Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Soil swell

[Subject Prev][Subject Next][Thread Prev][Thread Next]
On 21 Dec 2004, at 19:48, GSKWY(--nospam--at) wrote:

> Is there a field test I can do to estimate how much a soil will swell when fifteen feet of it are
> excavated?  This is a glacial till (New England)  not Texas or California clay.
> Or can I assume a certain percentage of and not be too far off?  I'm mostly interested in how much
> room it will take up when it is excavated.
> When I am putting it back,  can I put the lower lifts (greater than 10 ft depth or so) back in
> fairly thick (i.e. more than a 6 in. lift) and assume the subsequent lifts will compact it,  or do I
> need to do it all at 6 in. lifts to get good compaction?
> Gail Kelley

According to the Pocket Ref by Thomas J. Glover, 2nd Ed. p 329,
the bulking factors for sand or soil w/clay are between 20-30%.
For soil w/ clay the book reports an in-place density of 1.76
and a density after mined of 1.41.  These are actually specific
gravities.  This in-place of 1.76 or about 110 pcf, is possibly
on the high side, but a sand cone test of the soils that you are working
with should tell you what the in-place density is.  On a recent
project of mine, I tested the in-place density of an SC soil type
at 94 pcf. If there is a bit of larger rock in the soil, larger than 3/4",
then you'll have to request an in-place density test by water 
replacement methods.  I would be a bit skeptical of using a 
nuclear density gage without sufficient correlation to the soil
type.  The sand cone test will be more accurate.

As far as replacement and recompaction of the removed
soil, you definitely want to specify thin lifts 6-8" loose and
compacted to the needed density at proper moisture content.
I usually use 95% of ASTM D1557, the modified Proctor, for
soil under structures or for soil under something with a long
design life, and I use 90% of ASTM D1557 for backfill conditions
that won't have structures over them and therefore won't be
too critical with future settlement.

If you use thick lifts, thinking that the soil above the lower lifts
will compact the lower lifts, then you need to allow for natural
settlement and compaction of the soil before building over it.
This could take anywhere from 1 year to 15 years depending
upon the type of soil and the water content of the soil over
that time.  Mechanical compaction is much quicker.

Lloyd Pack

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at:
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*   Questions to seaint-ad(--nospam--at) Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: 
******* ****** ****** ****** ******* ****** ****** ********