ABSTRACT

A state-of-the-art review is presented of information on design, installation and performance of grouted piles. Grouted piles are finding increasing use as foundation elements for offshore structures where hard soil conditions, calcareous sands and/or deep embedment for high axial capacity preclude installation by conventional pile driving methods. Purposes of this study were to consolidate performance data on axially loaded grouted piles and to interpret the data in view of predetermining ultimate axial capacity. Design procedures are given that are used by some in the offshore industry to predetermine axial capacity of grouted piles.

The influence of stress relief, moisture migration, technical disturbance, and drilling mud on the development of skin friction is discussed. Research studies are discussed which have potential for making significant improvements in the state-of-the-art.

INTRODUCTION

Axial load pile requirements for offshore drilling/production platforms (typically 1000 to 4000 tons) and/or difficult soil conditions (dense sand, hard clay, reefs, etc.) may preclude conventional pile driving as a viable installation technique for attaining typical design pile penetrations of 200 to 400 ft. When a design embedment cannot be attained, a supplemental installation method is required (31). A supplemental installation method may also be required for sites where calcareous sand deposits predominate. This is because pile driving disturbance can result in low lateral soil pressures which will reduce developable frictional resistance.

Methods of grouting a pile into an oversized hole or drilling and under reaming for a cast-in-place pile (Fig. 1) recently have received increased attention by offshore operators. Current technology for computing ultimate capacities of these types of foundation elements is based primarily on experience with drilled-and-undreamed shafts used for land installations. Typical measured ultimate capacities and penetrations of drilled shafts from land installations from which. empirical design parameters are derived are compared in Fig. 2 with typical design ultimate capacities and penetrations required for offshore installations. It shows that as much as a ten-fold extrapolation of the regime of these data must be made for typical offshore design applications.

Objectives of this paper are to present a state-of-the-art review of information on design, installation and performance of grouted piles and undreamed footings and to suggest research studies which have potential for making significant improvements in the design and installation of these foundation types for offshore applications.

ULTIMATE AXIAL CAPACITY
Mathematical Model

Ultimate pile capacity is derived from end bearing and from shear stresses developed along the pile shaft. The conventional mathematical expression for ultimate capacity of a cylindrical pile with radius R and penetration L is (regardless of installation method)

(Mathematical Equation Available in Full Paper)

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