The effects of upstream flexible barrier on the debris flow entrainment and impact dynamics on a terminal barrier

Abstract

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 m<sup>3</sup> and 6 m<sup>3</sup> 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.

How Flexible, Slit and Rigid Barriers Mitigate Two‐Phase Geophysical Mass Flows: A Numerical Appraisal

“…These analytical models, empirical coefficients ( κ and α ), and the Fr ‐related models established for rigid and flexible barriers are briefly introduced in Text S6 in Supporting Information S1. To facilitate a comprehensive analysis, a unique data set, comprising normalized data obtained from analytical models (Li et al., 2021; Song, Zhou, et al., 2021), empirical relations (P. Cui et al., 2015), experiments (Armanini et al., 2020; Choi et al., 2020; Hu et al., 2020; P. Cui et al., 2015; Song, Chen, et al., 2021; Song, Zhou, et al., 2021; Vicari et al., 2021), field events (Hübl et al., 2009), practical design values (Armanini, 1997; Hungr et al., 1984; Kwan & Cheung, 2012; Wendeler, 2016) and numerical results, is plotted in Figure 10 for comparison and also summarized in Table S1 in Supporting Information S1.…”

“…To facilitate a comprehensive analysis, a unique data set, comprising normalized data obtained from analytical models (Li et al, 2021;, empirical relations (P. Cui et al, 2015), experiments (Armanini et al, 2020;Choi et al, 2020;Hu et al, 2020;P. Cui et al, 2015;Vicari et al, 2021), field events (Hübl et al, 2009), practical design values (Armanini, 1997;Hungr et al, 1984;Kwan & Cheung, 2012;Wendeler, 2016) and numerical results, is plotted in Figure 10 for comparison and also summarized in Table S1 in Supporting Information S1.…”

“…Fundamentally, the overall impact processes of geophysical flows impacting flexible, slit, and rigid barriers are predominantly governed by two modes: pile‐up (momentum jump reflected upstream) and runup (high energy jet deflected vertically) (e.g., Kong, Li, & Zhao, 2021; Song, Choi, Ng, & Zhou, 2018; Song et al., 2017; Vicari et al., 2021), as illustrated in Figure 1. When a geophysical flow first impacts a flexible, slit or rigid obstacle, a slow flow produces a gentle pile‐up of the jammed debris upstream of the barrier (Figures 1a1, 1b1 and 1c1), whilst a faster flow gives rise to a runup or vertical jet impact (Figures 1a3, 1b3 and 1c3).…”

“…Abundant studies have investigated the interactions between geophysical flows and flexible barriers. Both the full‐scale and large‐scale tests offer valuable data but are relatively expensive (Brighenti et al., 2013; DeNatale et al., 1999; Tan et al., 2019; Vicari et al., 2021). Although the small‐scale experiments enable systematic investigations under well‐controlled conditions, they commonly use simplified flexible barriers, such as impermeable membranes (Ashwood & Hungr, 2016; Song, Zhou, et al., 2021) and uniform plastic meshes (Wendeler et al., 2019), which may fail to recover the barrier permeability and nonuniformity.…”

Bi‐Linear Laws Govern the Impacts of Debris Flows, Debris Avalanches, and Rock Avalanches on Flexible Barrier

“…For example, the cable‐based solution (Ferrero et al., 2015; Ng et al., 2017) calculates the total impact load exerted on a flexible barrier by summing the normal impact forces on all its horizontal supporting cables. This solution converts the cable tensile force to the impact load normal to the barrier face and has been widely adopted in experiments (e.g., Lam et al., 2022; Song et al., 2022; Vicari et al., 2021). The spring solution applies Hooke's Law to estimate the impact load acting on a flexible barrier, using an equivalent barrier stiffness and the maximum barrier deflection in the flow direction.…”