Mechanical Characteristics of the Hydrate-Bearing Sediments in the South China Sea Using a Multistage Triaxial Loading Test

Abstract

Methane hydrate is being widely considered as an energy source by countries worldwide due to its to environmentally friendly and large reserves. However, during the exploitation process, a series of geological engineering disasters can be induced. Therefore, it is necessary to comprehensively study the mechanical characteristics of methane hydrate before commencing with commercial development. Many researchers have used conventional single-stage triaxial loading tests to study the mechanical characteristics of hydrate-bearing sediments, and these have the disadvantages of being time-consuming and labor-intensive. A multistage triaxial loading test can shear a single specimen under different effective confining pressures to obtain a series of mechanical parameters (strength, cohesion, internal frictional angle, etc.). In this study, a high-pressure and low-temperature triaxial apparatus was used to perform multistage and single-stage triaxial loading tests under effective confining pressures of 0.25, 0.5, and 1 MPa, and the specimens were remolded from the South China Sea had porosities of approximately 40% and a hydrate saturation of approximately 30%. The results show that under the relatively low effective confining pressure (0.25 and 0.5 MPa) the stress–strain and volumetric strain–axial strain curves between multistage and single-stage triaxial loading tests are highly coincident, and stress accumulation and compaction seem to have little effect on the strength and volumetric strain in the multistage triaxial loading test. However, under a relatively high effective confining pressure (1 MPa), the stress–strain and volumetric strain–axial strain curves of the two methods present a certain difference. In addition, the elastic modulus obtained by the multistage triaxial loading tests was larger than that from the single-stage triaxial loading tests due to stress accumulation and compaction.