A case study on the determination of the strength of seabed sediments from SW Taiwan

In order to explore the natural energy resources in the offshore of south west (SW) of Taiwan, there has been systematical surveyed by geophysical and geomechanical methods. However, most of these methods put emphasis on estimating the potential quality of energy resources. There lacks of studying on the geological conditions of seafloor stability for the area across the continental slope and the shallower areas. A project is executed to investigate the seabed stability situations. The cored submarine mud samplers are performed laboratory tests to obtain engineering properties. On the other hand, the 2006 Pingtung earthquake had triggered numbers of submarine landslides in the offshore of SW Taiwan. By means of submarine bottom profiles acquired before and after this event, the back analysis approach can be used to evaluate the representative in situ strength and compares with the strength parameters determined by laboratory triaxial tests. The analysis result indicates the effective friction angle (φ’) of the sliding surface is 14_ with a cohesion (c’) of 6 kPa. According to the infinite slope stability theory, the landslide with a thickness of 30 m yields an undrained shear strength (c_u) of 37 kPa under the critical condition. These evaluated strength parameters are close to the results obtained from the isotropically consolidated undrained triaxial (CIU) tests (φ’ = 15.3°, c’ = 19.4 kPa).