Stress-strain curves for cement-modified soils

[dgillette]

Have a project involving numerical analysis of seismic deformation of a proposed earth structure. It is to be supported in part by cement-modified soil materials. (May be flowable; may be conventional compacted soil-cement.)

Know of any good references for stress-strain curves that include post-peak behavior? The big question is how fast the shear resistance drops off with strain after the peak strength has been exceeded. Direct simple shear would fit the boundary conditions best, but triaxial would also be a big help.

Thanks much,
DRG

 

[dgillette]

Stress-strain curves for the CMS, that is.

 

[howardoark]

You'd think it would behave in a brittle manner - reach the peak and then drop to a much lower stress value.

A Japanese team looked at it - "study of mechanical prperties of soil-cement mixture for a cutoff wall" Soils and Foundations Vol 37 no. 4 Dec 1997 - you can down load it free. In unconfined compression, they got brittle failures at very low strain. At higher confining pressures, they got a brittle failure, but no drop off in strength.

 

[Ron]

Stress-strain curves for soil cement are rather shallow. Only published curves I've seen are in Yoder and Witzcak "Principles of Pavement Design".

 

[dgillette]

Thanks, Howardoark. Haven't looked at it yet. Another one I found was Schnaid, Prietto, and Consoli, in Brazil. "Characterization of Cemented Sand in Triaxial Compression," ASCE JGGE, October 2001.

For a 5% mixture, in effect they found peak strength on the order of c = 270 kPa = 5600 psf, and phi' = 39. At 4% strain, the resistance was more like c = 0 and phi' = 42. Peak strength was reached at about 0.8 to 1.2% axial strain, and it dropped off to a constant value by 2 to 3%. It didn't drop off quite as sharply as I had expected, but still too fast to do us any good. (I had expected that it wouldn't do any good, but I needed some actual factual data like Schnaid's to nail the coffin shut to everyone's satisfaction.) The overall forms of the stress-strain curves and the strength envelope seem to make perfect sense.

Ron - I have a moldy (literally) old edition of "Principles of Pavement Design" by Yoder alone, but it didn't have the stress-strain curves. Apparently 1959 was too far back!

 

[Ron]

DRG...I'll try to pull my copy out of storage and post a copy of the page.

In the interim, contact Matt Witzcak at the University of Maryland or The Asphalt Institute...he might have something that is updated that he can send to you. He's a nice guy and helpful.

 

[dgillette]

Thanks, Ron, but don't go to any trouble. I think the stuff I already found was enough to nail (plus glue and duct tape) the coffin shut on the idea of relying on a brittle material might crack in that application. It will be necessary to use a higher-strength material where cracking won't initiate in the first place.