Schoolboy Physics

As a physics graduate (my colleagues at work should stop laughing at this point, and pay attention !) I thought I would try to relate these "Ground Bearing Pressures" in Newtons to something we all know and love so here goes with some schoolboy physics (or schoolgirl - sorry Louise)

So, using the gravitation acceleration constant, 'g', value 9.8 m/s2, the 34.6KNewton/m2 from the design converts to 3530 Kg/m2 or 3.5 Metric Tonnes/m2. Again, to get this into some form of context, that is 350g/cm2, which actually seems quite reasonable.

For comparative purposes I scoured the kitchen looking for something with a similar Ground Bearing Pressure. The best I could do was an upturned (i.e. cork end down) bottle of wine, which came out with a GBP of 226 g/cm2 (assuming you can prevent it falling over and smashing and that you can stop yourself from drinking it).

Taking this up to a larger scale, I thought I would try and work out the GBP of the contractors digger. After all, it has been happily sat on this soft ground for a week now, and hasn't sunk without trace. According to the plate on the side, it weighs 7380 Kg in Standard Spec. It has two caterpillar tracks which I carefully measured (after checking none of the neighbours were watching). To cut a long story short, the GBP works out at 3209 Kg/m2, which is remarkably similar to that quoted for the extension.

Just for fun, I then did an estimate for a swimming pool in place of the extension. assuming 2m average depth, and a 10m x 5m pool. Allowing extra for something to retain the water (always a good idea with a pool), GBP is 2495 Kg/m2.

So, to summarise :

• GBP for extension 3530 Kg/m2
• GBP for digger 3209 Kg/m2
• GBP for bottle of wine 2260 Kg/m2
• GBP for swimming pool 2495 Kg/m2

The ground has been demonstrated to support a bottle of wine, and a digger, hence is likely to be able to support the extension. What is there to worry about ?

Here endeth the lesson.