Foundation Base Material Strength Assessment for Drilled Pipe Piles Using Force and Displacement Data-Paper

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The paper presents a case study using force–displacement testing to assess the material at the base of two open-end drilled pipe piles for a bridge in Fredrikstad, Norway. The piles were installed into steeply sloping bedrock using down-the-hole hammers and designed to carry loads through end bearing. Because poor visibility prevented reliable camera inspections of the pile bases, conventional confirmation of rock contact was not possible.<br /><br />The authors used a Shaft Quantitative Inspection Device (SQUID), lowered to each pile base on the drilling strings. Its penetrometers measured resistance while retractable plates recorded displacement. Local criteria classified the base material as competent if it resisted at least 30 MPa with no more than 8 mm of displacement.<br /><br />Ten test runs were completed in pile P02-04 and 13 in P02-05. Average results were 35 MPa at 7 mm displacement for P02-04, and 38 MPa at 7.2 mm for P02-05. Both piles met the specified criteria. Differences among individual penetrometer curves suggested that the bases were not uniform; changes in curve shape were interpreted as transitions from softer or weathered material to more competent rock.<br /><br />The study concludes that SQUID force–displacement testing can provide a useful qualitative and quantitative alternative or supplement when coring or visual inspection is impractical. However, penetration resistance has not yet been correlated with standard soil or rock strength parameters, such as unconfined compressive strength. Results therefore require interpretation by a qualified geotechnical engineer.

Keywords

force-displacement testing

drilled pipe piles

pile base inspection

SQUID device

bridge foundations

end bearing

bedrock contact

geotechnical engineering

penetration resistance

Norway case study