Spread Footing Settlements
Spread Footing Settlements
(OP)
I am trying to design a square spread footing on a very stiff sandy silt with clay N >50. I dont have any consolidation test results. I assume that the soil is over consolidated but not sure about OCR??. My boring goes 18 ft. below B.O.F. I am trying to calculate the consolidation settlement and not sure what assumptions to make and what H value should I use in the OC settlement equations. Do I take it as one layer just to the bottom of boring (H=18) and calculate effective pressure (P0') and use Boussinesq equation to calculate Pv at the middle of the H layer. Is there any design example around..?. Thanks





RE: Spread Footing Settlements
Using Boussinesq, calculate the change in vertical effective stress with depth. Integrate this stress curve to depth (this will essentially be solving for the area of the delta-sigmaV v. depth curve. Your units will be psf*ft, or pounds/ft. If you then divide this by the soil modulus (using consistent units), you'll get units of feet, which will be the anticipated compression under the foundation load. Some folks multiply this by 1.2 to account for long term soil creep.
Hope this helps. My professor (Mike Duncan) agreed with this approach when I was in graduate school and it's simpler than using the Schmertman method (especially if you don't have cone data).
f-d
¡papá gordo ain't no madre flaca!
RE: Spread Footing Settlements
RE: Spread Footing Settlements
Yes.
Additionally, in many instances a sandy silt displays elastic behavior, expecially if the silt is non plastic. Normally, I'd want to know LL and PI, but for N>50 it's kind of a moot point.
f-d
¡papá gordo ain't no madre flaca!