About the research
The Minnesota Department of Transportation (MnDOT) issued a tech memo in 2015 assigning a granular equivalent (GE) factor of 2.0 to multi-axial geogrids. Due to the advance of geogrid materials, this GE value may underestimate the performance benefit of geogrids, resulting in overdesigning the thickness of aggregate base layers. The mechanistic-empirical flexible pavement design program, MnPave, does not currently contain a geogrid design module. City engineers in Mankato have used geogrid manufacturer’s design methods (e.g., Tensar’s SpectraPave4-PRO) as an alternative to analyze and design such pavement structures. However, this causes an inconsistency of standards and methodologies in pavement structure designs and difficulties in quality control and quality assurance (QA/QC) testing of roads systems. The cost analysis shows that in some projects, the geogrids can reduce the thickness of aggregate base and asphalt top to make it a more cost-effective solution. A good example is Madison Avenue between Victory Drive and Trunk Highway 22 in Mankato that the city constructed around 2012.
The objective of this project is to evaluate the performance benefit and cost effectiveness of geogrid in road systems by addressing five questions: (1) What strength enhancement is offered by the use of geogrids? (2) In which layer in a pavement structure is geogrid most effective? (3) How should geogrids be in the MnPave software application? (4) How would it be possible to evaluate the effectiveness and reliability of proprietary geogrid design? (5) How would it be possible to evaluate cost versus benefits of geogrids in different soil conditions?