Design a flexible pavement system using the AASHTO method. $[$Design the surface

course HMA thickness and aggregate base thickness for a $20$ year pavement design life,

considering:

Traffic: $1^{st}$ year traffic of $120,000$ ESALs increasing by $6\%$ annually.

Location: Asqarea.

Subgrade: clayey silt; water table at $20$ ft depth during spring. Spring $M_r$

$=6$ksi.

Reliability: $R=0\mathrm{.}95$ and $S_0=0\mathrm{.}35$

Serviceability: Initially assume PSI $=4\mathrm{.}2$; PSI should not dip below $2\mathrm{.}0$

HMA resilient modulus $(E_{\text{I}})=200$ksi

Granular Base resilient modulus $(E_2)=50$ksi.

Assume that the granular base is subjected to moisture levels approaching

saturation $1-5\%$ of the time and that water is removed within $2$ hours.

Determine the difference in pavement thickness if Reliability is reduced to $R=\mathrm{.}85$