79_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011

# 79_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011 - over...

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ps2 For surface loading, Hooke's law may be rewritten as: E z =qC~) where: q Iz = surface contact pressure = strain influence factor Iz varies only with Poisson's ratio and the location of the point for which the strain is to be evaluated (similar to previous immediate settlement analyses), The theoretical depth distribution of Iz is shown below at left. Strain distributions for cohesionless soils measured during model studies and non-linear finite element studies by Schmertmann are shown at right. (B is the footing width.) Theoretical Iz Distribution I 0.2 0.4 0,6 0,8 Iz Observed I z Distribution I 0,2 0.4 0,6 0.8 Iz zlB 0,5 1.0 1,5 2,0 --- 11 ~ 0,5 - - / , , - ",' I...l= 0.4 - 0,5 1,0 zlB 1,5 2,0 "'. _- Finite Element Analysis Model Test D r = 44% Model Test or= 85% The distortion settlement, p, at the surface may be calculated by integrating the strain
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Unformatted text preview: over the depth of influence, z ~ ~ in the limit: - but practically the depth of the pressure bulb depth (z = 2B), p~ S: E z dz = J: qm dZ and thus p =q r(~)dZ Axisymmetric Footing 0.2 0.4 0,6 0.8 Iz 2B 1B 3B , , , , , , ,,' "'-. . Strip / / Footinq 4B ' For approximation purposes, Schmertmann proposed idealizing the distribution of Iz as a triangle with a maximum influence factor between 8/2 and B depending on the footing dimensions, as shown at right. Then he suggested splitting the soil mass into homogeneous layers and summing the settlement calculated for each layer using the appropriate value of Iz. z /...
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