Overturning stability of L-shaped rigid barriers subjected to rockfall impacts

Abstract

Reinforced concrete barriers are commonly used as defence measures in hilly areas to contain falling boulders and landslide debris. These barriers are conventionally designed to satisfy the conditions of force and momentum equilibrium with a factor of safety. A major limitation of this approach is that the inertial resistance of the barrier is neglected such that the design could be over-conservative. This paper presents a novel displacement-based approach for the assessment of overturning stability of rigid L-shaped barriers subjected to rockfall impacts. Analytical solutions, which are derived based on conservation of momentum and energy, are used to take into account the contributions of the self-weight and thus the inertial resistance of the barrier in resisting an impact. The actual amount of energy transferred from the impacting boulder to the barrier is considered by including the coefficient of restitution between the two objects. The accuracy of the analytical solutions has been confirmed by laboratory impact experiments.Numerical assessments conducted using the new solutions indicate that a reasonably sized rigid barrier, due to its own inertial resistance, may adequately withstand the impact action of a heavy boulder rolling down a hillslope without relying on any anchorage to its support. A range of geometric design of the barriers with L-shaped cross sections also have been considered and analysed. The new approach presented in this paper is easy to apply in practice and will be useful for engineers designing concrete barriers as passive rockfall mitigation measures.

Finite element analysis for rockfall and debris flow mitigation works

“…For debris flows, the impact loading is commonly assumed to be in the form of an areal pressure. If boulders along the flow path are mobilised, they may be engulfed to form part of the flow and may accumulate at the front (Jakob and Hungr 2005; D r a f t 4 (Lam et al 2018b;2018c). In the force-based approach, the transient impact load acting on the barrier wall is assumed to be a sustained pseudo-static load.…”

Experimental and Analytical Assessment of Flexural Behavior of Cantilevered RC Walls Subjected to Impact Actions

“…This equal energy approach may over-state the flexural action if mitigating effects such as dissipation of energy on impact and inertial resistance generated from within the wall have not been accounted for. Both force-based and equal energy approaches as described can result in an overly-conservative design of the RC barrier (Kishi et al 2009, Lam et al 2018a.…”

Contact force generated by impact of boulder on concrete surface

“…A design impact force which is derived, typically, by employing momentum and energy principles as per stipulations by many codes of practices is essentially the equivalent static force (Eurocode 1, Australian standard AS 5100.2, Japanese code by Japan Road Association) [1][2][3][4]. Impact actions causing global movement (bending, sliding and overturning) can be represented by the analysis of an equivalent static force [5][6][7] whereas the local actions of the impact causing denting, local crushing, punching, and perforation would need to be analysed using a different approachan approach which involves consideration of the amount of force which is generated at the point of contact (referred herein as "contact force") [8,9]. Contact force lasts only for a very short duration, but the magnitude of the force can be many times higher than that of the equivalent static force [10,11].…”