Cyclic Behavior and Critical Stress Ratios of Methane Hydrate-Bearing Sediments under Varying Effective Confining Pressures via Undrained Cyclic Loading

Abstract

Natural gas hydrate reservoirs are subjected to direct natural disasters such as earthquakes and tsunamis, as well as indirect cyclic loads transmitted through deep-sea platforms induced by waves and ocean currents. In engineering practice, the critical cyclic stress ratio (CSRc) is commonly used as a key parameter to assess soil failure potential under cyclic loading. In this study, the cyclic behavior of methane hydrate-bearing sediments (HBS) was investigated via progressively evolving cyclic (PEC) loading on undrained specimens under controlled experimental conditions. Hydrates enhance the liquefaction resistance of the soil, and increasing hydrate saturation further improves the cyclic resistance of the specimens. The threshold CSR and CSRc for HBS are derived from the double inflection points identified on the cyclic modulus and normalized cumulative excess pore water pressure curves. Compared with hydrate-free specimens, the CSRc of HBS increases significantly but decreases with increasing effective confining pressure. Constant-amplitude cyclic loading tests have validated the reliability of the PEC loading method for determining the CSRc. At the engineering application level, the PEC loading testing approach proves to be more accurate and reliable when confronted with complex, long-term loads in deep-sea environments.