An interstate highway pavement composed of a HMA surface course, a cement treated base course, and a sand?gravel subbase is to be designed for an ESAL of 1.2 x 10 ⁶ . The quality of drainage is considered fair because water can be removed from the subbase within a week. However, there is a large amount of precipitation, so more than 25% of the time the pavement will be exposed to moisture levels approaching saturation. The materi-al properties are as follows: effective roadbed soil resilient modulus = 5500 psi, resilient modulus of subbase = 15,000 psi, unconfined compressive strength of cement-treated base at 7 days = 500 psi (see Figure 7.15c for correlation), and resilient modulus of HMA = 4.3 X 10 ⁵ psi. Assuming a minimum thickness for HMA, determine the thick-nesses of the surface, base, and subbase courses required. [Answer: 3 in., 6 in., and 9 in.]

FIGURE 7.15

Correlation charts for estimating resilient modulus of bases (1 lb a 4.45 K14, 1 psi = 6.9 kPa). (After Van M1 et al. (1972).)

0.20 0.18 0.16 0.14 0.12 0.10 Structural coefficient-a 400 200 Unconfined compressive strength (psi)-7 day break (c) Cement Treated 10.0- 9.0 8.0 7.0 6.0 5.0 Modulus-105 psi