Evaluating the performance of guardrail posts installed by driving through asphalt layers.
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2015-12-01
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Abstract:The preferred procedure for guardrail installation in the State of Georgia includes a layer of asphalt (usually
referred to as a “mow strip”) placed to retard vegetation growth around the guardrail. The objective of this multi-phase
research program is to develop effective alternatives to post installation methods that incorporate a leave-out around the
post. The work described in this report represents Phase I of the overall research effort. The research team evaluated
the structural performance of guardrail posts installed in accordance with current GDOT (Georgia Department of
Transportation) procedures that include an asphalt mow strip, as well as alternative installation options developed in
conjunction with GDOT personnel. The current state of practice related to the use of asphalt vegetation barriers in the
United States was identified through on a nationwide survey. An experimental program was carried out in accordance
with applicable AASHTO guidelines. In parallel with the experimental program, a three dimensional finite element
model was developed for a guardrail post installed through an asphalt layer. Results from the experimental program
and finite element analyses were used to develop a series of quantitative criteria to evaluate the performance of the
various post/mow strip configurations. Parametric studies were conducted on pertinent geometric variables in terms of
the quantitative performance criteria. The results of this Phase I research program demonstrate that (1) there are
potential combinations of mow strip thickness and rear distance that are likely to result in satisfactory dynamic
performance, and (2) two techniques appear effective in reducing the ground-level restraint imparted by a mow strip on
a guardrail system: decreasing the mow strip rear distance behind the post, and pre-cutting the mow strip in the region
behind the post.
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