Backfilling after foundation work - does this look correct?

10,199 Views | 19 Replies | Last: 6 yr ago by Gary79Ag
Wiggletrace
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AG
We, unfortunately, flooded during Harvey, but we are taking the opportunity to expand our master bathroom. In doing so, we needed to move some drains.

When our contractor started cutting/jackhammering the slab, we discovered that there were huge cavities under the bathrooms.

We had all of the underslab plumbing replaced and foundation work done in August of 2015. I have contacted that contractor to ask questions and was told that they usually leave a gap to prevent "heaving." I am a geologist and have an extensive knowledge of clay mineralogy and skrink/swell capabilities, and I think this is not an acceptable backfill. If this isn't good workmanship, I plan on starting a case for a warranty claim.

Can any of you comment on this or offer some insight? Does this look right?


Master bathroom. The cavity where the toilet drain is about 30" or so below the slab.


Master bath at toilet drain:


Guest bath:


Thanks in advance.
Martin Q. Blank
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Quote:

I am a geologist and have an extensive knowledge of clay mineralogy and skrink/swell capabilities
And you come here for advice?
Wiggletrace
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AG
Martin Q. Blank said:


Quote:

I am a geologist and have an extensive knowledge of clay mineralogy and skrink/swell capabilities
And you come here for advice?
I am not an engineer... i readily admit that. It's the integrity of the slab that I am more concerned with.

I don't care if you have water sitting on that soil for a week: it's not going to swell enough to make up that space.
Vivificus
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AG
DO you have pictures of this part of the home during the previous slab repair? Were there any interior holes dug during the repair.

During my foundation repair, "mud" was pumped into the gaps under the foundation after the piers were set and the lift was completed. That should close up a majority of the gap between foundation and the ground.
Viv
Aggietaco
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AG
Unacceptable. Your slab is likely not designed to span those gaps unsupported..
sts7049
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AG
holy hell. is the gap just where the plumbing work was done?
Wiggletrace
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I don't have pictures, but I know that they tunneled these areas during the work. I have no reason to believe that this is washout.
hurricanejake02
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I know that, depending on who you ask, they'll tell you that they used to pump mud under the foundations to fill the gaps - but then ran into issues with heaving, and stopped that practice.

If they tunneled those areas during the previous repairs, are there piers that aren't shown in the pictures supporting those areas?
Wiggletrace
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AG
No. All of the piers are on the beams. No piers were supporting the span between the beams.
schmellba99
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AG
Depends on the type of slab design.

From the looks of it and the fact that the main slab surface is fairly thin, I'm going to say no - this is not acceptable and a function of your previoius contractor not doing backfill before replacing the slab.

If you have a true pier and beam house, then you should or could have areas where there are spans above subgrade because the piers and the beams are supporting the loads of the slab down into the subgrade. A slab on grade design should not have voids like this.

Any work that required removal of subgrade materials should be done with replacement subgrade material - could be a low PI engineered fill or a flowable fill concrete prior to placing concrete slab.
Million
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Is the void a result of the foundation being lifted or the plumber's excavation under the home not being backfilled completely?

Some foundation companies perform work called "mud jacking". This is where a slurry is pumped under the slab to fill the void. The slurry usually consists of a mixture of sandy loam or some other type of dirt and cement to give it some rigidity. Based on those pictures, it doesn't appear any sort of cement/dirt mix was pumped under your Home.
Wiggletrace
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AG
Million said:

Is the void a result of the foundation being lifted or the plumber's excavation under the home not being backfilled completely?

Some foundation companies perform work called "mud jacking". This is where a slurry is pumped under the slab to fill the void. The slurry usually consists of a mixture of sandy loam or some other type of dirt and cement to give it some rigidity. Based on those pictures, it doesn't appear any sort of cement/dirt mix was pumped under your Home.


You are correct. There was no slurry OR engineered soil used after the work was done.

The original contractor is trying to tell me that this is adequate.
Gary79Ag
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AG
kornut11 said:

Million said:

Is the void a result of the foundation being lifted or the plumber's excavation under the home not being backfilled completely?

Some foundation companies perform work called "mud jacking". This is where a slurry is pumped under the slab to fill the void. The slurry usually consists of a mixture of sandy loam or some other type of dirt and cement to give it some rigidity. Based on those pictures, it doesn't appear any sort of cement/dirt mix was pumped under your Home.


You are correct. There was no slurry OR engineered soil used after the work was done.

The original contractor is trying to tell me that this is adequate.
Well pardon my French, but he's full of sh't...
Million
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kornut11 said:

Million said:

Is the void a result of the foundation being lifted or the plumber's excavation under the home not being backfilled completely?

Some foundation companies perform work called "mud jacking". This is where a slurry is pumped under the slab to fill the void. The slurry usually consists of a mixture of sandy loam or some other type of dirt and cement to give it some rigidity. Based on those pictures, it doesn't appear any sort of cement/dirt mix was pumped under your Home.


You are correct. There was no slurry OR engineered soil used after the work was done.

The original contractor is trying to tell me that this is adequate.


My immediate thought is what are his qualifications to make such a claim? The majority of foundation repair guys do not have any formal education in structural engineering. They are in the business of selling foundation work and are usually more salesman than anything else.

Whenever I buy a property, I always have the foundation looked at. I never have the inspection done by a foundation company. They are in the business of selling foundation repairs. I always use a structural engineer that is not only formally educated in the subject, but also has no bias towards me needing foundation work.

I would call a structural engineer while you still have the floor open and see what he thinks.

I am also curious how your contractors are going to pour back the demoed portion of your concrete slab with the giant void under your house.
Wiggletrace
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AG
My current contractor has already completed the work.

They back filled and used an engineered soil to get the soil level up to where they could pour the new slab.

They drilled into the existing slab with 1/2" rebar and created a grid prior to pouring cement.


We are trying to put our house back together after the flood and I authorized them to do so in order to get back to some sense of normalcy in our home.
tgivaughn
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AG
There's no heaving design at work that I've encountered since even the 70's
The plumber needs room to work, so they box out a small area for drain "P"s.
Sometimes in high dollar construction this is backfilled with NOT expansive soils and pest treated.
There are some trades that have neglected to supervise worker to insure proper backfilling/compaction, which includes plumbers.

The other rare observations have been sugar sand or similar eroding from out under the slab over time. Usually this path follows poorly compacted utility lines and most always downhill or into a ground sink.
Wiggletrace
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AG
RESOLUTION:

Had the original contractor come and agreed that a void that large was not acceptable. They are issuing me a check for the amount it cost me to remedy this.

Thanks for all of the help.
bco2003
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AG
Great news! Thanks for the update.

How much is that going to cost?
agracer
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AG
kornut11 said:

RESOLUTION:

Had the original contractor come and agreed that a void that large was not acceptable. They are issuing me a check for the amount it cost me to remedy this.

Thanks for all of the help.
Well post his name so we know who is honest.
Wiggletrace
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AG
agracer said:

kornut11 said:

RESOLUTION:

Had the original contractor come and agreed that a void that large was not acceptable. They are issuing me a check for the amount it cost me to remedy this.

Thanks for all of the help.
Well post his name so we know who is honest.
It was SandTech.
Gary79Ag
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AG
kornut11 said:

agracer said:

kornut11 said:

RESOLUTION:

Had the original contractor come and agreed that a void that large was not acceptable. They are issuing me a check for the amount it cost me to remedy this.

Thanks for all of the help.
Well post his name so we know who is honest.
It was SandTech.
Maybe they should change their name to SandlessTech...
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