Pressure distribution under CFA rig

[GeoX]

Could someone provide information (or an internet link) on pressure distribution under a CFA (continuous flight auger) rig. Is the rig ballanced (i.e. exerting uniform pressure on the foundation soil) or is an eccentric pressure distribution within the foundation soil more appropriate. In the later case one would assume the manufacturer should have relevant information on eccentricity...

Thanks in advance for any information.

 

[GeoPaveTraffic]

I would expect that most rigs have a higher pressure under the rear of the rig than under the front. However, there are so many different types, kinds, and configurations of CFA rigs that no one answer is possible. If you describe your situation and problem we may be able to provide some meaningful discussion.

 

[GeoX]

Thanks for the quick response. The only additional information I have available at present is that it is a track-mounted rig with track dimensions of approx. 4.8m by 0.7m (each), a working weight of 67 metric tonnes (670 kN) and the rig type is B150E. From my perspective, I'd like to understand the eccentric pressure distribution in the clayey subsoils (if applicable) as not to exceed the bearing capacity and to provide for sufficient granular working base as required...

It is likely that my question is more appropriate for the rig manufacturers (could someone provide reference?) but I hoped that someone in the geotechnical community may be able to provide some insight....

 

[Focht3]

Agreed. Why the interest in weight/pressure distribution?



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[SirAl]

Interesting question. I found a photograph of a B150E at this link:

http://www.hjb.co.kr/equip_g/drill/supply/casagrande/b110b120.htm

More info is required including out-rigger arrangements, up-lift capacity, etc. Your best bet is to contact the actual contractor for details.

 

[GeoX]

SirAl: thanks for the link

Focht3: this question came up on a meeting due to some concerns with weak clay seams and burried services - I realized that I am not fully aware what the actual/working stresses in the subsoil are underneath a heavy rig - hence my posting....

In the meantime, I understand that some contractors use the front half (or the back half - depending where the mast is) of the tracks as an effective loading area, with uniformly distributed pressure underneath to account for non-uniform loading.

 

[PSlem]

I've watched a number in soft dirt and they seem to be balanced. The auger is going to want to pull the front down so you limit feed speed to keep it balanced. Since it's so dynamic you won't get a static bias that means anything.

 

[BigHarvey]

It should be kept in mind that one day the excavated pile will have to be concreted and the point loads coming from the concrete truck will certainly be much more of a problem than the distributed stresses induced by a crawler rig.
The thickness of a working platform is generally not calculated but chosen using rules of thumb between 30cm and up to 1 meter !This should be left to the contractor.

 

[Focht3]

Agreed.



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