Liwan 3-1: How deep water sediments from South China Sea compare with Gulf of Guinea sediments

摘要

The first deep water geotechnical survey in South China Sea has been performed at Liwan 3-1 Field in Pearl River MouthBassin. The investigation comprised Piezocone Penetrometer Tests (PCPT), T-bar, insitu vane tests, pore pressure dissipationtests, jumbo piston cores, box cores, along with advanced laboratory testing. The in-situ and laboratory data results obtainedhave been used together with the geophysical data (AUV data) to provide the soil design parameters used for the design ofthe deepest PLEM and Manifold foundations (i.e. between 1300 and 1500m WD). The high quality and variety of in-situ andlaboratory tests performed enable a sound comparison with other deep water sediments. Most of the soil properties of theLiwan 3-1 clays are in the range of those encountered in the Gulf of Guinea (Colliat et al. 2010). The use of scanning electronmicroscopy (SEM) revealed highly structured clay what is in accordance with the relatively high sensitivity of about 5 to 9obtained from T-bar tests after 30 cycles. However some particularities arise in their mechanical behavior. The shear strengthanisotropy (i.e. answer under different modes of shearing) is for example not significant. It can also be noted that the increaseof shear strength with time or with the rate of shearing (i.e. respectively the thixotropy and rate effects) are less pronounced.