Holdfast Training Services Trial Blog

Nothing significant to report on my site as we haven’t started the installation yet and so we are still in the process of procuring and reviewing RAMS.  Personally I have a plant movement package out to tender with the supply chain and I am in the process of reviewing tender returns for AHUs, and procuring some steelwork for some chillers and cooling towers as well procuring a temporary ventilation system for a tunnel – which is turning into a bit a nightmare as the current design does not sit well with the insurers (yes this will become a future blog……..).

Anyway I thought I could post another blog about off-site manufacture and modularisation focusing this time of the importance of off-site inspections.

Yesterday I visited Skanska Fabrications in Slough where 22 pre-fabricated tunnel modules are being manufactured.  These modules will be used to for chilled water, high grade hot water, low grade hot water, domestic water, low voltage, high voltage, data and fire alarms.  Each module is 3.2m wide and 6m long and weighs 4000kg and to give an idea of the scale of these goliaths, the picture below shows one module and the lower large orange-capped pipes are 400mm in diameter – so not small!!

The tunnel into which these modules will be installed has a decline of 0.537 degrees along the lower half and 5 degrees along the upper half.  The plan for installation is to drop each module down the centre shaft on to pre-installed rails and then allow gravity to move the modules down the shallow slope first, using a winch to control the decent.  The modules will then be built back to the centre shaft.  Once half of the modules have been installed, they will be dragged up the steeper slope using the winch and again modules will be installed end on end working back toward the centre – well that is the plan anyway!!!

These modules were designed using BIM and BIM also was used to simulate the modules being moved by a winch to ensure there was enough clearance in the tunnel for the winch cable and also to calculate the size of the walkway to ensure the winch cable could be ran through the centre of the installed modules in the latter stages of the installation.  A picture of the BIM model showing the winch cable analysis is above.  Since the modules were designed using BIM, every part of each module has its own asset code and a QR code sticker is placed on every pipe section, tray, bracket etc.  These QR codes can be read by our iPads on site and they are linked to the BIM model using Naviswork BIM360 Field meaning that if I required any information about a component during installation all I have to do is scan the QR code with my iPad and I will be provided with design data, flow rates, mass, supplier and several other data sets.  I have been very impressed with this system so far.

It is my responsibility to install these modules in the 132m, 4m wide tunnel and so I am regularly visiting the factory to check the quality of the finished product and identify any issues so changes can be made prior to delivery to site.   One of the first issues that stood out to me was the lack of lifting points and winching points and so the fabricator is going to develop a suitable design solution and I will arrange a factory visit for the lifting Sub-Contractor to check the design and final fabrication.

The second fabrication issue that became apparent during my visit was the use of corrugated kick-plates which prevent the floor panels from being lifted out, significantly hindering future maintenance.  Again the fabricators are going to redesign these and opt for a flat kick-plate.

Another issue is whether or not the modules will slide down the 0.537 deg slope under their own weight.  The Project Manager responsible for this design was adamant that they would slide as PTFE slip pads are used between the modules and the rails but I was confident that they will not and this debate has been going on for several weeks.  Anyway rather than guessing I decided to use some GCSE physics to calculate whether or not it would slide.  My calculation was that it would not and in fact it would need a 1.7kN force to get it moving.  This for me was one of those moral courage moments as I did not want to blatantly challenge a senior PM but if it didn’t move, it would be my problem to resolve on site and the requirement to push or winch the first modules would fall outside of the package scope and would incur additional cost.  So I was keen to mitigate this risk early to reduce costs and avoid any unnecessary delays.

So this short visit has confirmed to me the importance of off-site inspections and inspecting a physical product rather than purely relying on a BIM model.

 

I thought this post may induce some debate over the benefits of this pre-fab approach.  The client and senior leadership team seem very happy with it but I am not convinced.  The main issue with this design is that we have to wait until the tunnel is completed before installing the modules where as if we were using a traditional installation, we could be mounting brackets, trays and pipes directly behind the slip formwork as it moves along the tunnel, casting the secondary lining.  Plus looking at sustainable development, these modules will be a challenge to remove when the product reaches the end of its life as the centre access shaft will be capped and backfilled.  Also I think the module frames will make maintenance much more difficult.  Thoughts?

On a personal note, I have got my aircraft flying again and so I am once again terrorising the skies above Essex and Hertfordshire.  I would therefore recommend avoiding flights out of Stansted or Luton for the foreseeable future.