ABSTRACT:

A modified load transfer (t-z) analysis for axially loaded piles is presented in this paper. The method can be used to predict the full load-displacement behaviour of a pile, and unlike the conventional t-z analysis It IS also capable of indicating the complete mechanism of load transfer as well as the complete stress path at the pile-soil interface. It is able to do this by assuming as input a constitutive model for the pile-soil interface that permits coupling between the shear and normal modes of deformation. The use of the technique is illustrated for a driven and grouted pile in calcareous soil

INTRODUCTION

Many fixed offshore platforms used for the recovery of natural hydrocarbons are supported on pile foundations. In a number of regions of the world, e, g. off the coasts of India, Australia and in the Persian Gulf, the sub-sea soil conditions Consist of significant deposits of calcareous soils. This soil type has posed a number of difficult problems for designers of these offshore platforms. These low values of skin function are largely a result of the crushing of the Soil around the piles during driving, which gives rise to low normal stresses acting on the pile and hence low frictional shear resistance. Recently, some offshore platforms have been designed to be supported on piles which are either fully or partially grouted into the calcareous medium. In some cases, primary piles are driven to the appropriate depth, and then secondary piles are constructed by augering a cylindrical hole and grouting a steel pipe insert below the primary piles. In other cases the piles are driven and then cement grout IS injected through tubes that pass down the inside and through the walls of the pile. The latter are referred to as driven and grouted piles.

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