soil support calculation if some sinking is OK

I need to support 12,000 lbf on about 8 inches x 8 inches(hopefully less) in a variety of soils, when the ground is dry enough to run heavy equipment. The load can sink in 3 or 4 inches. So far I've only found soil specifications for building foundations, which I assume would be too
conservative. How do I calculate this?

Thanks,

John

 

[GeoPaveTraffic]

If I'm understanding your post correctly, you are trying to support a 12kip load on a concrete pad that is 8"x8" (0.44 sq. ft.). That works out to 27,000 psf bearing pressure. Unless you are on good rock, failure will occur and the equipment/machine, whatever the load is, will move. The movement will not be just down (sinking) it will also tilt.

For a varitity of soils, I expect that the smallest footing/slab that you could place that much load on would be about 1.5x1.5 feet.

If you provide more information on what you are doing and the equipement/machine, the opinion may change.

 

This will be a steel plate acting as the foot for a hydraulic cylinder, similiar to a stabilizer pad on the rear of a backhoe. The load is essentially vertical and will hold for less than a minute before being retracted.

 

[GeoPaveTraffic]

In most soils it is going to sink and sink alot. I think you need a larger bearing pad, at least a foot square, more would be better.

 

[VAD]

Can you not put some wooden planks below the 8" by 8" plate as I presume that this is a temporary operation moving from location to location

 

I'll start with 12 kip/sqft by using lower pressure on the 8x8 pad. The pressure center of the pad must be close to another structure so a bigger pad or auxilliary support is not an option. Thank you.

John

 

[civilperson]

Why not use a 8" wide beam for support with the length to give larger area for lower pressures, i.e. 12 kip load on a 72" x 8" area = 3000psf?

 

[Taro]

All the equipment operators I have seen (mobile cranes, concrete pump trucks, etc.) carry wood planks with them to spread the load from their outriggers. Pretty cheap insurance to keep their expensive rigs from tipping over.

 

[emmgjld]

You might try a search on these Eng-Tips and a general Google for crane padding or outrigger padding.