Holdfast Training Services Trial Blog

Period Covered  22 May – 14 Jun 12

Summary:  Dewaterng

A really busy few weeks, ensuring that the Dewatering Package was given State Approval, the contract was signed between JHG and the Subcontractor (Mobile Dewatering) and making sure all of the necessary prep work and safety paperwork was in place for their arrival.

To be brutally honest I have learnt an awful lot and though John Holland are happy with everything I would do things differently if I had my time again….I have learnt valuable lessons about risk V programme but am pleased to report as I write this with things are getting back on track, abeilt with a significant delay.

Key lesson learnt – Water has the potential to be very dangerous…..

During this period I have completed the following on top of routine work:

• Consultations with client to convince them original dewatering plan is most sensible and to discount sewer option.
• Written Groundwater Management Plan
• Dewatering Activity Method Statement written.  The mountain of other H&S paperwork (Plan Hazard Assessments, Task Risk Assessments, Induction paperwork)
• Chaired subcontractor kickoff meeting
• Dewatering Co-ordination and installation (including installation of 1 x Monitoring Pizo)
• Re-infiltration licence approval from Department of Water
• Emergency storm repairs
• Dewatering QS work
• State approval reports written for bus stop relocation and Sunday working

Work on site.

Dewatering Set Up slide show…. from start to finish (Sorry its in 3 ppts)

Dewatering Pres 1

Dewatering Pres 2

Dewatering Pres 3

So its all about me at the moment.  Works has slowed to a crawl as the site waits for the dewatering to begin.  The delay is a result of a combination of factors but the finger can be pointed to some slow work by the John Holland contract administrators and the client perusing an option that they had discounted 2 months earlier.  All this meant the subcontractor did not start on site until 5 days after dewatering was due to start.  With 10 days of set up and installation required this is a significant delay.

I will cover the whole saga and the different options to dispose of the water in my next AER, but in short the water table needs to be lowered by 0.5 -1m around 180 pile caps and up to 2.5m around the cores (10 in total).  The water will be treated on site and reinfiltrated back in to the ground through 30 recharge spears.

Temporary work:  Part 1

Due to the delay in mobilising to site, a temporary solution for disposing of the extracted water was proposed whilst the permanent system was being installed.  A temporary reservoir/sump was dug.  Unfortunately this was way too small and breached over the first night.  Unfortunately the water did not flow in the direction of the open “floodplain” we had cleared but cut a deep channel at 90 degrees to the proposed overflow area.  This resulted in 2 legs of an access scaffolding being undermined and another subcontractors compressor being tipped over.  As a result Saturday morning was spent doing a lot of emergency works to rectify this issue.  Thankfully no one hurt, but a reminder of the danger of trying to contain a large body of water.

Temporary Works Part 2.

Having learnt this lesson you would think we couldn’t possibly try this again, but the pressure on the work package manager to remain on programme is such that a second larger reservoir was constructed in another corner of site.   Understanding the permeability of the soil better and the flow rate I calculated that this second reservoir was very likely to overflow after 16hours and it was not worth the risk involved (dewatering needed to last at least 4 days to bridge the gap to the permanent system).  Overruled, the pumping began….as you can see in the photos this very nearly ended in disaster again, with the pump being turned of with just 10cm to spare at 630am the following day.

As a result of these 2 instances the decision was made to wait for the main reinfilatration system to be set up.

This began on 20 June and so far has worked very well.  Currently a  110m2 area is being dewatered with the number of excavation steadily increasing over the next 2 weeks – due to the limitation of the treatment units the amount of water which can be dewatered at one time is 30l/s so careful manageme

View from my Site Shed looking at collapsed tower crane on enighbouring build

nt and programmeing is required

In other news…has Chris W been let loose on the cranes in Perth (view from my site office looking out on the new cancer centre building).  Strong winds in Perth, Western Australia, took the luffing jib of a tower crane over the back and onto the roof of a hospital on Sunday as winds as high as 140kph caused widespread damage to the region. While not yet fully confirmed we believe that the site was closed when the incident occurred and the crane was parked up with the jib at around 75 degrees and the slew brake left on, rather than the crane being allowed to ‘weathervane’.

Further Work

• Dewatering Programme Planning
• Environmental Monitoring
• Work on use of Stormwater System
• Post Tensioning Tender Review (awaiting for State to lift moratorium on all tenders…….long story!!)
• AER 3  – Dewatering, Health and Safety Paperwork and Boundary issues on Site, Relationship between Client, Existing hospital and JHG.
• TMR 2 Research – Project Bespoke Contract v NEC3/ICE 7^th