299
Figure 7.8 illustrates the plot of ED against qc for most of the
test sites. The scatter of the data may be attributed to spatial soil
variability within and between test sites. Also, the variability in the
relationship between ED and qc could be affected by soil type, moisture
content, and stress history. Regression analysis of the combined data
resulted in the following equation:
ED = 3.46 qc Eqn. 7.2
(R2 = 0.830, N = 224)
Due to the possible effect of soil type on the ED-qc correlations,
further regression analyses were performed to establish separate rela-
tionships for sandy and for clayey soils. The regression equations are:
For sandy soils:
ED = 3.423 qc Eqn. 7.3
(R2 = 0.852, N = 154)
For clayey soils:
ED = 4.141 qc Eqn. 7.4
(R2 = 0.637, N = 70)