Mechanical properties of sandy sediment containing methane hydrate

Triaxial compression tests are performed on artificial sandy sediment containing methane hydrate to clarify the factors controlling the mechanical strength of hydrate-containing sediments in the deep ocean. The mode of hydrate occurrence in the pores of the sediment is found to have a substantial effect on the strength characteristics of the hydrate-saturated specimens. Strongly bonded hydrate and sand, formed by pumping methane gas into wet sand under pressure, exhibits a marked increase in strength with hydrate saturation, whereas weakly bonded specimen, formed by growing hydrate in an ice and sand mixture only displays an increase in strength at high hydrate saturations. The presence of water in the pore space is found to lower the mechanical strength, whereas methane gas does not have such an effect. The present experiments therefore show that the mechanical properties of hydrate-containing sandy sediments are controlled by the mode of hydrate occurrence in the pores. (Author)