Engineers Australia

Climatic factors for AS2870 for New South Wales

I. Chan and G. Mostyn


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.

Further to work done by the authors in 2004 and 2008, this paper extends the TMI map to regional New South Wales, and includes the entire TMI dataset for ease of use at particular towns and cities. 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 NSW for classification of residential sites under AS2870-1996.