Marine fine-grained sediments contain relatively large biogas bubbles. Initial water depth affects the existence state of bubbles and thus the strength of gassy soils, which may either increase or decrease the strength of soil. In this study, a series of undrained triaxial tests were carried out to compare the shear characteristics of gassy soils with the same consolidation pressure but different initial pore water pressures （related to water depth）. It is found that the shear strength of the gassy soils varies with initial pore water pressure. The excess pore pressure caused by undrained shearing depends on the initial water depth and can be either lower （due to partial dissipation of pore pressure into relatively large bubbles） or higher （related to collapse of relatively small bubbles at high） than that in the saturated sample with the same consolidation pressure. In a word, the presence of bubbles has beneficially increased undrained shear strength at relatively low pore pressure and vice versa. However, the critical stress ratio for remolding gassy soil is not affected by the initial pore water pressure.
Key words
offshore wind turbines /
soil mechanics /
shear strength /
critical state /
triaxial shear test
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