Dynamic Gassy Soils Behaviour, Gulf of Mexico-Paper

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The study investigated how gas affects marine soil behavior under dynamic loading, using methane-bearing clay and carbon-dioxide-bearing sand from a Gulf of Mexico site.<br /><br />For clay, researchers conducted static and rapid undrained direct simple shear (DSS) tests on soft and firm samples with varying gas contents. Gas-bearing clays generally responded faster than gas-free clay, and the results suggested a short-term hardening effect as gas bubbles compressed and interacted with the soil structure. The strength trends depended on consistency: in soft clay, samples with less gas generally performed better than those with more gas during rapid shearing; in firm clay, samples with more gas performed better than those with less. The authors attribute this difference to firm clay’s greater ability to contain gas pressure, but emphasize that more tests are needed.<br /><br />For sand, three cyclic triaxial tests compared samples with different initial degrees of saturation. After 25 cycles, the fully saturated sample developed substantially greater axial strain and pore pressure than samples containing free gas. More free gas generally corresponded to lower strain and pore pressure, indicating greater cyclic resistance in the tested conditions.<br /><br />Overall, the findings suggest that gas can alter dynamic soil response and produce transient hardening in clay. In the tested dense to very dense sands, free gas did not appear to worsen cyclic behavior and may marginally stiffen the response of deep pile foundations. These conclusions are preliminary because the testing program was limited.

Keywords

gas effects

marine soil behavior

dynamic loading

methane-bearing clay

carbon-dioxide-bearing sand

direct simple shear

cyclic triaxial tests

undrained shear strength

pore pressure

cyclic resistance