Grouted piles are used extensively in offshore deposits of calcareous soils, because of the relatively low shaft capacity of driven piles. Two construction techniques may be used: drilled and grouted piles, where steel pipes are grouted into predrilled oversize holes; and grouted driven piles, where driven pipe piles are pressure-grouted through valves distributed along the pile shaft The paper describes the results of a comprehensive set of field and laboratory tests on grouted piles that were undertaken in calcarenite in Australia, to validate pile design for the calcareous deposits which predominate off the coast of Australia. The experimental results were used to validate and calibrate a numerical load transfer model, that simulates degradation and accumulation of permanent displacement under cyclic loading. The paper provides a recommended design approach for grouted piles in calcareous soil, with due account taken of construction technique, pile diameter and soil strength as indicated by the cone resistance.
Drilled and grouted piles are commonly used for offshore foundations in the compressible calcareous soil deposits found off the coasts of countries such as Australia, India and Brazil. Despite their prevalence, design rules remain largely empirical, with a limited database of field and laboratory tests.
Over the last decade, an alternative construction method for grouted piles has emerged. Instead of grouting a steel tubular into an open-hole (a relatively costly and potentially unstable sequence), piles are first driven into the formation, and then pressure-grouted along their lengths through pre-installed valves. Rickman and Barthelemy have described this so called ‘grouted driven pile’ construction method, although the technique has still to be used for a major offshore structure.
EconomicalIy, there appear to be a number of advantagesfor grouted driven piles:
The pile may be installed in one piece, using a single installation method (driving), compared with a driven primary pile, drilling out of the primary and hole for the insert pile, and installation of the insert pile.
In principle, grouting may start from close to the seabed, rather than from below the primary pile.
The pile diameter remains at the maximum that will fit the jacket sleeves throughout its length, with no step down from primary to secondary.
From a risk viewpoint, the potential danger of hole instability for the drilled and grouted pile must be weighed against the uncertainty of grout coverage for the grouted driven pile. From a technical viewpoint the pressurisation of the grout for the grouted driven pile is likely to entail higher shaft capacity than for a drilled and grouted pile. However, the difference may be of secondary importance compared with risk and eeonomic considerations.
