Evaluation of installation effects on set-up of field displacement piles in sand

Abstract

The paper presents results from a new series of tests on displacement piles in sand, involving different installation modes, and combines these with results from previous tests at the same site as well as with test data at two other well-investigated sand sites to provide fresh insights into factors affecting “short-term” capacity and set-up of shaft friction. It is shown that the shaft capacity measured shortly after installation reduces systematically with the logarithm of the number of impact blows or jacking increments per unit shaft area imparted during installation. However, the degree of set-up of shaft friction for piles increases with an increase in the number of blows, and piles installed using a large number of blows can attain highest “long-term” shaft capacities, despite having the lowest short-term capacity. The tests indicated that the driving impact frequency had a relatively small influence on shaft friction, while piles installed by vibration attain short-term capacities comparable to driven impact piles, but showed negative set-up.

A field investigation into the mechanisms of pile ageing in sand

“…Tavenas & Audy (1972) found that the axial capacity of driven pre-cast concrete piles increased by approximately 70% over a 20 day period after driving. Similar trends were reported by Fellenius et al (1989), York et al (1994), Long et al (1999), Axelsson (2000aAxelsson ( , 2000b, Jardine et al (2006), Anusic et al (2018) and others, see Fig. 1.…”

Large-scale model tests of a single pile and two-pile groups for an offshore platform in sand

“…This is now a well-known and yet still not fully explored phenomenon, which can be briefly defined as the time-dependency of pile bearing behavior. The causes and consequences of this complex and peculiar aspect of foundation engineering are treated extensively in contributions such as Jardine et al (2006), Lim and Lehane (2015), Anusic et al (2019), andCarrol et al (2020) among others. In this work, the restrike test results indicate an average increase in capacity of 6.8% after 7.0 to 7.9 days (RS1 against RS2) and of 20.0% after 25.8 to 27.5 days (RS1 against RS3).…”

Discussion of “Evaluation of installation effects on set-up of field displacement piles in sand”

“…The data in Table 3 of Anusic et al (2019) correspond to different pile installation procedures in different types of sands and field conditions. For one sand type and installation method at one site, there are not enough data to evaluate pile capacity as a function of time; and for example, examine the behavior of C D with elapsed time after pile installation.…”

“…D2 with constant values of C D in the range of 1 to 9 has been superimposed on the pile capacity data in Fig. 1 of Anusic et al (2019). Although in one location in Jebba, Eq.…”