The in-situ vertical effective stress may be calculated easily by 

 integrating the buoyant unit weight of soil overlying the sample in- 

 situ with respect to depth. The parameter, A u , can be related approxi- 

 mately to sediment type (Table VI, taken from Ladd and Lambe, 1963). 



The parameter K Q is critical and may be difficult to estimate. If 

 the soil is clearly normally consolidated, K Q may be assumed equal to 

 about 0.5. Many surficial seafloor soils, however, display either true- 

 or pseudo-overconsolidation effects, and K Q may differ significantly 

 from 0.5. For these overconsolidated soils, Brooker and Ireland (1965) 

 provide an empirical technique for estimating K through a plot relating 

 plasticity index, K , and the overconsolidation ratio (maximum past 

 pressure divided by present in-situ vertical effective stress) . This 

 plot, shown in Figure 4, appears to be a reasonable means of estimating 

 K , although it does require the performance of a consolidation test to 

 obtain the maximum past pressure (Casagrande, 1936). 



Also, in using the curves of Brooker and Ireland (1965) , it must 

 be assumed that all soils which appear overconsolidated react in the 

 same way in terms of lateral stress development. This assumption will 

 need to be reexamined in future research since some overconsolidation 

 effects may occur as a result of factors other than the removal of pre- 

 existing overburden. The manner in which K varies during these other 

 processes is currently not known. 



In the present study a large number of consolidation test results 

 were available (Herrmann, Rocker, and Babineau, 1972) for the 100-foot 

 and 600-foot sites. Maximum past pressures were determined from these 

 data and overconsolidation ratios were calculated. The 1200-foot site 

 appeared to be normally consolidated (overconsolidation ratio of 1.0). 

 The curves of Brooker and Ireland (1965) were entereed, and values of 

 K Q were obtained. These were inserted into Equation 1 to obtain the 

 reference residual pore pressure, u . Table VII summarizes the param- 

 eters used in calculating the u ps distribution at each site, and Table 

 VIII lists the values of u ps calculated. 



Ratios of measured field to laboratory vane shear strength and 

 measured to reference residual pore pressure were calculated. These 

 ratios are plotted in Figure 5. There is considerable data scatter, 

 possibly because each data point incorporates four inexact measurements 

 or estimates. There does, however, appear to be a definite correlation 

 between the two ratios. 



To indicate the influence of the various forms of sample treatment 

 and the soil type variations among the sites, the strength and pore 

 pressure data for each treatment-size combination were averaged. A 

 plot of these average points is presented in Figure 6. Here the corre- 

 lation is significantly improved since a good deal of the random error 

 is averaged out. Also plotted in this figure is a curve adapted from 

 Ladd and Lambe (1963) for the well-known Weald clay, an estuarine 

 deposit. Although this curve was developed strictly from laboratory 

 testing using different parameters, Ladd and Lambe suggest that it 

 should be used in an essentially identical way. It appears to fit the 



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