# Handout18 - 1500 = 12.5 ft 120 O"i =(7.5(120(20(110...

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Floating Foundations: Suppose we want to construct a building that weighs 1500 psf DL + LL at the following site: 20' Hard Clay y = 120 pet Soft Clay (Normally Consol.) 40' y = 110 pet C = 0.45, C = 0.08 c r eo = 1.2 Using stresses at mid-depth of clay: O"i= (20)(120) + (20)(110 62.4) = 3352 psf O"f = 3352 + 1500 = 4852 psf S ==_1-H o C 10g(0"f J = 1 (40)(0.50)IOg( 4852J = 1.46' - This is the settlement 1 + eo c 0' 'i 1 + 1.2 3352 that would occur if we place the full load of the building on the surface of the hard clay Suppose now that we excavate a weight of soil equal to the weight of the building and then place the building in the excavation:
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Unformatted text preview: 1500 = 12.5 ft. 120 O"i = (7.5)(120) + (20)(110 - 62.4) = 1852 psf -if soil swells fully after excavation and before building is built O"f = 1852 + 1500 = 3352 psf - after building is built O"max = 3352 psf S == _1-H o C 10g(~J == 1 (40)(0.08)IOg(3352J== 0.37' r 1+e o O"i 1+1.2 1852 0.37' « 1.46' The settlement of 0.37 feet assumes that the soil fully swells before the building is built. If the soil doesn't swell at all, the initial and final effective stresses will both be 3352 psf and theoretically the settlement of the building would be zero. Page 1 of 1...
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