Design and optimisation of a protective device for bridge piers against debris flow impact

In Western China, a large number of bridges are located in debris flow gullies and are exposed to a great risk of damage in case of a geological disaster. To ensure the safety of the bridge and extend its service period, in this study, we propose a modular protective device for bridge piers against the impact of debris flow, especially large boulders. The device is composed of a set of independent modules in the form of a closed-cell aluminium foam-filled composite structure (AFCS) that are set at predetermined spacings and fixed by prestressed steel fasteners. The mechanical behaviour and energy absorption characteristics of five AFCS configurations were evaluated by quasi-static compression testing using both experimental and numerical modelling methods, which produced similar results. The two-layer foam-filled lattice structure AFCS05 exhibited the best comprehensive energy absorption performance, and the effects of the material and geometric parameters on the performance were investigated based on the validated finite element models. A prototype protective device based on the AFCS05 design was attached to a model bridge pier. The dynamic response of the prototype indicated that the device prolonged the impact duration and reduced the largest impact force by 84.89%, and absorbed 81.96% of the impact kinetic energy, which effectively protected the pier. The device design and production can be standardised, making it convenient for installation and on-site repair.