problem
An employee parking lot, measuring approximately 10.000 m2, is associated with the premises of the Pennsylvania Employees Credit Union (PESCU) located in Harrisburg, Pennsylvania. This facility and the parking lot were constructed in 1987. Subsequently a large number of depressions (of various sizes) were observed in the bituminous concrete pavement pertaining to the parking lot. In 1996, investigations attributed the depressions to the miscellaneous, uncontrolled fill materials immediately underlying the pavement.

solution
After carefull geotechnic investigation and design, it was recommended that the bituminous concrete pavement be reconstructed upon a base reinforced with layers of geogrids. The purpose of the geogrid was to bridge potential voids, minimize differential settlements, and enhance the bearing capacity of the foundation system. Three layers of geogrids were incorporated to reinforce the pavement foundation for a relatively large parking lot.
TENAX multi-layer geogrids have ‘more tensile elements’ per unit area. This increased number of tensile elements allows for more effective interaction with the soil. The increased interaction with the soil greatly improves the pull out resistance of the geogrid in a wide range of soils. TENAX MS 330 geogrid has 3100 tensile elements/m2 compared to 1200 tensile elements/m2 for a conventional single-layer geogrid.
TENAX multi-layer geogrids also have a ‘variable aperture size’. Multi-layer geogrids are comprised of multiple layers of high strength extruded, bi-oriented polypropylene grids. The multiple layers are rolled and stitched together without superimposing the meshes creating a geogrid with variable sized apertures. The variable sized apertures greatly improve the geogrid’s interlocking capacity with the soil.
This is especially true when deploying the typical aggregate fill used for road construction that has particle size distribution of 20 mm stone down to fines. The variable sized apertures are even more beneficial when the project calls for a fill material that is already on the project site with less than favorable soil characteristics. The different size of the openings allows for better filling of the void spaces in the cross section during placement of a soil with an extreme soil distribution curve, thus providing a better interlocking capacity.

conclusions
The TENAX MS geogrids allowed the construction of a long lasting and durable road section. The three geogrid layers reinforced base created a stiff platform highly resistant to traffic loads.