Question $3$

$($a$)$ A $10m$ high reinforced concrete retaining wall with a vertical back supports a

purely granular backfill. The backfill was compacted in two distinct lifts, which

resulted in two different compacted densities and strength created within the

fill:

a$.$ The lower $4m$ of fill: $=20k\frac{N}{m^3}$;${}^{\text{'}}=35$

b$.$ The upper $6m$ of fill: $=18k\frac{N}{m^3}$;${}^{\text{'}}=30$

The fill carries a uniform surcharge of $20$kPa extending well beyond the back

of the wall.

Using Rankine's theory, determine the total active thrust placed on the back of

the wall and the height above the base of the wall at which a single line load

representing this total thrust acts.

$(15$ marks$)$

$($b$)$ If the wall in part $($a$)$ is to be designed in accordance with Eurocode $7,$ explain

the key stages in the design process that should be followed to ensure the wall

would not slide forward or overturn.

Do not perform any calculations. Rather, only describe the steps taken in the

approach for establishing safety against both sliding and overturning.

$(10$ marks$)$

$($c$)$ Describe the conditions that might lead to a tension crack developing behind a

retaining wall.

Further, describe how the presence of a tension crack is dealt with when

determining the lateral earth pressure distribution acting on the back of the

retaining wall.

$(5$ marks$)$