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 Chan and Mostyn (2004), this paper includes the complete TMI dataset for the metropolitan Sydney area. This paper provides improved estimates of Hs that can be considered in the calculation of characteristic surface movement (ys) in metropolitan Sydney when classifying residential sites under AS2870-1996.