Question $3[20$ marks$]$:

Design a flexible pavement to carry a design ESAL of $10,000,000,$ over a design period of $20$ years,

based on the following information:

$16-$Civ$-$A$6$ December $2019$

Page $3$ of $17$

The effective resilient modulus of the subgrade $Mr=7,000$

The subbase layer is an untreated silty sand with a resilient modulus $($ESB$)$ of $20,000$

The base layer is a cement$-$treated base with an unconfined compressive strength of at $7$ days

of $450$

The elastic modulus of the asphalt concrete at $20C($EAC$)$ is $400,000$

The pavement structure will be exposed to moisture levels approaching saturation for $25\%$ of

the time and the quality of drainage is poor

Initial Serviceability index value: $p_0=4\mathrm{.}5$

Terminal Serviceability index value: $p_t=3\mathrm{.}0$

Reliability and Standard Deviation: $R=90\%$ and $S_0=0\mathrm{.}4$

Assume reasonably any missing information and justify your assumptions.