Inefficient installation of pile foundations may lead to high risks of material damage, inadequate pile capacity, and time delays that can have significant financial implications to any kind of project, both onshore and offshore. Therefore, there is high demand for a comprehensive driveability analysis that considers key aspects of the installation process, such as the soil conditions, the pile-soil interaction and efficiency of the driving equipment used.
The total resistance during pile driving is usually estimated through numerical simulation techniques based on the wave equation, whereby the main inputs are the hammer, pile and soil properties. Commercially available driveability software, such as AllWave PDP, enable the modelling of the hammer-pile-soil system and simulate the stress wave phenomena during the installation process. Moreover, these programs have an integrated database of a variety of hammer models (hydraulic, diesel and more) that are used in practice, and also static and dynamic parameters for a variety of soils.
One of the key aspects in which this Thesis focuses on, is the static component of the driving resistance, referred to as SRD. Over the years, various SRD models have been developed, with the aim of estimating the static soil resistance during driving, while the dynamic components of the total resistance (increasing resistance due to inertial and viscous rate effects) are commonly being quantified in terms of damping factors.
This Thesis investigates the performance of frequently used traditional driveability models, such as the Alm & Hamre (2001), Toolan & Fox (1977) and Stevens et al (1982), in predicting the SRD in dense sand conditions. Furthermore, it examines the application of the Unified Method in SRD estimations. The Unified Method is a recently developed static capacity design approach for driven piles in silica sand. This design method will be included in the forthcoming 2022 edition of the ISO guidelines and will replace the four CPT based design methods (ICP, UWA, NGI, Fugro).
The performance of the aforementioned models has been evaluated through predictions of blow count profiles by utilizing pile driving records from five sites in the Netherlands, namely the Eemshaven (project known as Euripides) and APM, RWG, SIF and HHT terminals in the Port of Rotterdam. The diameter of the open-ended steel tubular piles examined in this study, is 0.762 m for the Euripides project and 1.42 m for the rest of the projects.
This research, will eventually highlight advantages and disadvantages of the commonly used SRD models, while it will further prove that by modifying the Unified Method, overall better driveability predictions can be made for a larger range of pile diameters than the current methods. The gain is that on one hand, with improved driveability predictions it is possible to minimize installation risks, optimize driving acceptance criteria, and select an appropriate hammering equipment. On the other hand, having a set of formulas that can be used both in estimating the SRD, as well as the static axial capacity, can reduce the engineering effort.