Going further underground...

Here we have the deepest hole so far, this is about 4 metres below ground level, and is part of a lift pit. Note the sheet driven piles around the edges, like large crinkled sheets of corrugated iron, these sheets are driven into the ground, usually by a pile driver and then the ground is excavated. At the base of this pit a concrete slab is about to be poured, two layers of steel bars are tied together, and spaced apart to form a raft of steel. The concrete is delivered ready mixed and poured onto the steel, and is usually vibrated into place to ensure that no voids are left. What I am checking for is that the steel sizes are as per the Engineers design details, that the steel bars are lapped well, tied together, that there are spacers (in this case steel chairs - usually plastic spacers are used), the spacers are to ensure that the concrete covers the steel by a minimum of 25mm to ensure that no water gets into the steel and causes it to rust. Basically, I was taught on my first job to ensure that the steel is free from crisp packets and cans of coke, not much else can go wrong.