How do I repair this void underneath the steps to our basement? (Long)
July 20, 2011 7:18 AM   Subscribe

How do I repair this void underneath the steps to our basement? (Long)

We live in a house with a full height basement. The basement has an exterior entrance via concrete steps from ground level to a landing where the basement door is. The steps on one side abut the exterior basement wall. The steps are bounded on the other side by a 6" thick concrete wall.

During & after heavy rains I would notice dirt on the steps themselves. I could not figure out where the dirt was coming from. The ground slopes away from the house at the top of the steps and around the house (and there is no dirt missing on the surface). I attributed it to topsoil being washed away from a garden I had years ago nearby. Unfortunately after the garden was replaced with grass, this no longer explained continuing dirt, almost silt like on the steps after rains.

During a recent heavy downpour I watched water coming over the basement door threshold. I knew the drain in the landing of the basement steps was blocked. I opened the door and saw the drain was clogged with leaves etc. When I looked "up" the steps I saw water spouting out of the exterior block wall of the house! (See picture picture here and another picture here). I later figured out that it was actually coming from behind the stucco veneer and not from behind the wall itself.

After the rain, I probed around the top of the steps as there was no way the water streaming down the steps was just from the rainfall on the steps and it didn't explain the dirt on the steps themselves.
A 6" area of grass and dirt "fell in" beside the cement pad at the top of the steps (see pic of the hole before I dug it out) and looking into the hole but not much too see as I didn't want to drop my phone down the hole.

I opened this area up with a shovel and discovered that there is a void underneath the steps, and between the exterior wall of the house and the wall adjoining the steps approximately 1.5 - 2' below the steps and going down the steps at least 8'. The steps are 4' wide. I can actually put my arm in the hole, and see the bottom of the rebar of the steps, the rebar in the outside wall, and the exterior wall of the house. It's a big area. I can't really figure out where the dirt was going except that it was filling with water and being pushed out through the stucco (and I remember repair a large crack in the stucco a few years ago now).

How do I repair this? Obviously I need to get something under the steps to keep them from caving in. But this is a much bigger job than filling with bags of Quikrete.
posted by bellastarr to Home & Garden (6 answers total) 2 users marked this as a favorite
This is way bigger than a few sacks of Quikrete. It appears that you have water running into and along the trench that was originally dug to build your foundation. When it was built, there should have been a foundation drain system installed if there was any chance that water would flow down into the trench after the house was built. It appears that this problem has existed for a long time. What you are seeing is, most likely, just the tip of the iceberg. You need someone who is experienced and qualified in installing a drainage system around foundations. They need to install a french drain around the house, fill in and re-compact any areas that have been washed out and get the drain to carry the water well away from the house.
posted by Old Geezer at 8:08 AM on July 20, 2011

I think you have two problems:

1: Where is the water coming from ? (how is it getting back there) and how can you stop it.
2: Are there structural issues to worry about now ? (not just missing dirt, but rust/decay/damage from the water)

Until you fix 1, 2 isn't addressable.

1 should be discoverable on your own, though how to fix it may not be immediately clear. (downspouts, water direction, water flow, water table, hydrostatic pressure etc)

For 2, find a structural engineer to consult for you. They can assess the damage and provide ways to fix/address it. (note: find a consulting engineer, ie one that won't do the fixing just do the assessment and provide suggestions/direction. Then find a contractor to do the work).
posted by k5.user at 8:09 AM on July 20, 2011

Response by poster: There is good compacted soil around the rest of the house. I used a probing rod to test down in several locations around the rest of the house. I believe this only exists on this corner where the steps are.

There was a PVC drain pipe (you can see the top of it in one of the photos) behind where the hole is that was the drainpipe for a gutter downspout. I don't have the gutters on the house right now as I am repairing fascia boards.

I believe the downspout would overload this pipe (particularly if it was clogged), back up around the steps, and seek the lowest level, which unfortunately may have been poorly compacted soil around the steps when they were built. Years (decades) of this and the void is formed.

Or at least that is what it appears to me.
posted by bellastarr at 8:17 AM on July 20, 2011

A few thoughts ..

Get the gutters back on. (and once back on, keep them clean/clear so they drain correctly).

Where does the PVC drain go ? Into the sanitary sewer (or traditional storm sewer) ? Or does it go to some type of leech field or discharge somewhere downhill from you ? Are there leaks in the PVC pipe ?

Where do the other gutter drains go ?

And then, again find a structural engineer. Given the erosion, there may be foundation issues to deal with as well as the staircase etc. (If you were in my area, I'd suggest my neighbor, as this is something he does.)
posted by k5.user at 12:29 PM on July 20, 2011

Response by poster: I can't replace the gutters until the house is painted. I'm working on that now.

The PVC drain goes about 12 feet away from the house and opens on to the ground. I am ripping that drain pipe out entirely as it tends to clog easily and doesn't drain the stuff away from the house. I'll replace with another drain that goes above ground for some distance (it slopes down) and into a field drain in the yard (that is part of a french drain system). They won't actually connect but they will be within a few feet of each other.

The other gutter drains drain much, much farther away from the house than this one. Some as much as 150' away (yes they are all draining free & clear - I check them yearly).
posted by bellastarr at 12:35 PM on July 20, 2011

Best answer: I have seen two similar processes for repairing concrete with voids. Mud jacking and foam jacking. They drill a hole in the concrete, stick a tube in and squirt pressurized mud/foam into the hole until it raises the concrete back to level.

What you might be able to do is fill the hole with some kind of fill- rocks or dirt- and then have one of those places fill it in with mud or foam, preventing the stairs from eventually settling down. (Ask the company first what to do, of course. It seemed like it wasn't all that expensive, and it was less expensive than re-pouring concrete.)

Possible complication: one of those pictures made it look like there might be a service line under there- gas, electric or water? If that's true, this complicates things. In that case, you might call the city building inspector and ask them what to do.

(If it was my stairs and my hole, I'd probably just fill it with concrete. But that's likely not the right way to solve the problem.)
posted by gjc at 3:06 PM on July 20, 2011

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