boulders, pebbles, gravels, and mud was assessed. It was noticed that all four villages got lots of destructions in terms of loss of life—people and animals, and property damage—land, crops, and infrastructural facilities. This study shows that the location of the settlements along with the proximity of the streams, which are very violent during the monsoon season, has led to the high impact of debris flow on the affected villages. We suggest that the old inhabited areas, which are located in the risk zones, can be relocated and the new settlements can be constructed in safe places using suitability analyses.

Assessing debris flow impact on flexible ring net barrier: A coupled CFD-DEM study

<p>The presentation considers natural-technological accidents that were triggered by the impacts of debris flows on infrastructure facilities. As input data, the information collected in the author's database of natural-technological accidents and emergencies that occurred in the Russian Federation from 1991 to 2020 was used. Based on the statistical and geographical analysis of the data, the main types of natural-technological accidents caused by the impact of debris flows have been identified. Various linear structures are mostly exposed to the debris flows. The most vulnerable to the debris flow impacts are facilities of the transportation infrastructure, as well as power lines, pipelines, and other lines of communication. During the above period under consideration, road and railway accidents, traffic disruptions, accidents in power, warm, water, and gas supply systems caused by debris flows were registered in the database. Natural-technological accidents and emergencies due to debris flow impacts on the infrastructure were recorded in the Far East of the Russian Federation including Sakhalin and Magadan Regions, and Primorsky Territory, as well as in the Republics and Territories of the North Caucasus. The long-term average frequency of their occurrences was estimated; their seasonal distribution was investigated. The proportion of natural-technological accidents caused by the impact of debris flows, in the total number of events caused by other adverse and hazardous natural processes and phenomena, is relatively small. However, the potential danger of such impacts must be taken into account when constructing transportation and other lines of communications, especially in areas of increased risk of debris flows.</p>

Physical building vulnerability to debris flows is defined as the potential damage degree of buildings for a given debris flow intensity. In this paper, the physical characteristics of both debris flow intensity and building response are considered. Uncertainties in building capacity and debris flow intensity are explicitly quantified to evaluate the damage probability of a typical reinforced concrete building subjected to debris flow impact. Four damage states with clear failure mechanisms are defined using multi-source information from field observations, numerical simulation, and expert experience. Two series of fragility models are proposed based on practical debris flow impact pressure models. Several debris flow intensity measures are investigated. A better indication can be provided using the intensity measure that represents a specific failure mechanism; e.g., impact force (hv2) for force-dominated failures or overturning moment (h2v2) for moment-dominated failures, where h and v are debris flow depth and velocity, respectively. The corresponding fragility surfaces best express potential building damage. The intensity thresholds in the proposed fragility curves are consistent with those in empirical vulnerability curves. The methodology presented in this paper promotes vulnerability assessment using physics-based modeling, leading to a more reliable evaluation of building damage caused by debris flows.

Based on the coupled SPH-DEM-FEM numerical method, this paper analyzes the dynamic interaction of solid debris flow particle-liquid debris flow slurry-retaining dam in order to explore the dynamic response of retaining dam under the impact of the solid-liquid two-phase debris flow and delves into the process of the debris flow impact on the dam, the impact force of debris flow, and the elastic-plastic time-history characteristics of the dam under different slopes of trapezoidal grooves. The calculation results show that the coupled SPH-DEM-FEM method can vividly simulate the impact behavior of the solid-liquid two-phase debris flow on the dam, reproduce the impact, climbing, and siltation in the process of the debris flow impact; the dynamic time-history curve of the retaining dam is consistent with the law of the literature, and the result of the debris flow impact force obtained is close to that of the empirical formula. Moreover, this paper studies the impact force distribution of the debris flow impact process. The results have a certain reference value for the study of the dynamic response of the retaining dam under the impact of the solid-liquid two-phase debris flow and the engineering design of the debris flow-retaining dam.

Because of the climate warming and the serious ecological damage of the valley slope, the frequency of debris flow in the valley is increasing frequently. The solid deposits in the debris flow are, transported at high speed under the action of water flow and self-gravity, have a great impact on the piers along the line, which greatly destroys the integrity and stability of the pier. Through the theoretical analysis and numerical simulation of debris flow, the transient dynamic response of the pier under the impact of debris flow is analyzed. It is concluded that the pier is subjected to the punching and shearing form load, and the impact damage of the coarse solid particles in the debris flow to the pier is more obvious. The pier displacement reaches the maximum at the second impact of the debris flow; the maximum displacement is 10.9mm, which appears at the 5m above the bottom of the pier. A tensile stress concentration zone appears at the bottom of the pier, and the maximum tensile stress is 1.84MPa, which exceeds the concrete strength of the pier and so we can take corresponding measures to guard against this problem so as to ensure the safety of bridge structure.

Experimental study on the performance of CFRP-strengthened masonry structures under debris flow impacts

High-strength flexible net barriers have achieved a certain effect in mountainous debris flow prevention, but research on the mechanism of structural stress and deformation is still developing. This study first presents an analytical model based on the quasi-static mechanical equilibrium to evaluate the geometric nonlinearity and the load performance of the structure and then conducts a flume experiment to reveal the load mechanism of the structure. Then, a full-scale simulation is performed to investigate the deformation and failure of the flexible net barrier impacted by the debris flow via PFC3D software. The results show that the deformation of the flexible net barrier occurs not only in the direction of flow but also in other directions to make the structure force balanced under debris flow impact. The load impacting on the barrier is far less than the total impact force exerted by debris flow. The flexible barrier has an obvious effect to block a coarse debris flow, and the blocking capacity is related to the volume of debris flow and the slope gradient of the flume. The displacement patterns of loaded cable in the experiment and the simulation are different, but the cable under non-debris flow impact is only dragged by the mesh rope showing a regular parabolic shape, and the tension inside the flexible mesh is far less than that of the transverse cable. In addition, the model shows the failure characteristics of flexible barrier under large-scale debris flow, which plays a guiding role in practical engineering design of the structure.

With the increasing popularity of high-speed railway, more and more bridges are being constructed in Western China where debris flows are very common. A debris flow with moderate intensity may endanger a high-speed train traveling on a bridge, since its direct impact leads to adverse dynamic responses of the bridge and the track structure. In order to address this issue, a dynamic analysis model is established for studying vibrations of coupled train–track–bridge system subjected to debris flow impact, in which a model of debris flow impact load in time domain is proposed and applied on bridge piers as external excitation. In addition, a six-span simply supported box girder bridge is considered as a case study. The dynamic responses of the bridge and the running safety indices such as derailment factor, offload factor, and lateral wheel–rail force of the train are investigated. Some influencing factors are then discussed based on parametric studies. The results show that both bridge responses and running safety indices are greatly amplified due to debris flow impact loads as compared with that without debris flow impact. With respect to the debris flow impact load, the boulder collision has a more negative impact on the dynamic responses of the bridge and train than the dynamic slurry pressure. Both the debris flow impact intensity and train speed determine the running safety indices, and the debris flow occurrence time should be also carefully considered to investigate the worst scenario.

Experimental and numerical study on the performance of novel RC frame structure encased with shaped steel under debris flow impact

Debris flows often cause local damage to engineering structures by exerting destructive impact forces. The debris-flow–deformable-barrier interaction is a significant issue in engineering design. In this study, a large physical flume model test device was independently designed to repeatedly reproduce the flow and impact process of debris flow. Three physical flume tests were performed to investigate the effect of barrier stiffness on the debris flow impact. The flow kinematics of debris flow with three barrier stiffness values are essentially consistent with the process of impact–run-up–falling–pile-up. The development of a dead zone provided a cushion to diminish the impact of the follow-up debris flow on the barrier. The peak impact forces were attenuated as the barrier stiffness decreased. The slight deflections of a deformable barrier were sufficiently effective for peak load attenuation by up to 30%. It showed that the decrease of the barrier stiffness had a buffer effect on the debris flow impact and attenuated the peak impact force. And with the decrease of the barrier stiffness, when the barrier was impacted by the same soil types, the recoverable elastic strain will be larger, and the strain peak will be more obvious.

Rack railway systems, generally constructed in mountainous areas and particularly susceptible to debris flows, may undergo beam deformation and a decrease in line smoothness, thereby threatening the operational safety and stability of rack vehicles. To this end, a coupled dynamic model of vehicles-rack-bridge under the impact of debris flows is developed in this article and carry out the line test, incorporating both the nonlinear dynamic engagement behavior of the gear-rack and the nonlinear dynamic contact behavior of the wheel-rail. Subsequently, the impact of debris flows on the basic vibration characteristics and safety of the rack railway system is explored, and the threshold value for the horizontal stiffness of bridge bearings is further proposed, providing theoretical guidance for the construction and maintenance of steep gradient rack railways in mountainous areas. The results reveal that, under the working conditions studied in this article, the impact of debris flows exacerbates vibrations near the transverse natural frequency of the bridge. Furthermore, the vibrations and line changes of the rack induced by the debris flows have triggered unstable gear-rack engagement, consequently leading to the issue of gear and rack disengagement. Additionally, under the excitation of the debris flows, the maximum derailment coefficient of the vehicle can reach 0.88, indicating that it exceeds the safety limit of derailment coefficient and poses a threat to the train operation safety.