Brunnholen Bridge: Norway - Design and Supervision of Foundation Works-Paper

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Brunnholen Bridge is a 245 m highway bridge near Stavanger, Norway, founded on six groups of large drilled steel pipe piles. The 914 mm diameter, 14.2 mm thick piles are filled with reinforced concrete; 46 piles, up to about 75 m long, are drilled through fill, granular deposits, stiff clay, boulder-rich moraine and soft rock, extending at least 1.5 m into solid rock. Some piles are inclined. This was the first use in Norway of piles of this size at such depths.<br /><br />Drilled piles were selected over caissons and driven piles because they could transfer high axial loads to rock while avoiding extensive excavation and difficult driving. Design followed Eurocode 7 and used three-dimensional soil–pile–structure interaction analyses with nonlinear soil springs based on API guidance. Iterative coordination between structural and geotechnical consultants established foundation stiffness and loads. Analyses checked serviceability displacements, pile capacity and foundation stability across numerous load combinations.<br /><br />Installation used down-the-hole hammer drilling with reverse circulation. Geotechnical supervision focused on confirming penetration into solid rock, minimizing ground disturbance, cleaning pile bases before underwater concreting, and ensuring sound contact between concrete and rock. Drilling records and cuttings were used to identify solid rock; flushing pressures and drilling practices were controlled to limit pore-pressure effects and ground deformation.<br /><br />Because one foundation was close to a railway, settlement and pore pressure were monitored. Pore pressures varied during drilling and temporarily decreased, then returned toward initial levels after pile-base grouting. Railway settlement remained within acceptance limits. Inspection and core sampling revealed occasional gravel or cuttings at pile bases; affected piles were subsequently injected.<br /><br />The project demonstrates the importance of detailed soil–pile interaction analysis and continuous geotechnical oversight for deep, large-diameter drilled piles. Close monitoring also allowed installation issues and deviations to be addressed without major disruption to construction.

Keywords

Brunnholen Bridge

Norway

highway bridge

drilled steel pipe piles

deep foundations

Eurocode 7

soil-pile interaction

geotechnical monitoring

reverse circulation drilling

pile base grouting