Soil cement slope protection

[peterb1441]

Does anyone have any idea of what sort of 7 & 28 day compressive strengths you would want for soil cement stabilised slopes? Let's assume a nominal cement content of around 5-8%.

 

[blueoak]

http://www.cement.org/water/dams_sc_faqs.asp

States 400psi for 7 day.
Detail can be bought at:

http://www.cement.org/bookstore/profile.asp?itemid=IS166

The Portland Cement Association has a couple of nice manuals you can buy too. Your cement content seemslow at first glance for a slope protection. Is water and/or freezing unlikely? Your percent sounds like a dry slope or not on a water storage dam.

 

[cvg]

around here the spec value is generally 600 - 700 psi at 7 days. Natural soil is generally sand or silty sand and 4% cement content will generally be sufficient. This is used for channel bank erosion protection and stabilization.

However, cement content vs. compressive strength is highly variable depending upon the type of soil you are using. Without knowing the gradation and %fines, you can't estimate the strength without doing trial mix design. With a high percentage of fines, you could easily double the amount of cement required to achieve your desired strength.

Are your slopes to protect against flowing water, or just to stabilize from sliding and movement?

 

[mytu]

You must to send to lab samples of soil you plan to use and make that folks to testing it with different %s of cement. Then you know what is the percent of cement whit the max strength. Have in account the content of water.

 

[MissouriPE]

Just curious - why are you using cement? In my experience, this will fail (ie. crack, heave, etc) in the next 10 years. Our city has actually removed this as an option for stabilization in most conditions. I'm personally a big believer in vegetative methods, gabions, and turf reinforcement (all depending on the slope, soil, flows, etc). We have had many locations around town where we get erosion underneath the cement and major voids are created.

Maybe it is different in other locations and I am always wanting to learn more.

 

[cvg]

missouripe - tell us about your soil cement failures. What type of use and failure modes? This is news to me as I have designed many and see them used all over around here, for well over 10 years and have not ever seen a failure.

 

[MissouriPE]

After thinking about this, I'm guessing a lot of our failures have to do with the tight clay soils we have. First, you get a lot of swell during wet weather that can cause heaving leading to cracks in the surface where water can get in and further the problem. You also will get a lot of shrinkage which can create voids underneath the cement. Between these two things, water will find a way underneath the concrete and erode the soil underneath the cement. I've walked along the end of a channel like this and lost an entire foot/ankle into a void at the edge. The problem is a vicious circle until finally there isn't enough holding up the hard armor and it just crumbles up.

Also, the way it was put in around here 10-15 years ago, little thought was given to toe protection and it is often undercut with caverns forming underneath the bottom of it.

I still find a great deal of value in vegetative methods because of infiltration and filtration and on steeper slopes have been quite impressed with how long gabion systems have lasted for us. But to each their own.

 

[cvg]

that all makes sense and maybe soil cement in areas with expansive soils doesn't work well. Gabions, riprap or vegetative methods may work better for you.

We have mostly sandy and gravelly soils around here so expansion is minimal and the native alluvial soils create a very strong soil cement without adding very much cement. Toe down is critical and generally ranges up to 10 - 15 feet deep around here. Method of installation is also quite conservative, using stair stepped 8 foot wide lifts and going up at 2:1 or 3:1 slope.

 

[reddog99o]

Vegetative Growth or Gabions are the real deal. Sand Cement is really only workable in granular soils but can be forced into compliance with other soils. You can get hydro-seed to grow on anything and gabion mats need no type of sub-surface prep.

Good Luck,

Rick Hassett, P.E.

R.A. Hassett, P.E.
rah1616@hotmail.com