Residential Foundation Built On Top Of A Trench!!! 6

[courtnvm]

I received a phone from a resident in Kentucky wanting me to look at the foundation of his house. Supposedly the house was built approximately six years and recently they were adding a slab-on-grade patio and discovered a trench that had been filled with debris. Well they started to notice there was some settlement issues with the house. They discovered that this trench filled with debris continues underneath the foundation of the house. They had a foundation stabilization company come out and put steel piles underneath the foundation where this trench exists. The owner wants to know what should be done with the existing trench filled with debris. He stated to me that one engineer had told him to pressure grout the trench and another engineer told him to remove the debris from the trench and fill it will a flowable fill such a concrete.

Does anyone have any suggestions? It seems to me that the best thing to do would be to remove the debris and fill in with some lean concrete. Also, their homeowner's insurance is involved with this situation and that is why I am asking for anyone's opinion.

Thank you for your time and attention

Sincerely,

Val C.

Val Courtney, PE
Optimal Engineering, Inc.

 

[PSlem]

We fix a lot of these for insurance. Underpin the house and dig out the trash adjacent to it and grout the remainder. You risk too much damage removing debris from under the house.

 

[Slowzuki]

You mention trench and debris, was is purposely built on a trench filled with a uniform stone or just garbage?

The reason being is a somewhat common foundation is called a rubble trench but it really has compacted crushed rock or round stone in it. My house has a continuous footing on top of this type of foundation. It extends below the frost line and hase drain tile installed at the bottom with filter fabric lining the trench.

 

[jdonville]

Val,

I agree with PSlem - compaction grouting should do the trick. Too tricky to remove the debris without introducing more distress.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[PEinc]

You can underpin the house to prevent settlement of the footings, but if the trench is filled with decomposable debris, there will be decomposition over time that could also settle the slabs on grade. I pretty much agree with PSlem. I would grout with flowable, cement grout so that it could travel easily around the debris and fill voids. The problem would be, if the trench extends over a large area, the grout take could be large.

 

[courtnvm]

Slowski,

I believe the trench has just garbage debris in it from what the owner has explained to me.

PEinc,

I believe the house has steel piles installed under the footings to help stabilize the footings and prevent the house from future settlement. If this is fully true, then I think it would probably be advisable from what I have gathered to fill with a compaction grout. I have not gone to this house yet. From what the owner tells me he has had one engineer tell him to remove the debris and fill with a flowable fill and another engineer told him to use a compaction grout.

Thank you all for your input!!! All of you have been a great help!!

Val Courtney, PE
Optimal Engineering, Inc.

 

[BigH]

Has the piles obviated the noted settlement issue of the house? If so, why do anything with the debris filled trench under the house - if the settlements are still occuring, then are they occuring where the pin piles were? . . . or of the house slab not supported on piles? If the later, I would try the compaction grouting. If the settlements have ceased, I'd leave it alone.

 

[PSlem]

You need to consider grouting as there is also termites, methane, water, and migration of surrounding soil into the void. The pin piles were probably just the exterior footing and the slab could settle. The grouting does not need to be compaction grouting, but slurry grouting. We do a 5' grid of cored holes, drive 1" pipes to refusal with a 90# breaker, test with air to clear the drive rivet, and grout in lifts. Average takes are 10-20CY as these trenches are about 8' wide and rarely over 15' deep. GA finally banned burying debris on lots as this spawned an entire repair industry. If the house was built wider than expected, or shifted for a side entrance garage, it ended up on the trench.

 

[PEinc]

I still agree with PSlem.