Mechanical behaviour of gas-charged marine plastic sediments

Understanding how free gas modifies the mechanical behaviour of marine plastic sediments remains a challenging issue. Special triaxial tests were carried out on natural sediments recovered from the Gulf of Guinea. Special attention was devoted to the laboratory preparation procedure, involving saturation of natural marine sediment samples with carbonated water and generation of free gas following undrained unloading. Experimental data show that soil destructuration and damage generated by gas expansion and exsolution are at the origin of (a) the increase in the isotropic compressibility and decrease in the preconsolidation pressure, and (b) the decrease in the peak undrained strength and abrupt increase of the pore pressure during undrained shearing. The experimental data also show that flooding of gas bubbles and dissolution of free gas do not imply a complete strength recovery of natural sediments.