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Retaining wall backfill step building questions
So, I show up at Mutual Materials, our local hardscape supplier, to place an order for materials for a retaining wall. When asked a question about construction the guy said, "We don't build 'em, we just sell the stuff". Yeesh.
So, I come to the experts here.
When building a gravity wall without geogrid the mfr. instructions say to construct the back of the wall with a drain and compacted gravel all wrapped up in landscape fabric.
With geogrid the instructions are a little fuzzy. It says to use compacted gravel sandwiched between geogrid all wrapped up in landscape fabric. Then in another place it says with geogrid the site soil can be used as backfill, which sort of makes the landscape fabric useless except to cover the gravel area immediately surrounding the drain. If the geogrid is sandwiched exclusively with compacted gravel it will take about 12 yards of gravel since the geogrid will extend 4' behind the wall for 80' of 4' high walls.
What's the right way to do it with red clay soil?
Also, need to build steps. These blocks are expensive. I'd like to construct the steps by building a four wall box, with the side walls stepped, and then fill it with compacted gravel using the blocks only as risers. Will that work?
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Retaining wall backfill step building questions
The red clay is porous enough that it passed a standard septic perc test. When we get a lot of rain one big depression might have a few feet of water accumulate which then soaks in at a rate of about one foot/day.
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Retaining wall backfill step building questions
Thanks, guys. So my plan is to suck it up and buy a bunch of good draining aggregate. The 4' wall will be built with 4' of compacted aggregate behind it, separated from the soil by geotextile fabric. Every few courses geogrid will be layered into the aggregate but it will not penetrate through the geotextile fabric into the soil. A fabric-wrapped drain tile will be slope down from one end of the wall to the other and drain to daylight. Sound OK?
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Retaining wall backfill step building questions
Thanks, Murf. It would be easy to bring the top end(s) of the drain lines to the surface and two drain lines would be easy. I may tie one of them into the gutter drains for the shed above the wall to drain that to daylight as well.
One last question please. The local sand and gravel company offers 3/4 minus, something called round drain rock (commonly used in drain fields and french drains), and pea gravel. It seems the pea gravel would compact best but I'm not sure how it will drain.
Which would you choose? The price is about the same.
Thanks again!
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Retaining wall backfill step building questions
Thanks, Murf. OK, since there will be a trench to daylight it's almost as easy to run a separate drain for the shed gutters so that will be done. I'll rent a gas plate compactor too. Picture 21 in my album shows the area where the new wall will go. You can see the need for it  The plan was to build two walls but the cost is higher than expected and too much to do in one shot this year.
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Retaining wall backfill step building questions
That's a good point. We decided against that because we'd like to turn that hill into flat terraces that can be used. Because the house is so tall I need to occasionally get a boom lift in there (the main reason for construction overkill) and my wife would like a small greenhouse built on one one of the terraces.
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