Geotechnical laboratory tests on soil samples recovered from eastern Nankai Trough

The world's first offshore test of gas production from methane hydrate is planned in the eastern Nankai Trough; the extensive distribution of high-amplitude BSRs suggest that a large amount of methane hydrate may be present here. In order to produce methane gas safely while minimizing the environmental damage, several wide-ranging issues need to be addressed. One issue involves assessing the stability of the seafloor; we are investigating whether deformation of the seafloor occurs during the production of methane gas from methane hydrate. Geotechnical properties of the seafloor have significant effects on deformation behavior. Soil samples were recovered from the gas-production site in the eastern Nankai Trough. This paper presents the geotechnical properties of the samples, as determined on the basis of the results of laboratory tests. Soil index tests, consolidation tests, and triaxial compression tests were conducted to obtain the geotechnical parameters that are necessary for a deep seafloor stability analysis.