Influence of salinity on the mechanical behaviors of CO2 hydrate-bearing silty sand

The mechanical behaviors of hydrate-bearing sediments are influenced by multiple factors, and the strata of deep sea bed are in a salty environment. So far, however, the influence of salinity on the mechanical behaviors of hydrate-bearing sediments has been less reported and its influence laws have not been well addressed. In this paper, CO2 hydrate-bearing silty sand is prepared by using sodium chloride solution with different concentrations, and triaxial shearing tests are performed under different confining pressures, so as to reveal the influence laws of salinity on stress–strain relationship, strength, rigidity and dilatancy. And the following research results are obtained. First, salinity leads to the migration of the phase equilibrium line of hydrate-bearing soil. Under the same initial water content, salinity results in the decrease of hydrate saturation in the soil and the increase of unhydrated water content. Second, to form the same hydrate saturation, the initial water content of hydrate-bearing soil with salt shall be higher than that without salt, so the shearing strength of hydrate-bearing soil with salt is weaker than that without salt. Third, salinity has a greater influence on the cohesion of hydrate-bearing soil. With the increase of hydrate saturation, the cohesion of hydrate-bearing soil with salt increases slightly, while that without salt increases significantly. In conclusion, the influence of salinity on the shearing strength behaviors of hydrate-bearing silty sand is generated as the unhydrated water content changes. The more the unhydrated water, the lower the soil strength, the smaller the secant modulus and the less obvious the dilatancy. What's more, the strength behavior of hydrate-bearing soil is not only related to hydrate saturation, but also in a close relationship with unhydrated water content. Traditionally, only the influence of hydrate saturation on the shearing strength of hydrate-bearing soil is taken into consideration, which makes it impossible to accurately describe the evolution of the strength behavior of hydrate-bearing soil under physical–chemical action. © 2022 Natural Gas Industry Journal Agency. All rights reserved.