I was lucky enough to get a tour of the Phase 1 Quay works at the London Gateway Port project last week. The works are progressing at an impressive rate and work is about to start on installing the enormous tie bars. Read on to learn more about what they are doing, some of the innovations they are adopting and to see a selection of photos.
The London Gateway Port is an epic project and you can read more about it on previous blogs. In July of this year I organised a visit for ICE members and guests and on that visit we were able to see the diaphragm wall installation that had recently started at the east end of the project. You can read about that visit here.
On this occasion I had been invited for a look around by Laing O’Rourke (LOR) graduate engineer Matthew Fitch. I had been in touch with Matt as he and two of his fellow engineers – Orestes Adamou and Edward Labinksi – were keen to get signed up as ICE schools ambassadors. As it happened, Peter Sutton of ExploreSTEM was there when I arrived to do the paperwork and training for the three of them.
With formalities dealt with we headed out in one of LOR’s site 4×4’s with all three guys aboard. We toured the work from the east to west. On arrival Orestes and I jumped out whilst Matt and Edward were called away to do some work. Orestes and I walked along the works and Orestes very ably talked me through what was going on.
At the far east end of the quay the capping beams to both the quayside wall and anchor wall were complete (excepting the final part which is to be done after the crane rails are in place) and excavation was underway for the installation of the not inconsiderable number of tie bars. Excavation was not down to full depth as dewatering is required for the final 1.5m or so – and that was only just being installed.
The ground outside of the quayside wall was also being excavated – Orestes explained – to avoid differential loading on the quayside wall before the tie bars were installed. Orestes also noted how the position of the capping beam on the quayside wall has been set to take into account both temporary and permanent movements of the wall so that in the final permanent works case the distance between the capping beams and hence crane rails is correct.
We walked on and came to an area where the first few tie bars are being assembled on specially designed supports. Each tie bar is some 33m long and they vary from 117mm to 130mm in diameter. The east end of the quay is where the enormous quayside cranes will be offloaded from ship to shore and hence where the larger diameter tie bars and beefed up capping beams are located.
The tie bars – weighing in at a total of over 3.5 tons each – are supplied in 3 sections and are connected with substantial turnbuckles. At each end the tie bars have forged cup ends which allow rotational movement when connected to special fixings which themselves are connected to cast in anchors in the diaphragm walls (see photo).
Orestes and I continued walking west and saw the various stages of the capping beam construction. First was the breaking down of the diaphragm walls to the design cut-off level. This was being carried out using remote control mini excavators fitted with hydraulic breakers. The use of remote control machines means the operatives can stand well back and hence reduce the impact of noise and eliminate vibration. Excellent use of new technology.
Before the breakers set to work however the top section of the diaphragm walls are being mechanically split just above the cut-off level. Plastic sleeves were included in the wall panel reinforcement cages that provide holes through the wall panels just above cut-off level. Hydraulic expanding jacks are then used to fracture the concrete to release the top section from the main wall. This makes subsequent breaking out easier and eliminates the risk of damage to the remaining sections of diaphragm wall.
Orestes showed me the reinforcement being fixed for the quayside wall capping beam (see photo). The capping beam – some 2.0m deep and 4.0m wide (some capping beam) – has reinforcement fixed either side of the diaphragm wall panels as discrete beams with top and bottom connecting reinforcement bars threaded through later. Orestes explained that this was the most effective way of detailing the reinforcement as trying to lay out bars through the diaphragm wall starter bars – 50mm and 60mm diameter and not always equally spaced after breaking out of the concrete – would be virtually impossible.
Walking back eastwards a little way on the river side of the wall we saw a section of the quayside capping beam that had been concreted and the formwork stripped (see photo). The deepened sections where the fender panels will eventually go could be seen along with all the cast in anchors for the fender and ancillary fixings needed. The size of the capping beam could really be appreciated from this viewpoint.
We continued our walk westward passing by the now abandoned bentonite lagoons used for the first half of the diaphragm wall works and pausing to look at one of the anchor wall rebar cages. Orestes explained the welded on hairpin bars that are used during the lifting and installation of the reinforcement cages.
We then crossed the works and headed inland and up onto the surcharge fill that covers a vast area of the site. Looking west we could see the diaphragm wall operations continuing on the western half of the works. They are now working 24hrs a day which I guess is to keep ahead of the follow-on works. At their peak, they are achieving 17 panels a week with three rigs which at up to 400m3 per panel is astonishing.
We were then rejoined by Matt and Edward and continued our tour in the 4×4 which was nice. We drove awhile on the surcharge and Edward explained what we were seeing and the different areas. He explained that the surcharge at the far eastern end of the site will soon be able to be removed to allow drainage, ducting and eventually paving works to take place. Edward also explained the criteria for when the surcharge can be removed based on the actual settlement and the contractual settlement requirements over the next 2, 5 and 20 years. Very interesting.
We stopped alongside an area where a trial was being carried out in preparation for the later duct and drawpit installation. Matt explained how – to avoid the duct groups floating in the sand fill when it is subsequently compacted around / over them – they are trialling using single length ducts and filling them effectively with a very weak cement grout before backfilling. A material which can be subsequently removed afterward. Sounds a very interesting technique.
The tour ended with a walk up onto an even higher area of surcharge which allowed a great panoramic view of the site. Edward explained that the increased surcharge was because of some failures in the wick drains installed due to the nature of the underlying ground. Increased surcharge allows the settlement to occur quicker and hence to keep up with that occurring in neighbouring areas.
All in all the tour of the site took around 90 mins and a very enjoyable time it was too. I was genuinely impressed with what was being achieved on the project and the knowledge and professionalism shown by the three young graduates who showed me around. Many thanks to Laing O’Rourke and particularly to Matt, Orestes and Edward.
A selection of photos included below demonstrate the works in progress. Clicking each image will open a larger image in a new window.
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