Climatic Factors for AS2870 for the Sydney Region
AS2870-1996 “Residential Slabs and Footings – Construction” correlates depths of design suction change (Hs) to regional climatic zones as delineated by the Thornthwaite Moisture Index (TMI). TMI is a measure of aridity, quantifying the cyclical wetting and drying of soils. TMI is a function of rainfall, potential evapotranspiration and soil water-holding capacity, and provides an indication of moisture balance.
In this paper TMI is calculated for various Bureau of Meteorology sites across Sydney, based on meteorological records. The results are plotted and contoured to give a map of TMI isopleths for the metropolitan region. This paper complements previous work in other States, and will provide improved estimates of Hs needed for the calculation of characteristic surface movement (ys) in metropolitan Sydney, for classification of residential sites under AS2870-1996.