Frozen Clay fill
Frozen Clay fill
(OP)
Hi all,
I am looking for advice on a office building I had built in 2009. The ground was actuallly scraped in October of 2008. Up here in the Dakotas, it turned very cold and due to the elevation of the existing lot, fill had to be hauled in to reach floor height. The building was scheduled for a four inch concrete slab floor. The elevation of the finished floor was to be 836.5 feet above sea level. The beginning elevation of the existing lot was 833. The elevation of the bottom of the footings was 830.2. The interior of the building was filled with lean clay that was in 20 degree below zero farienhiet. The exterior walls and roof was in place at the time of the floor pour. No windows were in and no heat in the building. They did use heat blankets in an attempt to thaw the ground, but no soil compaction tests were done prior to the pour. I now have a beautiful office building with a floor that has significant settleing Ff of 20 and Fl of 7.6. Their are areas that drop 2 3/4 of an inch in 3 feet. In short it was back filled with frozen clay. Is it commmon to do this type of backfill in -20 temperatures and get it compacted good enough to prevent settling?
densedds
I am looking for advice on a office building I had built in 2009. The ground was actuallly scraped in October of 2008. Up here in the Dakotas, it turned very cold and due to the elevation of the existing lot, fill had to be hauled in to reach floor height. The building was scheduled for a four inch concrete slab floor. The elevation of the finished floor was to be 836.5 feet above sea level. The beginning elevation of the existing lot was 833. The elevation of the bottom of the footings was 830.2. The interior of the building was filled with lean clay that was in 20 degree below zero farienhiet. The exterior walls and roof was in place at the time of the floor pour. No windows were in and no heat in the building. They did use heat blankets in an attempt to thaw the ground, but no soil compaction tests were done prior to the pour. I now have a beautiful office building with a floor that has significant settleing Ff of 20 and Fl of 7.6. Their are areas that drop 2 3/4 of an inch in 3 feet. In short it was back filled with frozen clay. Is it commmon to do this type of backfill in -20 temperatures and get it compacted good enough to prevent settling?
densedds





RE: Frozen Clay fill
RE: Frozen Clay fill
RE: Frozen Clay fill
RE: Frozen Clay fill
RE: Frozen Clay fill
As for going forward, the only real option will be to remove the entire floor slab, remediate or replace the fill with properly compacted fill, and reconstruct the floor. In order to prove the problem and get someone to pay for it, the fill will need to be sampled and densities determined. This can most easily be done by removing a section of floor about 5 by 5 ft. and then testing and sampling the fill. Alternately, the floor could be cored and hand equipement used to sample the fill.
You have a very real and large problem. I assume you have an attorney and an engineer working either for you or your attorney. If you don't, you need to get one hired now. This is a problem that will only get worse with time. Total settlements could easily exceed 6 inches.
Good Luck, I'm affraid you are going to need it.
Mike Lambert
RE: Frozen Clay fill
RE: Frozen Clay fill
But it's also possible that the soils beneath the floor slab have have been compacted over time, so a current compaction test may not represent the finished conditions prior to placement of the floor slab, possibly affecting the validity of your evidence.
Good Luck
RE: Frozen Clay fill
RE: Frozen Clay fill
I would not make that assumption
RE: Frozen Clay fill
A field density test is not enough though. For each field density test you should also obtain a bulk sample (i.e., at least 75#) and return that to the laboratory. You see it's in the laboratory that you test for the "maximum" density. It's the comparison of the field density to the maximum laboratory that yields the "percent relative compaction."
There are multiple ways to take the field density. Most engineers will use the nuclear gauge. I'm a fan of the nuclear gauge also. Problem is when you are working in a cut out of a concrete slab, you run the risk of some defendant saying the nuclear gauge results are influenced by the slab or work being done in a recessed area. This may be "BS," but it's something to consider. I'd certainly have the field engineer also perform a "sand-cone" test to gauge whether the results are the same. Either that or just use the sand cone method.
There are companies that specialize in concrete floor leveling. They use a grouting process to relevel the slab. I'm not sure that adding concrete to the top of the slab would be best.
Is this an office building? You see in the future, folks may move their cubicles, file boxes, desks, or relocate walls. Each of these changing loads run the risk of triggering more settlement.
There are acoustic methods to "see" map voids below slabs. I don't know this from first-hand experience, I've just seen such surveys done by others.
Sorry about this bad construction. Earthwork using moisture-sensitive soils should not be done in freezing weather. Granular fill would have been the right advice. . .
f-d
¡papá gordo ain’t no madre flaca!
RE: Frozen Clay fill
Mike Lambert
RE: Frozen Clay fill
RE: Frozen Clay fill
f-d
¡papá gordo ain’t no madre flaca!
RE: Frozen Clay fill
Mike Lambert
RE: Frozen Clay fill
RE: Frozen Clay fill
RE: Frozen Clay fill
Mike Lambert
RE: Frozen Clay fill
My suspecion is that there are voids below the slab in all sorts of random locations. My suspecion is that the areas with the greatest damage may not be the only areas with chronic problems. They may just be the areas with the greatest traffic or where the current loading is the greatest.
There are always alternate sampling stregigies. You can grid the site and use a random number generator if you want to. You can shoulder the responsibility to the engineer doing the forensic evaluation. You can collaborate with the engineer to reach some consensus on locations and budget. You can use an acoustic method to "screen" for potential voids and then target the test locations to those areas.
I like a minimum of three tests locations however.
You may need to return for greater sampling (after all at this point we don't know whether this is a 40,000 sf building or a 400,000 sf building).
f-d
¡papá gordo ain’t no madre flaca!
RE: Frozen Clay fill
RE: Frozen Clay fill
f-d
¡papá gordo ain’t no madre flaca!
RE: Frozen Clay fill
If it were me, I would be willing to incurr the cost of coring thru the floor at a number of locations.... if the building is 40,000 sq feet, a 40 x 40 foot grid would require 25 corings. This would be much less disruptive than digging test pits in the slab, and would provide clear easily understandable data that a judge might consider in the event you continue into litigation. Depending on the results, I might consider pumping grout into the voids to reduce further settling
RE: Frozen Clay fill
Given the fact that you appear to have records that the fill was made using clay material in temperatures of 20 below zero, with arguably no moisture conditioning and no compaction test, all of which does not comply with the recommendations in the design report nor with any standard of care - in my opinion that is ample evidence to prove to a judge that huge mistakes were made during construction.
RE: Frozen Clay fill
RE: Frozen Clay fill
Went through with the cone/ Pit compaction test. Interesting, I learned alot. Attached are photo's of the 1+ inch gap under the slab. When making the final cut, the slab actually dropped and pinched the saw blade. I should get my report in a few days.
Paul
RE: Frozen Clay fill
RE: Frozen Clay fill
It would appear that some form of compaction grouting will not only do some good at "compacting" but will fill voids and create a stable situation, even raising settled slabs. What about buried piping? That can be damaged by compaction grouting.
Not just any "slab jacking" contractor should be used, but one experienced in "compaction grouting".
You may even have to leave pipes for future lifting of slabs that still may settle.
RE: Frozen Clay fill
RE: Frozen Clay fill
I'd have an experienced engineer watching (that is one who has seen many of these jobs done) to watch for problems.
RE: Frozen Clay fill
RE: Frozen Clay fill
If piping penetrates the slab and the slab moves, than the pipes will probably be damaged.
RE: Frozen Clay fill
RE: Frozen Clay fill
RE: Frozen Clay fill
I think I'd be more inclined to either reconstruct the slab and require subgrade compaction to 100% Proctor (relative compaction) or fill the underslab void with grout, floable fill or foam. The problem with foam is it may not offer the same slab support as the other options.
In all cases you are ending up with a compromized condition. Fracture grouting may be too risky with your utilities.
f-d
¡papá gordo ain’t no madre flaca!
RE: Frozen Clay fill
RE: Frozen Clay fill
How much money is at stake? I mean, what's the size of the slab on grade? Replacing or trying to fix the subgrade and reconstructing the slab might be a bit expensive, unless we're talking about a small area in which case I would consider it as an alternative. Otherwise.. how about a cement-bentonite fill grouting tratment under the existing slab, followed by a series of small-diameter (3"-4") pin piles? Regards to all of you.
RE: Frozen Clay fill
I'm assuming that the slab is independent from the foundation, the perimeter foundation is to proper depth for frost protection, and the building has conditioned air. I also understand the function of subbase aggregate below the slab on grade. My suggestion to "reconstruct" the slab, was intended to include the subbase aggregate, 'cause it's the subgrade soils that need recompaction. You'd have to harvest the stone for reuse (if possible) or haul in new prior to pouring concrete.
I did design work for a mausoleum and for that case, yes the entire slab on grade had to be protected from frost.
f-d, p.g., p.e.
¡papá gordo ain’t no madre flaca!
RE: Frozen Clay fill
What do you think of pin piling the slab? Regards.
RE: Frozen Clay fill
RE: Frozen Clay fill
RE: Frozen Clay fill