Design Approach for Grouted Driven Piles in Calcareous Soil
Authors: Gunasena U. , Jeer H.A. , Randolph M.F. 
Published: October 2008

Piles driven into sediments of high calcareous content generally have very low shatl capacity, due to the crushing and rearrangement of the soi/ grains adjacent to the pi/e shait However, the tictional capacity may be fullyrecovered by injecting grout into that zone. Such â??grouted driven pilesâ?? are significantly cheaper to install than conventional drilled and grouted piles, and avoid the potential problems of hole stability in the latter type of pile.

The paper describes a systematic program of laboratory tests undetiaken to explore the grouting operation and subsequent shafl friction in reconstituted calcareous soil cemented to different strengths. Grouting at this reduced scale is considerably more challenging than at field scale, and yet it has been shown that consistent results, with high shaft friction, can be obtained in all soil types. Design rules are presented in terms of expected grout coverage and relationships between shafi friction, cone resistance of the soil and grouting pressure. .

INTRODUCTION

Grouted driven piles have the capability of replacing drilled and grouted piles in the many parts of the world where calcareous sediments abound, such as off the coasts of Australia, India and Brazil and in the Middle East. Even where conventional driven piles may provide sufficient capacity (mainly in end-bearing), postinstallation grouting will improve the shaft capacity with resulting savings in the total length and cost of the piles.

In the calcareous sediments off the coast of Australia, shaft friction for driven piles is generally less than 30 kPa and in extreme cases appeam to fall to below 5 kPa (Poulos et al, 1988; Randolph, 1988). By contrast, tests on sections of drilled and grouted piles have indicated values of shaft fridlon in the range 200 kPa to over 800 kPa (Hyden et al, 1988; Fahey et al, 1992).

The use of pressure grouting to improve the capacity and stiffness of piles is now widespread for onshore applications. A common technique is to inject grout into a small (50 mm diameter) tube, known as a tube a manchette, with a pattern of holes in the wall of the tube that allow flow of grout into the surrounding medium. For cast in situ piles, the tube may protrude below the tip of the pile (for base grouting), or be attached to the reinforcing cage within the main pile. In the latter case, grouting is undertaken when the pile concrete is still green, typically 24 hours after pouring.

For driven piles, a tube A manchette may be installed adjacent to the pile shaft after driving the pile, in order to allow grouting of the shaft. Alternatively, grouting tubes may be pre-installed within the pile itself, with connections (and one-way valves) through the pile wall. The latter approach has been described by Rickman and Barthelemy (1988), where average shaft friction values of 150-200 kPa were achieved on a driven pile in a calcareous deposit, where shaft friction for the untreated pile wasbelow 5 kPa (Nauroy et al, 1988).

The latter scheme has significant advantages for offshore applications.