Triaxial Test System for Gas Hydrate-Bearing Sediments with Stable Conditions

Abstract

Under the seabed, gas hydrates are buried as solid materials that consist of water and gas molecules. Dissociation of gas hydrates induce mechanical properties change because solid-phase gas hydrates transformed to gas and liquid phase. Due to dissociation of gas hydrates, the bearing sediments can be collapsed or subsided. The triaxial test is a method for evaluating the mechanical properties of soil. Confining stress is applied to the specimen for simulating in-situ condition of the soil and axial loading is applied to induce shear failure. The modulus value can be derived through the relationship between the applying load and the strain level. Also cohesion and friction angle can be obtained based on the peak strength value according to various conditions of the confining stress. In the case of gas hydrate-bearing sediments, the mechanical properties change by the cementation effect of the gas hydrates. Therefore, experimental research for mechanical properties of gas hydrate-bearing sediments are required to understand mechanical behaviors of the sediments. However, high pressure and low temperature conditions are necessary to maintain stable condition of gas hydrates during the experiments. The triaxial tests should be conducted under the gas hydrate stable environment. In this study, in order to simulate the gas hydrate-bearing sediments, we constructed a system that can perform triaxial tests under high pressure and low temperature environment. Then, triaxial tests were carried out using specimens of gas hydrate-bearing sediments. Mechanical properties that achieved from the triaxial tests can be used as input parameters for the numerical analysis, which simulate the gas hydrate dissociation process.