ABSTRACT
Extensive deposits of stiff fissured clays occur at depth beneath the harbours of Newcastle and Botany Bay in New South Wales. The clays from both Botany Bay and Newcastle shows substantial variations in index properties and classify as stiff, fissured clays and clayey silts of high plasticity. The history of coastal and sea level movements, combined with the infilling of Botany Bay sediments derived from various sources has resulted in it being possible to recognise various geological horizons within the sediments. Direct shear tests peak strength showed somewhat less scatter probably because at Newcastle horizontal fissures were generally rough and unpolished so the very low strengths did not occur along the horizontal failure plane forced by the test, while at Botany Bay the effect of lignite bands was excluded. In the triaxial tests the samples were carefully examined after testing to define whether failure was along a fissure, through the substance or some complex mixture.
