Effects of Cyclic History on the Ageing of Shaft Friction of Driven Piles in Sand-Paper

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The study investigates how cyclic loading affects the time-dependent increase (“ageing” or set-up) of shaft friction in driven piles in sand. Researchers tested 12 steel pipe piles, 89 mm and 165 mm in diameter, driven 4 m into siliceous sand at Shenton Park, Western Australia. Piles were either tested in tension at different times after installation or subjected to low- or high-level one-way cyclic tension loading before failure tests. Results cover up to 300 days.<br /><br />For piles loaded monotonically for the first time, shaft capacity increased by about 25% per tenfold increase in elapsed time; capacity at 300 days was 43% greater than at one day. Cycling at levels up to 60% of short-term static capacity generally did not interrupt ageing and increased capacity by approximately 5–30% in some tests. Piles allowed to age after cycling developed greater capacities than those tested immediately after cycling.<br /><br />The findings support accounting for ageing in pile design, while showing that the magnitude of gains varies and was lower than in some previous studies. The results are preliminary, based on a limited number of tests at one site; further testing is needed to establish how widely they apply, particularly to large offshore piles.

Keywords

cyclic loading

pile ageing

shaft friction

driven piles

sand

set-up

tension tests

capacity increase

pile design

offshore piles