$($b$)$ Explain how the Mohr $-$ Coulomb failure criterion is used in the design of a gravity retaining wall.

$(15\%)$

$($c$)$ For the gravity retaining wall shown on Figure $3,$ determine the horizontal thrust on the wall.

$(55\%)$

Ground level

Water level $=$ ground level in front of wall

Soil behind and beneath the retaining wall comprises a clayey sand with effective friction angle $({}^{\text{'}})=35$ deg. and effective cohesion $(c)=10$ kPa

Figure $3-$ Retaining wall

$($d$)$ Derive the bearing capacity equation for the case of a footing resting at the surface of a clay soil which has an undrained shear strength $=Cu.$

$(15\%)$