Dewatering plans and generator needs for construction

Welcome back to another site update. It might not look like much has changed on the surface, but behind the scenes we’ve been busy on planning, coordination, and early-site preparations.

Tie-downs, screw pegs and minor works

We’ve installed tie-down straps and screw pegs at each corner of the container—there’s still a spare screw peg stored underneath. We also installed two-ton tie-down straps and added a few twists to the front strap ends to reduce wind-induced vibration and resonance. One strap was buried and the top of another is visible in place.

We also top-dressed the lawn with sand to try to level it out. It was a bit of fun and helped tidy up the area around the site.

Progress on procurement and plans

A lot of our time has been spent talking with contractors and finalizing technical documents.

Key items:

Sheet piling: We’re in regular contact with the sheet piling company. Once we submit the final information, we can book their mobilization. There’s currently a four-week lead time to get on-site.
Dewatering and vibration management plans: We’ve been waiting for the geotech’s dewatering and vibration management plans for several months. We were told the documents would arrive last week, but they haven’t yet. Those plans are essential before we finalize the sheet piling details.
Development Approval (DA): We’re expecting DA this week, which will trigger coordination with three or four contractors.

Power and dewatering equipment

Dewatering will require a reliable power supply. We have a temporary meter box on site and plan to have an electrician install a 32A three-phase connection to power the dewatering plant. We’re confirming the dewatering plant footprint and how close it needs to be to the power source. We may also need a custom extension cable.

We’re discussing options with the electrical engineer and generator supply companies. The house design includes a large generator (originally specified as 120 kVA with a 60 kVA ATS), but we need a smaller three-phase generator on-site that can connect to an auto-transfer switch for the dewatering system. If dewatering loses power overnight, the basement will flood quickly, so an automatic backup is essential.

Groundwater checks and a test hole We dug a test pit down to groundwater level to observe site behaviour. The pit has been collapsing slightly, so it’s not as deep as it was initially. Over two days, we measured water-level differences hourly between high tide and low tide using a laser level.

Findings:

The water level inside the pit was consistently higher than the water level in the nearby canal.
This suggests water within the site is not free-draining to the canal; it’s retained and drains more slowly—likely due to soil composition.

Implication:

That’s actually good news. It means the soil isn’t constantly being fully surcharged by the tidal level. Once dewatering is running, it should be easier to keep the site dry because groundwater isn’t being quickly replaced by tidal inflows.

Survey work and setting references

We’ve raised a purchase order for an iDent survey. Typical iDent fees range from $2950 depending on the area. The surveyor will reestablish boundary pegs, perform searches, and set reference points. We’re using reference marks in the curb and across the street to avoid relying on potentially misplaced boundary fences. Accurate, independent reference points prevent future disputes with neighbours and ensure the house is built in the correct location.

When the surveyor sets benchmarks across the street, we’ll finalize the sheet piling top level (RL). That helps avoid later cutting of piles if they were driven too high. After sheet piling and dewatering, we’ll place timber along the sheet piles and set internal benchmarks. These internal references will be used to set slab heights, basement levels, pit depths—basically the entire internal layout.

Costs, options and decisions

Dewatering is a high cost item: it’s likely to run about $7,000–8,000 per week. The goal is to get dewatering in and out as quickly as possible.

Pile options and estimated costs:

Sheet piling: costs roughly $220,000 for installation plus dewatering which runs at around $7000 per week with a minimum of 6 weeks hire. Total for this options is around $400-$450,000.
Secant piles: typically start at about 450 , 000  f o r  p i l i n g ,  p l u s  d e w a t e r i n g  o n t o p . This puts secant piles at around $650-$700,000

That puts the difference between the two approaches at approximately $200,000 in favour of sheet piling.

Engineering discussions

There have been robust discussions with the structural engineer. The engineer prefers secant piles and has designed for them, but for this specific residential site we’re leaning toward sheet piling because:

This is not a high-rise project.
Neighboring properties are sufficiently distant to limit vibration impacts.
We believe appropriate vibration controls and monitoring can mitigate risk.

We’re awaiting the geotech’s vibration management plan and will install vibration monitors on neighbouring houses. If vibration exceeds limits, we will stop work.

We’re also trialing a new polymer with the sheet piling company to help measure and potentially reduce vibration—this will be the product’s first field trial.

Contract administration and budgeting

Since the last update, we’ve been firming up quotes and reviewing the budget. I’ve been inputting the December estimate into our contract administration software, checking the line items and allowances, and making sure there are no obvious gaps in the estimate.

Summary

Progress may look slow on-site, but we’re moving ahead with the essential planning and procurement that determine how fast and smoothly construction will run.