site. The complete results of this study were reported in a UCLA masters 

 thesis (Beard, 1972). 



ANALYSIS 



The major portion of the data analysis phase of this investigation 

 involved developing a procedure for predicting in-situ strength given 

 tests on partially disturbed samples. As discussed previously, the 

 approach selected for this development was the derivation of correla- 

 tions between measured parameters including sample vane shear strength, 

 sample residual pore pressure, and field vane strength. It appeared as 

 if the best means of developing this correlation was through a plot of 

 the ratio of in-situ to sample strength versus the ratio of the measured 

 residual pore pressure to a reference residual pore pressure indicative 

 of the in-situ stress conditions. The residual pore pressure which 

 would result from the removal of in-situ shear stresses and no other 

 disturbance was selected as a suitable reference residual pore pressure. 

 This reference pressure has been termed the "perfect sampling" residual 

 pore pressure by previous investigators. The strength ratio is the 

 desired quantity in any sample strength correction procedure. However, 

 it is also a measure of the amount of disturbance the sample has under- 

 gone. Likewise, since the pore pressure ratio represents how the sample 

 quality changes as the sample progresses from an "ideal" (reference) 

 condition to an actual (final) condition, it is also a measure of amount 

 of disturbance. Therefore, since both ratios are measures of the same 

 quantity, they should correlate directly with each other. Of greater 

 importance, however, procedures have been developed by Ladd and Lambe 

 (1963) for estimating without in-situ test data, the residual pore pres- 

 sure which would result from in-situ shear stress removal. Therefore, 

 a good empirical correlation between the two ratios can be used practi- 

 cally to estimate in-situ shear strength. The pore pressure ratio can 

 be calculated on the basis of laboratory tests. It can then be corre- 

 lated with the strength ratio which can be used directly to calculate 

 the in-situ strength when given the laboratory strength. 



To calculate the reference residual pore pressure, Ladd and Lambe 

 (1963) suggest the following equation: 



-u - a [K + A (1 - K )] (1) 



ps vo L - o u o J 



where u = reference residual pore pressure 



ps 



a = in-situ vertical effective stress 

 vo 



K = coefficient of lateral earth pressure at rest 



(ratio of lateral to vertical in-situ effective 

 stress) 



A = reference pore pressure parameter 



15 



