Mechanical characteristics of overconsolidated hydrate-bearing clayey–silty sediments with various confining pressures

The mechanical characteristics of hydrate-bearing sediments (HBS) are not only dominated by the cementing and filling effects of hydrate, which makes them show the characteristics of overconsolidated soil, but also easily become overconsolidated sediments under the influence of the surrounding environment. In this paper, marine clay collected from hydrate-bearing areas in the South China Sea and quartz sand were used to remold hydrate-bearing clayey–silty sediments (HBCSS). A series of consolidated-drained triaxial tests of HBCSS were carried out to obtain the mechanical characteristics of overconsolidated fine-grained HBS under the combined influence of overconsolidation ratio (OCR) and confining pressure. The results show that the improvement in OCR can significantly improve the strength and stiffness of HBCSS and easily lead to strain softening and dilatation. Increasing confining pressure can weaken the strain softening caused by OCR, while particle breakage is easily caused by double compaction of overconsolidation and confining pressure. In addition, a new parameter strain hardening rate was proposed, which can effectively describe the hardening and softening of stress–strain relationship. The effect of overconsolidation on the mechanical properties of HBCSS is essentially compaction, and the shearing mechanism lies in the continuous evolution of particle breakage and compressive hardening.