Full-Scale Impact Test of Four Traffic Barriers on Top of an Instrumented MSE Wall

Abstract

This paper presents the results of four full-scale impact tests against barriers placed on top of an instrumented mechanically stabilized earth (MSE) wall. The impact was created by a head-on collision of a 2,268-kg bogie going at about 32.2 km/h. The barriers were New Jersey and vertical wall barriers with a 1.37-m-wide moment slab in 9.14-m-long sections. The wall was 1.52 m high with one panel and two layers of reinforcement. The reinforcement was 2.44-m-long strips, 4.88-m-long strips, and 2.44-m-long bar mats. The backfill was crushed rock. The instrumentation consisted of accelerometers, strain gauges, contact switch, displacement targets, string lines, and high-speed cameras. The test was designed to represent a commonly used installation in current practice including an impact load on the barrier at least equal to 240 kN. Most of the barriers sustained significant damage but overall the behavior of the wall was satisfactory since the displacements of the panels were minimal (less than 25 mm) and the panel damage was acceptable except possibly in the case of the 4.88-m-long strips. The loads measured in the reinforcement indicate that the reinforcement was brought to its ultimate capacity for the duration of the impact but since the impact duration was so short and since the displacements of the panels were within tolerable limits of 25 mm, this is considered acceptable. The use of the longer strips (4.88-m-long strips) leads to slightly smaller panel displacements and higher panel stresses as evidenced by a bending crack in the panel. The 2.44-m-long strips permitted more displacement of the wall panels, but the magnitude of the displacement was considered to be tolerable. The measured maximum dynamic loads in the strips were found to be 3–5 times higher than the calculated maximum static loads by AASHTO guidelines.