Performance of CPT-based methods to assess monopile driveability in North Sea sands

Abstract

53Offshore pile driving is a high-risk activity as delays can be financially punitive. Experience of pile 54 driving for offshore jacket structures where pile diameters are typically < 2m has led to the development 55 of empirical pile driveability models with proven predictive capability. The application of these 56 methods to larger diameter piles is uncertain. A major component of driveability models involves 57 estimating the static resistance to driving, SRD, a parameter analogous to pile axial capacity. Recent 58 research on axial capacity design has led to improved models that use Cone Penetration Test, CPT data 59 to estimate pile capacity and include for the effects of friction fatigue and soil plugging. The 60 applicability of these methods to estimating pile driveability for larger diameter piles is of interest. In 61 this paper, recent CPT based axial capacity approaches, modified for mobilised base resistance and 62 ageing, are applied to estimating driveability of 4.2m diameter piles. A database of pile installation 63 records from North sea installations are used to benchmark the methods. Accounting for factors such 64as pile ageing and the relatively low displacement mobilised during individual hammer blows improves 65 the quality of prediction of pile driveability for the conditions evaluated in this study. 66 67

Installation of Large-Diameter Monopiles: Introducing Wave Dispersion and Non-Local Soil Reaction

“…Furthermore, Byrne et al [13] introduced a modification factor in the aforementioned approaches, which resulted in improved and adequate drivability predictions. However, in a subsequent extensive study [15], both the existing and the modified approaches were proved not to provide reliable predictions of the blow counts.…”

Optimization of Impact Pile Driving Using Optical Fiber Bragg-Grating Measurements

“…Residual loads can be significant when the base capacity is similar to the shaft capacity, as in sands (Briaud and Tucker 1984). Residual loads are thought to be low during the driving of large-diameter fully coring tubular piles (Byrne et al 2018) for which large locked-in tensile loads are not expected. The zero-drift observed may be a result of (1) locked-in stresses in the steel or in the steel groove which are shaken down during driving, and/or (2) changes in strain due to changes in temperature, shown by calibration to be significant, as the pile transmits heat to the surrounding chalk.…”

Empirical Shaft Resistance of Driven Piles Penetrating Weak Rock

“…In the case where this material collapses, arching may occur meaning the effective stresses acting on the pile might be low. This is especially significant for increasing h / D , where h is the distance from the pile tip to a given soil horizon and D is the pile diameter (Byrne et al 2018 ).…”