New light-weight concrete foam to absorb debris-flow-entrained boulder impact: Large-scale pendulum modelling

Abstract

Rock-filled gabions are widely used to attenuate concentrated impact loads exerted by boulders entrained in debris flows. However, rock fragments used to construct gabion may not always be available and the performance of rock-filled gabion can be highly variable, depending on size and angularity of the rock fragments used. In this study, light-weight concrete foam is proposed as an alternative cushioning material to overcome some of the limitations of rock-filled gabion. Physical large-scale pendulum impact tests were conducted to study the performance of concrete foam, which was used to shield a reinforced concrete barrier from boulder impact. Six successive boulder impacts were carried out at energies of up to 70 kJ. Two different concrete foam thicknesses, 0.4 m and 0.6 m, were investigated. Increasing the cushioning thickness from 0.4 m to 0.6 m can reduce the maximum transmitted load by 48% and 71% for the first and sixth impacts at an impact energy of 70 kJ, respectively. The larger cushioning thickness enhances load spreading on the wall and reduces stress concentration. Furthermore, the maximum penetration depth on the 0.4-m thick concrete foam is 0.29 m for the sixth impact at an impact energy of 70 kJ, which is equivalent to 72% of the initial cushioning layer thickness. Based on the existing design guidelines (ASTRA 2010) and the Gibson and Ashby model, the required minimum thickness for up to six successive impacts at an impact energy of 70 kJ is 0.58 m.