The destructive nature of debris flows is mainly caused by flow bulking from entrainment of an erodible channel bed. To arrest these flows, multiple flexible barriers are commonly installed along the predicted flow path. Despite the importance of an erodible bed, its effects are generally ignored when designing barriers. In this study, three unique experiments were carried out in a 28 m-long flume to investigate the impact of a debris flow on both single and dual flexible barriers installed in a channel with a 6 m-long erodible soil bed. Initial debris volumes of 2.5 m³ and 6 m³ were modelled. For the test setting adopted, a small upstream flexible barrier before the erodible bed separates the flow into several surges via overflow. The smaller surges reduce bed entrainment by 70% and impact force on the terminal barrier by 94% compared to the case without an upstream flexible barrier. However, debris overflowing the deformed flexible upstream barrier induces a centrifugal force that results in a dynamic pressure coefficient that is up to 2.2 times higher than those recommended in guidelines. This suggests that although compact upstream flexible barriers can be effective for controlling bed entrainment, they should be carefully designed to withstand higher impact forces.

Immersive media technologies, such as virtual and augmented reality, have recently enabled a more holistic way to comprehend natural hazards. In this work, we aim at visualizing the temporal and spatial evolution of a debris flow in a virtual reality environment. We develop a framework to integrate the output results obtained from a debris flow numerical model into virtual reality. To guide the framework, a real debris flow event, which happened in Hunnedalen (Norway) in 2016 and blocked a road network, is considered as a case study. The debris flow is back-calculated using a depth-averaged numerical model and the simulation results are imported into a dedicated game engine to construct a digital model of the debris flow event. The debris flow is visualized using a Head-Mounted Display. We therefore discuss a wide range of potential applications of virtual reality to manage and grasp landslide phenomena: training for rescue operations; improving decision-making; studying early warning systems, and educating communities affected by natural hazards. We finally provide a quantitative evaluation of the hazard perception for a road user. We show that the debris flow movement is perceived at variable delayed times from the triggering of the landslide, depending on the position along the road where the debris flow is observed. Evaluating the realistic perception time of the natural hazard may be fundamental to designing more effective road networks, signs, and mitigation measures.

Flexible barriers may be installed upstream in debris flow channels to reduce entrainment of bed material. Simulating both the entrainment and the impact on a barrier by the same numerical tool remains challenging. For this purpose, a three-dimensional one-phase material point method (MPM) software is used herein to back-calculate two large-scale flume experiments. These experiments were conducted to measure the entrainment of an erodible bed and the impact on a flexible barrier. To simulate the entrainment of the wet bed, a Mohr–Coulomb softening model is introduced. In the model, the apparent friction angle of the bed material decreases as a function of the distortional strain, effectively reproducing the pore pressure increase observed in the experiments. From the tests and the numerical simulations, we identify two main mechanisms leading to entrainment: (i) the direct rubbing and colliding effect of the flow on to the bed and (ii) a significant bed shear strength reduction. Concerning the first mechanism, existing models only consider the rubbing of the bed surface by a shear stress parallel to the slope. However, we observe that a ploughing-type erosion occurs due to normal stresses acting on the bed in the flow direction. The additional ploughing explains why beds which are mechanically stronger than the flow can also be partly entrained. Larger entrainment volumes are found when the bed material loses shear strength due to pore pressure buildup that eventually leads to a self-propelled entrainment where the bed no longer has frictional strength to carry its own weight.

No abstract

<p>Rainfall-induced landslides represent an important hazard in mountainous regions worldwide. Landslides commonly impact the functioning of infrastructure assets such as roads and railways and occasionally damage buildings or result in fatalities. In the Nordic region, rainfall-induced landslides constitute a significant hazard, accounting for a considerable amount of Norway's national landslide database entries.</p> <p>Because of climate change, the frequency of rainfall and soil moisture conditions that usually trigger landslides will become more variable. This leads to weaker predictions for the location and frequency of future landslide events from current models. Understanding how the landslide hazard will change can help plan mitigation along linear infrastructure and reduce the risk to the population.</p> <p>Here, we report the findings from the NordicLink project, financed by Nordforsk, where a methodology to characterise landslide hazard at a global scale has been adopted to develop Nordic hazard maps.</p> <p>The methodology to characterise the landslide hazard at a global scale has been developed within the activities of the "Global Infrastructure Resilience Index" (GIRI) project, funded by the Coalition for Disaster Resilient Infrastructure (CDRI). The method combines landslide susceptibility and rainfall to compute landslide probability at a global scale. The susceptibility map classifies terrains into five susceptibility classes by combining slope, vegetation, lithology, and soil moisture information from global datasets. Rainfall information has been obtained from the W5E5 dataset for the period 1979-2016 and the IPSL-CM6A-LR climate model from ISIMIP3b dataset SSP126 and SSP585 scenarios for the period 2061-2100. To characterise the rainfall triggering potential, the 24 h rainfall intensities have been used to distinguish between five rainfall hazard classes. Finally, a hazard matrix has been employed to combine landslide susceptibility and rainfall. The output is a probabilistic hazard map covering the world with a resolution of three arc seconds (approximately 90 m at the equator).</p> <p>In the NordicLink project, higher-quality Nordic-scale data and landslide inventories are used as input to the above-mentioned procedure to obtain probabilistic hazard maps covering Norway, Sweden, and Finland. The study concludes with a comparison between the NordicLink hazard maps and the (global) GIRI model. As expected, landslide hazard is higher in western Norway and decreases towards the East. Finland is the country with the lowest landslide hazard.</p>