Shear Modulus of Kaolin Containing Methane Bubbles

Abstract

Measurements of undrained shear moduli are reported from a program of laboratory tests on reconstituted kaolin samples containing relatively large bubbles of methane gas. The experimental program included low‐frequency torsional stress‐strain loops and torsional resonant column tests, providing values of shear moduli for shear‐strain amplitudes from 0.0004% to 0.1%. At all values of strain amplitude, the reduction of shear moduli caused by the presence of gas bubbles was greater than predicted by a theoretical elastic expression. This pattern of behavior was attributed to the formation of local yield zones around the gas‐bubble cavities during consolidation prior to shear testing (a phenomenon that would also occur in‐situ within offshore sediments). The results of the research program suggest that reductions in shear moduli of up to 50% could be caused by relatively small volumes of gas bubbles, occupying just a few percent of the total soil volume. This would have considerable significance for the displacements of offshore foundations constructed on sediments containing undissolved gas.