to a hydrostatic stress state by a confining fluid and to a superimposed 

 axial stress by a loading ram (see Figure 19). The soil specimen 

 is capped at its ends by porous discs which permit passage of water 

 out of the sample to a closed volume change and pressure measuring 

 system. The specimen and discs are sealed off from the surrounding 

 confining fluid by a rubber sleeve. The confining stress, 03, applied 

 via the surrounding cell fluid, is resisted within the soil specimen 

 by two components: partly by the specimen pore fluid, as a specimen 

 pore pressure, u (see Figure 19); and partly by the specimen soil 

 structure, as an effective minor principal stress, 03. An additional 

 axial stress, aj > is superimposed on this isotropic system by the 

 axially-acting loading ram, such that the axial total stress applied 

 to the specimen is a-\ = a^j + 03 and the axial effective stress 

 is ai =0^+0^. If the axial stress is greater than the confining 

 stress, then a-\ is, more properly, the effective major principal 

 stress (Reference 38, pp. 117-119). 



Soil specimens of this series were first subjected to 

 a hydrostatic confining stress, 03, and the specimen pore water 

 was allowed to drain into a volume change measuring device, at 

 least until the end of primary consolidation had been attained, 

 as dictated by a triaxial volume change versus time plot (similar 

 to Figure 18), i.e., the end of primary consolidation was noted 

 by a slope change in the volume change data plot. Then the specimen 

 was sealed off from the drainage system, the confining pressure, 

 03 was maintained, and the specimen was loaded axially, until 

 shear failure occurred (Reference 29, pp. 125-126). Shear failure 

 was defined herein as occurring at the maximum principal stress 

 difference, (oi"Cf3)niax = ^d ™^^ (Reference 22, p. 177). This type 

 of test is referred to herein as a CIU test, that is, consolidated 

 isotropically and sheared undrained. 



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