Results 



Principal Stress Difference . Three specimens were taken from Box 

 Core 4, from about the same elevation in the sample, so that all specimens 

 were of about the same composition and had experienced about the same 

 stress history. These specimens were consolidated to different isotropic 

 stress states by application of consolidation pressure, a^,, of 6.5, 37.9, 

 and 109.8 kPa (0.94, 5.49, and 15.93 psi) . The specimens were then 

 sheared undrained by increasing the principal stress difference (0-1-03), 

 that is, by applying an axial load via the load ram. The resulting axial 

 strain response of the three specimens to the change in principal stress 

 difference is presented in Figure 14. The first two specimens (o^. = 6.5 

 and 37.9 kPa) behaved similarly with increasing principal stress difference 

 to 13 to 18% axial strain, after which the principal stress difference 

 remained near constant with strain. These specimens bulged uniformly 

 with continued axial strain, and no shear failure plane could be 

 identified. The third specimen (a^ = 109.8 kPa) , on the other hand, 

 exhibited a definite peak stress difference, with a reduction of some 

 15% with continued strain. This specimen exhibited a well-defined 

 failure plane. An examination of foraminifera tests near the failure 

 plane is planned to identify test crushing which may have occurred 

 during this latter shear test, and which could contribute to the 

 strength reduction with axial strain. 



Failure Envelope. To determine the significance of these stress- 

 strain data, the relationship (a-^-o^)/^ was plotted versus (0-1+02) /2 

 for the duration of each shear test and is presented in Figure 15. Such 

 a data plot for a shear test is known as a stress path; the quantity 

 (ai-a3)/2 is a function of the shear stress on a plane within the 

 specimen; and the quantity (01+03) /2 is a function of the normal stress 

 on that plane (Reference 38, pp. 105-115). The stress paths of Figure 

 15 are indicative of the stress history of the calcareous ooze material 

 (Reference 38, p. 427). The paths indicate that the specimen con- 

 solidated to 6.5 kPa was overconsolidated, in terms of behavior, when 

 sheared; the specimen consolidated to 109.8 kPa was normally consolidated; 

 and the specimen consolidated to 37.9 kPa was inteinnediate in behavior. 

 A soil element is defined as being normally consolidated if it is at 

 equilibrium under the maximum stress it has ever experienced, and as 

 overconsolidated if it is at equilibrium under a stress less than that 

 to which it was once consolidated (Reference 38, p. 74). The overcon- 

 solidated behavior of the first specimen, that consolidated to 6.5kPa, 

 need not necessarily be indicative of the sample condition on the sea- 

 floor but may be largely the result of sample state change during coring, 

 transit, storage, and specimen set-up. The source of the behavior 

 will be clarified by future testing of those calcareous ooze samples 



13 



