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Shear Modulus of Carbonate Sand-Silt Mixture with THF Hy- 2 drate

: Maximum shear modulus ( G max ) is an important factor determining soil deformation and closely related to engineering safety and seafloor stability. In this study, a series of bender element tests was carried out to investigate the G max of hydrate bearing Carbonate sand (CS)-silt mixture. The soil mixture adopted a CS : silt ratio of 1:4 by weight to mimic the fine-grained deposit of South China Sea (SCS). Tetrahydrofuran (THF) was used to form hydrate. Special specimen prep- aration procedures were adopted to form THF hydrate inside the intra-particle voids of CS. The test results indicate that hydrate contributes to a significant part in the skeleton stiffness of the hy- drate bearing CS-silt mixture and its G max at 5% hydrate saturation ( S h ) is 4 to 6 times that of the host 22 soil mixture. Such stiffness enhancement at the low S h may be related to the cementation hydrate 23 morphology. However, G max of the hydrate bearing CS-silt mixture is also sensitive to the effective 24 stress for S h ranging between 5% and 31%, implying that the frame-supporting hydrate morphol- 25 ogy also plays a key role in the skeletal stiffness of the soil mixture. Neither the existing cementa- 26 tion models nor the theoretical frame-supporting, i.e. Biot-Gassmann theory by Lee (BGTL) could 27 alone give a satisfactory prediction of the test results. Thus, further theoretical study involving a 28 combination of cementation and frame-supporting models is essential to understand the effects of 29 complicated hydrate morphologies on the stiffness of soil with substantial amount of intra-particle 30 voids. 31