Evaluation of test methods designedtoobtain the undrained shear strength of muds

One parameter needed for the stability analysis of seafloor mud‐covered slopes is the undrained shear strength, cu, of the mud. A literature review dealing with mudslides shows that six methods exist to measure the cu of muds either in the laboratory or in the field. These methods are: 1) the vane shear test, 2) the cylinder‐strength meter test, 3) the sphere‐strength meter test, 4) the cone penetrometer test, 5) the pullout test using a cylinder, and 6) the use of the vertical profile of a mudslide in the direction of movement. The present study reports a laboratory investigation of the undrained shear strength of artificially prepared muds using the six methods in order to evaluate their accuracy. It was found that for mud samples with low clay content (less than 45% by weight), the cylinder‐strength meter test, the mudslide profile test, the cone penetrometer test, and the pullout test gave similar results for cu and therefore compare well. However, the sphere and vane shear tests gave values that are larger than those obtained by using the other methods. Reasons for the discrepancies are related to the fact that requirements associated with the vane test theory are not met when muds are tested by the vane, and the effect on the cu values of the assumption involved with the sphere‐strength meter test theory. As the water content of the muds decreases (due to an increase in clay content beyond the 45% by weight), their cu values measured by the test methods diverged somewhat. This is because the cu of muds with low water contents was found to be sensitive to their changes by evaporation that takes place during the non‐simultaneous testing of the muds using all the six methods.