Turning tides18 April 2019
The Thames Tideway project in London replaces a Victorian sewerage system that was a wonder in its day. Julian Champkin looks at the many lifting tasks and problems of such a huge infrastructure project.
In the summer of 1858 Parliament all but shut down because of the stench from the river Thames flowing by it. The event was known as the Great Stink; the river was quite simply an open sewer.
Four years earlier cholera had killed 600 people in London. Physician John Snow used brilliant medical detective work to show that the source of it was raw sewage leaking into a drinking water pump at the corner of Broad Street in Soho. As legend has it, in the face of official obfuscation and disbelief Snow ended the epidemic by removing the handle of the pump so that no-one could use it. He earned a place in medical history and the gratitude of citizens, the latter expressed in a way that perhaps meant most to them: the pub on the corner of Broad Street is today named after him.
These events prompted one of the greatest civil engineering projects of Victorian Britain: Joseph Bazalgette’s sewerage system. He designed and built 1,100 miles of cast-iron street sewers, disgorging into 82 miles of brick-built main sewer that ran beside the Thames to the Essex marshes, far downriver from the city. Bazalgette used hand labour, 318 million bricks, 2.7 million cubic metres of excavated earth and 670,000 cubic metres of his own specification of Portland cement and created, as an incidental by-product, London’s Embankment. Until then it had been a muddy stretch of tidal foreshore. The iconic stretch of riverside road past Big Ben and Parliament is, in reality, simply the top surface of the sewers that he built—with an underground railway, today’s Circle Line, added in there for good measure. Steam pumping stations along the way were a marvel of Victorian ironwork and engineering.
In the process Bazalgette banished cholera. A later historian wrote that no other Victorian official had done so much good or saved so many lives. He also built his tunnels at twice the diameter of even the largest estimates of need, using the simple rule of thumb that the city was bound to grow, and that no future engineer would ever again get the chance to disrupt central London on such a large scale.
Thanks to that foresight his works have served astonishingly well until now. The city has indeed grown. Tower blocks have increased urban densities beyond what even he envisaged; and now, a century and a half later, London is in need of a replacement.
A newer sewer
The Thames Tideway scheme is exactly that. A 25km underground tunnel, the socalled ‘super-sewer’, will be 7.2m in diameter and up to 66m deep; the cost is an estimated £4.2bn. Bazalgette-scale disruption is being avoided by using only seven access points, vertical shafts at different points along the river, down which all the tunnelling equipment is lowered and up which all the excavated spoil is raised.
It is as big and as complex an infrastructure project as you will find in the country. As such, it needs a multitude of lifting apparatus, from small hoists with tunnels to the largest machines that can handle lifts of hundreds of tonnes. They have been supplied by a multitude of contractors, subcontractors and crane hire specialists.
“We installed a GH overhead gantry crane at Tideway’s Kirtling street site, by Battersea Power station” says Simon Pickersgill of PLS (Professional Lifting Services). “There are two 55t gantry cranes on steelwork, moving up and down to take spoil from the shaft. When we installed them they were still finishing the acoustic shed, which they build at the top of each of the shafts to reduce noise.” Outside the sheds, work is permitted only between 08:00 and 18:00 to reduce disturbance to residents. Inside, tunnelling and lifting can carry on continuously. “We had noise restrictions ourselves on site; we had to get licenses to operate and so on.
“It was quite a complex operation really. We had a 500t mobile crane on site to lift the gantry crane. We had planned on using a 300t crane at shorter radius; but in the event the site we were allocated for it was a bit further from the shaft, so we needed to work at a greater and so bring in the larger crane. On these kinds of site you have to be prepared for changes halfway through like that.
“Another change was timetable slip. We had planned to do it in July, which would have been perfect. By the time they were ready for us it was the back end of the year so we were facing the elements. The installation itself was straightforward; it was the surroundings, in the middle of the city, that made the lifts complex. I am not sure that the planners quite appreciated the size of the mobile crane we would be using, and how we would have to manoeuvre it through the heart of London.”
The project is divided into three sections, Tideways West, Central and East. “We sold a Sennebogen 613 telescopic crane on crawler tracks, with 15t capacity, to Tideway East,” says Jon Phipps of AGD. “They are using it on general lift duties. They have ordered a second one as well from us, so they must be happy with it. We have rented a 40t Sennebogen 643 to Tideway West; they have lowered it, by gantry crane, to the bottom of their shaft, where it is happily working away underground, so that says something about the scale of the operation. The tunnel is 8m in diameter: there is plenty of room for it to go down the tunnel if it is needed.”
London is a crowded congested city with narrow access roads and little or no spare space, especially towards its centre. It does, however, have a wide river running through the middle of it—and a river which, happily, is the route of the Tideway scheme. Transporting big lifting gear to sites by water is an obvious solution that has been made full use of.
The largest prices of kit are the tunnel boring machines. There are six of them. Each is the diameter of the tunnel it is to bore and around 100m long. ALE moved two of them, weighing 821t and 832t when assembled.
ALE began by constructing two cradles for the TBMs in Tideway’s central riverside lay-down area. In January 2018 the second phase began with the delivery of components from barges to the site. There were 72 components in all, weighing between 9t and 119t. A specially-designed sheerleg system unloaded the heaviest items, and a crawler crane lifted the lighter ones. “By designing the sheerleg to specifically fit within the capacity of the jetty, we could provide the most cost-effective solution,” says Chris Horan, ALE’s project manager. “The bespoke equipment we designed allowed us to complete the first two phases swiftly and safely.”
The components were transported to the lay-down area using an eight-axle-line arrangement of self-propelled modular transporters (SPMTs). Once there, the components were assembled onto the cradles by the client; ALE then began phase 2 of their project: to move the machines to the 65m-deep shaft and lower them down it.
For this phase, ALE used 42 axle lines of SPMT to lift the first TBM within its cradle and transport it to the acoustic shed building that covered the opening of the vertical shaft.
Inside the building, ALE constructed a specially-designed strand jack lifting gantry on skid tracks, adjacent to the shaft.
Both space and headroom were limited so ALE needed to devise an innovative way of lifting the TBMs without using cranes. ALE used its Lift ‘n’ Lock system to raise the gantry, then slid the TBM beneath it and lowered the gantry around it.
Next, the gantry lifted the TBM from the SPMTs and skidded it over the shaft. Strand jacks lowered it down the shaft. The jacks had greater capacity than the crane and were much lighter.
Darren Porter watched it happen. “Getting that huge machine down the shaft, with minimal clearance, was a great piece of engineering,” he said.
He is Morgan Sindall’s appointed person for lifting; as such, he is responsible for all their lifting projects on the western section of the project. “We have cranes from 5t tiddlers to 1,500t giants doing various jobs. The TBM itself has vacuum lifters and mechanical hoists attached to it, to add to the variety.
“Half the problems are trying to get the concrete segments that line the tunnels up the river and to the site,” he says. Almost uniquely for a capital city’s river the Thames is still tidal where it flows through London, and this adds to the complexities. “The segments arrive by barge. We can work at any stage of the tide, but the barges cannot; so they arrive according to the tide and tie up by the side of the river. We have a Liebherr LHM 280 mobile harbour crane to unload them.
I spent a week at Liebherr’s Germany factory learning about it. It is sited 16m from the river wharf, and has 84t capacity at 10m, 22.5t at 40m. The cab is 21m up on the crane, and that gives a view over the riverside wall into the barges, which is one reason we chose it.
We have a mechanical hook on it that can rotate by 360°; that saves having a man on the barge to put his hand on the load. An automated bridle grabs four segments at a time and lifts them to dry land outside the acoustic shed. A 25t Konecranes gantry crane moves them into the shed; then a 40t gantry crane lowers them down the shaft. So essentially they are handed from one crane to another: it is crane-to-crane linear transport.
“There will be 4,068 tunnel lining rings in our Western section, each of eight segments, each segment weighing 4.3t; so that makes 32,000 segments to be lifted. The reverse part of sending all those segments down the shaft is bringing all the excavated spoil up it. It comes up on a conveyor below; we have a clam-shell bucket for the gantry crane in case the conveyor should break down. The LHM 280 also has a grab for getting the muck onto barges; they take it downriver to Rainham in Essex where it is being used to create a nature reserve. That river transport is keeping 5,500 lorries off the roads. Every kind of crane is on this job.”
Luke Shaw has been operating a Leibherr lattice crawler with a 50m jib unloading concrete tunnel lining rings at Kirtling Street since November 2018. He is expecting to be on the job for two years more. His Liebherr came up-river on a barge, from Tilbury, and tracked itself onto the pontoon barge where it now works.
Each ring on his section weighs 40t and arrives in two halves of 18 and 22t. “We have a special hydraulic clamp for lifting them. It is harder when there is no tide,” he says. “At slack water the barge we are on and the barge we are unloading from tend to go round in circles. Every lift is the same but different. You pick up a load and put it 20m away, something moves and when you come back it is 21m away.
“The lining rings are fragile, so you try not to damage them. There are 30 complete rings per barge and we unload a barge a day, which makes 60 lifts a day.
“They are bigger than any tube train or metro tunnel. Our operating space is not too constricted, but we cannot slew all the way round because there are houseboats in the way. Last week we shifted the tractor through 180° to even out wear on the slew ring; otherwise by the end the project it would be heavily worn on one side and unused on the other.
“I unload them onto Morello motorised trolleys which take them into the shed or the yard. There is space for up to 100 rings, that is three bargeloads, in the yard and a few more in the shed, and we have cradles on our pontoon to unload them onto as well.
“Before moving to Kirtling Street site I worked on the Embankment helping build a coffer dam for the project. That was operating a 100t Liebherr LTR 1100 telecrawler, moving the smaller bits and pieces; two other Liebherrs, a 160t from Select and a 250t from Weldex, drove the sheet piling.”
As with Darren Porter, he is experiencing the complexities of such a huge project: “Everything is interconnected. Today the barge at the loading crane at Rochester broke down; that will knock us back until Friday.” Still, there are compensations: “I will remember this project. It is nice to be on one of the big things and to be able to say ‘I built that!’”