It's been a couple of weeks since the last video because not much has changed on site visually, apart from cars being shuffled around. That doesn't mean nothing's happening. Most of the work lately has been paperwork and coordination to get into early works.
DA approved and next steps
We received the Development Approval (DA) last week. The conditions were straightforward, so I reviewed them and passed the requirements on to our consultants: the hydraulic, structural and electrical engineers and the architect. No major issues, which is good.
Now the priority is the early works building approval pack. The structural engineer needs to provide the Form 15 (the engineer's design compliance certificate the certifier needs before issuing building approval) and the completed design for the basement slab, basement walls and build-over-sewer detail.
Because we're using sheet piling to hold back the excavation, we also need the sheet piling design, but that needs the contract and construction insurance in place first.
Insurance and contractor coordination
We've asked our brokers for construction insurance quotes. One came back unacceptably high, so we're waiting on the broker to find a better option. Once insurance and the contract are finalised, we'll submit everything to the sheet piling company.
We've pencilled in an installation date for the sheet piling, and we'll separate it from the dewatering installation, which the piling contractor is fine with. The piling runs continuously around the site, under the driveway and along the boundaries. Continuity is critical: there's groundwater under the site, so if the dewatering pump or backup power fails, the piling has to hold the water out until it can be pumped.
Dewatering plant and power setup
The sheet piling company has confirmed the dewatering plant size: roughly 7 m x 3 m and about 52 tonnes. The plant needs a three-phase, four-pin, 50 A circuit, and the pump runs on a 10 A circuit. Both will run back to the meter box, less than 10 metres from the plant, so an electrician will add another three-phase outlet there.
We'll also have a diesel generator with an automatic transfer switch as backup, so if mains power fails the dewatering keeps running.
Technical checks and plans
I've sent the geotechnical reports and dewatering management plan to the sheet piling company, and we're waiting on the vibration management plan. We'll monitor vibration at two neighbouring houses during piling, to stay within the controls and keep the neighbours onside.
Site clearing and excavation
We removed more of the crossover and hardstand to make way for the piling. I've been digging to expose where the top of the piling will sit, so the contractor can install the piles to the nominated reduced level.
A reduced level (RL) is a height measured from a fixed survey datum, instead of from the ground, which changes as you dig and fill. The surveyor sets marks off site (ours are in the kerb across the street), and every level on the job is measured from the same reference.
We set the top of the piling at RL 2.8 m so it won't need trimming later. Cutting sheet piling after it's in is costly and slow.
Small excavations with a three-tonne machine cleared the pile line and let us confirm finished floor levels. They also open up access in tight spots and help locate the top of the piles, so backfilling can restore the final landscaping levels later.
Neighbouring boundary walls and structural strategy
During demolition we found remnants of old concrete and damaged boundary walls, some already leaning. We'll remove those sections and rebuild them properly. The structural engineer and I have worked through how to rebuild the walls and form new footings.
Boundary wall plan:
- Remove failing wall sections along the side boundaries.
- Extend the basement slab out to the boundary.
- Form a large footing at the base and build a retaining wall back up. In one tight spot we may use strip footings first. The main issue is the piling machine's distance from the neighbour's wall, about 600 mm, and making sure there's room to excavate and pour. If clearances allow, we may use the sheet piling as temporary formwork for the footings.
Consultants and approvals
There's ongoing back-and-forth with the consultants. The structural engineer is waiting on some architectural details, and the architect has been slower than ideal, but everyone's busy. Ideally some of that detail would have been done earlier to speed up the structural design, but we're working through it.
To complete the early works Building Approval (BA) pack we need:
- Form 15 from hydraulics and other specialist designs (completed or in progress)
- Civil, structural documents
- Insurance, QBCC and QLeave details (already started). QLeave is Queensland's portable long service leave levy, paid before approval on building work of $150,000 or more.
We also need a structural design for building over the sewer. Certifiers have changed how they handle build-over-sewer approvals and many won't take on that liability any more, so we prepare the application and submit it directly to the water authority (Urban Utilities, in Brisbane) and wait for their approval. Once the pack is complete we'll lodge it and expect about a 30-day turnaround.
Other small updates
- Demolition cleanup: removed leftover concrete and finished some side excavations.
- Trialled sandbags on site (not for construction).
- Site notes: the portable toilet is still pink, and the barbecue is still on site.
Summary
There's a lot of paperwork and coordination right now: insurance, contracts, engineering details and approvals. Visible site work will ramp up when the sheet piling and dewatering start, and we'll film that phase for the next update. For now, it's steady progress behind the scenes.
