Experimental Study on the Shear Band of Methane Hydrate-Bearing Sediment

Abstract

The occurrence of a shear band is often thought as the precursor of failure. To study the initiation of shear banding in gas hydrate-bearing sediments, two groups of triaxial compression tests combined with a CT (computer tomography) scan were conducted by triaxial CT-integrated equipment under two confining pressures and seven hydrate saturations. The macro stress–strain curves and the corresponding CT scanning images of the micro-structure and the distribution of the components were obtained. The geometric parameters of the shear bands were measured based on the CT images at four typical axial strains, respectively. The distribution characteristics of soil particles, water, hydrate and gas were also analyzed. It is shown that the existence of methane hydrate changes the mechanical property of hydrate-bearing sediment from plastic failure to brittle failure when the hydrate saturation is over 13%, which occurs in the range of the tests in this paper. The peak of the deviatoric stress increases with the hydrate saturation. The shear band is in either a single oblique line or inter-cross lines depending on the hydrate saturation, the effective confining pressure and the initial distribution of the gas hydrate. Most of the shear band surfaces are not straight, and the widths of the shear bands are almost non-uniformly distributed.

Triaxial Tests of Hydrate-Bearing Clayey-Silty Sediments Under Different Hydrate Saturations and Effective Confining Pressures

“…This shows that with the increase in hydrate saturation, the stress−strain curve of sediments changes from strain hardening to strain softening. This is similar to the experimental results of sand sediments containing methane hydrate developed by Lu et al 40 They indicate that when the hydrate saturation exceeds 13%, the existence of methane hydrate changes the deformation failure of hydrate-bearing sediments from plastic failure to brittle failure. However, this is quite different from the failure modes of HBCS with high clay content (36%) and pure clay sediments.…”

“…Hydrate Saturation Calculation Method. In this paper, the gas-excess method is used to generate hydrate, 40 and the hydrate saturation in sediments is indirectly estimated by controlling the water content in the sample. Assuming that all the water in the sample forms hydrate, the saturation of hydrate in the sediments can be converted according to the law of conservation of mass.…”

Instability and Failure of Subsea Structures

“…To investigate the shear band initiation within gas hydrate-bearing sediments, triaxial compression tests were conducted, combined with a computer tomography (CT) scan [17]. Their observations indicated that the shear band either occurred in a single oblique line or inter-cross lines depending on the hydrate saturation, the effective confining pressure and the initial distribution of the gas hydrate.…”

Active Methanotrophs and Their Response to Temperature in Marine Environments: An Experimental Study

“…1 Average abundance of pmoA genes calculated from the two treatments at each temperature. 2 One-way ANOVA was conducted with abundance of pmoA genes obtained from all six experimental treatments. 3 d.f is degree of freedom.…”

“…At present, gas hydrates are the most abundant source of methane on the earth [1][2][3]. A great amount of methane is released due to the decomposition of gas hydrates from submarine reservoirs [4], which are gradually consumed by anaerobic methanotrophic archaea (ANME) in anoxic sediment layers and aerobic methanotrophs in oxic layers [5,6].…”