The cone penetrometer test data (Figures 17 and 18) show excellent 

 replication between all six tests; the six tests were plotted as two 

 figures to prevent clutter. The characteristic small unit cone load 

 discontinuities are present as on previous cone penetrometer test records. 

 The test results reveal a somewhat stiff soil layer between 10 and 20 

 inches after which the cone load tends to increase linearly with depth. 



A plot of peak undisturbed vane shear strength versus average 

 penetration depth is presented in Figure 19. Even though considerable 

 data scatter exists, there is a noticeable trend shown by the line of 

 best fit. The results of test SCN-V6 are not valid because water leaked 

 into the load cell. It is interesting to note that a stiff soil layer 

 is not present between 10 and 20 inches as exhibited on the cone 

 penetrometer load profile. In fact, low vane shear strength values are 

 encountered in the top 20 inches of soil. A linearly increasing shear 

 strength is encountered beyond 20 inches. The strength increase for 

 the remolded soil (Figure 20) is linear with depth to 90 inches; however, 

 the rate of increase is not as great as for the undisturbed soil. 



ANALYSIS 



Comparison of Laboratory and In-Situ Vane Data 



The estimated laboratory and in-situ vane shear strength-depth 

 relationships for Site 1 and Site 2 sediment are presented in Figures 

 21 and 22. There is reasonable agreement between the laboratory and 

 in-situ results; however, for both sites the in-situ vane shear 

 strengths exceed the laboratory strengths. There are many factors which 

 could influence the laboratory and in-situ vane shear test results and 

 cause this disagreement. 



Shear Rate . Laboratory and in-situ vane tests are both performed 

 at rotational velocities of 6 deg/min; however, actual shear rates 

 differ. Shear rates vary in direct proportion to vane blade width. 

 The in-situ vanes used vary from four to eight times larger than the 

 laboratory vanes, therefore in-situ shear rates can be four to eight 

 times faster than laboratory test rates. The faster in-situ test shear 

 rates could result in higher shear strengths due to viscous effects 

 introduced by shearing the soil rapidly. However, the slower laboratory 

 shear rates could also result in higher shear strengths due to partial 

 drainage. Skempton (1948) performed in-situ vane shear tests in a soft 

 clay at shear rates varying by as much as a factor of 50. His conclusion 

 was that in normal testing practice, the influence of shear rate is not 

 of the first importance. According to Skempton' s test results, the 

 variation in NCEL test data due to shear rate effect should not exceed 

 2 percent. 



14 



