QUESTION $1$

$($a$)$ An interstate highway pavement is composed of a HMA surface course, a natural gravel base course, and a sand$-$gravel sub base to be designed for an ESAL of $1\mathrm{.}5{10}^6.$ The quality of drainage is considered excellent because water can be drained from the sub base within one hour. However, due to the large amount of precipitation, more than $25\%$ of the time the pavement will be exposed to moisture levels approaching saturation. The material properties are summarized below:

Effective roadbed resilient modulus $=6000$ psi

Resilient modulus of sub base $=30000$ psi

CBR of base $=80\%$

Resilient modulus of HMA$=450000$

Assumptions:

$\frac{}{P}SI=1\mathrm{.}7,R=95\%,S_0=0\mathrm{.}35$

Assuming a minimum thickness for HMA, determine the thicknesses of the surface, base and sub base required.