A 650-kN column load is supported on a 1.5 m square, 0.5 m deep spread footing. The soil below is a well-graded, normally consolidated sand with 훾 = 18.0 kN/m3 and the following SPT N60 values:

Explanation:

Determine the weight of footing

Where is the weight of footing, γ is the unit weight of concrete,  L is the length of footing is the width of footing, and D is the depth of footing

Substitute for γ in the equation

Therefore, the weight of the footing is 35.4 kN

Determine the initial vertical effective stress.

Here,   is initial vertical stress at a depth below ground surface  γ is the unit weight of soil, D is depth and u is pore water pressure.

Substitute for u in the equation

Therefore, the initial vertical stress is 36 kPa

Determine the vertical effective stress.

Here,   is initial vertical stress at a depth below ground surface  γ is the unit weight of soil, D is depth and u is pore water pressure.

Substitute in the equation.

Therefore, the vertical stress at a depth below the ground surface is

9 kPa

Determine the influence factor at the midpoint of soil layer,

Here is the influence factor at the midpoint of soil layer   is initial vertical stress, is vertical effective stress, and is bearing pressure

Substitute in the equation

Therefore the influence factor at the midpoint of the soil layer is 0.693

answer:

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explanation: