Test: Bearing Capacity & Shallow Foundation - Civil Engineering (CE) MCQ

As per Terzaghi's bearing capacity equation,
q_ult = cN_c + γD_f N_q + 0.5 γBN_γ
For a purely cohesive soil,
N_q = 1 and N_γ = 0
∴ q_ult = cN_c + γD_f
But q_net,ult = q_ult - γD_f
⇒ q_net,ult = cN_c + γD_f - γF_f ⇒ q_net,ult = cN_c

Changing the width of footing does not affect the bearing capacity of clays.

Corrected SPT value

In the case of loose sand there may be loose pockets causing differential settlements. Raft foundations reduce the differential settlements and higher, allowable soil pressure may be used for design of rafts on loose sands.
Under-reamed piles are suitable to bear the swelling pressure caused by black cotton soil.

Load intensity for 4.5 kN load on 30 cm square plate will be,

Load intensity for 200 kN load on 2 m x 2 m footing will be,

Since load intensity is same so, 

According to Terzaghi there are three zones:

Zone-1: Elastic zone of wedge shape located beneath the loaded strip wherein the major principal stress are vertical. This remains in elastic equilibrium and behaves as if it were a part of footing itself and ∠CAB = ∠CBA = ϕ.
Zone-2: Radial shear zone where arc CD is logarithmic spiral. (Circular when ϕ = 0).
Zone-3: It is called Rankine passive zone. An overburden pressure q = γD_f acts as a surcharge on this zone.

Terzaghi’s bearing capacity factors N_c, N_q and N_γ are function of angle of friction only.

According to Terzaghi,
q_nu = 0.5 γB N_γ for strip footing 
= 0.4 γB N_γ for square footing Using the above equations,

For strip footing,
q_nu = 0.5 x 1.2 x 250 = 150 kN/m²

q_nu = c_uN_c
where c_u = 50/2 = 25 kN/m²
N_c = 6(1 + 0.2 D_f/B)
for D_f = 0, we get N_c = 6
∴ q_nu = 25 x 6 = 150 kN/m²