Oldie but Goldie Deep Piles at Geneva with Base Enlargement, Tested Bi-Directionally with Osterberg Cells is a Smart and Economical Alternative to Conventional, Larger Piles-Paper

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The Rolex factory extension in Geneva required foundations through up to 30 metres of weak clay and silt to reach competent moraine. The original design called for large, deep piles, which would require substantial drilling, concrete, spoil removal and equipment.<br /><br />Implenia proposed 800 mm bored piles with enlarged, or underreamed, bases in the moraine. A purpose-built tool cut each enlargement in stages. Before adopting the solution, the team tested a full-scale pile using an Osterberg cell (O-cell), which applies load upward and downward simultaneously. The test supported the design assumptions: it indicated an estimated end-bearing capacity of about 10 MN and confirmed the pile’s load-transfer behaviour.<br /><br />The revised scheme replaced the originally planned 1,500 mm piles with 41 piles, each with an 800 mm shaft and a 1,850 mm enlarged base. Compared with the initial design, the alternative used roughly 30% of the concrete and generated about 30% of the spoil—reductions of around 70%. Concrete use fell from approximately 59 m³ to 19 m³ per pile. The project estimated that the change avoided about 420 tonnes of CO₂-equivalent emissions, alongside savings in transport, construction time and cost.<br /><br />The report concludes that underreamed piles can offer a technically effective and economical alternative to conventional deep piles in suitable ground. Their design and construction require attention to soil stability, enlargement geometry and workmanship; load testing can help verify performance and optimize the foundation.

Keywords

Rolex factory extension

Geneva

underreamed piles

bored piles

foundation design

Osterberg cell

load testing

moraine

concrete reduction

CO2 emissions