Sink hole forming

[rickyb01]

I have a house lot that slopes front to back with back being lower. The previous owner had a concrete building built into the hillside in the backyard like a root cellar. When we purchased the home I put up a retaining wall and extended my back yard. The retaining wall starts on both sides of root cellar. I also but a dual French drain around the root cellar and ran to daylight. Retaining wall is about 7 tall. My problem is we have sandy soil and when it rains I get a lot of sand that comes out of French drain. This creates a sink hole at the back corner of root cellar. The sink hole is 7 up from French drain but I know all that sand coming out of the drain is causing the sink hole. When I had the French drain put in we dug out all the dirt around the root cellar and filled it up with crushed stone. Any idea on how to fix this or what way to even be thinking of fixing this. Seems like just filling it up with gravel doesn稚 help. Thanks Ricky

 

[Streetcar]

Can you install filter fabric stound French drain

 

[rickyb01]

I did but seems like sand is mixing with water and going thru it.

 

[Granthol]

It either came off when you buried it or has a tear, etc. no way sand can get through the fabric if properly installed.

 

[rickyb01]

That’s going to be a huge undertaking to dig that pipe up and put a sock around it. When I installed it I placed the fabric in a U with the pipe at the bottom or about 4” off the bottom. The fabric came up about two feet on each side. I then filled up the whole thrench with crushed stone. I just have no clue on where the sand is eroding and causing the void. Down at pipe or along the transition area of crushed stone and dirt.

 

[bcp]

I think I would first keep on adding rock to the hole, and keep it topped off. Eventually all the sand that can go in will be gone.

But if this doesn't work, then dig it up and re-do.

Bruce

 

[DJ54]

If you ran the gravel underneath the pipe, clear to the very end, I'd have to guess that's how the sand is getting out. You might try digging back into the bank far enough to get to your fabric, remove the gravel under the pipe, and replace it with dirt to seal it off. You can wrap the end of the pipe with fabric, to keep the dirt out.

Depending on how much fall you have, the level at where the bottom of the gravel ends, and dirt put in, in place should be the same level, so as not to hold 4" of water. That will eventually fill in with sediment, until it reaches the level where it can drain out completely.