Study of dynamic debris impact load on flexible debris-resisting barriers and the dynamic pressure coefficient

Abstract

The use of steel flexible barriers to mitigate landslide risk on natural hillsides is becoming common in the last decade in Hong Kong. The current design approach for this kind of barrier structure involves the adoption of the hydrodynamic load model to predict dynamic impact forces, followed by non-linear structural analyses of flexible barriers using numerical programs based on the pseudo-static method. From local guidelines, the dynamic pressure coefficient is taken as 2.0. This empirically considers the effect of impacts from boulders up to 2.0m in diameter. With a view to rationalising the design approach, a series of physical impact tests and numerical analyses was conducted to investigate the dynamic impact on flexible barriers and the resulting barrier response. The tests involved up to 9m³ of debris resisted by a 1.5m high steel barrier, conducted at the 28m long flume facility at the Kadoorie Centre, Hong Kong. Numerical modelling using computer programs LS-DYNA and NIDA-MNN was conducted to analyse the dynamic response. The study aims to evaluate the dynamic pressure coefficient and to verify the current design approach. Results indicate that a coefficient of 1.0 is in general appropriate for design purposes for debris comprising primarily water and fine-grained particles.

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

“…Based on the impact process shown in Figure A1b and A1g-A1i illustrate alternative simplified solutions that rely on barrier deformations, cable forces, and ring-ring contact forces. These solutions have been adopted in experimental and in-suit tests to estimate the impacts of geophysical flows on flexible barriers (Ashwood & Hungr, 2016;Lam et al, 2022;Ng et al, 2017;Song et al, 2022;Tan et al, 2019;Wendeler, 2016). For instance, the spring solution (Figure A1g) is expressed as:…”

“…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.…”

“…Estimating the peak impact of geophysical flows on flexible barriers for practical designs relies primarily on analytical solutions, including hydrostatic, hydrodynamic and hybrid models (Berger et al., 2021; Kwan & Cheung, 2012; Lam et al., 2022; see Appendix A). They require theoretical functions and empirical coefficients in conjunction with the Froude number (Fr) of impinging flows, which have been investigated in extensive studies (Kong et al., 2022; Li, Zhao, & Soga, 2021; Song et al., 2021).…”