Undrained Triaxial Shear Properties of Clayey-Silty Sediments from the Overlying Strata in the Shenhu Area of South China Sea

Abstract

The overlying strata are the main bearing layer of offshore engineering activities for the natural gas hydrate (NGH) exploitation in which the sediment along the installed piles or anchors would be remolded. Since the undrained shear properties of remolded sediments are important in the design of offshore infrastructure, a series of undrained triaxial compression tests has been conducted on normally consolidated (NC) and overconsolidated (OC) remolded clayey-silty sediments from the overlying strata in the Shenhu area in South China Sea (SCS). Effects of the consolidation ratio (OCR) on the undrained shear properties are explored. The results show that the isotropic compression index λ and isotropic swelling index κ are 0.175 and 0.003, respectively. The undrained shear strength Su is proportional to effective confining pressure p0' for NC samples with an averaged normalized undrained shear strength Su⁄p0' of 0.425, while the Su nonlinearly increases with OCR increasing. The Su⁄p0'  of NC clayey-silty sediments differs between areas ranged from 0.25 to 0.43. In addition, relations of the Su⁄p0' and OCR are investigated to develop a semi-empirical model to predict Af. Finally, the developed model is extended to hydrate-bearing sediments via the knowledge of effects of hydrate on the Su⁄p0' and cohesion.

Keywords: Undrained shear strength, Overconsolidation, Isotropic compression, Pore pressure coefficient, Hydrate-bearing sediment