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Graham Construction are currently undertaking the design and construction of a renewable fuels terminal for Associated British Ports’ (ABP) in sunny Immingham. The port facility will give ABP the capability to import, store and onward transfer wood pellets primarily to the Selby based Drax power station , as they transform 3 of their 6 coal-fired power generating units to biomass fuelled units.
Once completed, the 11.5-acre facility will be a fully automated bulk-handling terminal that will handle biomass for the region’s power generating industry. The terminal will have the capability of handling around three million tonnes each year, and be able to store up to 100,000 tonnes of wood pellets. Four storage silos will have a total capacity of 168,000m3; equivalent to over 60 Olympic-sized swimming pools. The design and construction project comprises:
• Provision of continuous ship unloaders for offloading the wood pellets from ships
• Conveyor systems – circa 1.2km of conveyors
• Storage facilities – capable of storing 100,000 tonnes of wood pellets
• Road vehicle loading facility
• Rail load-out facility
• Extensive safety systems required to ensure safe handling of wood pellets
The Graham team includes Ramboll, local consultant HBPW Consulting; materials handling contractors Whitwick Engineering; and local electrical firm Lectec Services.
In essence the wood pellets are taken from the ships and placed onto a conveyor system that fills the large silos from the top for storage. When needed they are vibrated through a central hopper onto another conveyor system running underneath the silos in a tunnel to the lorry or rail load out point as required.
The four main silo walls had been completed prior to my arrival with the Graham team working 24hr shifts from 07 Nov – 11 Dec 13, fixing 2400tonnes of rebar into place and pouring 10800m3of concrete during the slipform process. The 56m high, 36.5m diameter silos were poured utilising 2 sets of slipform equipment to maintain the construction speed of around 3m per 12 hour period.
This week has seen the silo section completing an as built survey at the top to ascertain the position of the bolts for the fabrication of the steel roof trusses and conveyor systems that will be craned into place in the spring. The floors of the silos are currently being graded to a slope of 10degrees towards the central hopper that drops the pellets down onto the conveyor system in the central tunnel running underneath the length of the silos. These floors will then have a 300mm slab cast on top and vibrating panels constructed to move the pellets.
The foundations and slabs are already in place for much of the conveyor system from the silos to the rail load out point and the steel superstructure is being erected.
In addition the smaller load out silo over the rail head itself has also been completed and it is being capped by a 37t steel cupola lifted by a 1000t crane this morning.
On arrival I was allocated to the silo section but after a quick rethink by the project manager I was reallocated to the section responsible for ‘everything else’, as that is where the majority of the work now sits. To that end I have been working with one of the site engineers on a number of tasks from setting out of various foundations, formwork and services to preparation of the previously mentioned steel cupola. After a couple of weeks to get my head around the site the Section Manager is going to put me in charge of a section, likely to be the piling and slab foundation construction for the conveyor system from the quayside to the large silos. Can’t wait.
One observation that I have made immediately is the lack of preparation that has occurred prior to the lifting of this steel cupola. The rail load out silo was completed some time ago (slip form video at the following link https://www.youtube.com/watch?v=0_EehR17JVg), with the initial bolt layout for the steel cupola being set into the structure along its 0.45m top ring. Once complete, the as-built survey was conducted and the steel designers noticed that the bolts were 120degrees out of position. The bolts were cut out where required and new ones drilled and grouted into position followed by another as-built survey. This data was sent to the fabricators who built the steel structure and assembled it on site. Once constructed, measurements were taken between the bolt holes in the column base plates of the cupola and checked with the bolts on the top of the silo and they still did not match. This was noticed some time ago but came to a head on Tuesday when the very expensive 1000t crane turned up to lift it into position. A significant amount of standing around and head scratching resulted in nothing being done. The high winds on Tue – Thu resulted in the crane being sat idle until a window presented itself to manage the lift (this morning). On the weds I went up with the Section Engineer to take some further measurements, to again confirm that the bolts would not line up with the column base plate holes, and when I was up there I was astonished to see that there were bolts everywhere. Not all of the previous bolts had been removed and as we moved around to take the measurements the Section Engineer had to continually check which bolts were the ones that were to be used. It was also quite clear that the scaffolding hand rail for the walkway on the inside on the silo was protruding past the silo edge and the cupola would not be able to drop down past it without catching.
In my mind the bad weather provided an ideal opportunity to prepare everything for the lift to be as smooth as possible in what would likely be a small lift window. This would also reduce the risk of a failed lift and potentially greater cost to Graham as the crane would have to be rehired for another day. I suggested simple things to the Section Engineer such as spraying the bolts that were to be used for easier identification on the lift day, measuring the scaffolding handrail and adjusting it as required and removing the unrequired bolts prior to the lift. As the new kid on the block, not responsible for anything to do with the lift, I did not push any of these points again…
The lift happened this morning . Problem No1. The cupola would not drop past the scaffolding handrail. Queue frantic stripping out of the scaffolding handrail. Problem No2. The plate holes would not position over the bolts due to the unrequired bolts. Queue frantic action with the grinder to remove unwanted bolts. Problem No3. Only 5 of the 22 column plates actually fitted over the bolts correctly. Queue frantic hole enlarging and plate cutting of the remaining plates. The lift was completed and it took 6 hours. A bit of simple foresight and preparation could have reduced the whole operation to at least half that time reducing the risk of a failed lift. The weather is now howling once again and it has been completed literally at the last safe moment. No cuff too tuff I suppose?
On reflection I’m not trying to pat myself on the back for making some very simple observations, that should have been made, but it has surprised me how little thought goes into the conduct of reasonably significant costly procedures. In defence of the operation the surveying on the top of the silos is very difficult at best. The working platforms are 50m up on the inside of the silos and the initial location positions are shot from the ground in almost continuously high winds, making setting out and surveying extremely difficult. In addition, apart from the obvious preparation issues that I have mentioned, I think the design is fundamentally flawed. The bolts along the top edge of the silo are fixed into position, meaning there is absolutely no play in the positioning of the cupola column plates that could have taken up the small surveying errors. I have asked on several occasions why the bolts are cast in situ like this and not placed into cones as every other column foundation on this site is, but have just been told ‘that was the design’. A cone would seem all the more pertinent as the designers forecast an element of outward deflection of the cupola during the lift meaning the column plates would naturally flex past the fixed bolts. There is ample space along the 0.45m rim for the cones but the same design has been used for the larger silos and I foresee the same problems come the time for their roof structures to be lifted into position.
That’s all I have for this week.
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