ABSTRACT

The problem of the shear behaviour of interfaces between drilled and grouted piles and surrounding carbonate soils is addressed. Results of laboratory shear tests on artificially cemented carbonate soils are presented and the implications of the results for the design of offshore piles are discussed.

INTRODUCTION

In offshore conditions, large structures are often founded on piles which are either driven or drilled and grouted into a weakly cemented soil mass. Piles driven into these soils depend largely on the frictional behaviour of the pile-soil interface to develop their load carrying capacity, whereas drilled and grouted piles rely on both bonding and the frictional resistance at the interface. Drilled and grouted foundations are becoming increasingly popular as a means of supporting offshore oil and gas platforms in Australia. For such foundation piles, the interface between the cement grout and the surrounding calcareous soil is subjected to cyclic shear loading as the wind and wave forces acting on the platform are transmitted to the seabed. Understanding the mechanical response of cement-soil interfaces under these loading conditions is therefore of major importance to the design of drilled and grouted offshore piles. It is well known that calcareous soils may undergo large volume reductions when subjected to relatively moderate stress levels. The application of both shear and hydrostatic stress components can induce these volume changes, which can lead to excessive foundation movements, and can significantly reduce the ultimate load capacity of foundations in these soils. Numerous papers describing these phenomena and other important geological and engineering features of carbonate soils are contained in the conference volumes edited by Jewell and Andrews (1988).

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