QUESTION $3$

$[$Total $=25$ marks$]$

$($a$)$ Retaining walls are used for supporting the soil mass laterally so that the soil can be retained at certain height. There are three groups of retaining walls i$.$e$.$ gravity wall, embedded wall and reinforced$-$earth wall. With the aid of sketches, explain and give an example of these three groups of retaining walls. $($CO$2,$ PO$2,$ C$3)$

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$($b$)$ A $6\mathrm{.}0m$ high retaining wall with a vertical back face is shown in Figure $3.$ For the backfill, the soil properties are given as shown in the figure.$($CO$2,$ PO$2,$ C$4)$

i$)$ Determine the distribution of the active force behind the wall and the location resultant on the wall

marks$]$

ii$)$ If the water table rises to $4m$ from the bottom of the retaining wall, determine the new active force and the location of the line of action.

marks$]$