Self-boring pressuremeter tests at the National Field Testing Facility, Ballina NSW

Accurate prediction of foundation settlement is increasingly important in onshore and offshore geotechnical design. Reducing land space requires construction on non-ideal soils or above buried infrastructure onshore while offshore shallow foundations require optimization of size to facilitate installation while ensuring tolerances on attached rigid infrastructure such as pipelines are not compromised. The accuracy of settlement predictions depends on the accuracy of the measured soil stiffness, which is non-linear and dependent on stress level, stress path and stress history. Consequently, the quality of a settlement prediction is inherently tied to the relevance of the testing method that is used to derive the stiffness values. The self-boring pressuremeter (SBPM) enables the non-linear stress-strain response to be captured at different in-situ stress levels (depths) over a large range of cavity strain, and derivation of undrained strength, stiffness and creep characteristics. This paper summarizes a program of pressuremeter tests conducted in a soft clay deposit in Ballina, NSW, Australia.