This paper presents the results of a series undrained cyclic, loading tests on an artificially cemented calcareous soil. The effects of the mean stress, stress amplitude, effective confining stress, and drainage in between periods of undrained, cyclic loading have been investigated. The results have been presented in the form of a fatigue S-N curve relating stress to the number of cycles to failure. For undrained tests significant reductions in strength can occur under cyclic loading. The number of cycles to failure increases with decreases in both mean stress, and stress amplitude, and as a result of allowing drainage. Comparisons with cyclic tests of uncemented calcareous sand show that the cementation has a significant effect on the cyclic strength.
Calcareous" sediments are found in many offshore regions where oil and gas have been discovered (e.g., The North-West Shelf and Bass" Strait off Australia, the Arabian Gulf, and the Gulf of Mexico). The effect of cyclic loading on offshore structures and their foundations in these regions has been investigated by many researchers" (e.g. Angemeer et aI, 1973). Interest in the behaviour of these soils has recently increased as a result of the difficulties encountered with the foundations of the North Rankin A platform (Jewell and AndrewS, 1988). Cyclic triaxial tests on the naturally cemented calcareous soil from the North Rankin site have been reported by Carter et, aI:, 1988 in which only relatively small numbers of cycles were considered, and more recently by Airey and Fahey (1991) when the soil was, subjected to larger numbers of cycles. Both papers have, shown that compressive cyclic stresses can cause a significant strength reduction., However the variations, in the cementation of the naturally cemented samples made it difficult to estimate an appropriate static reference strength, and thus to interpret the results from the natural soil.
