Backfill retaining wall?

[Crazy Legs]

Hey everyone, its getting warmer here and the snow is melting, i'm gettin excited to start on my garage but first i've to get a sound base. I've got my railroad tie retaining wall done last fall & i've let it settle throughout the winter freeze. I'm getting ready to backfill it so even when the ties wrought off my fill & garage won't move. (this wall is a little less than 4' high at the highest point and 2' at lowest point about 50' long.)

Question is: Should i use broken up concrete fill or clay to back fill this at a gentle angle? (i'll try to post a pic so you can understand a bit better.) Once this is all backfilled i'll pack down my 160 tons of clay fill so i can get started, i'm just worried if i pack it before its backfilled, my wall will move or break

 

[twostory]

Not sure what you are filling, but you need to do it in lifts of 4 to 6 inches at a time. You should not just fill the 2 feet up with dirt, then try to compact it. (it will not compact)

To compact the 4 to 6 inches of dirt/rock/concrete, I rented a small (walk behind) vibrating sheep's foot roller to compact my fill dirt. You could use a "jumping jack" if the fill area is not very large. I filled a 1,100 sq ft area, up to 4 ft thick.

 

[bluesman2a]

I'm no expert here, so please take this with a big grain of salt...

I would look into setting up something for drainage. Start with 3/4 crush at the base of the wall, lay in a perforated drain pipe with a sock, cover with more 3/4 crush, THEN backfill.

 

[Crazy Legs]

yep, i forgot to mention that the fill i'll put there as back fill i'll pack it as i go every 6" or so.
Do you think i should use the broken concrete or clay as the backfill though? My thought on the concrete is, it won't move or wash away, but there would be huge voids in between the pieces. if i used clay it'd be packed and dense but maybe move over time...... ?? (I can't figure out how to insert the pic)

 

[twostory]

Do you think i should use the broken concrete or clay as the backfill though? My thought on the concrete is, it won't move or wash away, but there would be huge voids in between the pieces. if i used clay it'd be packed and dense but maybe move over time...... ??

Apply a silt fence fabric to the retaining wall before you backfill. This will stop the dirt from moving thru your retaining wall. I bought a roll of this fabric at Costco, it is 3 ft wide on the roll.

I agree with blueman2a on the drainage rock and drainage pipe with a fabric sock over it.

 

[kbs2244]

It sounds like you already have the garage area filled in and are now worried about support around the outside of your wall so it won't blow out?
If you have the busted concrete, use it. No pices bigger than a foot ball. Spread the pices around one layer thick, then fill in the empty spaces and cover with your clay. Pack it, and do it again. Wether you need to put in drainage or not depends on what is downhill from your garage. It sounds like the garage will be sitting high and you are going to have plenty of slope away from it. With backfill that is mostly clay under the final topsoil for the sod, you shouldn't have any water retentsion worries as long as the water has some place to go to once it is away from the garage. Clay can be a blessing or a curse. It absorbs water to a point, then sheds it. If you use it like a shield under your sod, it can help protect your fill from water by promoting runoff. The top of the clay will swell up and then the water will run down, through the sod. But if the water has nowhere to go, and builds up from the bottom, the clay can swell and break things. That is why they do not use it in backfill around basements.
I have seen rubble and rough dirt, including clay, islands built in low areas, though. No retaing walls, just a pile of dirt with nothing steeper than a 30 degree slope away from the building. Once the water table stabilizes, a winter wait is good, they are good for building on. The local hardware store is on such a man made island.

 

[ownsaglock]

As mentioned if the concrete chunks are too big the voids will cause settling. We had a inspector backfill behind new bridge abutments with the old busted up abutments and it took 2-3 years of patching to correct the settlement.

The walk behind compactor & thin clay lifts would be the best fix IMHO.As long as the clay can swell out away from the garage I wouldnt think it would push in your retaining wall. I have seen clay push in basement walls but it was trapped below grade.

All good suggestions on the drainage too.

 

[boiler7904]

Backfilling behind a retaining wall with clay will cause the retaining wall to fail prematurely. You could probably use the broken concrete if the pieces are small enough and you fill the voids with clean gravel. The biggest problem with using clay is that it swells when wet. If it happens to freeze once it gets wet, it swells even more causing the unsupported wall to move out. Use landscape fabric to keep your native soil from contaminating the stone backfill. I'd also see about getting drain tile behind the base of the wall to let it drain.

Definitely fill and compact in lifts. A vibratory plate compactor will do a better job than a jumping jack will and faster too.

 

[russlaferrera]

Boiler told ya right. I HAD an 3 X 50 concrete block wall that was standing for 18 years . We received a lot of rain and the whole wall fell down in one piece. Looking at the construction there was no drainage installed. Water pressure does amazing stuff.

 

[ownsaglock]

Vibratory plates are just about useless unless you are using sand. Then they still stink compared to a jumping jack. We've banned the vibratory plates on almost all our projects.

What was on the other side of the wall that fell down?