Foundation issues 1

[jbm4cnc]

thread274-287721
I have a customer with a foundation issue that he does not want to admit.

First off, this machine weighs 45,000 lbs. There is a 12,000 lbs mass on top of it that can move at 18ft/min. The customer was given the spec of 24" of reinforced concrete and 12" of compacting base with a soil bearing of 10T per meter squared. What the contractor did was 6" of #57 stone (did not compact cause he said it was self compacting) and 18" of reinforced concrete. The machine is designed to handle .0001 accuracy positioning. We are finding the moving part of the machine, running parallel to the ground is leaning back over 30 days .0006" and causing the machine not to be square to hold the .0001. Customer says the pad is sufficient to hold tolerances. Yet, we measure floor movement, indicator from old pad and reach over the isolation membrane to new pad, we see floor dip .001". How can i prove to this customer that his contractor didnt do it right. By the way, the civil engineer specified compacted material and 95% proctor (dont know what that means)

Thank you.

 

[JedClampett]

Are you representing the machine manufacturer? If so, tell your customer that due to the deflections being out of tolerance, you won't honor the equipment warranty. I've seen this done with turbine foundations, until we (the engineer) could prove that deflections were within allowables. That will get the customer's attention and either get them to deal with the poor construction or do their own maintenance on the machinery.
Was there any field confirmation testing performed? Concrete thickness and foundation compaction should be inspected by the customer's personnel.
As far as investigation, you can core drill the slab and determine its thickness and then use the core to determine the amount of rock under it.

 

[jbm4cnc]

Hi and thanks.
Have my engineers in there this week getting the machine square again. They said yesterday, we found the pad to be sufficient and will not be addressed any more. Needless to say, they have yet to prove to me its sufficient. No core samples except I did get the initial 9' hand auger results before the foundation was put in. I feel that what is happening, based on the 12K load going back and forth, that part of the stone is compacting causing a lever action in the slab and causing it to lean back. I do not know what field testing was done, but no core pulled. It was made aware and is on record that the contractor did not compact the stone. The weight of the concrete is equal to the weight of the machine. Foundation is in a plant, so it was not dumped by a truck, most likely wheeled in and raked out to a thickness of 6". This is a top 5 defense producer...im the little guy they are pushing around. I asked already, so when foundation moves, what then....no reply.
Thanks.

 

[jbm4cnc]

Ps...the "they said they found the pad to be sufficient" that was the customer stated it.

Wanted to clarify.

Thanks

 

[shobroco]

I'm not familiar with "#57 stone" but I am familiar with Proctor density & I'd never accept less than 100% Proctor under anything susceptible to settlement. Greater than 100% is frequently achieved in the field, 100% simply meaning the density achieved with the test equipment in the lab. 95% is okay under a sidewalk but not under your machine base.

 

[concretemasonry]

Make sure you document what was used. One the equipment is in place, it is unlikely that there will no good opportunities to verify.

1. The concrete is 18" and not 24", so there is an insufficient mass for long term reliability and operation. There is little substitute for foundation mass when dealing with moving industrial equipment. That is not much concrete for a major (I assume) piece of equipment in a plant that is expected to operate for many years with distortions increasing with time. I was involved in a plant with a 40,000# piece of cyclically slowly vibrating equipment and we had 6' thick foundations and there was no question of varying because mass concrete is cheap.

2. #57 is not necessarily "self compacting" because it will settle/be forced into the native soil and receive fines form areas. I have even had contractors say you need some organics and roots by contractors building heavily loaded trucks (over 60,000# with only 2 or 3 axles). The lack of thickness should be documented.

Apparently, your position is to document what was done during construction.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[cvg]

ASTM #57 which is an open graded crushed rock product is not the best choice, I would have recommended a well graded aggregate base such as road base, compacted to at least 100% of standard proctor with QA testing to confirm it. 6 inches also seems a bit thin.

the ground below the compacted base might also be settling due to the dynamic loading, no way to know that without geotechnical analysis and information on how large the foundation is. 9 foot hand auger boring may not be sufficient.