Calculate the total horizontal thrust $(P)$ on the $9m$ high retaining wall shown below using the

methods specified:

Using Rankine Lateral Earth Pressure Theory,

b$.$ Using Coulomb Lateral Earth Pressure Theory $($Find the most critical failure plane by examining the

failure planes that make an angle of $55,60$ and $65$ with the horizontal. You can accept the friction

angle between the wall and the ground as $=20\%.$

Compare your result with the one obtained by the formula.

c$.$ Using a log$-$spiral failure plane. You can benefit from pumpkins. Alternatively or additionally, you

can also reach the result by calculating the horizontal force that will hold the failure plane that you

have determined as an arc in a slope stability analysis program, at the impact point shown for $P,$ with

$FS=1\mathrm{.}0.$

D$.$ Repeat options $a,b$ and $c$ for the case where GW is on the surface.

Explain which method is more accurate and give reasons.