Geological and Environmental Sustainability

Geo-Technical Investigation Techniques

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The geotechnical behaviour of natural soils and weak rocks suggest that the shear stiffness controlling wave propagation in near-surface materials will be similar to those which geotechnical engineers wish to measure, and use to calculate movements of the ground around engineering structures. Field seismic techniques which have been found suitable for stiffness determination are reviewed. The benefits of using geophysical methods, as compared with the use of routine geotechnical techniques, are discussed. These techniques allow the study of the spatial and temporal variations of geological structures. Until recently, geophysical techniques have been relatively little used for the reconnaissance of landslides for at least two main reasons. The first one is that geophysical methods provide images in terms of physical parameters, which are not directly linked to the geological and mechanical properties required by geologists and engineers. The second reason shown through this study probably comes from a tendency among a part of the geophysicists to overestimate the quality and reliability of the results. A comprehensive site investigation was performed offshore the island of Chek-Lap Kok as part of the civil engineering design studies for the proposed replacement airport at Hong Kong, The program included conventional drilling and sampling carried out from floating craft, as well as extensive in situ testing, including piezocone penetration, field vane shear, and permeability tests. The results of the field and laboratory tests are synthesized to develop engineering properties appropriate for reclamation design. Correlations between the piezocone data and field vane shear tests are presented, as well as correlations of compressibility parameters with index properties. Normalized strength parameters for the two marine clays are also presented.