Triaxial Compressive Properties of Artificial Methane-Hydrate-Bearing Sediments Containing Fine Fraction

In this study, drained triaxial compression tests were conducted on artificial methane-hydrate-bearing sediments containing fine fraction. Toyoura sand (average particle size: D50 = 0.230 mm, fine fraction content: Fc = 0%) , No.7 silica sand (D50 = 0.205 mm, Fc = 1.1%) and No.8 silica sand (D50 = 0.130 mm, Fc = 11.5%) were used as the skeleton of each specimens. Axial loading was conducted at an axial strain rate of 0.1 %/min at a constant temperature of 278 K. The cell pressure and pore pressure were kept constant during axial loading. We found that the strength of the hydrate-sand specimens is almost independent of the type of sand forming the skeleton of the specimen. On the other hand, the stiffness of the specimens containing finer sand particles is lower, probably because fine sand particles can more easily penetrate between the sand and hydrate particles, resulting in larger axial deformation. During the dilatant behavior, the lateral expansive displacement of specimens containing finer sand particles is smaller because the compaction process may continue to occur even when the dilatant behavior becomes the dominant mechanism. The formula expressing the secant Young's modulus obtained from the triaxial compression tests was constructed as a function of methane hydrate saturation and effective confining pressure and was introduced to a numerical simulator. The compressive displacement observed in the earlier work concerning the laboratory-scale experiments of methane hydrate dissociation was simulated by the numerical simulator.