Plastic or Soil Fabric Backing for a Short Retaining Wall?

[rbattelle]

I've got a retaining wall that I had to tear out because it stopped retaining anything (dirt was flowing right through it). It was put in by the original builder of this house, and no gravel backfill was used! The wall was simply erected, and dirt was filled in behind it. That's it.



So I've removed the wall and excavated about 1' behind it. I intend to fill that entire space with washed #57s. I also intend to drop a 4" perforated PVC pipe at the base. The wall is 33" high and about 11' long.



My question is, what should I use to line the back of the wall? Thick plastic? Soil fabric? Roofing felt?



Ryan

 

[CKelley1]

10 mill visqueen on the wall pipe and gravel with soil fabric on top of the gravel

 

[Hoefler]

Never have used anything between the gravel and the wall, the perforated PVC drain tile will be all you need. I have built these wall as high as 22' and never used anything but clean gravel against the block.

 

[Bill Stockard]

I had a contractor put in a 30" high retaining wall about 75-ft long. He poured a 12" wide x 4" thick reinforced concrete footing below grade and placed concrete locking decorative retaining wall blocks above it. Before backfilling with our native sandy loam, I placed a woven fabric behind the wall that is designed to be used behind retaining walls built on lakes to hold back the soil, but let the water pass through and supposedly lasts 25-30 years. It's been six years and not a bit of the sand has washed through the retaining wall block; however, the rain runoff from our gutter and downspouts passes right through it. I don't remember the name of the fabric but I think I remember it was made by BF Goodrich. It was more expensive compared to the stuff they have at places like HD.



Bill

 

[CKelley1]

bill you gave a better explanation than i did, the only reason for the plastic was to keep water from entering where the snapties are and freezing i agree it is overkill but for $5 he can make the decision

 

[rbattelle]

I don't remember the name of the fabric but I think I remember it was made by BF Goodrich. It was more expensive compared to the stuff they have at places like HD.

Where did you get it?



-Ryan

 

[rbattelle]

I have built these wall as high as 22' and never used anything but clean gravel against the block.

Good point. I may have been overzealous in wanting to run the fabric against the block. If the fabric is against the soil, then soil won't enter the gravel. Plus, it occurred to me that the gravel will fill the empty spaces between blocks, which is almost certainly a good thing.

This wall will be sitting on a 4" concrete slab, not on dirt. Behind the wall I excavated just down to the bottom of the slab (~4"). I'm thinking of running the fabric under the gravel as well - why not, it doesn't add significantly to the cost to do so.

I went to Home Depot and Lowes to see what they offer for landscape fabric.

Lowes: Dupont Weed Free Pro 25-year grade 4'x100' roll, $43 .

Home Depot: EasyGardener Weedblock 30-year grade, 4'x100', $48.

This week I'll visit a local landscape shop and see what they offer. BTW, it's my intention to apply 2 layers of the fabric for "extra protection".

-Ryan

 

[Hoefler]

Your concrete footer, is it below grade?? How deep?/

 

[CKelley1]

do not use the fabric on bottom you only need one layer on top if you wanted to you could use the fabric on the dirt side of the ditch. the purpose of the fabric is to keep dirt from filling in between the rock we use 3/4" crushed rock this has more area for the watter and will not enter the holes in the pipe. we buy our febric in 20x100 foot rolls but the ones you found will be about the same product

 

[Bill Stockard]

Your concrete footer, is it below grade?? How deep?/

A couple of inches. It's there to prevent the retaining wall from settling. The first layer of blocks on top of the concrete is in mortar to hold them level and to prevent them from moving horizontally on the concrete. Our sandy loam soil doesn't shift much from wet/dry conditions. I wanted the wall to remain straight and level for a number of years and after nearly six years, it hasn't moved.



Bill

 

[rbattelle]

In my case, the concrete slab is actually a patio, not a footer for the wall, per se. It's a 4" thick slab, so it's 4" below grade, plus a couple inches of gravel as a base.

I called two local commercial landscape supply shops and neither one seemed to have any clue about their soil fabrics. One shop claimed to have a small quantities of "Sunbright" brand, which I can't find anywhere online. The other shop wanted to sell me this geogrid.

So I'm a bit disillusioned with the local landscape supply shops. Thinking I'll just go with a double layer of the HD stuff.

Why not put a layer of fabric below my gravel backfill? I mean, why only on top and against the vertical dirt wall?

-Ryan

 

[Hoefler]

The GEO Grid is for wall retention, keeps it from falling over. Your wall being under 3' tall, you should not have problem. I would not worry about any kind of fabric, with the size wall you are planning, clean gravel and a drain tile is more than adequate. Fabric on top of the gravel is only needed if your top soil is on the sandy side.

 

[JLitton]

I put a retaining wall using 18" retaining wall block that is 140 ft starting at 18 inches and going up to 6 ft tall in the middle. My neighbor is a contractor with the local brick yard and he told me exactly what to do. I laid about 4 rows of block the entire length of the wall and then lined the back of the wall with typar which is fabric for use under gravel roads to keep the gravel from disappearing into the ground. The fabric was cut to four feet. After lining the back of the wall, I placed a 4 inch drain line which was wrapped in fabric to keep anything other than water from entering the line. I then backfilled the wall with 57 river rock. I then flipped the fabric back over the gravel and continued to build my wall up another 2 feet. At that point, I pulled the fabric back to the backside of the wall and backfilled again. Anything over four feet needs to geo grid to tie the wall back into the backfill to keep the wall stable. To do this, I laid the fabric on top of the existing rows of block extending straight back over the river rock backfill until it met the existing earth. I then continued to lay the block up to the finished height. The block will hold the fabric in place and then backfill over top of the fabric to the top of the wall.



The wall has not moved an inch and nothing comes through the wall. This was a lot of work, but I know I did not take any short cuts and if it should happen to fail at some point, I know it wasn't because I did something to save a dollar or a bead of sweat.



My wall consisted of 28 pallets of block and I used a total of 74 ton of river rock to backfill. Luckily, my neighbor had a bobcat that he would bring over to backfill the wall as I went. Just in case you didn't know, the walls are prone falling backwards if you build them too tall without backfilling every couple feet as you build them. You also want to put the first row of the wall under grade to act as a toe hold for the bottom of the wall.



Sorry for being so windy, but hey, that's the beauty of this site. To hear other people's experience. Right?

 

[JLitton]

I just remembered. Check with the local brick yard for the fabric. They should be able to hook you up if they sell landscaping blocks or material.