Abstract :
A very extensive vane shear testing program of sediments from potential manganese nodule mining areas was conducted in 1975 during Leg III of NOAA´s DOMES program. This effort was performed in conjunction with planned USGS studies. Replicate vane shear tests were made on 51 large box cores recovered from the three DOMES study sites A, B, and C. The statistically designed coring program (nested type), combined with efforts to sample major topographical features provided an ideal opportunity to more accurately assess the strength characteristics of nodule area sediments, including the macro- and micro- variability of this parameter. Test results demonstrated that the original vane shear strengths for the majority of cores tested from all three sites agree very closely. Average original strength profiles for each site increase from approximately 0.5 to 1.0 psi in the first 3-6 inches of sediment depth, thereafter values remain nearly constant or increase to about 1.4 psi in the rest of the depths examined. Average sensitivity values (ratios of original to remolded strength) however, were higher for Site C than Sites A and B. Analysis of the vane shear strength lateral variability showed that the largest percent of the variability is contributed by differences between cores from the same station, and the next largest percent by differences between tests conducted in the same core. At all test depths, strength differences between different stations and different sites were found to be less significant. These results clearly indicate the need for more detailed sediment sampling within relatively small seafloor areas.
