A field investigation into the mechanisms of pile ageing in sand

Abstract

The design of axially loaded piles has been an area of focus for the offshore industry in recent years. A number of studies report substantial increases in the shaft capacity of piles driven in sand, known as pile ageing. The offshore industry has been slow to implement ageing into practice because of uncertainty over the mechanisms controlling ageing and variability on the impact of ageing. This paper presents the results of tests using an instrumented pile with two separate installations considered, one where the pile was load tested 4 days after installation and the second where the load test was performed after an ageing period of 116 days. Data from the installation, ageing period, load testing and pile extraction provide further insights into the mechanisms governing the effect of time on the axial capacity of piles in sand.

Investigation of Cyclic Loading of Aged Piles in Sand

“…Increased cementation and cohesion as a result of chemical processes such as the dissolution and precipitation of silica or calcium carbonate at particle contacts (Mitchell and Solymar 1984;Baxter and Mitchell 2004). The mechanisms of pile ageing are less well known, although notable developments have been made in recent years (Jardine et al 2006;Rimoy et al 2015;Lim and Lehane 2015;Gavin et al 2013Gavin et al , 2015Gavin and Igoe 2019;and others). Chow et al (1998) considered three possible mechanisms for pile ageing: 1.…”

“…Chemical corrosion resulting in an increased pile surface roughness and interface friction angle δ f . As part of a long-term field investigation into pile ageing, Gavin et al (2013) and Gavin and Igoe (2019) presented results from the installation, ageing, load-testing, and extraction of field-scale driven piles in Blessington, which are directly related to the field tests discussed in this paper. Based on these findings and previous work by other researchers, the authors suggest the primary mechanisms for pile ageing are increased constrained dilation (Mechanism B) and physiochemical processes (Mechanism C), resulting in cementation of the shear zone formed during pile driving.…”

“…Multiple static and cyclic loading tests performed on four steel piles, designated S2, S3, S4, and S6, are discussed in this paper. First-time "fresh" tension tests from each of these piles have been previously reported in Gavin and Igoe (2019) and Igoe et al (2013). Tension testing was preferred over compression testing to reduce the uncertainty related to separating the shaft and base resistance components for open-ended piles.…”

“…Tension testing was preferred over compression testing to reduce the uncertainty related to separating the shaft and base resistance components for open-ended piles. All piles had identical geometries with an outer diameter D of 340 mm, wall thickness of 14 mm, and embedded length of 7 m. Pile S6 had two diametrically opposite steel channels welded onto the outer shaft to house strain gauges, and radial stress sensors were embedded in the pile wall at locations offset circumferentially at 90°to these channels, as described in Gavin and Igoe (2019).…”

“…The total blow counts required to reach the final penetration of 7 m varied between 529 and 739 blows for Piles S2-S4 using the 4-t hammer and ∼1,500 blows for Pile S6 with the 5-t hammer, albeit at a lower hammer drop height for most of the installation. The maximum energy transferred into the piles (EMX) was estimated using the approach adopted in Gavin and Igoe (2019), which was based on linear fit to measured EMX data for the same piling hammers from Flynn and Mccabe (2016). A comparison of the estimated EMX is provided in Fig.…”