OFFSHORE QUATERNARY SEDIMENTS AND THEIR ENGINEERING SIGNIFICANCE IN HONG-KONG

Investigation works undertaken for coastal engineering projects in Hon g Kong has provided abundant information on the Quaternary sedimentary sequence beneath the sea floor. Although the significance of such inf ormation may not have been realized at the time of these projects, val uable lessons have often been learnt afterwards. Some examples of the important engineering applications concerning offshore Quaternary sedi ments include: (1) The provision of information on water movement, sed iment transport and sedimentation rates during the Holocene period. (2 ) The identification of exploitable offshore sand and gravel resources . (3) The interpretation of marine geophysical data through the availa bility of reliable borehole descriptions. (4) The enhancement of engin eering soil testing results and their interpretation. (5) The predicti on of rates of long-term ground settlement in coastal land reclaimatio ns. (6) The selection of offshore sites for waste disposal. (7) The re duction in cost of coastal engineering projects through choosing the m ost cost-effective site. (8) The provision of baseline data to assist environmental impact assessment. A new geological model is proposed fo r the offshore Quaternary sedimentary sequence of Hong Kong. The engin eering properties of the sediments are found to be closely related to the palaeo-environmental changes.