Engineers Australia

Dealing with reactive clay soils through a national standard

Donald A. Cameron


Australia has had a national standard for site classification and design of footings for reactive soils for nearly 30 years. From the outset, the Standard, AS2870, has implemented a simple rational model for quantifying reactive soil foundation movement. The parameters of the model have from necessity been calibrated against empirical observations. The philosophical approach adopted in the Standard envisages that footing designers, builders and homeowners all have parts to play in managing sites on reactive soils. This paper reviews the background to the Standard and its development over time. The paper presents the site classification process, tests to quantify clay soil reactivity, design suction changes, the Thornthwaite climate index, the impact of trees on footing design and current practice. Examples are provided of ground movement calculations for normal site classification, classification adjusted for reactive soil fills and tree-drying settlement. Research areas which are needed to improve the Standard are discussed.