Preparation of Poor Soil for a Big Recip

[zdas04]

I'm in the midst of setting a fourth Waukesha 7042GL driving an Ariel JGK-4 two stage on an existing site that has had a lot of geotechnical problems (machines sliding, a lot of vibration, broken piping--the vibration analysis said it was all mechanical, no pulsation-created problems). To reduce risk, I contracted with both a Geotechnical Engineer and a Civil Engineer. Both were very familiar with the site and its problems.

They agreed that the best solution was to excavate down to stable "clay rock" and fill the pit with "Lean Concrete" up to the base of the conventional foundation and 2 ft outside the conventional foundation. We did that and poured 182 cubic yards of a 3000# sand, 2 sacks of Portland, 36 gallons of water mix with no rebar. It looked great and gave us a really stable surface to set forms on. We put a grid of #5 rebar sticking up to marry the lean-concrete with the actual foundation.

As we were finishing the forms and setting the rebar for the real foundation, a rotating-equipment specialist from the client company showed up on site and said that the lean concrete was the worst possible thing that we could have done and suggested excavating it and refilling the hole with 5,000 psi concrete with re-bar. We didn't and today we poured the foundation.

Now I'm in the middle between the Civil and Geotech guys who stand behind their original recommendations and the rotating equipment guy who is telling everyone who will listen that we did a stupid thing.

Does anyone have any examples of preparing a compressor-foundation underlayment using lean concrete. I'd like to hear either success or failure stories. We'll know in a few weeks if this machine will vibrate or not, but a lot of words will be dumped on a lot of conference tables between now and then.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

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[lewtam]

David - I've been keeping an eye on this thread to see if anyone could help, obviously no takers.

I'm not familiar with the use of lean concrete, but I have been involved with a field compression plant located in an area with terrible soil conditions. If it rains or doesn't rain enough, the soil shifts and has caused hell with the pipelines. The group responsible for installing the 3 compressor sets excavated down to bedrock (1.2m)and filled with gravel, compacted at regular intervals. The foundation pads haven't moved at all in 4 years - the pipework leading up to the plant manifold is another story.

I believe that by engaging 2 relevant consultants, you've done all you can.

Hope it goes well.