Holdfast Training Services Trial Blog

We are finally building! After weeks of delays waiting for the demolition contractors to handover the basement area and only have sketches of what will be built to look at, we finally got hold of area 1.1 (number 1 of 21 areas) where we will be constructing a 1.25m raft slab. This area in particular has a lot going on; temporary and permanent drainage, a tower crane, two sumps and several columns.

The initial task once handover hand been completed was to waterproof the area of the pour. This involved laying ‘egg crate’ (drainage membrane) on the ground where it will act to  diffuse pore pressure and stop any water that enters underneath the slab from building up enough head to affect the slab. The waterproof system that is being used is SIKA. From what i can see this system seems to be a licence to print money. SIKA will only provide their 15 year warranty after one of there representatives has inspected it, and will only sign it off if their products have been used.

   This ‘egg crate’ will be laid across the entire site.

Once the egg crate had been installed, a 50mm layer of blinding was placed on top before the steel fixers moved in. Unfortunately one of my duties at the moment is ordering and managing all rebar for the basement. After initially laughing off suggestions that this was one of the harder/stressful things for an engineer to manage ( I believe I said “how hard can it be?”) it has become the absolute bane of my life. After 6 deliveries there has been something wrong with almost every one; late, wrong or has bits missing. This would not be so bad if the site has stock rebar lying around, however the QS department will not allow such a thing and we are only allowed to have the exact bars that we need on site. This means that when a bundle of 50 bars is left in the yard in Wales and doesn’t  make it to London it becomes a major issue. The construction manager does not want to hear the word ‘delay’ at any time!

When the correct rebar is on site the steel fixers throw it in very quickly. This pour alone had just over 35 tonnes of rebar.

Bottom mat being installed alongside one of the sumps.

Further work on top and bottom mat. Drainage being installed on the foreground, crane base can be seen in the background.

The crane base was particularly tricky to install. Four concrete plinths had to be cast into the bottom mat and the base lifted into position on top of them. There is a 0mm tolerance between the four legs. Therefore this required a lengthy exercise of adding/removing steel shims from underneath the legs and tightening the leveling screws. This is much easier said than done and it took a few hours before there was a 0mm difference between all four legs.

Plinths ready for a crane.

crane base in position.

After 6 days of of steel fixing, carpentry, welding and lots of other things the area was ready for concrete. 320m³ was poured in one very hectic day, it took around 12 hours to get it finished and this is not the biggest pour on this project by a long shot. At peak periods we will be pouring around 3 slabs a week.

The area ready for some concrete

About 10hrs into the pour.

the pour would need to be power-floated. Note the large puddles forming due to the torrential rain that came down all day. The gaps between the crane base and the concrete will be grouted at a later date.

A busy few weeks on site and only set to get busier. The main issues encountered so far have been:

• Stores – Expanded operate by using a ‘just in time’delivery philosophy. The materials they need will turn up at the right time in the right place, therefore removing the need for large stock piles of equipment on site. In theory this is a good way to go about it, however, in practice there are many times when the right stores do not turn up or are sent to the wrong place thus creating a threat to the project timeline.
• Logistics – the site is very restricted and has a complex logistics system that goes with it. The gatesmen will turn away a vehicle if it is not on their list so all deliveries have to be booked in a week in advance. Again, this does not work well in practice as there are always last minute deliveries and changes to the schedules. I have had to sweet talk them on more then one occasion to get them to let a last minute delivery in.
• Overzealous construction manager – not really that much of an issue, more a minor bugbear. The is a very specific schedule with pours taking place simultaneously and lots of moving parts. One of those moving parts is the construction manager. He has been a coiled spring waiting to start work and now that we have it is hard to reign him in. Everything must be done NOW, regardless of whether there is the stores or manpower with which to do so. He has been nicknamed the Tasmanian Devil as he sweeps through the area and causes havoc and confusion but somehow manages to get the job done.

On a separate note, today I brought another cat. I am one step closer to becoming a crazy cat person.