Stabilisation of aggregate layers over weak subgrade soils is frequently accomplished using geogrid for unpaved roads, working platforms, or foundations. The performance of various stabilised aggregate layers over a soft silty clay subgrade soil was evaluated at full scale under highly controlled loading conditions. In order to provide the required reaction load, a moveable loading platform was constructed onto which 4 loaded gravel trucks could be driven. The overall system consisted of a moveable steel load platform that was placed over a trench within which multiple test pads were constructed with different combinations of gravel, thickness and geogrid layers. Load was applied to a 1m2 plate area by a hydraulic piston capable of reaching well over 1000 kN, thus representing loading fully at field scale. All tests were taken past ultimate bearing capacity failure to a maximum stroke of 250 mm. A photogrammetric procedure was developed to define in 3 dimensions the deformed surfaces of the gravel surface and the interface with the soft clay subgrade below. The photogrammetry procedure yields digital elevation models, which clearly illustrate the nature of the displacement of the ground surface, the geogrid reinforcement, and the aggregate – subgrade interface. The variations in the precise pattern of deformation serve to highlight aspects of the aggregate – geogrid interaction and serve to highlight the specific soil-geogrid interaction behaviour. Combined with future numerical modelling back-analyses, the data from these full-scale tests will contribute to an improved understanding of the interactions between the clayey subgrade, the stabilising geogrid and the aggregate.
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