Rebuilding Retaining Wall

Piper1

I have retaining wall issues at the end of my paved driveway! The walls are made of 4 x 4's and are leaning outward badly due to frost heaves. I am going to rip out the 4 x 4's and replace it with mortared rock. My question - is it safe to dig out from behind the current (and new) wall and fill with crushed rock (this would be partially under the driveway). Also, if I mortar the back half of the wall (to make it appear like a dry stack wall) do I still need to prepare a batter wall that slants 1 inch per 1 foot in height?

Maybe this isn't an issue but I can use some advice.

Msradell

In order to give you any advice we're going to need to know how tall the retaining wall is, etc. Pictures would definitely help.

Piper1

Good point - I am new and short on deatils. The height is only two feet above ground and four feet wide - most is covered by sloping land (see attached pics). I realize I will need to build off a rebar reinforced concrete base below the frost line. My main questions is:

1. Based on this, is it safe to dig out under the exisiting driveway (approx. 1 foot) and replace the dirt with crushed rock to ensure better drainage? My fear is that the driveway may cave with a less solid base.
2. If I don't do this and build the retaining wall wider than it currently is I am trying to think how I can tie it into the driveway and still make it look nice.

All suggestions are welcome.

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Msradell

Definitely do not take anything out from under the driveway! It would be virtually impossible to compact anything he replaced it with sufficiently. It would just let the driveway deteriorate quite rapidly and cave in.
In my opinion your best bet would be to replace the existing retaining walls with new concrete ones. Remove the existing wood and dig a couple of post holes 3on each side to give good support. Then place your forms on three sides, leaving the side towards the driveway to be self forming against the remaining dirt that was behind the wood. I would make the concrete retaining walls 8"-12" depending on your preferences. Doing it this way would certainly be a lot more work and expense than some other options but would certainly provide a long-term solution!

You may also want to verify that the existing pipe under your driveway is in good condition because now I would certainly be the best time to replace it is necessary.

kmc

Is that a drain tunnel under the driveway?

Piper1

Yes it is a drain culvert underneath the driveway and it is in good condition.

I am not sure if I understand correctly re: putting in posts. If I did this would there also be a secondary support (over and above the concrete wall) to ensure that frost heaves and moisture don't force the wall to cave again (something like a heavy duty wire mesh)?

Instead of using crushed gravel for drainage, and since I can't excavate under the driveway, is there an alternative mentod to ensure excess moisture drains and the freeze thaw cycle doesn't bulge the wall?

Msradell

The post holes would be filled with concrete as you pour the forms. They would just give the wall more support to keep it from falling over. You can actually put some rebar down into the holes and tie them together if you want to make it even stronger. You can buy rebar at the big box stores in small quantities.

Piper1

Msradell

That should work fine as long as you compact the gravel well. Actually you could build the new wall first before you remove the old one by doing it this way which may make things a lot easier.

Piper1

I have another question now - I live in Canada with heavy freeze/thaw cycles. I want to make sure that the wall does not heave upwards on me. Instead of starting my wall 4 feet deep, can I use enough crushed rock under the base of the wall (i.e. 2ft) to negate the frost pressure and ensure a stable wall? Traditional wisdom says go below the frost line but I haven't seen this done with any rock wall I've researched. Looking for answers!