Slab-on-grade Settlement
Slab-on-grade Settlement
(OP)
I was curious of how you all calculate settlement below a slab-on-grade including depth of significant influence (vertical stress increase) and soil improvement depth (if necessary).
Would the Hough Method be an acceptable approach? I have read that this method can over-predict the settlement by a factor of 2 or more. Or, maybe using one of the charts on the Theory of Elasticity or Westergaard's Theory (depending on the subsurface conditions) to calculate the increase in vertical stress beneath a corner of uniformly loaded rectangular area, and multiplying by 4 for the center of the slab. Is the Schmertmann Method an acceptable method? I was told by one of the old PE's that used to work here that it should not be used for mat foundations. I know the analyses of immediate settlement and consolidation settlement; my questions pertains more to cohesionless soils.
I guess my main question is, do you treat the slab as a mat (one large load)? Does a slab-on-grade behave like a mat? I would think the mat would be much stiffer. I feel like I'm losing my mind on this probably not so difficult analysis. I can't find any references that specifically address slab-on-grade settlement.
Would the Hough Method be an acceptable approach? I have read that this method can over-predict the settlement by a factor of 2 or more. Or, maybe using one of the charts on the Theory of Elasticity or Westergaard's Theory (depending on the subsurface conditions) to calculate the increase in vertical stress beneath a corner of uniformly loaded rectangular area, and multiplying by 4 for the center of the slab. Is the Schmertmann Method an acceptable method? I was told by one of the old PE's that used to work here that it should not be used for mat foundations. I know the analyses of immediate settlement and consolidation settlement; my questions pertains more to cohesionless soils.
I guess my main question is, do you treat the slab as a mat (one large load)? Does a slab-on-grade behave like a mat? I would think the mat would be much stiffer. I feel like I'm losing my mind on this probably not so difficult analysis. I can't find any references that specifically address slab-on-grade settlement.





RE: Slab-on-grade Settlement
My spread sheet calcs compute for one foot layers below the loads and so one can go down as far as he wants, but usually only am concerned only to the point where added pressure is more than 10% of existing. A spreed sheet method is easily modified to fit ones job details. You can play with pre-coompression also very easy.
RE: Slab-on-grade Settlement
Here is the paper:
http://files.engineering.com/download.aspx?folder=...
RE: Slab-on-grade Settlement
RE: Slab-on-grade Settlement
RE: Slab-on-grade Settlement
Your statement "may consolidate" is a guess. By drying, yes, but not usually due to its own weight. Slabs re amazing at what crap they can traverse and not have any lasting effect.
RE: Slab-on-grade Settlement
RE: Slab-on-grade Settlement
One caution if rolling surcharge is used. That material usually had to be hauled in. The contractor does not want to haul it off site ater. They may want to use if for raising the grade at the site some place. Never allow it near any proposed or future building area if there is any question of that area settling!!!!
RE: Slab-on-grade Settlement
RE: Slab-on-grade Settlement
RE: Slab-on-grade Settlement
RE: Slab-on-grade Settlement
RE: Slab-on-grade Settlement
Your displacement method has been used along with excavation in front in Michigan DOT for many years crossing peat marshes. About 1960 I managed to sneak that into a project for a Wisconsin road job. It was not in the plan. It worked so well it also was adopted here. That treatment would leave a road fill that later did not settle (noticeably)ever.
RE: Slab-on-grade Settlement
RE: Slab-on-grade Settlement
I have the second edition, 1973. He shows it there also, but doesn't name Michigan. I learned about it from a PHD student at UW who had worked in Michigan. I think their Soils Manual had that spelled out. On that first job, we (at the Wis DOT) took some test borings through the fill and found complete displacement to 30 feet.
RE: Slab-on-grade Settlement
http://mdotwiki.state.mi.us/construction/index.php...