Higher ratios of cone resistance to vane shear strength for 

 granular materials is simply explained by the ratio of the sliding 

 surfaces generated by each tool. Assuming that the shear strength of 

 the soil is constant, the ratio of cone sliding surface to vane sliding 

 surface is greater for granular soils than for cohesive soils. The 

 sliding surfaces for the vane tests are cylindrical, and they are approxi- 

 mately the same for all soils. However, according to Figure 25, 

 (Begemann, 1963) the sliding surfaces produced during static cone tests 

 differ markedly for granular and cohesive soils. Begemann (1963) shows 

 that the sliding surface produced by the cone depends upon the drainage 

 conditions and the friction angle of the soil. A larger unit cone 

 resistance is expected for a granular soil than for a cohesive soil, and 

 the ratio of unit cone resistance to vane shear strength will also be 

 proportionately larger. 



The plot of the ratio of unit cone penetration resistance to 

 maximum vane shear strength versus depth for the Site 1 sediment displays 

 a large experimental scatter. The values range from 8.3 to 18.8 with 

 an average value of 13.9. These values are considerably higher than 

 the ratios presented by Skempton. However, the average agrees favorably 

 with Begemann' s results, but the scatter is rather extreme. 



The data for Site 2 exhibits a very high ratio of cone resistance 

 to vane shear strength to a depth of 10 inches. This high ratio which 

 may be explained by the presence of a sand layer (Figure 14 and 15) 

 approximately 15 inches deep behaves according to Begemann' s theory. 

 The ratio of cone resistance to vane shear strength for the deeper clayey 

 silt is very consistent. The values range from 10.4 to 11.6 with an 

 average ratio of 10.9. The values compare favorably with results of 

 both Skempton and Begemann, and they tend to reinforce the performance 

 accuracy of the test device. 



A plot of the ratio of unit cone penetrometer resistance to peak 

 vane shear strength versus the percent clay at the test depth is presented 

 in Figure 25; it is an attempt to explain the scatter of data in Figure 

 23. The trend is toward an increasing ratio with decreasing percent 

 clay. This trend appears reasonable because the percent clay should affect 

 the shearing behavior of a soil. Unfortunately, there is very little 

 data presently available to verify this relationship; however, more data 

 are being obtained. 



If this relationship can be established for ocean sediments, the 

 static cone penetrometer will be a more economical tool than the shear 

 vane for obtaining the "undrained" shear strength of the seafloor soils. 



Sensitivity 



The ratio of undisturbed vane shear strength to remolded vane shear 

 strength for a soil sample at a constant water content is known as the 

 sensitivity of the soil. Figure 26 presents all the sensitivity data 

 for Site 2. Remolded vane tests were not performed at Site 1; therefore. 



16 



