Frozen Clay fill 5

[densedds]

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

 

[fattdad]

yes, there is actually a device that looks like spikes on a cylinder that you can drag across a slab to "listen" for voids. I just can't remember what it's called.

f-d

¡papá gordo ain’t no madre flaca!

 

[miningman]

What is your immediate priority?? Is it to prove in court that the contractor is liable... which gets you absolutely nothing unless he agrees to fix the problem without additional litigation , or is it to remediate the building to a standard that it can be used... perhaps not to ideal standards, but usable.

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

 

[cvg]

I'm not convinced that filling the voids with grout will stop future settlement. And slab jacking would be required to bring the slab back up to the correct elevation. I think this might be only a temporary fix.

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.

 

[densedds]

I've committed to the pit tests and the contracter is on his way over as I write this to look at the areas of slab removal. Tomorrow the testing people are comming over to take their samples. A report will be generated next week. This just keeps getting sader and sader as I was on a conference call earlier with the subs that poured the slab and my attorney and they we very open about the communications they had with my general. They expressed that on more than one occasion they mentioned their concern for the fozen soil and also weeks following the pour with the dropping slab.

 

[densedds]

Well Guys,

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

 

[densedds]

photo of slab drop

 

[oldestguy]

Then comes the fix up

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.

 

[densedds]

They mentioned today doing some type of compaction grouting or "foam jacking". Can you tell me the prs and cons for such a procedure? Aslo, most of the research I have found on these procedures deals with outside applications. Is this suitable for a clinic type office where the floor is way out of wack and soil compaction is as low as 75% of proctor?

 

[oldestguy]

I did a Bing search on the Internet and the firm at the top of the "compaction grouting" list is a well known dependable firm. With any of them, be careful about all the possible problems as well as how payment is figured. Underground piping can be damaged.

I'd have an experienced engineer watching (that is one who has seen many of these jobs done) to watch for problems.

 

[densedds]

There is plenty of mechanical (plumbings,gas,heat) in the floor. It has been determined that the soil was not compacted properly. Is chemical or foam grouting a technique suitable for releveling and stabalizing a office floor for the long term on such soil?

 

[cvg]

compaction grouting is not suitable for clay soil. slab jacking with foam or other types of grout can raise and level the slab. however, it will not prevent future settlement. if the subgrade continues to settle than the slab might also continue to settle. no guarantees on eliminating the floor movement without improving the subgrade first.

If piping penetrates the slab and the slab moves, than the pipes will probably be damaged.

 

[crcivil]

In my opinion Fracture Grouting is the most suitable grouting method for clays. It would increase the density of the surrounding soil, fill voids, and could even raise and level the slab. Regards.

 

[densedds]

Can you tell me the negatives involved with Fracture grouting or any other type of grouting? I have an office with alot of piping under the slab.

 

[fattdad]

In my opinion, the fill has contracted (densified) from decreasing moisture content and it's in better condition now than it was from the onset. The $1M question is how do you intend on using the building? I mean if it's really a lightly-loaded slab on grade, then there's much less risk than if the slab is for heavy industry or warehousing.

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!

 

[EITGeotechnical]

The 100% compaction on your silty clay materiel will not solve the issue. Before placing your concrete slab you should have 200 mm of Non-Frost Susceptible (NFS) compacted to minimume of 98% SPDD to prevent heaving on the winter.

 

[crcivil]

densedds,

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.

 

[fattdad]

The 100% compaction on your silty clay materiel will not solve the issue. Before placing your concrete slab you should have 200 mm of Non-Frost Susceptible (NFS) compacted to minimume of 98% SPDD to prevent heaving on the winter.

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!

 

[crcivil]

fattdad,

What do you think of pin piling the slab? Regards.

 

[densedds]

One the the problems we are running into is that the floor was settling during the construction of the internal walls and such. Thus if someone comes in at this point and raises the floor to level, the walls, roof, doors, and such will all be raised as well and end up throwing everything else off. This is a dental office with vacuum, air, water, computer, electical, hydronic heat, and drains to all operatories. I tend to agree with the remediation plan that leaves the soil as is and replace the slab with a structural slab in hopes of not disturbing all the the said utilities. This would also allow leaving some of the interior walls that have been shimmed alone or replacing on a as needed basis. I have also been told that this remediation plan allows us to test all of the lines before we pour the new floor in contrast to chemical grouting or "jacking" where we would be fixing probles after the fact.

 

[densedds]

Exactly what risks do I run with a remediation that involves compaction grouting to stabalize the soil and chemical grouting to fill in the voids under the slab?