ABSTRACT:

Shearbox tests under conditions of constant normal load and constant normal stiffness have been performed to investigate the interface response of piles in calcareous soil. Both monotonic and load and displacement controlled cyclic tests have been performed. Large displacement cyclic tests have been found to, cause a rapid drop in normal stress, and hence shear stress that can be mobilised on a pile. Attempts have been made to re-impose the normal stress to model the behaviour of driven and grouted piles. A limited improvement in shear capacity has been found in these tests.

INTRODUCTION

The low axial capacities of driven piles in calcareous sediments have provided major problems for the designers of offshore structures founded on these soils. These sediments are widely distributed on the continental shelves in tropical and temperate regions of the world, and are found m many areas containing major oil and gas reserves (eg. the Arabian Gulf, and Bass Strait and the North-West shelf off Australia). Both of these solutions require costly drilling operations so to avoid this an alternative piling method has been proposed using driven and grouted piles (Barthelemy et aI, 1986). The idea behind this technique is to increase the normal stresses acting on the pile, and hence increase the frictional stresses and axial capacity. A number of small scale model tests have shown that this method can lead to similar strengths to those obtained with drilled and grouted piles. However, uncertainties remain as to the effect of limned grout cover, the effect of the grouting pressure, and the mechanisms leading to the greatly Improved performance over driven piles. Whichever piling technique is used there IS also uncertainty regarding the so called "load-transfer" response relating the mobilised friction to the pile displacement m calcareous soil.

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