A footing 18 m X 25 m is located at a depth of 15 m below the ground surface in a deep deposit of an overconsolidated clay The groundwater level is 2 m below the ground surface The undrained shear str

The equation for the short-term bearing capacity of a footing on overconsolidated clay is:

qallow = cNc Sc + 0.5γBNq

where: c = undrained shear strength = 120 kPa Nc = bearing capacity factor for cohesion = 35.7 (from table) Sc = shape factor = 1.3 (for footing width/length ratio of 0.72) γ = unit weight of soil = Ysat = 20 kN/m3 B = width of footing = 1.8 m Nq = bearing capacity factor for surcharge = 19.6 (from table)

First, calculate the effective overburden stress at the depth of the footing:

σ'v = γ (Df + H) = 20 (1.5 + 2) = 70 kPa

where: Df = depth of footing = 1.5 m H = depth to groundwater table = 2 m

Next, calculate the bearing capacity factors:

Nγ = 2Nc(Sc - 1) / (Sc + 1) = 47.6 Nq = 19.6

Finally, calculate the allowable bearing capacity:

qallow = (cNc Sc + 0.5γBNq) / F.S. = (120 x 35.7 x 1.3 + 0.5 x 20 x 1.8 x 19.6) / 3 = 308 kPa

Therefore, the allowable bearing capacity for the given conditions is 308 kPa.