UNDRAINED STRENGTH OF UNDERCONSOLIDATED CLAYS AND ITS APPLICATION TO STABILITY ANALYSIS OF SUBMARINE SLOPES UNDER RAPID SEDIMENTATION

Of several triggering mechanisms of submarine slope instability, the effect of rapid rate of sedimentation is focused on. When subjected to rapid sedimentation, the clayey material in the seabed is in a state of incomplete consolidation or underconsolidation. In order to understand the undrained behaviour of underconsolidated clay, triaxial compression tests were conducted on laboratory-reconstituted samples of soft Bangkok clay which were consolidated under various total pressures and degrees of consolidation. The test results indicated that the undrained strength of the clay increases with the degree of consolidation, while the cohesion and friction angle in terms of effective stress are independent of the degree of consolidation. It was revealed also that the underconsolidated clay develops a slightly greater amount of excess pore water pressure during shear than the normally consolidated clay. Using the above findings, a finite element program was developed to analyze the stability of submarine slopes undergoing rapid sedimentation and increasing height with time. It was shown by an example calculation that the degree of consolidation of the slope decreases with time, eventually resulting in a failure.