Laying the Foundations (exterior)

With the external demolition complete, much of the work in recent months has focused on preparing the ground and putting in foundations, both external and internal.

Preparing The Ground

With the demolished buildings removed, the leftover basement areas were scraped out, filled in with hardcore, and levelled to create a piling mat. This provides a solid, flat, level surface that the piling rig can work on top of to put the piles into the ground that will support the new structure.

Kier’s surveyor then takes the drawings and with equipment that uses precise GPS coordinates, marks up the piling mat with all the pile positions.

In the plan below, the black block to the right is the sandstone auditorium block, the building next door is shown in grey at the top of the image, and Gorbals Street would on the left. The main area of the plan shows the arrangement of piles and foundations under what will become the new foyer and bar areas.

The red dots show the new piles that we are putting into the ground and the blue circles indicate the piles from 1989 building. We discovered a great deal more of these old piles than were originally indicated on the historic plans and our engineers have had to carefully rework the arrangement of new piles around them, as we cannot put new piles in on top of old ones.

All the old piles need to be exposed and cropped down to a height that doesn’t interfere with the new floor slab.

Piling

The area to the north-west of the building uses mini-piles; short piles that are driven into the ground.

They are hammered into the ground with a weight that is thumped up and down inside it. Once it is in far enough it is filled with steel rebar and concrete.

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In the main areas to the West and South of the building much larger CHD piles are used. These piles are up to twenty-five metres long and use a substantially larger piling rig. Instead of hammering these into the ground an auger is used, sort of like a giant drill bit, to screw them in, causing much less disturbance to the adjacent historic building.

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Shuttering and rebar

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Concrete starting to go in

The concrete is poured with just the bolts sticking out (now protected and highlighted with yellow caps). These bolts will be used to connect the steel frame that makes up the bulk of the structure of the new building. Bolt cones are used to create a cavity around the top of each bolt to provide bit of wiggle room so there is a bit of play when it comes to aligning the pre-fabricated steel elements to the bolts later on.

Some areas of the new foundations are a couple of levels underground. To make it possible to dig down this far, massive sheet piles are used to hold back and support the ground around the excavation area. In the image below you can see articulated sheets of interlocking metal that have been rammed deep into the ground.

This area will eventually form the access to the historic stage machinery under the stage, some basement storage areas, and also house the goods/passenger lift that runs from basement to the second floor.

In the first picture above is a ring beam that will support the bottom of the new lift shaft. The black door above is at stage level so you can see how the new foundations are a good couple of storeys under the ground.

In the second picture you can see the sheet piles have been cut down to size and staggered to step down into the deepest areas, ready for the concrete to be poured for the new foundations. This video below shows a bit of the process of the concrete going in.

Below, is the same area shown from the opposite end once it has been built up a bit more. You can see the pit for the lift being formed in the middle.

In these images Alin Covasa, Kier’s site manager, can be seen in the cherry picker over the lift pit area marking up coordinates on the sandstone wall for the surveyor.

With the new foundations completed, we are really starting to get a sense of the new footprint of the building.

At the front of the building some steel work has already arrived and started to go up.

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It will be fantastic to start to see the three dimensions of the new building taking shape. I will cover that in detail in a future post. I will also be taking a look at what has been happening with the foundations inside the theatre walls as well as welcoming back the statues to the Citizens Theatre.

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