Practice Question: Bearing Capacity of Strip Footing
NCEES Civil PE Specification Soil Mechanics: Bearing capacity
Problem
A clay soil layer exhibits the following properties:
Unit weight \(= 120\ lb/ft^3\)
Angle of internal friction \(= 12°\)
Unconfined compression strength \(= 2,400\ lb/ft^2\)
The minimum factor of safety for ultimate bearing capacity is 3. The allowable bearing capacity (\(lb/ft^2\)) of a strip footing having a width of 6 ft and a bottom of footing depth of 3 ft is most nearly:
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Solution
Width of foundation\(= B_f = 6 ft\)
Depth of foundation \(= D_f = 3ft\)
The following are values of the bearing capacity factors for friction angle \(φ=12^°\) ;
(Ref:Civil PE Reference Handbook V2.0, Section: 3.4.2 Bearing Capacity Equation for Concentrically Loaded Strip Footings, page 91)
\[N_c=9.3\]
\[N_q=3\]
\[N_{\gamma }=1.7\]
For a soil with small angle of internal friction, cohesion is approximately half the unconfined compression strength \(= 1,200\ lb/ft^2.\)
For a strip footing, bearing capacity equation yields:
