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Question DetailsAsked on 4/16/2016

It has been suggested I have a spring under my slab. How do I check this?

I live on a slope and have had major water problems in my back yard. I have a french drain but this has done nothing to stop the water. My tile floors cracked and have been replaced with wood, I have had ceiling cracks that have been repaired. Could there be a spring user my house causing the foundation to shift?

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1 Answer


Not a spring as such - by definition a spring rises to the surface. But you could well have a high water table.

You don't say where your french drain is located, or how deep relative to the foundation slab.

You cracking may be due to water issues - or swelling soils, or slope movement ...

You would need to have it investigated by a Geotechnical Engineer - usually work for a Civil Engineering firm (not an AL category). They would have to bring in a drilling company to put in a cased hole along the foundation, and/or put a threaded sleeve in the foundation slab to drill through to see if there is water pressure under the slab. The casing is necessary to provide for shutting off the water in case there is artesian pressure (groundwater pressure enough to make it to the surface). You do NOT want to just dig a hole to see if there is pressure - because if there is you could cause a blowout which could seriously erode soil and possibly damage your house. Did an insurance inspection on one house in Virginia that literally slid downhill because of that type of investigation error - a spring source that was drilled into became a mudflow taking the house with it.

Unfortunately, it is likely - indeed VERY common - that your french drain (assuming you mean one right along your foundation) was not done right. They are commonly put at or above the top of strip footer elevation - so at the same level as the slab. Therefore, they do not draw the water level down below the slab, so you can have a functioning french drain and still have a wet slab. The french drain should typically be at least a foot below the bottom of slab elevation.

Even with that, if you have a high groundwater table, while that might draw down the water level at the foundation, if your water table is high the water level can rise under the slab, so sometimes you also need underdrains under the slab leading to a sump pump.

Generally, in high groundwater or spring areas you need to intercept the water at the high side of the house ewith french drain and waterproofing membrane on the foundation, plus put in either underdrains and sump pump or better if topography allows, put a drain field (similar to a septic leach field) under the slab leading to a drain pipe on the low side of the house leading to free drainage - or if necessary due to topography, a wetwell with pump to discharge it.

However - until a geotechnical engineer determines the water level around the house, you won't know what the issue and possible solutions are. Then engineer would typically be $1000 - plus another $1000-1500 ballpark typically for an exploratory driller to drill the test holes and then regrout them to prevent possible upwelling. This assumes decent drilling - if in hard bedrock can run more like $1500-2500 for probably three 4-8 inch diameter test holes.

One thing you said that rings odd to me - you say the tile floors cracked and were replaced with hardwood - unless you have a splendid vapor barrier seal, if that has not gotten wet and warped and gone fungusy, at least you do not have water reaching the bottom of the slab. If your floors are dry, especially if you have crawlspace/basement that are dry, high water table would seem to not be the most likely cause of the issue - I would personally be looking closely for slope instability causing movement of the house or soil pressure against it damaging the foundation.

The geotechnicall engineer - perhaps in conjunction with a Structural Engineer (so find a Civil Engineering or Architect/Engineer firm with both geotechnical (soils/foundations) and structural engineer on staff to be able to evalluate the cause of your cracking in one consulting firm.

Answered 4 years ago by LCD

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