Vehicle Impact Loading on Soil-Embedded Piles Installed near Slopes

Guardrails, composed of soil-embedded steel piles connected by a rail, are critical roadside safety barriers that protect errant motorists from hazards and reduce injury risks. The Midwest Guardrail System (MGS) is a widely adopted design due to its proven crashworthiness and adaptability, including installations on or near slopes. The standard MGS features 1.83-m (6-ft) W6 × 8.5 or W6 × 9 steel posts spaced 1.91 m (75 in.) apart and embedded 1 m (40 in.) deep in strong soils, meeting MASH 2016 criteria. However, when installed at the break point of a 2H:1V slope, the reduced soil support behind the posts can reduce impact resistance, leading to increased rotation and lateral deflection during impacts, potentially compromising the system’s redirection capability. This study evaluates the performance of soil-embedded posts in MGS installations on steep slopes using a series of dynamic bogie (surrogate vehicle) tests. Test results highlight the influence of post embedment and terrain conditions on system behavior, identifying configurations that maintain acceptable deflection and working width. These findings provide preliminary guidance for roadside barrier deployment near slopes, particularly in conditions that deviate from standard installation guidelines.