Some observations of the effects of time on the capacity of piles driven in sand

Abstract

Piles driven in sand can show remarkable increases in their axial shaft capacities in the months that follow installation. Many practical benefits follow if service capacities can be relied upon to exceed the levels proven in site tests, which are usually performed within a few days of driving. This paper reports findings from a programme of mainly tension tests on steel pipe piles performed in dense sand at Dunkirk, northern France. The tests demonstrated more marked shaft capacity growth with time than expected. The aged piles also showed surprisingly brittle failure modes; prior testing to failure both degraded capacity and modified the ageing processes, leading to non-monotonic shaft capacity–time traces that fall far below the intact ageing characteristic (IAC) defined by tests on fresh, previously unfailed, piles. Capacity–time trends inferred from repeatedly tested piles can give misleading results. The new findings allow the ageing effects to be characterised more clearly, and permit a re-evaluation of existing databases involving piles of various types driven in a range of silts, sands and gravels. Important practical conclusions are drawn regarding pile design and the interpretation of field pile load tests.

The ICP Design Method and Application to a North Sea Offshore Wind Farm

“…The background research and design methods developed from it are summarized by Jardine et al (2005), who cite multiple earlier references including Jardine et al (1998), Saldivar and Jardine (2005) and Jardine et al (2006) which present full details of the methods. Further investigations of the effects of time on the axial capacity of piles driven in sand are described by Jardine et al (2006) and those concerning cyclic loading effects by Jardine & Standing (2012). The main considerations in sands and clays are summarized below.…”

“…Pile end bearing capacity is not thought to change significantly with time. Pile load tests performed at different times after driving in dense sands at Dunkirk, northern France, are reported by Jardine et al (2006). The multiple 'first-time' loading tests demonstrated marked increases in capacity over the months following installation, and multiple re-tests revealed a brittle failure mode applied to the aged piles.…”

Time dependent factors in pile quality and capacity control

“…Such an influence reported by Skov (1988) and Svinkin (2005) should be significant, especially in the case of stiff cohesive soils where so called soil "setup effect" accompanied by dissipation of pore pressure at the soil pile interface zone may last for years. The detailed analysis of setup in sands is a subject of recent studies by Jardine (2006) and König (2006). Even a 20% increase of bearing capacity in sand is noteworthy in terms of money.…”

“…It is observed, almost in all of the ground types, that the load capacity increases in time (the phenomenon described in literature as "setup" (Skov, Denver, 1988, Svinkin, Skov, 2005, Jardine et al, 2006and König, Grabe, 2006 and thus reducing the testing time does not bring about the risk of overestimating pile load capacity (Rybak, 2008). When, contrarily, the result of the load capacity test is negative, such test may be always repeated after the time necessary for the reconsolidation of the subsoil around the pile.…”

A new and openly accessible database of tests on piles driven in sands

“…Simple expressions were developed that captured the above shaft capacity phenomena and also pile end bearing capacity. Subsequent research has considered additional factors, including N the influence of load cycles imposed during installation (White & Lehane, 2004;Jardine et al, 2013a) N time effects (Jardine et al, 2006;Gavin et al, 2013;Karlsrud et al, 2014) N how particle breakage under the tip and surface abrasion affect the stresses and the development of a well-defined interface shear zone (Yang et al, 2010) N the stress regime developed in the surrounding soil mass (Jardine et al, 2009(Jardine et al, , 2013b N the influence of cyclic loading (Tsuha et al, 2012). Yang et al (2014) and Zhang et al (2014) have gone on to relate stress measurements from experimental investigations and numerical analyses by other workers.…”