Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmos32a..07l&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #OS32A-07
Physics
4217 Coastal Processes, 4219 Continental Shelf And Slope Processes (3002), 4262 Ocean Observing Systems, 4294 Instruments And Techniques
Scientific paper
Geotechnical analysis of the conditions leading to slope failure on the slope of the Fraser River Delta has resulted in a design for the installation of an array of instruments to measure liquefaction and failure events that will utilize the VENUS underwater observatory. It is known that the bed at shallow depth fails periodically due to tidal drawdown resulting in excess pore pressures. We further hypothesize that storm surges and seismic activity lead to pore pressure increases and corresponding decreases in sediment strength. Instruments will therefore include piezometers to measure (pore) pressures, in the water column and at two depths within the bed over time scales of milliseconds to years. The seabed in this area contains a significant volume of gas (1%), which leads up to an 80% attenuation in pore pressure within the top 5m, and which also likely affects the shear strength of the soil. To measure the extent and variation in gas, hydrophones will be placed at strategic locations to allow acoustic measurement of gas content and calculation of sediment bulk properties and effective stress. Accelerometers will measure seismic activity, and inclinometers will measure associated strain. Pore pressures are also affected by seasonal groundwater flows which will be measured by the combination of piezometers and thermistors. A 'sacrificial' package will be placed in an area of known high activity in the hope of capturing events leading to failures. Deployment and networking of the instruments will be facilitated by the Victoria Experimental Network Under the Sea (VENUS) Project. The project will install an underwater fibre optic network allowing real time observations so that the parameters described above can be studied in great detail. The array will consist of six seismic piezometers, ranging in water depths from 10m to 100m, and down to sediment depths of 5m. It is hoped that in the future the instruments may be used as an early warning system to large, and life-threatening, failures which are known to occur in this area. VENUS will facilitate development of methods and geotechnical instruments for use in related fields. For example, there is interest in using the array as a test ground for offshore gas hydrate studies.
Hill Patricia
Lintern G.
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