Behaviour of a thin compressible clay horizon under geogrid reinforced sand with a wide platform load

Abstract

Basal reinforcement, where high tensile strength geogrids are employed beneath structures, is becoming an increasingly accepted construction technique along the eastern coast of southern Africa. The presence of compressible, soft, thin and shallow clay horizons usually associated with complex estuarine or lagoonal deposits are a major consideration when using basal reinforcement as a founding technique. In order to define the deformation behaviour under a wide platform load, three centrifuge tests were undertaken. These tests compared the behaviour of the clay horizon in three scenarios, namely (1) without reinforcement, (2) with a single layer of reinforcement, and (3) with a double layer of reinforcement. It was found that the inclusion of geogrid reinforcement increased the vertical load-bearing capacity of the system and the inclusion of an additional geogrid layer further increases the load bearing capacity. Additionally, the inclusion of geogrid reinforcement also changed the deformation mechanisms of the materials. Without reinforcement, deformation is localised to the portion of clay directly beneath the applied load from the platform. Whilst the inclusion of geogrid reinforcement allows the applied load to be spread to the sand beyond the platform, which contributes to an increase in load-bearing capacity, it comes at the disadvantage of deforming a wider portion of the clay horizon.