Holdfast Training Services Trial Blog

G’Day from Melbourne, Australia!

The work is just starting to pick up on my site at the West Gate Tunnel Project (Maribyrnong River Crossing Site) as we prepare to start installing precast concrete piles on land based bridge piers and steel tubular driven piles in the river (due to start over the next 2-3 weeks).

The precast piles are being utilised for foundations across almost the entirety of the WGTP, culminating in thousands of individual piles in total. Although the project has its own precast yard, the procurement of precast piles has been subcontracted to piling specialists ‘Keller’s’, who are manufacturing the piles, delivering them to site and driving them into position.

 Today saw the first four piles for my site cast. As part of the quality assurance, the IREA (third party auditor) are required, under the Inspection Test Plan to conduct inspections of the reinforcement and concrete mixture, under a Hold Point, prior to pour. I decided to go along for the day and capture this procedure and provide assurance that checks were being carried out in accordance with the ITP.

The Casting yard is a rather simple and effective set up, involving runs of four moulds for approximately 100-150m or so. The reinforcement cages are lifted into moulds, onto spacers (to ensure cover requirements are met) and then cast continuously throughout the afternoon from concrete agitators. As mentioned previously, Keller’s are manufacturing thousands of these piles, in various lengths and with several reinforcement details. Meaning a slick manufacturing operation is now in process. A typical day runs as:

1. 0600 – strike previous days cast from mould and stack onto dunnage;
2. Clean moulds and prepare lengths;
3. Install reinforcement cages;
4. Conduct QA checks;
5. Cast moulds (checking concrete mixture through slump and cubes samples)

The piles are stored in the yard for 7 days, at which point they are transported to site, where they must continue to cure for a further 7 days prior to driving; this allows adequate time for compressive strength of the concrete to be achieved (60MPa in this case).

Today, I got the chance to witness the importance of slump testing. The slump test for the concrete mixture had a range of 160mm-240mm slump. The second mixer to arrive on site was tested on arrival (as are they all) by a subcontracted specialist (Construction Sciences), and a slump of 110mm was measured. This resulted in the concrete batch initially being refused; not great considering half the pile lengths were cast and continuous pouring was required. As the slump water/cement ratio was too low, a simple solution was possible, add more water!

Clearly the question to be asked was, ‘how much water?’. Of interest was to see the difference in approach between the engineers and concreters on site. The engineers, as you’d expect, started conducting calculations to estimate the volume of water needed to reach the required slump. The concreters decided to go with the more traditional ‘this is what we did before, that looks right’ approach, as if from nowhere, to which they tried to argue was correct; clearly the calculated route was taken forward …. and proved correct.

From this experience, I learnt the importance of simple and quick testing on site and the need to take a calculated and measured approach to problem solving as it appears the ‘guys’ on site will just crack out the ‘this is what we did before’ line; something that you seem to hear a lot.

I’ll be sure to put some stuff up once the piling starts, especially the marine piles and the dynamic testing involved.