The Shaft Capacity of Displacement Piles in Clay: A State of the Art Review

Abstract

The rapid expansion of the offshore wind sector, coupled with increasing demand for high rise structures, has placed renewed demand on the driven piling market.In light of this industry growth, this paper reviews the evolution of design approaches for calculating the shaft capacity of displacement piles installed in cohesive soils. The transition from traditional total stress design towards effective stress methods is described. Complex stress-strain changes occur during pile installation, equalisation and load testing and as a consequence, the selection of parameters for use in conventional earth-pressure type effective stress approaches is not straight-forward. These problems have led to the development of empirical correlations between shaft resistance and in-situ tests, such as the cone penetration tests. However, many of these approaches are limited because they were developed for specific geological conditions. Significant insight into pile behaviour has been obtained from recent model pile tests, which included reliable measurements of radial effective stresses. These tests have allowed factors such as friction fatigue and interface friction to be included explicitly in design methods.Whilst analytical methods have been developed to investigate pile response, these techniques cannot yet fully describe the complete stress-strain history experienced by driven piles. The use of analytical methods in examining features of pile behaviour, such as the development of pore pressure during installation and the effects of pile end geometry on pile capacity, is discussed.2

Characterization of model uncertainty in predicting axial resistance of piles driven into clay

“…Detailed summaries of the methods for resistance calculation can be found in Doherty and Gavin (2011) and Niazi (2014). It is clearly observed some empirical coefficients (e.g.…”

“…1. Theoretical imperfections of the α-methods (Doherty and Gavin 2011) are that (i) soil behavior governed by effective stress and the change in the stress-strain relation arising from the pile installation cannot be completely described by the initial undrained strength profile and (ii) the effect of the friction along the soil-shaft interface on the location of failure surface on which the shear resistance develops is not considered. pile geometries and/or soil properties) is outside the domain of the calibration database, additional uncertainty will be introduced.…”

Analysis of the Behaviour of Very Slender Piles: Focus on the Ultimate Load

“…s represents a shaft resistance; in the literature there is a wide variety of approaches for its evaluation [43][44][45]; the most popular considers its estimation related to the undrained shear strength (total stress approach) as: α is an adhesion factor; even in this case, different expressions are found in the literature for its computation [46,47]. The American Petroleum Institute (API) recommendation (1987) is used in this case, according to which: Table 3 shows the unit base and shaft resistances, evaluated through Eqs.…”

Numerical simulation of installation of jacked piles in sand using material point method

“…These effects can produce changes in the properties and state of the soil, modifications on the lateral and vertical stresses, and therefore changes in the capacity and the stiffness of the pile-soil system. Although this problem is well known, there is still a great deal of empiricism in the estimations of pile installation effects; hence, some further experience is needed to do an accurate evaluation of changes in pile load capacity (Doherty and Gavin 2011). Pile installation effects are particularly important for displacement piles, where the soil is radially and vertically displaced, creating a total displaced volume of soil of, at least, the nominal volume of the pile.…”