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APPLICATION OF GEOGRIDS AND GEOCOMPOSITES IN DESIGNING WORKING PLATFORMS ON COHESIVE SUBGRADES; CASE STUDY: HARVEY NORMAN BULKY GOODS DEVELOPMENT, AUSTRALIA

In the construction of heavily trafficked areas such as working platforms, a stable subgrade with sufficient bearing capacity is required. Economical and environmental advantages of construction methods with geosynthetics, especially on soft soils are already well known. Soil masses that need to be excavated, transported and installed can be dramatically reduced by the inclusion of geosynthetics. The best example is the improvement of soft subgrades with geogrids or geocomposite products. In this paper, the general design procedure is presented for working platforms using geosynthetics according to Building Research Establishment (BRE). A project constructed in SE Queensland Australia using a unique geocomposite is then discussed in further detail. This geocomposite which is a combination of a geogrid with a high secant strength and an integral nonwoven geotextile, encapsulated between the cross laid welded bars, was successfully installed directly on top of the subgrade with CBR value as low as 1%, providing not only improvement of the subgrade bearing capacity, but also a positive separation and filtration layer between fine subgrade materials and imported granular platform materials. A 350 mm granular platform was then installed on top of the CombigridĀ®. This method could make the construction of thin granular platform layer on the soft subgrade possible, reducing construction costs and construction time for the client and the contractor. Also, the reduced requirement for imported quarried materials in the working platform had significant additional environmental benefits.