From placement of TBMs to the removal of muck generated by the excavators, lifting forms a vital part of any tunnelling project. "The importance of the lifting equipment cannot be underestimated," says Steve Chorley, field service Director at TBM manufacturer Robbins. "It is the key to a successful assembly, and failure to provide the right lifting equipment or correctly rated lifting equipment can often end in disastrous results," he says, adding that employing highly skilled personnel is just as important.
The most challenging components to lift are usually the shields themselves. "To reduce the assembly time contractors would prefer to leave as much equipment installed inside the shields. This can alter the centre of gravity making the lift more challenging," explains Chorley.
World’s largest
Perhaps the most challenging lift undertaken recently was the erection of the largest diameter TBM in action in the world, a 17.5m-diameter, 7,000t beast known as Bertha. The machine is currently boring the Alaskan Way Viaduct Replacement Scheme (SR99) in Seattle, replacing the original earthquake damaged structure. Manufactured in Japan by Hitachi Zosen, the machine was delivered to the contractor Seattle Tunnel Partners, a JV of Dragados USA and Tutor Perini, in April. "The target was to design and manufacture the TBM in as big blocks as physically possible to save disassembly time in factory and assembly time at the jobsite and to mitigate the lack of room besides the launch pit that did not allow us to stage a huge amount of small components on it," says Juan Luis Magro, construction and equipment manager for Dragados USA. This meant delivery of 41 components the heaviest of which weighed in at nearly 850t.
From the beginning this required some heavy duty lifting equipment. TBM manufacture was carried out at the Sakai Works in Osaka, Japan which is a former vessels factory, and had direct access to maritime transportation. "Our launch pit is adjacent to the water as well, right besides the Elliot Bay. Since we knew there are heavy lift shipping and loading means available in the market, we designed and set the construction of the launch pit accordingly," says Magro.
Therefore the assembly and disassembly in Japan was performed using ‘Mushashi’, a 3,700t floating crane owned by Fukada Salvage and Marine Works. The ‘Fairpartner’ vessel, a heavy-lift cargo type J1800, owned by Netherlands based Jumbo Maritime then shipped the TBM from Osaka to Seattle. This featured 2x900t floating crane to self-load TBM components from barges and offload without additional cranes at Port of Seattle. Local firm Barnhart Crane & Rigging then employed self-propelled module transporters known as Goldhofer trailers, to haul TBM components from the Fairpartner vessel to the staging area besides the launch pit approximately 500 yards (457m) away. These had to be carefully placed to ensure that they were sitting in correct sequence for lifting into the 80ft (24m) deep launch pit. Barnhart supplied a 1,200t Modular Lifting Tower for lifting the largest of the components and used a Demag 1800 crawler to erect the MLT gantry as well as to lower the smaller TBM components. "The 1,200t MLT gantry was set specifically for TBM assembly and was removed upon termination. Then a 63t gantry crane manufactured by Spain’s GH took over the top of the shaft, to lower segments down to launch pit," says Magro. These then also loaded the segments on to rubber tired vehicles supplied by Metalliance of France which moved the segments to the rear of the TBM known as the back-up where they were then offloaded and transported to the ring assembly area. Muck will be conveyed by means of a tunnel and overland conveyor belt system of 2,800t per hour capacity, supplied by Germany’s H+E Logistik. This material will then be placed on top of barges that will haul it to a nearby abandoned quarry in Port Ludlow, Washington.
Heavy duty
Given the scale of the job and the complexity of the lift it is not surprising that Magro lists the coordination as being the biggest challenge for the team. "The technical front was well covered by our very own team of engineers and those of our subcontractors and suppliers. However, getting every third party involved understanding the complexity of the operation and ultimately, being on the same page was the real deal of this amazing operation and in the end, it worked pretty well," says Magro.
As a result Magro says that the TBM hauling and assembly has been performed in record time, ahead of schedule without impacting any of the project neighbours. The final piece, the cutterhead, was lifted in on 31 May. For the lifting team the next major activity will be removal of the machine from the North Portal, which has limited dimensions of 70ft by 100ft (21.3m by 30.5m). Magro says the removal strategy is still under discussion. "It is still a work in progress, although the TBM was designed and built to be removed in blocks smaller than those of the assembly," he says. "Ultimately, a large crawler or hydraulic crane will be necessary on top of the extraction shaft to lift up the TBM pieces taken apart at the bottom and upended by means of a small gantry and/or sliding and tipping over system to be installed down there."
If the team do decide to use a crawler crane they will be in good company as large crawler cranes are a common site on tunnelling projects. In Germany in June a Liebherr LR1600/2 was used to lift the segments of a tunnel boring machines from the barge on which it arrived along the River Spree, into the 20m deep launch shaft where it was assembled. Supplied by Riga Mainz the machine when complete weighed in at 700t with the heaviest component 135t and is now being used to bore a new 2km connecting tunnel for Berlin’s underground system.
Crawlers too feature on London’s Crossrail project where contractor Dragados Sisk is responsible for construction of the eastern running tunnels on the huge GBP 14.8bn (USD 23bn) link. The scheme connects Abbeywood in the east with Heathrow airport in the west and involves 42km of underground tunnels along with extensive work to build new stations. Most of the Crossrail TBMs were driven into the bore from launch pits but as part of its contract Dragados Sisk had to launch two 6.2m diameter, 586t TBMs from the 40m deep Limmo Shaft. Lifting of both machines was achieved using a Liebherr LR11350 crawler supplied by Weldex Crane Hire. It was rigged in a week and configured on a 48m boom with a 42m derrick mast with 300t of counterweight. The first TBM named Elizabeth was lifted at a radius of 21m with an additional 350t of counterweight. The second machine (Victoria) was lifted at a 31m radius with an additional 600t of counterweight.
The contractor has also used gantry cranes extensively on its sections of the project and it sourced these from Spain’s GH. Three of these are at the Limmo Shaft, two of 32t capacity and one at 18t, two 32t gantries are used on other sites and a further four are being used at the precast concrete segment factory in Chatham. Two of these are 20t capacity and two are 10t. These segments are sailed from the Chatham site where a Liebherr LR 1140 lifts them onto one of four purpose built barges, these then sail to the Limmo Wharf dock where a gantry unloads them. For this section of the project muck removal is achieved using a vertical HAC (high angled conveyor) which uses two belts to squeeze the muck between them until it is lifted out onto waiting conveyors.
Another company supplying gantry cranes to Crossrail is UK overhead crane and hoist specialist Street Crane. It currently has 10 gantries in use on the scheme including a 40t Goliath crane which was used to build the new western ticket hall at Tottenham Court Road. This crane is a double girder box beam design with twin custom built TVX hoists, each capable of lifting 20t. The crane has a total height of lift of 37m with a maximum normal speed of 15m per minute and a minimum 1.5m per minute. Hoist speed can be boosted to 23m per minute for light loads of 2t or less. Large ground beams, 1.5m deep, were cast 31m apart on which the rails for the Goliath crane legs run. The crane spans the beams and has an additional 5.1m cantilever at one end so that spoil skips can be offloaded onto awaiting trucks that are outside the protected excavation area.
Sales director for Street Crane Chris Lindley-Smith says that there are a few important considerations to be taken into account when using gantry cranes for underground work. "You have to make sure that the hoist unit has true vertical lift. Lowering something down a vertical path, the hook path has to stay constant. With a lot of wire rope hoists you find that the hook moves laterally as it is raised and lowered so you have to use a specific design to make sure that the path stays central. You also have to make sure that the speeds are correct."
Size and stamina
The duty class of the crane is also important. "You have to make sure that the hoist is of the correct duty and the motor is of the correct duty. A crane being used 24 hours a day for lifting operations has to be a higher duty class than a maintenance crane in a turbine hall that is used twice a year, otherwise it will just wear out," he says.
For heavy lifting mobile cranes rope length and weight is a vital technical consideration. Gregg Melrose is founder of Sydney based Melrose Cranes and Rigging. He says that this is often overlooked. "A lot of people forget to consider how long the winch rope is. Sometimes you have to use a bigger crane than necessary because of the winch rope length. For example a contractor might decide that they can lift their load with a 300 tonner but that machine has 350m of rope on the drum and the lift needs 450m of rope, so you have to use a 400t machine. For deep shafts that rope length is the main consideration."
Melrose is currently sharpening his pencil to tender for lifting services on a major tunnelling project set to start in Sydney in 2014. The AUD 8.3bn (USD 7.65bn) North West Rail Link was awarded to the Theiss/John Holland/ Dragados joint venture in June and involves construction of 15km twin bore tunnels using double shield hard rock gripper TBMs starting construction at either end of the bore. "On a job like this you generally need something like a 450/500t mobile hydraulic to put the TBMs down the hole. Then you might use a 220t or 200t mobile to service the shaft afterwards with equipment and generators," says Melrose.
The firm has several large machines with such capacities including all terrains such as the Grove GMK7450, the Demag 500AT as well as a 600t Terex CC2800-1 crawler crane. At the same time Melrose anticipates that the job will need service support from smaller Franna Cranes, also known as pick and carry cranes. These 18t-25t machines were developed in Australia in 1980 and named after creator Francis and his daughter Anna, the company is now owned by Terex.
Tunnelling projects are nothing new for Melrose which recently worked with other Australian lift specialists Kennards Lift & Shift and A Noble and Sons to lift a TBM from underwater in Botany Bay. The 98t Herrenknecht machine had to be lifted at six points to ensure the integrity of the machine joints. "The engineer told us how many points he wanted it to be lifted along the length so we had to work out how to achieve equalisation at all of those points. There are a few ways to do that. Our friends at Kennards had the modular bar at the top with the right rating, and we had the small bars so a combination was put together using our experience," explains Melrose.
Back in the UK Ainscough Crane Hire special project manager Bob MacGrain also says that rope length is critical when lifting down into tunnels, and says that the self weight of this can be considerable. "Even if you have got enough rope then you need to take into account that if you are working close to the crane capacity the self weight of the rope can be considerable (up to 10t). As you start lowering the TBM you are paying out more and more rope which is hanging below the boom head which means that the safe load indicator adds it on to the load on the crane. If you are near the maximum lift capacity at the start of the lift you could find that part way down the hole the crane has reached its safe working limit from the added load of the rope as it pays out."
Contractors must also be careful with their hoist drum, and MacGrain says that in the past some lifts have struggled with the top layers of wire cutting into the spool. "When you are lifting a very heavy load the top layer of rope will be under a lot of tension. What can happen is that as you are lowering off, the top layer can cut down through the slack layers beneath. It is a well known issue in the wind industry where taking redundant turbines off high towers can cause exactly that problem. "I have known situations in the past where the hoist rope has cut in so badly that it will neither go out or in," he says. However he says that modern spooling systems do address this problem. "Ideally when you stow the rope back onto the drum you need enough weight to make it coil tightly which the self weight of the hook block should do for you, but if you are using a very light hook block because it is a relatively light lift, then the rope on the drum is not going to be tight."
And of course what goes in must come out again. Extraction of the machines, particularly in built up areas can be even more difficult than placing them in the first place. Rope length again can affect the choice of machine. "I am considering a situation at the moment where a 550t crane could remove a TBM but it only has a single hoist drum and it is very neat for available rope length, it would have to run all the rope off to reach the criteria that we need," says MacGrain.
"So I have stepped up to a 600t crane because it can run two hoist winches simultaneously to an equalised hook block so instead of having 10 falls of rope off of one hoist drum I am running five falls off two separate drums," he says. As each drum has 900m of rope, this solution becomes much more comfortable, however the downside is that the manufacturers say that for the equalised hook blocks the operator should be able to see them during lifting to ensure that the blocks don’t go out of synchronisation. This is not always easy in a deep shaft.
Technical considerations aside, contractors have a large range of lifting devices at their disposal from a mature industry well used to underground work. Many tunnelling projects manage to use everything from gantries and crawlers to mobiles, tower and barge cranes in some combination. Experts say that the determining factors in planning the lifting strategy are largely site specific with constraints on land, noise, ground conditions, access and the size and shape of components all influencing the final methodology.
Contractor perspective at Tottenham Court Road
Upgrading Tottenham Court Road station, part of the UK’s London Underground system, epitomises some of the biggest challenges that face both the lifting sector and the tunnelling industry. The site footprint is tiny given the scale of the work, cranes are shared by an array of construction teams working on what is effectively six projects in one location, tunnelling equipment and construction materials must be lifted into tight shafts or new station boxes held open with an array of props to limit ground movement creating unusual and limited spaces for lifting operations. Above ground the space for cranes is minimal, competition for lifting gear is fierce and the programme is tight.
At peak construction in August 2012 there were two tower cranes and five crawlers being used at the site supplied by the contractor along with the likes of hire companies Weldex, AGD, HTC Plant and Ainscough, and manufactured by Kobelco, IHI and Woolf. "We could have used a third tower crane," explains Colin Dunkerton, appointed manager for cranes, Taylor Woodrow BAM Nuttall. "But given the tight site and the load bearing capacity of the excavation support structures around the new ticket hall, we decided to stick with two."
The two tower cranes were chosen instead of crawlers for two key reasons – site space and the load bearing capacity of the access road. "One of the big issues was that we were doing top down construction (to build the new Crossrail ticket hall) and the loadings on that road are 72t, so anything of the capacity with the radius to work in the ticket hall we wouldn’t have had the capacity to get it over the building so that is why we opted for the tower cranes," says Dunkerton. The largest of these was a 320B Woolf (Germany’s Wolffkran) with luffing jib. Set up over a weekend the crane had a concrete slab foundation supported by four cored piles. "We would have needed a very big crawler to get the reach that we needed. The 320B was on a 50m radius with 6.6t capacity," says Buck. Given the site constraints and the scale of the work it is not surprising that the team cite the logistics as being one of the biggest challenges. "We had to have daily logistics meetings," says Dave Harper, tunnelling section manager for the Taylor Woodrow BAM Nuttall joint venture. "We had one area in front of the tower crane and every section that wanted to bring in materials or equipment landed there. If they wanted to park an arctic they had to book a time."
Added to the complexity was that many of the 100 truck movements to the site arrived at night to reduce congestion on what is one of the busiest cosmopolitan areas in the world – London’s Oxford Street. "Tunnelling was 24/7 so we had to keep Dave [Harper] going and at the same time resource the rest of the site," says Dunkerton. This meant providing steel reinforcement, concrete, temporary props, shuttering materials, to the underground construction teams while also ensuring that muck could be removed swiftly. "Analysing hook time and how to keep people productive when you are sharing the tower crane between a number of operations, had to be balanced with trucks coming in and out," says Dunkerton. Not easy.
Coupled with this the team also had some unique technical work to undertake which required some lateral thinking when it came to lifting solutions. One neat innovation was the use of a monorail hung from the excavated primary lining of the new Central Line Interchange tunnel. This was used to winch in new 8m long composite steel and concrete beams that would form the base of two new overbridges to carry passengers over the existing Central Line to a new additional staircase. But before undertaking this activity Dave Harper’s team had to reinforce the ground with a series of horizontal piles to support an existing brick sewer running above the Central Line. "Over a weekend we slid the beams in over the tunnel and then opened to traffic on the Monday morning. Two bridges had gone in over the westbound platform and none of the drivers could tell," says Harper.
With the tower cranes, three medium sized lattice boom crawlers and a 40t gantry crane also service the site. Unlike the tower cranes which were removed in February and June once the main station boxes had been created, the crawlers remain on site today servicing the ongoing connection tunnel works and fit out activities. A 120t IHI CCH1200 crane supplied by AGD Equipment sits in the centre of the site, a Weldex supplied Kobelco CKE 1100t sits to the north of the site and an 80t crawler manufactured by IHI and owned by BAM Nuttall Plant services the Crossrail escalator decline.
One of the most challenging aspects of the work was tunnelling of the new concourse tunnels that connect the new ticket hall to the existing Northern Line. The IHI 120t crawler was used to lift the 22t excavator machine into the box where the sidewall drift method of sprayed concrete lining is being used to construct the connecting tunnels, passageways and escape tunnels. "This was the first time sidewall drift had been used in London since the [1994] Heathrow Tunnel collapse," says Harper. As a result the team was conservative in its progress, advancing just 1m at a time and spraying a fibre reinforced concrete lining varying between 350 and 600mm
