Installation of Offshore Driven Piles - Regional Experience

Abstract

The types of subsoil dealt with in the Gulf of Thailand and surrounding region are conducive to the installation of driven piles. Among the various aspects of driven pile design, pile driveability analysis plays a major role in the selection of the feasible hammer and determining pile make-up to suit, besides defining acceptance criteria to ensure a certain level of confidence of its fitness for purpose. The accuracy of a driveability study particularly depends on the selection of its parameters to best represent the in-situ scenario. The most uncertain of the parameters are those related to the soil model. It has been observed in recent projects in the Gulf of Thailand, that the consideration of suitable soil resistance to driving, coupled with soil dynamic parameters, significantly affects driving sequence planning, design, material, hammer selection and above all pile acceptance criteria. This is particularly true for a region that contains predominantly clayey subsoil resulting in large diameter, long friction piles susceptible to driving disturbances and slow strength recovery. Different researchers suggested suitable dynamic parameters and soil resistance during driving calibrated to specific regions. Our regional experience suggests a set of soil degradation and parameters to suit the different stages of driving which is corroborated by pile monitoring records in one of the sites during continuous and delayed driving scenarios. The most sensitive of all dynamic soil parameters is the skin damping in clay. While Smith’s wave theory approach considers a conservative assumption in selecting the parameters in absence of site-specific data, a different approach may be adopted based on consistency of the clay for a site where the geotechnical parameters are well defined. This paper includes an independent study on the effects of variations in dynamic parameters and resistance at different stages of driving and suitability of choices of different pile make-up and hammers for an optimum design. Earlier experiences, simulation studies and back-analyses of available driving records are undertaken in order to reach a reasonable judgment for the region.