Thursday, 28 February 2008

Ground Conditions

Allowable bearing pressure of 50kN/m²?

In most cases, it is essential that the ground underlying and adjacent to a scaffold be assessed in some way to determine the safe bearing performance of the ground. I’ve heard of all kinds of different methods of testing soils from the ‘finger pressure test’ to borings and trial pits.

If you have been advised that the safe bearing pressure on site is 50kN/m2, I would like you to consider the following:

I weight 77kg and in every step I take, the contact area (footprint) of one shoe is approximately 0.01m². What is my ground pressure? The ground pressure is equal to my weight divided by the ground contact area, therefore my ground pressure load = 0.75kN / 0.01m².

Pressure exerted on the ground from one of my shoes = 75kN/m²

With the above in mind, I would be very careful next time you’re on a site with an allowable bearing pressure of 50kN/m² and watch every step you take... You may sink like quicksand!

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