The paper presents the results of field tests performed to study the effects of the installation technique, degree of plugging, cyclic loading and ageing on the shaft resistance developed on openended piles in sand. Two instrumented model piles were jacked and driven into an artificially created loose sand deposit in Blessington, Ireland. The results from these tests indicated that the equalized radial effective stresses which are suggested to control the shaft capacity vary strongly with the degree of plugging and number of load cycles experienced during installation. A comparison of jacked and driven installations suggest similar radial stresses were developed provided the jacked pile had experienced a sufficient number load cycles. The degree of plugging experienced during installation controlled the radial stresses near the bottom of the pile, with closed-ended or plugged piles developing high stresses near the pile base and exhibiting friction fatigue up the shaft, compared with open-ended coring piles which exhibited relatively low stresses along the length of the pile shaft. A comparison with full scale 340 mm diameter pipe piles driven into the dense sand in Blessington noted comparable radial stresses when the pile was fully coring but exhibited a larger increase in radial stress near the pile toe as the pile became plugged. Further tests on the effects of ageing show a pile shaft capacity increase of 260% over 220 days after driving. Further research is underway in Blessington to investigate the mechanisms controlling this ageing behaviour.

Open-ended steel pipe piles are used to support jacket structures in the offshore wind sector. These piles experience significant tensile axial loading in-service and the tensile shaft resistance thus governs their design. Although pile ageing (increased shaft resistance with time) has been noted by a number of workers and incorporation in design could lead to significant efficiencies, there is a dearth of high-quality field test data that measure its effects. This paper presents the results from an experimental investigation designed to examine the effect of ageing on the tension shaft resistance developed by open-ended piles in sand. As part of this investigation, four 340 mm diameter open-ended steel piles are driven 7 m into a dense sand deposit in Blessington, Ireland. Each pile is subjected to a series of static axial tension load tests at different time intervals after driving and the effects of ageing are assessed. The tension capacity of the piles is seen to increase by as much as 185% over a period of 7 months after driving.