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Monday, May 23, 2011

Concrete footings

It amazes me when they poor great masses of concrete into holes in the ground for house footings.
Generally houses are in the range of forty tons and twenty tons is in the footings. Now if I were building a boat I would put all that weight at the bottom to keep the boat upright and this is a good thing. If I were to build a boat of forty tons I would get a stronger structure than a house, and the thing would carry a load of forty tons making it eighty tons.
The buoyancy of land to carry loads is greater than that of water. Let me explain, drive a heavily loaded truck on a road and its OK now drive it onto soft wet ground and it will get bogged, drive it into water and it will go straight to the bottom. So all three surfaces have a buoyancy, the road, the soft wet ground and the water. Now it is no good putting all that concrete into the ground if it is going to sink.
Lighter load for softer ground. Next to spread the load a boat has a surface area now put the boat onto the ground and it will support a massive amount of load with out sinking into the ground. Thats why big trucks have lots of tires to support the load so as not to sink into the road. If a building is going to move bigger and more concrete is not best. If I were going to build on soft ground I would go for surface area and allow the whole building to move as a whole.
I did work years ago as a drilling contractor and on one job in Corrimal in NSW. there was a skin of hard ground about three feet thick and below that the drilling rig would have sunk over eighteen feet threw the underlying mud.
How did I know well when we broke threw the skin I was able to push the drill bit that was three feet in diameter to the full extent of the machine with out turning the bit. The capacity of the machine was close to twenty feet for the depth of hole. So putting big concrete footing into the ground would have resulted in the building sinking over twenty feet threw the mud.
Any ground can be built on it just takes imagination as to how to over come a sites special needs.

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