The ultimate bearing capacity of a square footing on surface of a satu...
's theory) can be calculated using the following steps:
Step 1: Calculate the effective stress at the base of the footing using the equation:
σ' = σ - u
where σ is the total stress, u is the pore water pressure, and σ' is the effective stress.
In this case, assuming the footing is at ground level and there is no surcharge or water table, σ = γD and u = 0, where γ is the unit weight of the soil and D is the depth of the footing. Let's assume D = 1 m and γ = 20 kN/m3. Then,
σ' = γD - u = 20 kN/m3 × 1 m - 0 = 20 kN/m2
Step 2: Calculate the cohesion intercept of the soil using the unconfined compression strength (UCS) of the clay using Skempton's theory:
c = 0.22 × UCS
c = 0.22 × 50 kN/m2 = 11 kN/m2
Step 3: Calculate the bearing capacity factor (Nc) using the following equation:
Nc = [(Nq - 1) tan^2φ + 1] [(Nq + 1) tan^2φ - 1]^-1
where Nq is the bearing capacity factor for the soil and φ is the angle of internal friction. For saturated clay, Nq can be approximated as:
Nq = 2 + sinφ
Assuming φ = 0, then Nq = 2. The equation for Nc simplifies to:
Nc = 2
Step 4: Calculate the bearing capacity factor (Nγ) for the soil using the following equation:
Nγ = 0.5 + 0.4 (Df/B)
where Df is the foundation depth and B is the width of the footing. Assuming a square footing with B = 1 m and Df = 1 m, then:
Nγ = 0.5 + 0.4 (1/1) = 0.9
Step 5: Calculate the ultimate bearing capacity (qult) using the following equation:
qult = σ' [Nc + (Nq - 1) tan^2φ] + 0.5 γ B Nγ
Assuming φ = 0, then:
qult = 20 kN/m2 [2 + (2 - 1) tan^2 0] + 0.5 × 20 kN/m3 × 1 m × 0.9
qult = 60 kN/m2
Therefore, the ultimate bearing capacity of a square footing on surface of a saturated clay having unconfined compression strength of 50 kN/m2 using Skempton's theory is 60 kN/m2.
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