Effects of particle shape on the cushioning mechanics of rock-filled gabions
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RESEARCH PAPER
Effects of particle shape on the cushioning mechanics of rock-filled gabions Yuchen Su1 • Clarence E. Choi2 Received: 23 February 2020 / Accepted: 12 September 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Rock-filled gabions are commonly installed in front of reinforced concrete structures to reduce concentrated impact loads induced by rock fall and boulders entrained in debris flows. The cushioning performance of rock-filled gabions may vary depending on the shape of rock fragments used. In this paper, a parametric study was carried out using the discrete element method to discern the effects of particle shape on the cushioning performance of rock-filled gabion against dynamic boulder impact. Four particle sphericities were adopted to model angular, sub-angular, sub-rounded and rounded particles. DEM simulations reveal that the boulder penetration depth decreases with particle angularity. Thus, a thicker cushioning layer should be used in design if particles are rounded. More importantly, the impact and transmitted forces on a reinforced concrete barrier increased with particle angularity. This is because angular assemblies have more contact points, which enable more stable force chains that can sustain higher loads. The load diffusion angle for rounded particles is up to 20° larger compared to angular particles, suggesting that as particle angularity governs the load spreading ability of a cushioning layer. In general, rocks with rounded morphology should be adopted where possible to reduce transmitted loads and distribute loads more uniformly. Keywords Debris flow Discrete element method Particle shape Rigid barrier Rock-filled gabion Rock fall
1 Introduction Debris flow consists of a mixture of poorly sorted sediments, ranging in size from clay to boulder [13, 40]. The mechanism of particle size segregation enables large boulders to migrate to the front of a flow [41]. These boulders can then induce highly concentrated loads, which may cause significant damage to infrastructure [5, 11, 44, 45, 55, 59]. To arrest these boulders, reinforced concrete barriers are commonly constructed along the predicted flow paths [6, 18, 19, 24, 28, 30, 31, 34]. In front of these barriers, a layer of rock-filled gabion is commonly installed for additional protection.
& Clarence E. Choi [email protected] 1
College of Mechanics and Materials, Hohai University, Nanjing 210098, China
2
Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong SAR, China
To study the performance of cushioning layers, largescale boulder impact tests are commonly used [20–23]. Ng et al. [29] modelled up to six successive boulder impacts at an energy level of 70 kJ on a rock-filled gabion cushioning layer in front of a reinforced concrete barrier. They reported that by adopting rock-filled gabion cushioning layer, the design impact load can be reduced by a factor of two. The load reduction is mainly attributed to the collapse and
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