115
FWD deflections, the percent change in deflections due to changes in E4
increased from Dx to Dg. However, the rate of increase seemed to level
off from Dc to D. (see Tables 4.2 and 4.4). These are the farthest
O O
sensor deflections used in the FWD theoretical study.
Figures 4.21 and 4.22 show, for example, the relationships between
E, and D., D_, or D for fixed levels of E,, E, E, and t,. The
Hb/o 1231
subgrade modulus, E4, ranges from 5 to 100 ksi. Regression equations
and R2 values for each power equation are indicated on the plots.
Similar relationships with a high degree of correlation were obtained
for pavements with tx values ranging from 1.5 to 10 in.
Based on the unique relationships obtained for E4 and the last
three FWD sensor deflections, the database was combined and also
expanded to cover a large range of parameters listed in Table 4.1. The
following power law equations were obtained by regressing E4 against Dg,
or D?, or Dg.
General Case: For 1.5 < t < 8.0 in., 75.0 < E < 1200.0 ksi,
1 i
42.5 < E < 85.0 ksi, 30.0 < E < 60.0 ksi,
2 3
and 5.0 < E <40.0 ksi,
4
54.6122 (D )
1.03065
E
Eqn. 4.25
6
(N = 400, and R2 = 0.9974)
39.9899 (D )
7
0.98912
E
(N = 400 and R2 = 0.9992)
Eqn. 4.26