Residential Foundation Problems

[bldgdesign]

My grandfather's house is settling at one end, substantially. It is located in Huntington West Virginia. It is approximately 80 years old single story and is located along the side of a street where the land was stepped to place each house. The uphill side of the house is a retaining wall, 4 feet retained soil. The ground slope is approximately 1:1 with about 15 feet between the houses. The downhill side has a retaining wall, approximately 4 feet tall, which is located approximately 4 feet from the edge of the house. The retaining wall is leaning about 10 degrees. It is a mortared stone wall as old as the house. The downhill side of the house is the house that is settling. The original land prior to cutting in the house appears to have a 20% grade, maybe more.

Major cracks have formed, some over 3/4". A foundation contractor came in two years ago and installed jacking piers along that end of the house and jacked the house back up. Six months ago they came out and set up benchmarks to measure the settlement due to our complaints that it was still settling. We just got the results of another measurement, and that end of the house settled 1 inch, in 6 months. We are supposed to have a meeting next week to discuss plans to proceed.

I am a structural engineer, but don't specialize in residential foundation repair. i am looking for a reference that discusses the repair options, code of standard practice, etc. I would not expect that my client would be happy if I specified piles for my project and the building settles after installation. I am not looking to burn anyone, just trying to figure out why their repair is failing (footing rotation due to the bracket they used, pile tip did not reach bedrock or suitable soil, etc?)

I wasn't involved with the original repair. I don't know if the contractor actually had an engineer design the repair or even had a geotech come to the site. I would expect a geotech to have to take at least one boring to determine the required pier embedment depth.

Can someone provide me some direction so that I know the proper questions to ask? I tried to find a guidance document and haven't had any luck.

 

[MiketheEngineer]

There are a couple of ways of making that repair.

Most use some type of pile driven to bedrock(if possible) or to a point of refusal (where it refuses to go any further). These piles may be simple tubular steel or heli-coils that they drill as far as possible. Then they hook a ledger to the pile and under the footing and jack the wall back into place. Usually works quite well - IF THEY GO DOWN FAR ENOUGH.

Some people dig down under the footing, jack the wall and pour an additional "footing" - known as under pinning. Often cheaper but not generally considered as good.

Either way or any way it is is done - it is often guaranteed by the installer for "life".. I don't know whose "life"

But any reputable contractor should come out - no questions asked and FIX IT!!

That would include me watching him reset the piles until they hit refusal.

All that said - are you sure you are not over an old mine site?? I say this based on the location you mentioned. Old coal mines or any mine for that matter can and often wreak havoc on houses above regardless of the fix that was implemented. The whole area sinks and usually unevenly. I live in St. Louis and across the river in Illinois and old mine basically swallowed a brand new school (10 years old). It cracked so bad they had to abandon it. It was over an old mine they didn't know about!!

They had to rebuild about a mile away!!!

Good luck

 

[Ron]

IF THEY GO DOWN FAR ENOUGH.

This is a likely key. If the slope is sliding, as evidenced by the leaning retaining wall, then a shear plane exists beneath the structure. If the piers/piles/anchors do not intersect the shear plane with embedment to spare, they will do no good....they are moving with the soil.

Get a local geotech to take a look at it.

 

[Mccoy]

Sure such a settlement in a one storey house which has been around for 80 years is dodgy.

The old mine hypothesis should be evaluated, but probably the settlements should include more buildings in the neighborhood. Unless your grandfather has been so unlucky to build just above an old shaft.

Ditto for the shear plane with potential slope movement, usually more than a house is involved when the whole slope is unstable (the shear plane might be more of a local feature of course).

Otherwise, some local factor is more likely, like soil softening or piping due to water seepage, which here is the most usual issue with settlements. Seepage may come from somewhere else as the upslope residence

In the case of the presence of an old mine or an general slope instability local repair may be futile.

 

[EBSEngineering]

Ron has it. Get some geotechnical information. Ultimately the soil is causing the problem, so find out what is there. Once you have that, you can make a better decision on how to proceed or what is the best method of repair.

 

[msquared48]

Is your grendfather's house the only one seeing the distress?

Seems like this would be unlikely with either the old mine scenario, or a global rotational failure of the soil matrix.

Mike McCann
MMC Engineering

 

[FixedEarth]

I suspect couple of things. The downhill footing embedment may not be adequate, that is daylight distance is less than one third the descending slope height. The descending retaining wall may not have been designed for the ascending steep backfill. As for publications, try Robert Day's Foundation Engineering Handbook.

http://www.FoundEng.com

 

[Mercycity]

We can not talk of normal settlement of a single residential building which have been there for 80yrs. It is expected by 50yrs no more setlement is expected even if is clay soil. Something has triggered the settlement. It could also good to know the history of the cracking like when the cracking started. As other members have said, the contractor went very fast to do the remedial measure without consulting Geoechnical engineer or to understand the cause or mechnisim of the failure. He was supposed to understand something is wrong somewhere and to think out of the box. For my view the cause of the cracking is the movement of the ground below the building. This need thorughly investigation by looking other naighbouring buildings and surrounding environment. All the comments given above are very important.Two things to look out is slope failure which can be caused by many factors and any shaft which may exists below the building.

 

[MiketheEngineer]

I have to agree Mercy - If a house has been "stable" for 80 years and all of sudden "things" go wrong - there is a DEFINITE reason.

It make take some time and investigating - but you need to get to the core reason!!