A square footing foundation, 3 m by 3 m, and positioned on the ground surface of a soil deposit, supports a column load of 1,350 kN. Determine the vertical stress resulting from the foundation loading at a depth 3 m below the base of the footing for locations beneath the center and beneath the edge, assuming:(a) Boussinesq conditions apply.(b) Westergaard conditions apply.
A square footing foundation, 3 m by 3 m, and positioned on the ground surface of a soil deposit, supports a column load of 1,350 kN. Determine the vertical stress resulting from the foundation loading at a depth 3 m below the base of the footing for locations beneath the center and beneath the edge, assuming:
(a) Boussinesq conditions apply.
(b) Westergaard conditions apply.
(a)
The expression for the surface load is given by,
Here, q is the surface load, Q is the load acting over the point and A is the area.
Substitute the values in the above expression.
The ratio of depth and diameter is calculated as,
Use Boussinesq conditions.
Refer the graph of “Vertical stress variation beneath a foundation, according to Boussinesq analysis.”
The sub surface tension corresponding 1 value of Z/B is 38% of q beneath the center.
The sub surface stress is calculated as,
Refer the graph of “Vertical stress variation beneath a foundation, according to Boussinesq analysis.”
The sub surface tension corresponding 1 value of Z/B is 27% of q beneath the edge.
The sub surface stress is calculated as,
Therefore, the sub surface increase in stress at the center is 57 kN/m2 and the sub surface increase in stress at the edge is 40.5 kN/m2.
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