Experimental investigation of the response of guardrail posts embedded in road shoulder material under quasi-static and dynamic impact loading

The main functions of vehicle restraint systems (VRS) are to redirect errant vehicles and prevent them from entering an opposing lane or carriageway, as well as preventing them from colliding with structures along the road [1]. In the case of steel guardrail systems, fulfilment of these requirements greatly depends on the soil-post interaction, which influences the deformation and energy dissipations of the VRS during impact. To date, there is no unified method of modelling the behaviour of guardrail posts embedded in road shoulder material in crash tests simulations. For this reason, the influence of soil type and state as well as post characteristics on the observed motion of vehicle and VRS cannot be adequately evaluated, which is, however, necessary to improve and optimise a VRS without increasing the number of crash tests. This paper presents the findings of a series of static and dynamic full-scale loading tests conducted with different road shoulder materials and post types, the aim being to create an experimental database for modelling the soil-post interaction in crash test simulations. The novel dynamic and static testing techniques used ensures repeatability and enables the reliable evaluation and interpretation of the results. We found that not only the static and dynamic post response but also the failure mode are significantly influenced by the relative soil density and post embedment length. As long as there is no yielding of the post section, the dynamic post resistance varies with increasing impact energy until a maximum value, which depends on the dynamic horizontal bearing capacity of the post. Any further increase in impact energy has no influence on the post resistance.