Holdfast Training Services Trial Blog

As an update to what is happening on site here is a summary:

The Tower:

The level 29 and 30 slabs have now been poured.

Level 30 slab being poured

PC Harrington and Slipform International are constructing the slipform rig at level 30 with a deadline, of only one week now, prior to the commencement of the slip (to level 42).  This is expected to take 6-8 weeks.

Tower Crane 1 which services the tower was climbed last week to 130m without any problems. A third tie at level 28 was engaged to do this.  Cladding is starting to be installed too, between levels 1 & 15.

TC1 Climbed to 130m above ground (TC2 is the small one in front)

North Basement

The north basement excavation is down to stage 1, +2m AOD. (Existing ground is +4m AOD). The first whaler is in place and the props are being installed.

 The North basement excavation

West Basement

I approved the temporary works last week and work should begin this week to install a sheet pile retaining wall. Work will then begin to construct the ground level slab prior to top down construction.  (In the near-ground is the dewatering well be driven).  The main issue here is that the area above the retaining wall is a logistics delivery point for concrete lorries.  Agreeing a workable piling solution to allow deliveries during the excavation was the main issue and remain one to keep an eye on.

 The West Basement excavation.  In the near ground is the dewatering well and piles for a 10 storey central atrium core .

East Basement

In the East Basement the B1 slab beams continue to be poured in preparation for top down construction. However this is still no temporary works plan in place for the excavation as Sheet Piling UK (SPUK), who installed the sheet piles, have rejected PC Harringtons temporary works plan. SPUK were not happy with the amount of deflection in the piles since PCH were not planning to prop between the B1 and B2 slab.  (The piles in a place are a PU22-1 pile, 450mm in depth).

 The East Basement B1 beams.  The welder is preparing the top plate for a plunge column.

In summary:

It has been a busy last few weeks on site for me. Temporary works sign offs are required in all areas of the site and managing this has been interesting. There are still significant question marks about how the tower will be built. We have to leave six large pockets in the core when the slipform climbs the tower. Into each pockets a pre-fabricated steel hanger will be inserted. From this, Macalloy bars will be hung that support the 12 new storeys above (like a drawbridge works). The main issue is the installation method, size of pocket required and the temporary stability of the tower with the large pockets. I have proposed infilling some voids in order to provide vertical and horizontal load paths and this is now with a consultant engineer to model. Bearing in mind we only have one week prior to the commencement of the slip deciding this is critical. The first pocket is at level 33 so we don’t have long to decide!  Other issues include how the first six floors from level 30 are built.  The capacity of some existing permitter columns outside the core are near 100%.  Therefore we need to engage the Macalloy hanger as soon as possible.

I am in the process of preparing a more detailed blog on this issue of Macalloys bars, hangers and post tensioned slabs. It could be a possible subject for the first TMR.

In other news I ran the Paris Marathon this weekend in 4 hr 4 mins and 43 seconds.