Effective stress parameters for Western Sydney clays

Western Sydney soils are mainly stiff to hard clays derived from the weathering of fine-grained sedimentary rocks. They occur as alluvial, colluvial and residual deposits which are increasingly being encountered in major infrastructure and building developments as Western Sydney becomes more heavily developed. Mohr-Coulomb effective strength parameters are commonly used for geotechnical assessments and designs such as cut and fill slope stability, retaining walls and piles. These parameters can be obtained from laboratory tests on samples collected from the field as thin-walled tube samples and subject to triaxial testing. In the absence of such testing, it is widespread practice for cohesion and friction angle values to be selected based on ‘typical values’ in the literature and correlations with index tests. This paper presents analysis of a dataset of laboratory test results from various sites across Western Sydney to assess effective strength parameters for Western Sydney soils with respect to presumptive values in the literature and correlations with index properties.