QUESTION TWO $(15$ MARKS$)$

$($a$)$ What are the principles governing the Asphalt Institute method of flexible pavement design. $(5$ MARKS$)$

$($b$)$ As a consultant to NDDC$,$ you have been requested by the Board to design a $4-$ lane highway network from Patani to Asaba Ase. After preliminary traffic studies and soil tests the following parameters were obtained; initial daily traffic $=5000$ vehicles comprising of $6\%$ trucks having an average gross weight of $180$ KN $.$ Based on forecast that the road traffic growth rate is assumed to be $5\%$ per year. Average subgrade CBR along the proposed road is $7\mathrm{.}4\%$ and the design period is left at $20$ years. Design the pavement using;

$($i$)$ Full depth asphalt $(2\mathrm{.}5$ MARKS$)$

$($ii$)$ Hot mixed sand aspnalt base $(2\mathrm{.}5$ MARKS$)$

$($iii$)$ Emulsified asphalt base $(2\mathrm{.}5$ MARKS$)$

$($iv$)$ Untreated granular base $(2\mathrm{.}5$ MARKS$)$