Compression load tests on large open-ended pipe piles in dense North sea sand

As open-ended steel pipe piles increase in size, efficient installation methods ensuring sufficient bearing capacity are crucial. A combination of vibratory and impact driving is commonly used to install these piles. However, compression load tests on large-diameter piles installed in this way are scarce, questioning the reliability of design methods for axial bearing capacity. To investigate, four 1·22 m dia. open-ended pipe piles with fibre optic strain sensors were installed and tested at Maasvlakte 2, the Netherlands. All piles were vibratory driven to a depth of 29·5 m; two were then impact driven an additional 3·5 m and two an additional 8·5 m. Static compression load tests were conducted 30 or 70 days post-installation. Although the piles remained largely or fully coring during installation, all experienced ‘locking-up’ of the plug under static loading. The derived resistances were compared with the ‘Unified CPT-based method for driven piles in sand’. This method is intended to capture the capacities of fully impact-driven piles at around 14 days after installation, with further shaft capacity gains likely thereafter. The tests revealed axial resistances that increased over time, matching or exceeding unified method predictions. These findings can impact the design and assessment of open-ended pipe piles.