DISCUSSION OF RESULTS 



The following sections review in a station-bv-station sequence the 

 results of the laboratory and vane shear test programs. Each section 

 includes (1) a brief description of the geologic er"i ronment , (2) an 

 identification of the sediment, and (3) an evaluation ol .he vane shear 

 and laboratory test results. 



Before the test results are discussed, several paragraphs are 

 devoted to a critique of the sampling procedure. The critique considers 

 the physical makeup of the sampling device, since these characteristics 

 usually limit the quality of the sediment sample. 



General 



The gravity corer used to obtain the sediment sample has several 

 deficiencies. The deficiencies affect the sampling operation by pre- 

 venting the recovery of an undisturbed sample. Every corer disturbs the 

 soil to a certain extent; however, the significance of disturbance 

 changes as different disciplines are involved. 



The civil engineer judges the quality of the soil sample on several 

 parameters related to the corer' s physical configuration. If the values 

 of the limiting parameters are exceeded, the engineer considers the 

 sample disturbed. The parameters used most frequently to define sample 

 disturbance include the area ratio (Equation 1) , the inside clearance 

 ratio (Equation 9), and the outside clearance ratio (Eouation 10). 



C z (%) - 100 ^?- (9) 



where C = the inside clearance ratio 



LD = linear diameter 



ID - = inner diameter of cutting head 



C„ (» - !00 ^^2 (10) 



where C = outside clearance ratio 



OD = outer diameter of cutting head 



BD = barrel diameter 



According to Hvorslev (1965), the area ratio, inside clearance ratio, 

 and outside clearance ratio should not exceed 20%, 0.5%, and 3%, respec- 

 tively, if the sample is to be considered undisturbed. Hvorslev also 

 recommends that the ratio of core length to core diameter be less than 

 20 and that a piston be employed during recovery. 



21 



