Effect of compaction on lateral pressure. 3

[fyaure]

How does compaction of fill affect the lateral presssure on a rigid/fixed retaining wall? Besides the change in density and therefore the overall vertical pressure and change in the friction angle value, is there anything else that will affect the value of coffiecient of lateral pressure? If yes, what is the equation and where can I find it?

 

[BigH]

The large compactive pressures will leave in higher than "normal" residual lateral stresses - ko might be as much as 0.7 or more (e.g., large OCRs). Ingold wrote a book on this back in the late 70s I believe.

 

[amanpreet]

when you compact the backfill soil then the density and internal friction angle is going to be chnaged and you have to see to its new density to check the dry soil density and bulk density of the soilf for calculating the earth pressure.
you can perform any test to check out the density of the soil. and regarding calculating the new friction angle u can preform the SPT test.

regards
Amanpreet

 

[fyaure]

Thanks BigH and amanpreet.
amanpreet, I have already considered the density and friction angle factors....I am looking for a different kind of effect that leaves a residual lateral pressure even after the compacting force (or overburden)is removed (I assume that case exists).
Any more help is welcome.

 

[TDAA]

My Das text (2nd eddition) indicates (for sand) that Serif, Fang, and Sherif (1984) developed the following:

Ko=(1-sin(phi))+[(Gamma(d)/Gamma(dmin))-1]*5.5

where:
Gamma(d)=actual compacted dry unit weight
Gamma(dnmin)=dry unit weight of the sand in its loosest state


For clays, figure the OCR of the compacted material and multiply Ko by the square root of the OCR. If you are using clay backfill (local practice when expansive clayes is the retained material), I would limit the level of compaction only to what is needed to reduce settlement. This would result in not being over consolidated, and the above would not apply.

 

[DRC1]

The Geotechnical Journal published at least two papers on the subject several years ago. Localized stresses during the compaction process can be very high, exceeding Ko. That is why specifications require plate tampers near the new walls during backfilling. Search eiter the ASCE website for the articles or check Linda Hall(

http://www.lindahall.org)

 

[jdonville]

NAVFAC DM 7.2 pages 76 and 77 present a diagram (figure 13) showing the effect on lateral earth pressure due to compaction, based on the following work:

Ingold, T.S., Retaining Wall Performance During Backfilling, Journal of the Geotechnical Engineering Division, ASCE, Vol. 105, GT5, 1979.

Jeff




Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[dgillette]

Try Duncan et al: "Estimation Earth Pressures due to Compaction" in the December 1991 ASCE JGE, with erratum in March 1992, and discussion and closure in July 1993. They have some chart solutions of possible benefit.

 

[fndn]

Effect of compaction on rigid walls has higher than at rest pressures in the upper few feet of soils, then is constant for a middle zone and then is equal to the at rest pressure near the bottom of the wall.


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[fyaure]

fndn,
i cant find the reference to that figure...do u know where it came from?

 

[fndn]

fyaure;

I drew that for answering your post, and is what I use for estimates. You can make your own chart from this older Soil Engineering by by Spangler and Handy, 4th Ed, 1982. It is on pages 564-565. Basically what they found is that the pressure induced by the rollers are double of that estimated by Boussinesq's line load stress distrubuition for the upper 4-5 feet. Below this depth it follows the Boussinesq stress line. Also Gerber found similar resultes in 1929. Try online bookstores for a copy of thie soil engineering book-4th ed.