Mechanical behaviour of gas-charged marine plastic sediments

Abstract

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.

Mechanical behaviour of gas-charged fine sediments: model formulation and calibration

“…Sultan et al (2012) noted that the presence of gas has a similar effect on the G u of natural Gulf of Guinea (GoG) clay samples. Other results of triaxial tests reported by Wheeler et al (1991) revealed that the normalised Young's modulus measured at an axial strain of 0 .…”

“…85. The presence of gas bubbles can have significant effects on the consolidation behaviour and strength properties, with gassy soils reacting differently compared to saturated soils to environmental changes in load and temperature (Esrig & Kirby, 1977;Sills & Wheeler, 1992;Grozic et al, 1999;Sills & Gonzalez, 2001;Amaratunga & Grozic, 2009;Puzrin et al, 2011;Rebata-Landa & Santamarina, 2012;Sultan et al, 2012). Accordingly, gas-charging has important consequences for slope stability assessment, waste management and in turn for the planning of on-and offshore engineering operations Tjelta et al, 2007;Mabrouk & Rowe, 2011).…”

How to evacuate 10 km3 of mud: saturate with gas and decrease the pressure!

“…Sultan et al (2012) carried out experiments on natural mudstone samples filled by gas-saturated water under confining pressure, recovered by coring from the continental slope of the Gulf of Guinea at about 20 m below seafloor. The experiment showed that lowering the confining pressure resulted in immediate decrease of P-and S-wave velocities.…”

Editorial

“…The papers by Sultan et al (2012) and Torisu et al (2012) tackle the intrinsic response of soil in two different scenarios. Sultan et al (2012) are concerned with the effect of gas, which frequently occurs at offshore development sites, on the behaviour of soil and particularly when the gas comes into or out of solution.…”

“…The papers by Sultan et al (2012) and Torisu et al (2012) tackle the intrinsic response of soil in two different scenarios. Sultan et al (2012) are concerned with the effect of gas, which frequently occurs at offshore development sites, on the behaviour of soil and particularly when the gas comes into or out of solution. Torisu et al (2012) are more concerned with rate effects on the response of deep marine clays, and present experimental results with loading rates spanning two orders of magnitude.…”