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Technical paper: Geophysical evaluation of rock mass conditions for sub-sea tunnelling - Strategic Sewage Disposal Scheme, Hong Kong

by Keith C Maynard, AB2H Consultants, Hong Kong, and Ola K Fjeld, Geoteam, Trondheim, Norway.


A large geophysical survey has been undertaken as part of the site investigation for the Strategic Sewage Disposal Scheme, Hong Kong. The scheme proposes a series of deep rock tunnels and associated pumping stations and treatment works designed to improve the water quality of Victoria Harbour. The geophysical survey involved the integration of three techniques; analogue and digital reflection, and marine seismic refraction. The digital reflection and marine seismic ref’raction methods were used for the first time in Hong Kong.

Results from the survey have interpreted the depth to bedrock and rock quality (relating to seismic velocity), allowing the identification of possible weakness zones and amount of rock cover. Also, detailed information relating to the superficial fiments, bathymetry and seabed morphology have been determmed. In addition, the geophysical data has been used to optimise borehole locations, increasing the effectiveness of the drilling programme. 

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