What do I need to use as a retaining wall base?

So far as I can tell your major variable is soil plasticity, followed by moisture content. I live and work in Houston Texas. so I've never has to deal with frost lines, but we here on God's own coastline are accustomed to treating dirt as a liquid.

The soil here is a clay soil with a lot of rock to take into account when digging. The wall is a total of 8 feet tall which includeds a total of 18 inches of the wall being underground. From what I have researched I can use a compacted crusher run base and have to use geo-grid as far back into the earth as the wall is tall? Does anyone have a second opinion, it would be appreciated greatly? Thanks

<From what I have researched I can use a compacted crusher run base and have to use geo-grid as far back into the earth as the wall is tall? Does anyone have a second opinion, it would be appreciated greatly? >

Compacted Crusher Run Base will be FINE for all seasons.Geogrid will not be needed.

Re second opinion,-- yes -may I speak out?

Your wall above ground is only 6'-6" (2m)

If you have not committed to AnchorPro-you can purchase 2m Hi L shaped Reinforced Precast Concrete( available also with Stone-like outer looks). The beauty of the L lies in the fact that the retained soil will press down on the leg-- and the vertical 2m will remain vertical in most/all rainy/soggy weather.

visit http://www.wieserconcrete.com/guide/ltpanel2.html and find availability near you

Best

mm

I could not find design charts for the brand name you mentioned, but you will find design charts for a similar product at this site: http://www.keystonewalls.com/pages/DesignPro_pages/DP_design.html (sorry, link no longer available). The main variables are soil type, wall batter, soil gradient and surcharge pressure on the higher level. It appears to me that you will be a little conservative if you project the geo-grid eight feet into the earth. Use the Silt/Lean Clay table for your site. Needless to say, the firm who prepared these tables will not accept responsibility for their design, particularly if you use a competitor's product.

While it may be desirable to excavate below frost depth, it is not always practical. In central Alberta, for example, the frost is deemed to penetrate five feet adjacent to a heated building and eight feet in open terrain such as you would normally find at a retaining wall. Excavation to that depth is not very practical. Alternatives are (a) to provide insulation around the wall to limit the depth of frost penetration or (b) to simply accept the fact that the wall is going to move as dictated by soil movements. I tend to opt for (b).

You cannot omit the geo-grid as suggested in another post, because that is what provides resistance to overturning. The wall itself is not capable of taking any bending moment. It is not structurally continuous. Without the geo-grid, it would collapse.

It is true that a concrete footing could be used instead of the gravel pad. It would provide a nice flat surface to start the blocks and, as noted by others, would not cost much more. Perhaps one advantage of the gravel pad, however is its ability to drain water below the wall thus preventing the buildup of a hydraulic head on the high side.

One of the most important aspects of retaining wall design is good drainage. Drain tile behind the wall is okay, but in some locations, it can remain frozen even when melting conditions exist at surface. I like to provide 2" diam. drain holes through the wall at about 10' centres about six inches above the lower grade. It too can freeze, but the water only has to run a short distance to get out. Whether or not frost is a problem in your area I cannot say because I don't know where you are.

Good luck with your project.

I don"t think You need a soil engineer for this project. I live in an area where the frost, although I don't ever remember it going this deep, is forty inches. and anything made up of blocks must be set on a footer. If I were doing the job I would dig down to the frost line and pour 8 to 12 inches of concrete for a footer. Get this nice and level and the blocks will go up nice and even.

oilcan13

What real advantage is there in the crusher run base over a poured concrete footer, for block? By the time you put the rock there, and tamp it down seems to me you will still have potential problems and haven't saved that much.

Around here in NC we pour footers for retaining walls made of block, but will mount precast concrete on four inch gravel beds, so the suggested use of precast concrete sans the concrete foundation sounds good to me. Of course the concrete walls we use are tied together into a square or rectangle and are supporting each other instead of trying to hold the earth back in one direction.

I live in Charleston, West Virginia. The gravel is actually much cheaper. The wall will require 3.5 cubic yards of base. Concrete around here is somewhere around the cost of $80-$100 a yard while gravel is $17-$20 a yard. The job site is restricted access with only a 5' wide path that is 70' long from the street to the back of the residence where the wall is going to be placed. Any other tips for constructing this retaining wall? Thank you all for everything so far!

First thing I would do is check with the local building authority. There may be local building requirements and permits. Additionally, since the wall is greater than 5 or 6 feet, it is likely a structural retaining wall, and requires a stamped engineered design.

"Additionally, since the wall is greater than 5 or 6 feet, it is likely a structural retaining wall, and requires a stamped engineered design."

In my province (Alberta), a stamped drawing would indeed by a requirement of the authority having jurisdiction, however, it often happens that an individual builds without the necessary building permit, then after the work is completed, runs afoul of the authority and subsequently approaches an engineer, looking for sealed documents to justify what he has already done.

If he cannot obtain sealed documents, the authority can and will force him to remove the offending work or take such remedial measures as may be required by the engineer to allow him to place his seal on the documents.