The influence of the installation method on the static lateral response of displacement piles is presented using the results from reduced-scale field tests on piles in medium dense siliceous sand. In contrast to the importance of the installation method on shaft friction, it is shown that lateral response of piles to static lateral loading is largely insensitive to the installation method. The tests show that the lateral responses of impact-driven piles with different installation frequencies and jacked piles are very similar, while vibro-installed piles exhibit a somewhat stiffer response, reflecting effects of compaction. A comparison of load test results with the predictions obtained from two design methods reveals the suitability of a method that correlates the lateral soil response to the cone penetration test end resistance.

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.

With pile installation being an important part of the total project cost, improving the efficiency of the offshore operations would require resolving the uncertainties in how different installation methods influence pile capacity. This paper describes a programme of testing involving static loading tests on eight 165 mm diameter open-ended steel tubes driven into medium dense siliceous sand at a well-characterized test site in Perth, Western Australia. Six piles were installed by impact driving under two different driving frequencies, and two piles were installed by vibration with the aim of identifying the effects of impact frequency on the response of driven piles to static axial and lateral loading. It was found that the tension capacity of piles measured 1 week after installation was not significantly dependent on the impact frequency and that these piles had approximately the same capacity as the piles installed by vibration. First time load tests performed 4 months after the initial tests indicated that all pile types had a similar set-up characteristic. Inspection of static tests on lateral behavior of vibrated and impact driven piles suggests that installation method has no impact on the lateral capacity.

A significant number of large diameter monopiles (>6 m diameter) have been installed as foundations for offshore wind turbine generators (WTG) across Northern European waters over the past decade, where the self-weight penetration (SWP) during the installation process was recorded. The prediction of the SWP for offshore foundations, such as piles and skirted foundations, is an important installation design task. The prediction of the SWP is subject to great uncertainty, resulting in a large range between lower and upper bound SWP predictions. The methods available to predict the SWP range from simple empirical methods that derive the penetration resistance from cone penetration test (CPT) measurements using skirt and tip resistance coefficients to more advanced methods, based on bearing capacity theory requiring soil strength parameters as input. For the empirical methods, the prediction accuracy is directly dependent on the data used to establish suitable resistance coefficients. Investigating different soil conditions and foundation dimensions (scale effects), therefore, extends and improves the applicability of the empirical SWP prediction methods. This paper will use a portion of the recorded SWP data to benchmark existing SWP prediction methods and to establish improved resistance coefficients for the empirical method using a Monte Carlo type approach. For the Westermost offshore wind farm assessed in this study, the findings show that the existing SWP prediction methods generally under predict the observed SWP. The results of the Monte Carlo type analysis show that the new resistance coefficients are generally lower than the generic resistance coefficients provided by DNV (1992). The results also show that the tip resistance in coarse grained materials and the shaft resistance in fine grained have the largest influence on the accurate prediction of the SWP.