ABSTRACT
An experimental laboratory program to assess performance of triangular aperture geogrid reinforced bases in flexible pavements using a local subgrade was carried out. Two laboratory tests were conducted using a steel cylindrical mold with dimensions of 1.8 m (6 ft) in diameter and 2.1 m (7 ft) in height. The studied reinforced and unreinforced (without geogrid) sections consisted of a locally-obtained subgrade with an R-value of 40 and a minimum thickness of 1.5 m (5 ft) and an asphaltic surface course of 7.6 cm (3 in). The aggregate base layer thickness was 30.5 cm (12 in). A layer of triaxial geogrid was placed at the subgrade-base interface for the geogrid reinforced test section. The instrumentations included pressure cells placed at different locations of the test sections, foil strain gauges installed on the ribs of geogrids, and LVDT placed on top of the loading system. These devices were connected to a data acquisition system. A hydraulic actuator provided 40 kN (9 kip) repeated vertical load through a 305 mm (12 in) circular steel plate at a frequency of 0.77 Hz. The repeated loading was continued for at least 3 million cycles for each test sections. Performances of geogrid reinforced section was compared with that of unreinforced section. Test results revealed that inclusion of triaxial geogrid in flexible pavement reduced the surface rutting and vertical stresses in the subgrade-base interface. For the studied geogrid-reinforced pavement section, no tensile strain was experienced by the strain gauges installed on the ribs of the geogrids. The vertical pressure at the center of subgrade-base interface reduced by 21% for geogrid-reinforced pavement section. Using the results of rutting depth, it was found that use of geogrid increased the number of load applications by a factor of 2.2 to 4 depending on the rutting depth experienced at different loading applications. Using Base Course Reduction (BCR) method and the obtained rutting depth, inclusion of geogrid resulted in the base thickness reductions of 29 to 36 percent depending on the rutting depth experienced at different load applications. Using the pressure values at center point of subgrade-base interface, it was found that inclusion of triaxial geogrid reduced base layer thickness by nearly 7 percent.
