Regression analyses were also performed between the resilient (NDT
tuned) and dilatometer moduli. Table 7.8 lists results of the analysis
for the subbase and subgrade layers. The correlation coefficients are
lower than those obtained for the cone resistance in Table 7.5. Thus,
the CPT may be more reliable than the DMT in predicting the modulus of
layered pavement systems and subgrade soils. The ability of the CPT to
test stiffer soils such as base course materials make it more attractive
than the DMT. However, for weak subgrade soils the DMT may yield
reasonable modulus predictions. Further work on the interpretation of
both CPT and DMT results may be worth pursuing.
Table 7.8 Relationship Between Resilient Modulus, ER
and Dilatometer Modulus, ED
Dynaflect Moduli FWD Moduli
Layer Regression N R2 Regression N R2
Equation Equation
Base ---* --- --- ---* --
Subbase E3 = 4.317 ED 12(a) 0.874 E3 = 2.576 ED 13(b) 0.879
Subgrade E4 = 1.855 ED 14 0.697 E4 = 1.749 ED 14 0.882
ALL E4 = 3.476 ED 26 0.767 E4 = 2.294 ED 27 0.854
Dilatometer test not conducted in base course layer
NOTE: Some pavements were deleted in the regression analysis. Those
pavements are:
(a) SR 15C M.P. 0.055 and 0.065
(b) SR 15C M.P. 0.065