Holdfast Training Services Trial Blog

It turns out concrete can be pumped – I have been surprised how far it can be pumped if you try hard enough. The Bond Street East site contains a batching plant at Hanover Square (next to Oxford Street) feeding a pair of chunky concrete pumps.  These then feed vertically down a 5-story temporary pipeline to a massive thrust block tied into a group of RC piles by big steel beams.  This block enables a 90^o turn before the pipe travels another 1.1km along the running tunnels to the track work sites.

Batching plant surrounded by some very expensive flats. I hope they appreciate the token acoustic sheeting.

The scale of the temporary works on these sites is fairly mind-blowing. I sit opposite the guy responsible for making this pipe work; I can assure you it is blowing his mind as well.

Concrete pipes descending from the surface to level -5

The daddy of all thrust blocks enabling a 90 deg turn.

Concrete pipes disappear off into the distance to the work sites.

Unfortunately the scale of the project also creates a lot of inefficiency and interface issues. The above-mentioned pipes had to penetrate a ventilation bulkhead we had erected in a feeder tunnel.  Despite being part of the same Joint Venture there was no co-ordination put in place between the teams, leading to a chest-beating discussion about who had the priority.  Needless to say the concrete-pumpers won and we had to strip out our bulkhead, only to re-erect it this week.  Hopefully the new-fangled BIM will put all these issues to bed.   We live in hope.

Ventilation bulkhead, version 2.  Please ignore the photo-bomber in the window.

In other news I have occupied myself with a bit of ‘commercial awareness’ by firing a magazine of EWNs at Paddington station and following them through the commercial department.  Not as interesting as it sounds.

We have also been lifting in some 2m x 2m x 3m silencer pods to the -2 level through the only route big enough to take them; a 5-storey vent shaft.  Unsurprisingly it lost a bit of galvanisation from the corners on the way down.

Big steel box + no tag lines  = swinging load.  It bashed the rim of the shaft on the way in but was ok when it was inside the shaft.

Last week one of the small projects that I have been planning since I arrived finally finished – transferring the Emergency Department (ED) onto generator power, relocating the sub-mains cables and then transferring the power back to mains.

Figure 1: Delivery of 2x 350kVA Aggreko Generators.

Figure 2: Original location of the ED sub-mains, on the floor slab of L1 (previously this had been the roof slab of the 1 storey ED). Note, the mechanical protection has already been removed.

Figure 3: New location of ED sub-mains: Now on high level cable trays in main corridor.

Rather than detail the whole process, I will instead highlight some of the risks and difficulties  and how these were overcome.

• The ED runs 24/7, therefore there is no convenient time to turn off their power.  But following a week long investigation of power demand, Tuesday-Thursday was identified as the period of the lowest demand and therefore the “least busy period”.
• Sizing of generators:  Both 350kVA units was sufficient for the whole department, but to maintain redundancy 2 units were connects – one to Essential and one to Non-Essential (with an automatic switch between them in case of any issues).
• The hospital’s UPS (Uninterruptible power supply) was broken, therefore if power was cut all the critical infrastructure, e.g. life support machines, would switch off.  This little bombshell was dropped at 1600 on the Friday before the works was due to start.  The simple solution was to postpone until the UPS was fixed.
• During commissioning of the Emergency Department (2 years ago, by a different builder), the generator manual transfer switch was not tested.  The risk was the hospital’s to take, therefore they were required to conduct physical switch over – the mains power was maintained at the switch until after the hospital had confirmed that it had worked.
• Fuel:  although the generators had a fuel capacity to run for 28 hours at half load, in order to appease the client the tanks were re-filled every 6 to 8 hours.  At no point did the levels drop below about 75%.  This was a very conservative strategy but keeping the client happy is critical.
• Diesel exhausts blowing into the ED air conditioning intakes.  There was only one space that the generators could go – approx 25m from the intakes – other than extending the exhaust flue by 2m (the big pipe on the ground in figure 1), this was a question of keeping my fingers crossed that there would be no complaints.
• Over night noise – the generators were rated at 70 dBA at 7m, but with EchoBarriers installed this dropped to 55 dBA.  Although this made us code compliant, at 2am in a residential area it is still pretty loud.  This required some more crossed fingers that there would be no complaints.

The overall project success was due to a lot of planning with the various sub-contractor and consultation with the client.