Offshore geological investigations have played a vital role in Hong Kong's major new port and airport developments since the late 1980s. Knowledge of the Quaternary stratigraphy has been essential for identifying economically-dredgeable sand for use as reclamation fill and for designing offshore engineering structures. The initial exploration for sand was based on a simple geological model of Holocene marine muds overlying localised river sands in a variably-eroded surface of Pleistocene alluvial sediments. Investigations for the sand comprised extensive boomer seismic reflection profiling, correlated by means of continuously-sampled drillholes, vibrocores and cone penetration tests. Major economic sand deposits were found, where predicted, along Pleistocene drainage lines, with the volume of mud overburden generally thinnest where Holocene tidal currents were greatest. After detailed dredging assessments, c. 600Mm3 of exploitable sand reserves were identified between 1987 and 1996, sufficient to meet Hong Kong's anticipated needs for marine fill up to the year 2015. The exploration programme has enabled the geological model to be refined and the stratigraphy expanded to include four Quaternary formations. Much of the geological information has been entered into computerised databases and compiled into maps and memoirs by the Hong Kong Geological Survey. This knowledge is being applied in the design and construction of reclamations, seawalls, breakwaters, submarine slopes and pipelines.
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