Appendix 



DESCRIPTION OF ONE-DIMENSIONAL CONSOLIDATION 

 TEST AND TRIAXIAL SHEAR TEST 



CONSOLIDATION 



Consolidation was described earlier as volume change under 

 a state of increased hydrostatic stress, a condition of three- 

 dimensional volume change. Rarely is this condition of consolidation 

 under hydrostatic stress experienced in practice. Instead, the 

 usual consolidation condition is more nearly approximated by one- 

 dimensional vertical volume change. Thus, the usual practice is 

 to run a one-dimensional (1-D) consolidation test on a disc of 

 soil with a diameter-to-height ratio of about three or four [29] , 

 as shown in Figure 17. This disc of soil fits snugly into a thick 

 metal ring which limits lateral strain to essentially zero. Loads 

 are applied vertically, in increments, to the soil disc causing 

 the soil pore fluid to be squeezed out and the soil grains to be 

 reoriented into a denser configuration in response to that load. 

 The conventional loading sequence calls for doubling the previous 

 load (Reference 22, p. 149); for instance, if the specimen has 

 been consolidated under a load of 20 newtons, then the next increment 

 of load added would be 20 newtons, raising the total load on the 

 specimen to 40 newtons. Such a loading sequence is termed a ''load- 

 increment ratio'' of 1. 



The reduction in soil disc height due to each increment of 

 load is plotted versus the logarithm of time, as shown in Figure 

 18. Ideally, for a load -increment ratio of 1, this curve has a 

 well-defined inflection point marking the end of primary consolidation 

 and marking that point at which secondary consolidation becomes 

 controlling of the volume change function. The increment of height 

 change for each load increment is used to produce a curve of height 

 change (adtually void ratio, e, a function of height change) versus 

 the logarithm of vertical effective stress, called an e-log a 



V 



curve, as shown in Figure 12. In practice, these data plots are 

 then interpreted to predict the total settlement of the soil surface 

 at any point in time due to an applied vertical load. 



TRIAXIAL SHEAR 



A commonly used and widely accepted test configuration for 

 soil shearing deformations and soil failure strength is the triaxial 

 shear test [40] in which a cylindrical specimen of soil, of length- 

 to-diameter ratio 2 or 2-1/2:1 (Reference 22, p. 192) is subjected 



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