The design of working platforms typically involves the calculation of a two-layer bearing capacity. Existing calculation models are quite empirical with imprecise input parameters while other proposed methods have tended to involve multiple design charts and been suited to either strip or circular foundations only. It has also been difficult to incorporate the benefits of geosynthetics in an accurate way. The recently developed “T-Value Method” defines bearing capacity simply in terms of the ratio of strengths of the two layers. It also allows realistic incorporation of the benefit of multi-axial stabilising geogrid in terms of the enhanced shear strength of the upper granular layer. This is leading to significant cost savings due to thinner working platforms that are designed in a safe and scientifically rigorous way. The greater ductility of stabilised granular layers also provides greater assurance that the assumed failure mechanisms can be fully mobilised before strain softening in the granular layer occurs. This paper summarises the development of this new design method and describes some of the full-scale field tests that have been used in its validation.
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