A quickie from the front line. The bulk excavation got going on Thursday and Friday, and the dewatering has started to crank up.

Bulk and detailed excavation together

The 14-tonne excavator is pulling the sand out in bulk. At the same time, the 3-tonne is starting the detailed excavation: digging the shapes the basement slab needs underneath it.

  • The edge thickening runs right around the outside of the slab. It's a deeper, wider strip of concrete that carries the walls and stiffens the slab edge.
  • Internal thickenings go under each column in the basement. There are about four.
  • Pits are dug out for the stormwater pit and the sewer pit, the deepest points in the basement.

We should have most of it out today, with a clean-up tomorrow.

Profiles for the surveyor

Timber is being screwed along the sheet piling, all at the same height, with a laser level to keep it true. These are the profiles. The surveyor comes tomorrow to mark the grid lines from the architectural drawings onto them. From then on, everyone measures from the same marks, so the thickenings, columns and walls all line up with the drawings.

We also use the laser for the different trench depths, with the levels marked on my staff. There's a little shade structure and a table set up for the plans.

Section across the dig: the edge and column thickenings, the timber profile on the sheet pile and the laser level
Section across the dig: the edge and column thickenings, the timber profile on the sheet pile and the laser level

Daily monitoring: 30 mm so far

Every morning we read the sheet pile monitoring points (A to F). The most important side right now is the boundary. So far the sheet piles have moved about 30 mm. That's within what was predicted (up to 70 mm), and these are only 5 mm thick sheets.

The boundary wall has dropped about 19 mm. We think that's mostly the footing settling under the weight of the wall itself rather than the dig, but we're watching it. The tiling next door is on hold until the excavation is done, so we can see how far everything moves before we finish.

What's next

Bulk and detailed excavation carry on in parallel, and the surveyor is booked. The concreter and the engineer are meeting this afternoon for a Q&A session, going through the plans and clearing up any queries, so we can get into the blinding slab as fast as possible.