Axial resistance of piles during driving in chalk

The driveability and axial capacity of driven piles depend critically on their geometry, end conditions and the degree of drainage they experience during driving. This paper summarises the installation characteristics of 41 impact-driven piles driven for the ALPACA joint industry project (JIP). The installed piles covered open- and closed-ended steel tubular, sheet and reinforced square concrete piles with a wide range of diameters (from 139 mm to 1.8 m), wall thickness ratios (14 to 72), and embedment length-to-diameter ratios (6 to 40). Analyses that applied parameters interpreted from parallel piezocone penetration and dissipation tests indicated that pore-pressures of several MPa developed beneath large open-ended piles during rapid driving and led to surprisingly low shaft resistances. However, the slower driving of the closed-ended concrete and sheet piles permitted far higher degrees of dissipation and led to far greater shaft resistances. Signal matching analyses demonstrate how the End of Driving (EoD) shaft resistances were affected strongly by de-structuration of the chalk and the relative depth of the pile tip. The EoD shaft resistances corresponded closely with predictions made applying the short-term Chalk ICP-18 Soil Resistance to Driving (SRD) formulae. An updated base resistance formula was proposed that correlates with pile wall thickness ratio.