The drawings become a reality!
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.
Holdfast Training Services Trial Blog 
Hi Fred,
All sounds like you have your hands full. Can you explain how the egg shell works a bit more. Is any build up in ground water pumped out forever more? Are you on London clay, if so have the slabs been designed for heave?
Interesting that the QS team won’t allow some stock steel – I am surprised some is not required for drainage laying and that the cost of a bit of stock would not save costs in terms of reducing delays or paying for expressing deliveries.
Crane base looks like a shallow wide raft and not piled? Will the crane have quite a few temporary ties (or low tie) into the structure?
Hi Damo,
The egg crate works by allowing water to travel freely through it. The dimples in the egg crate create channels for the water to flow through (until it reaches the drainage system) thus preventing a build up of water pressure that could effect the slab. Any build up of ground water will be controlled using a system of sumps and pumps. The fact that the site is on top of an existing raft slab from the 60’s means that groundwater has not been that much of an issue. The same can be said for the London clay heave. The weight of the existing raft slab is enough to keep the soil in place whilst we construct the additional raft slabs.
I too was surprised by the aversion to stock steel, I assumed it would be a sensible approach to have a small amount of stock to get through any delivery mishaps. However this is very much not the case.
Crane base is not piled and will be tied into the structure as it goes up around it.
Nice to see you in action Fred,
Sika are a good company with many useful products but, yes, proprietary products are the Caxton engine of cash in the materials business. Xypex is a very similar setup. Do you think that issues would become apparent within the 15 year window given the thickness of the slab? What were the working hours for the 12 hour slab pour and what measure were taken to ensure concrete quality in the rain? The Australians would be horrified that a worker had to wear a coat!
On the stock steel side of life I would have thought you might order some of the straight bar required for the next slab so it is available for upside risks in steel fixing (i.e. if there’s nothing else to fix we can get on and work ahead to advance the programme) this would potentially act as stock if it were needed (not deliberately of course…). The need is to emphasise that this is not early call forward but steel required for ‘labour switching’. Just in Time (JIT) has a reputation for becoming Just Too Late (JTL) if there is insufficient foresight in terms of what is required and by when to deal with friction in the supply line.
“Sweet talk the gate to let a delivery in..” – whose site is this?
Cats are cool they turn a house into a home. You might think you choose to ‘own’ them but they soon own your home, your heart, and your head. Beware, dogs have owners, cats have staff.
This all looks very familiar! My site when I started was in about the same state. Damo’s too.
We used a very similar egg crate material within the secondary waterproofing detail for our clubhouse area. It worked really well. Where does yours drain into? Do you have linear drainage channels below leading to sumps? What fall have you laid it to?
Interesting solution to the crane base. I assume piling through the existing slab was discounted on cost? That being said, how are the vertical tension reactions at the crane base due to wind loading at the top being dealt with? Or are they being taken out at mid height by cross tying to the structure? How has the structure design be adapted to accommodate these additional loads?
Guz
“Humans are great – every cat should have one!” – Garfield
Rich,
The slab was poured continuously from 0800 to about 1930. There was additional concrete laborers bought in for the day so that they weren’t on the equipment all day! Quality has been a bit of an issue. The original plan was to power float the surface overnight. We had the equipment and the manpower primed to pull an all nighter but Canary Wharf contractors (the main contractor and whose site it is) decided that we were not allowed to work past 2200. This has caused an issue as no floating was done and now the slab has cracks in the top. Initial assessment by the project engineer says its just cosmetic but its not how we wanted to go about doing the first major pour of the project! There seems to be a lot of friction and hot air thrown about between the contractors as to how best to do the job.
Your solution to the stock steel solution would work (and is actually how I intend to go about doing it) however to order the rebar I need a bending schedule. The detailing company Expofor is currently running behind schedule and is not releasing the drawings and bending schedules fast enough. As a result I’m in a position where I can’t order steel for adjacent pours until the drawings are produced. Really rather frustrating as it just causes the job to be harder for the steel fixers.
Guz,
All drainage leads to sumps – there are 15 in the basement. most drainage is set on a fall of 1 in 60. As for the crane base, I’ll look into your query. The base is set into the large raft slab and I believe that this has been deemed sufficient to take the turning moment from the wind (there was an awful lot more steel put in around the crane base then the picture shows, as well as shear rails.). The crane will also be tied into each floor as the building grows around it.
As for the cats: cat number 1 is not happy at all about the addition of a new kitten….they currently have to kept in separate rooms. Nothing is ever easy!
Thanks Fred,
I wondered if there might have been an 0500 start to allow for over-run/ London traffic. I would ask what effect that would have had but the simple fact that it wasn’t float finished and cured correctly says it all!
Battersea have some very good advice online about introducing new cats to an existing family, as well as many other adoption issues. _ No you don’ get any additional leave to help with re-orientation of pets.
Fred
An excellent blog. I must really arrange to come and visit you soon. JIT is ok but it lacks flexibility. A typical HQ dept must add value and not add restrictions
All the best
Neil
Fred, to pick up on the just in time piece. While the construction manager can be difficult, they hold the key to getting the job done as I think you are finding (certainly that was my experience with laing O’Rourke). Therefore for the materials delivery issues I would recommend applying pressure the other way to get dates required by for the items needed. This means you have to be all over what might be needed but putting the ball in their court works well. With a rolling forecast 2 weeks out should help you plan/order and when something changes, as it will, despite continuing to demand for items immediately, there will be shared responsibility.
The other aspect with just in time is safety. At my site we reached a point of excess with trying to store way too much stuff: rebar to drainage parts to heave protection and so on. It got in the way of walkways and made it difficult to do anything. Therefore I would strongly agree that in constrained London sites excellent logistical planning is vital, although not easy.
To pick up on Guz’s point about crane ties, I assume the structure you are building is precast with an insitu stitch to join slabs (planks) to beams. Therefore how are the forces at the crane tie positions transferred through the stitch?
Fred, you say this pour is by no means your largest that will occur on site yet it incurred various problems due to the restrictions on site hours and the length of time required to complete the pours. Is it not therefore inevitable that similar problems will continue to occur with similar sized and larger pours? Could you not consider introducing pour breaks into the design to reduce the amount of concrete poured in one go to avoid such problems? This could have obvious implications on the programme but this vs rectifying defects might be a preferred solution. We have very strict conditions on site working hours (7am to 7pm) and the issue with working late is not necessarily the fines imposed but the frictions caused with the unions so its an absolute no go! We have had to incorporate pour breaks to ensure that we can achieve what we need to within the time frames we have available.
Another issue we have is not necessarily a JIT approach with the delivery of steel but a JIT approach with the design!!!! Left hand does not appear to talk to the right hand very well and although we have the designs for the pile caps, what we don’t have is the finalised reinforcement designs for the ground beams. There is an obvious link between the two in that we need to know the size and placement of the reinforcement in the ground beams in order to place the starter bars in the pile caps, which is preventing us from pouring. Another example of not identifying risk. It was assumed by the BMC team that the lower bars in the ground beams could be drill and epoxy – until they realised that the smallest bars are likely to be 24-32mm. Not a feasible option. It is 0930 hrs on Tuesday morning, they want to pour this afternoon and we are still waiting on the bar sizes. I’ll let you know whether it is achieve!
And yes, working in the rain…..the union reps would have a heart attack!! Skin must melt over here if it gets wet. It just doesn’t happen.
Damo, site congestion and safety is a bit of an issue here. We have vast amounts of stores arriving everyday with very little space to put them. The demolition contractor, McGees, are still working in our main area and have so far delayed their handover of the area by two weeks. Looking at the situation this week it is unlikely they will be able to handover the site until Friday at the earliest. This means that whilst in theory we have a large amount of space to put all these stores, in practice there is demolition plant in the way. We are fast reaching the point of excess!
Jo, it sounds like your site is taking the JIT approach to another level! There is a seven day lead time for ordering rebar to site here (is it similar in Aus?) so not having the right sizes on the day of the pour would definitely mean a delay and some very unhappy managers!
As for pour sizes this pour was done using only one concrete pump. for the other pours we will have a bit more real estate to work with so will be using two pumps for the larger pours (the largest one is about 450m^3).
Also, if we stopped for the rain we would never get anything done….you will be happy to know that England has been just as rainy as you would expect.
Needless to say we didn’t pour any concrete yesterday. Aiming for a pour this afternoon following certification from the engineer sign off. I think you have also literally quoted me word for word Fred – that was exactly my response when I was asked what we did in the UK when it rained!!
Ref the rebar lead time – we don’t actually order any ourselves. The whole project is done as a Design and Construct (or Build) so everything is ordered, delivered and handled by the subcontractor. If they haven’t got what they need – their problem – their fix, but the guys on site now have got additional rebar within 24 hours after they misread the engineers detailing and hadn’t scheduled the correct stuff.