Determining Acceptance Criteria to Optimise the Foundation Design and Installation-Paper

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The paper presents a site-specific method for setting pile-installation acceptance criteria at a 110 kV substation in Bolsward, the Netherlands. Very dense sand caused CPT refusal before the required investigation depth, creating uncertainty about whether precast concrete piles could reach their design depths without excessive driving stresses or damage.<br /><br />The team combined pile-driving predictions with PDA measurements on two trial piles, then used signal matching to estimate mobilized static capacity and calibrate the hammer-and-soil models. Although both test piles reached about 22 m depth, they experienced high blow counts and compressive stresses exceeding allowable values. Signal matching estimated capacities of approximately 3.5–4.0 MN, well above the required 850 kN.<br /><br />Post-analysis produced site-specific relationships between blow count and capacity. After applying code safety factors and accounting for negative skin friction, the study found that, with the tested hammer configuration, 20 blows per 0.25 m at the specified toe depths were sufficient to meet the design requirement. This allowed installation to stop based on verified resistance rather than a fixed penetration depth.<br /><br />The approach aligned the needs of the designer, piling contractor, and pile manufacturer, while reducing driving effort, installation time, risk of pile damage, and associated emissions. The criteria are specific to the tested hammer setup; changes in equipment or configuration require new predictions and adjusted criteria.

Keywords

pile installation

acceptance criteria

signal matching

pile driving

precast concrete piles

dense sand

static capacity

PDA measurements

substation foundation

Bolsward Netherlands