Ground Testing

The Ground Testing was done today and the early indications are positive. Eleven test holes were driven and they produced a consistent picture of solid ground between 4 and 6 metres down. This, presumably, marks the bottom of the in-filled quarry.

We need to wait for the official results but it looks like the mini-piles are a solution to our foundation problem. Phew. I have to admit to being more than a little worried that the results would be inconsistent, inconclusive, or simply no solid bottom would be found.

The testing is carried out with a rig that lifts a 50kg weight and drops it repeatedly onto a metre long 3cm diameter pole with a pointed end, thus driving the pole into the ground. Here is the rig :

The pole is marked with 100cm gradations and the operator notes how many hits are required to move the pole each 100cm. When it is fully driven, another pole is screwed into the top and the process repeated. It all stops when 50 hits fail to shift it another 100cm. This is deemed to be the point where solid rock has been reached. The hit count for each 100cm section will be plotted out graphically for us and it should show a nice curve of gradually increasing resistance, with a sudden increase when the rock is reached.

As I said, 11 test holes were done, positioned along the lines of the foundations. Actually, this was a part of todays work that I found a little shoddy. There was not much attention to accuracy over where the test holes were done. The operators didn't even bring a tape measure with them, so their view of where the holes are will be based largely on guess work. Fortunately, all the holes painted a consistent picture of the subterranean layout, so I do not think it will matter that some of them missed the line of the foundations. Needless to say I have been out this evening and taken some accurate measurements of my own ! In fact, with hind-sight, I wish I had marked exactly where I wanted the holes to be done myself - not leave anything to chance.

Oh well, another lesson learnt.

We should have the official results early next week.