The regression equation for sandy soils is almost identical to
Equation 7.2 which included all the test data. The correlation for the
clayey soils is poor. This poor correlation tends to agree with obser-
vations of Jamiolkowski et al. (50) that qc cannot be correlated to any
drained soil modulus for cohesive deposits.
The combined test data was also separated into above and below
water table categories for the purpose of assessing whether or not the
saturation state of the soils affected the ED-qc correlations. The
regression equation for above water table conditions,
ED = 3.64 qc Eqn. 7.5
(R2 = 0.926, N = 102)
is similar to Equation 7.3 for sandy soils. The equation obtained for
soils below water table,
ED = 3.946 qc Eqn. 7.6
(R2 = 0.778, N = 122)
is almost the same as Equation 7.4 for cohesive soils. It is evident
that the correlations were affected by the development of excess pore
water pressures in the clayey soils during penetration. An attempt was
made to measure pore water pressures using the piezocone. This was
unsuccessful due to the clogging of the porous stone by fine sand
particles.