Another retaining wall question

slopes

Hello.

I am looking at doing a versa-lok wall that will be 3ft high. I believe I interpreted their documentation to say that I don't need geogrid because the height is only 3 ft.

What it isn't clear about is what if behind the wall is a pretty steep and deep slope? The hill behind it is probably close to 45 degrees and runs for about 30 ft back. Assuming favorable soil conditions, do I need geogrid? All of their illustrations show a nice level area behind the wall.

Kurtzilla

Slopes,

In regards to Versa-Loks wall diagram on low walls, its safe to build what is refered to a gravity wall up to four feet in height with complete granular backfill.

That's if there is very little sur-charge behind the wall and that it is level in front of the wall.

Under your conditions, with the slope that you discribed, it would be best to put a layer of grid half way up the wall. Best grid to use for your conditions is a bio-directional grid, that are usually 4' wide by 50' lengths.

The grid will actually stabilize the soils behind the wall, thus creating a minature failure plain, instead of a large failure plain pushing on the base of the wall. Hope this helps.

Soil Identification & Sub-Grade Prep

http://www.goarticles.com/cgi-bin/showa.cgi?C=3087659

Daniel Holzman

The Versalok block wall is rated for local stability to approximately 4 feet tall without geogrid, assuming adequate drainage and granular backfill, and a moderate slope behind the wall. Your problem is much more complex, since you may have a global stability problem.

A global stability problem essentially means the entire slope can come down. Should this occur, the slope failure will take the entire slope with it, Versalok wall and all, including any geogrid you put in it.

Determining if a steep slope such as you describe is close to global failure is unfortunately very difficult. Telltale evidence includes evidence of tree movement on the slope, scalloped areas, or areas where it appears that vegetation has slipped. Unfortunately unstable hillsides may appear to be stable when dry, but may become unstable after prolonged rain.

Excavation for a wall at the toe of a slope can destabilize the entire hillside if the hillside is close to failure. You may want to consult with an engineer for this project. Versalok does not, and will not, perform a global stability analysis for you.