BAM Screw Piles 2.0: Validating Design for 'De Drie Hoefijzers' by Rapid Load Testing

Following an amendment on the Dutch Construction Decree in 2016 design parameters for end bearing of pile
foundations have been reduced by 30% on January 1st 2017. This amendment was motivated by research on load
testing data of foundation piles, which showed an overestimation of end bearing and consequential compromised
safety. The new situation potentially results in a considerable increase in installed lengths as well as cross-sectional
areas, with possible executional, economic and environmental consequences. A piling contractor can deviate from the
CPT-based design parameters by performing pile load testing. NPR7201:2017 offers the possibility to validate a
preliminary design based on freely chosen (assumed) design parameters, by verifying suitability up to design load
based test loads.
BAM was awarded the installation of the foundation for housing development project ‘De Drie Hoefijzers’ in the
central train station area in Breda. Because of the presence of sensitive objects in close proximity to the project area,
a pile system with low vibration installation is selected. The BAM Screw Pile 2.0 is an optimization of the CFA pile,
combining easy installation with minimal relaxation of the soil around the pile tip by introducing a permanent cast
steel, serrated drill bit. Experiences with the BAM Screw Pile 2.0 thus far show considerably higher capacities
compared to CPT-based design for standard CFA piles. Therefore it was decided to incorporate a pile testing program
to corroborate this experience and optimize the design of the foundation.
The pile load testing method selected was Rapid Load Testing (StatRapid system). Three test piles following the
preliminary design with assumed higher design parameters (20 m in length with a diameter of 800 mm) were subjected
to test loads ranging from 6.0 to 7.3 MN (design loads ranging from 2.8 to 3.1 MN). The piles did not exhibit soil
mechanical failure and as a consequence the preliminary design was validated. Effectively the approach saved 1 km
of pile length, reducing cost by €175.000, as well as a resulting reduction in CO2 production of 80 tons.