QUESTION $1$

$(25$ marks$)$

As shown in Figure $1,$ a development platform is to be formed at $4$ m above the existing ground level. A trapezoidal$-$shaped mass concrete wall, which will be retaining and founding on Compacted Fill, is proposed for supporting the platform The relevant material and design parameters are as follows:

Figure $1$

Based on the Lump Safety Factor approach, assuming that Coulomb's coefficient of active earth pressure $($Ka$)$ is applicable to assessing the active earth pressures acting on the wall:

$($a$)$ Calculate and sketch the distribution of active earth pressures along the wall back, with the direction of the earth pressures clearly indicated.