Pile Foundation Solutions in the Deep Quaternary Sediments of Botany Bay-Paper

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The Amcor B9 paper mill in Botany, New South Wales, required foundations capable of supporting heavy, variable and cyclic machinery loads while meeting stringent settlement limits: 6 mm total and 0.5 mm per metre differential settlement. Uncontrolled industrial fill, bedrock more than 25 m deep, and sensitive operating equipment made foundation design particularly challenging.<br /><br />The mill was supported by approximately 1,000 driven precast concrete piles, supplemented by continuous flight auger piles for uplift resistance. Piles were founded in the Botany Basin’s very dense, partly cemented Third Unit sands. These sands can provide high bearing capacity, but are interspersed with discontinuous peat and clay layers that cause local variation in pile performance.<br /><br />A comprehensive testing program combined driving records, Hiley formula capacity estimates, dynamic testing with PDA/CAPWAP on about 10% of piles, restrike testing, and a static load test. The static test showed largely linear-elastic behaviour, and its load–settlement response agreed closely with CAPWAP results. Hiley estimates generally overpredicted capacity, but comparison with PDA results enabled calibrated estimates for untested piles.<br /><br />Driving in the dense sands generated negative pore pressures and temporary strength gains. As these pressures dissipated, piles relaxed: some required additional driving, and capacity changes could continue for up to two weeks. The authors recommend allowing for this delay and using CPT dissipation testing where appropriate.<br /><br />The project demonstrates that sensitive, heavily loaded structures can be supported successfully in Botany Bay sediments when investigations, pile trials, testing and modelling are matched to the ground conditions. Preliminary pile trials can improve design assumptions and reduce costs. Careful assessment is also needed for groundwater drawdown, vibrations and variable buried materials.

Keywords

Amcor B9 paper mill

Botany New South Wales

pile foundations

driven precast concrete piles

continuous flight auger piles

settlement limits

dense sand

PDA CAPWAP testing

static load test

groundwater drawdown