Undrained Shear Properties of Shallow Clayey-Silty Sediments in the Shenhu Area of South China Sea

Suction piles are used to ensure wellhead stability during natural gas hydrate production in the Shenhu area of the South China Sea (SCS). Undrained shear properties of clayey-silty sediments play a critical role in the stability analysis of suction piles. However, it has not been fully studied. This study conducts a series of undrained triaxial shear tests on shallow clayey-silty sediments in the Shenhu area of SCS, and stress-strain curves under different overconsolidation ratio (OCR) conditions are obtained. OCR effects on undrained shear properties of clayey-silty sediments are discussed, and a model to predict the pore pressure coefficient at failure is proposed. Results show that the isotropic compression index is 0.175, and the isotropic swelling index is 0.029. The undrained shear strength is proportional to the effective confining pressure, and the proportionality coefficient is 0.42 for normally consolidated specimens, while the undrained shear strength of OC specimens nonlinearly increases with OCRs increasing. The proposed model aptly predicts the pore pressure coefficient at the failure of clayey-silty sediments of SCS with different OCRs.

Automated summary

A series of undrained triaxial shear tests were conducted on shallow clayey-silty sediments in the Shenhu area of the South China Sea (SCS) to investigate their undrained shear properties under different overconsolidation ratio (OCR) conditions. The results showed that the undrained shear strength was proportional to the effective confining pressure for normally consolidated specimens, while it nonlinearly increased with increasing OCRs for OC specimens. A model was proposed to predict the pore pressure coefficient at failure, which successfully predicted the behavior of the sediments with different OCRs.