Friday, 23 May 2014

Step 3 - Making the foundations - Testing the soil

well we finished Step 1 and step 2 and now we need to tackle

Step 3.......

Once we have excavated the soil down to the right level, it is time to do some more tests which will help us confirm the design of our raft foundation.

The test we do here is called a plate load test...

For this test we put a plate under load..... (you see its not that hard, is it?)
We choose around 10 areas around the site and then construct a series of pads, we place plates on the ground and then slowly in a series of cycles place the plates under increasing pressure using an hydraulic jack. We test these plates up to a pressure of 800 Kpa  (kilopascal... 80 tons to the ordinary man on the street.

This is 3 times the ultimate planned weight of the building on the ground

The plate itself is only 30cm x 30 cm  and this weight is the equivalent of around 16 full grown african elephants balancing on this single point...

I have heard a rumour that in the olden days, before the hydralic jack this service was an important source of revenue for circuses with elephants.

 Almost there,  80 tons of pressure.

For the test to pass we allow only a deflection of a maximum of 2.5 cm into the soil! If the soil fails the test, this area of the site will need to have this soil removed and a better quality of bearing material added in its place.

More detailed information on this process can be found here!