Building Commission NSW encourages all design and building practitioners to seek and rely on a detailed geotechnical report and not assume soil parameters according to preliminary reports. The reminder comes after a recent audit found a final geotechnical report was missing before the construction of a multi-storey building.   

Preliminary soil reports only indicate the site suitability for the proposed building based on the soil conditions at development application (DA) stage. While the design of buildings is sometimes subject to change from the DA to construction certificate (CC) stage, the preliminary soil investigation fails to address issues such as the updated number of basements, proper soil pressure or water exposure that must be known before construction.  

A final soil report includes detailed results from a range of soil tests onsite and in the laboratory, including soil classification, profile, bedrock level, and soil aggressivity (for example acid sulphate presence) and other chemical properties. It provides an in-depth analysis of soil characteristics such as earthquake factor and liquefaction possibility, which are crucial for understanding building stability.  

A final soil report can also propose excavation methods, soil stabilisation, foundation suitability, bearing capacity, potential settlement and groundwater assessment and management.

If you have any questions, contact Building Commission NSW via this Enquiry form.