Water in Grade Beam Void Space

[BoutDat]

thread507-223669
I noticed the above discussion and wanted to add that we have done some research and tested some aspects of the previous thread. With Expansive soil conditions to deal with, either expansive clays or frost heave, under certain and not so uncommon instances, water can and does accumulate in the subject voided space. One of the negatives of these occurrences is that any depth of accumulated water decreases the volume of available voided space. The volume of water then found to be occupying any portion of the subject void, transmits its volume as a hydraulic force equation at a 1 to 1 ratio. If you do a little self equation, the results can be quite troubling, and worth consideration, it is certainly worthy of discussion in this type of format. Boutdat...

 

[BAretired]

I have used Geospan, a product of Plasti Fab under grade beams with swelling soil and have never had a problem. Check out this link:

http://www.plastifab.com/applications/geotechnical/compressible_fill/geospan.html

BA

 

[apsix]

I can understand that free water under grade beams will exacerbate frost heave, but I can't yet believe that it's an issue with expanding clay soils. The water will find a way out with slowly increasing pressure.

 

[BAretired]

apsix,

If the soil is clay, as it is in most of the province of Alberta, water will not find its way out quickly enough because the soil has an extremely low permeability. It is better to have a waterproof cushion under the grade beam which expands or contracts to meet the pressure, but always fills the void space. In this way, free water cannot get in.

BA

 

[BoutDat]

I often use my own soil classification terms internally for the soils requiring void forms. I call it ”YUK”, on a scale of 1-5, but it’s YUK at any termed scale of magnitude. With particular focus on grade beam sections, the voided space is generally thought of as being “neutral” to transmitting or generating force, so long as the depth or volume of the voided space remains sufficient for its designed intent. Subsequent to a voided space volume being reduced by water or expanding material, the remaining air volume thought to be neutral may not be. Thus, a resulting increase in void space air pressure can also be experienced by the expansion. What would an additional 5-20 psi in unaccounted for uplift pressures do to your structural beam design? That’s “psi”, not “SF or CF…..