A shallow foundation of length 8 m and width 3 m is constructed. It exerts a uni

Question

A shallow foundation of length 8 m and width 3 m is constructed. It exerts a uniform downwards pressure of 300 kPa on the soil beneath it.
(a) Constructing the foundation causes changes in the levels of vertical stress at all points in the soil. One such point lies at the centre of the footing plan, and is at a depth of 10 m. Determine the increment of vertical stress there.
(b) List the assumptions that you needed to make to enable you to answer Part (a). How would you defend your use of them? (Try to imagine yourself in the position of someone having to justify their actions to a court of enquiry into a building collapse!)

Explanation / Answer

qz =q0 + B*L/(B+z)(L+z)

where
qz= stress at Depth z
B = width (breadth) of loaded area

L = length of loaded area

q0= applied stress = 300kpa

qz = 300 * (2so 4)/(3+10)(8+10) = 30.769 Kpa;

so increment of vertical stress = qz = 30.769 Kpa;

b) assunptions:

here we calculated the stress distribution is by means of the 2:1 method.

This method assumes that the load is distributed over an area that increases in width in proportion to the depth below the loaded area..

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