For the last, five-year long phase of the tunnel works the AlpTransit client has decided to put everything into the hands of one consortium, in one huge package contract. It covers signalling, the 16kV train power and normal voltage equipment power supplies, track laying, communications and some other mechanical and electrical work.
“It is the biggest contract we have let at CHF 1.7bn (USD 1.7bn),” says Renzo Simoni, the chief executive officer for AlpTransit since 2007. Equally significant, it is the first essentially turnkey contract on the project, placing all the coordination and organisation of its various parts into the hands of the contractor. The TransTec Gotthard group that won the job against one other major bidder, comprises Alpiq InTec AG, Alcatel-Lucent Schweiz, Thales Rail Signalling Solutions, AlpineBau GmbH, and Balfour Beatty Rail GmbH.
“To manage and synchronise these different elements ourselves would have meant a massive gearing up of staff,” says Simoni. “We examined the risk very carefully and concluded this was the right solution.”
A major difference to the tunneling work, adds chief engineer, Heinz Ehrbar, is that there are not the same kind of unknowns as there are with ground formations. Instead the issue will be to keep up with the technology, which in computers, signalling and communications can change very fast. The final operator of the tunnel SBB Swiss Federal Railways, is keen to ensure it has the state-of-the-art when it starts trial runs in 2017.
Currently that means installing the latest ETCS 2 radio-controlled cab display signalling system with its electronic detectors and axle counters and a variety of radio and telephone systems including GSM-R and GSM-P, thousands of kilometres of cable and fibre optics, computers and the precision catenary wires needed for high speed running.
Transtec began its work with an extended preparation period to plan its methodology and integration. Complete semi-permanent bases have been set up some 5km outside the northern Erstfeld portal and in Biasca in the south, again about 5km from the Bodio portal. Computerised logistic controls are installed in workshops, aggregate and cement stores, and loading bays.
A complex sequence of overlapping operations must cascade through the tunnel, beginning with track laying and with cable installation, communications, overhead catenary work and other operations following on behind on the new track. Cross passages must be fitted out with equipment and pressure doors.
The Railtrack work illustrates the detailed and disciplined logistical organisation needed to do the work. Transtec has invested in a carefullydesigned set of specialised plant and mobile machinery, some completely new, and on a large scale.
Central is a complete concreting train of 24 wagons for pouring the base of the slab track, which is used throughout the tunnel, a total of 115km. Some 39km of ballasted track will be made outside the tunnel.
Aggregate wagons are linked along the train with a conveyor system that brings a carefully tailored mixture of sands, and sized stones, to a concrete batching plant wagon at the forward end of the train. Water wagons and cement wagons also feed their materials into the batcher under computer control using pumps or pneumatic lines. On the most forward wagon finally sits a Putzmeister pump for delivery.
If a batch of concrete is bad when tested, it can be diverted to a waste wagon to prevent disruption of the work. Another wagon has a spare power unit, to ensure work can continue at all times. Only tunnel collapse or other disaster would stop operations.
“We have to be able to work completely self-sufficiently at the end of the track for a 15 hour period,” says Thomas Silbermann, the site manager for the trackwork installation group, which is formed from Alpine and Balfour Beatty Rail within the main onsortium. He adds that follow-on catenary, signal and other crews from the other companies “would not thank us pushing them back to get out again, breaking their carefully programmed sequences.”
Only at night will the train emerge for maintenance and recharging in the depot. However individual tunnel workers from his team of 85 and his four supervisors will be able to move in and out past the other crews.
The concrete train is needed for a few days at the end of a long tightly timed cycle of works lasting 20 days. “In that time we do a section between 1,680m and 2,160m depending on conditions,” says Silbermann.
First day brings a wagon with steel rail sections to the finished track end. Rail lengths of 120m are pulled onto the tunnel floor by a rubber-tyred machine, the Sause, which runs back for more and then butt welds them with a unit on a hydraulic arm. The tracks are supported with temporary fixings and the train runs forwards for a repeat.
On the second day a specially designed wagon arrives with the small sleeper blocks that support the track one on each side. They are made by local firm Tribeton and are fitted with rubber anti-vibration slippers. A fitted crane can pick up 60 blocks at a time and drop them through a slot into the centre of the track.
“Fourteen wagons on the train have all the blocks we need and other materials like shuttering are carried on three more wagons in front,” says Silbermann.
Two machines now run in and distribute the blocks. The first lifts the rail to its working level, the second positions the blocks along the rail and then twists them into the correct positon for fixing in a 45 second automated sequence. The machine was developed especially for the project. “The blocks are then fixed to the rail, the only part we do by hand,” says Silbermann.
A third machine put the rails onto a support frame and positions them to a rough accuracy of 15mm. Adjustments then follow to increase the accuracy. Shuttering is now added for the premade drainage ducts. Crack inducers are installed to ensure even contraction joints in the final rail slab, and and their supports are greased to prevent sticking by the concrete, and protective covers put over the rails.
A third and final measuring stage with a laser surveying tool now performs a final alignment check on the inner edge of the tracks to produce the necessary 0.1mm accuracy. Specialist consultants Grunder from Switzerland and Intermetric from Germany do the measurements.
Three people, the track superintendent, the quality controller and the survey engineer now have to sign off the section against a 50 point checklist. “And then it is out of bounds,” says Silbermann.
This whole process has taken six days. Now the 480m long concrete train arrives for the next 10 days of work, though its 1,700t weight must remain on the previously completed rail section.
A small fleet of yet more specialist machines comes into play.
First is a rubber-tyred mobile concrete shuttle-skip which carries 5t loads from the pump to a set of other machines waiting at the end of the precious day’s casting. All run on the two walkways along the side to stay clear of the rails heading slowly towards the concrete train.
Here it offloads the concrete into a hopper on the placing machine which pours the concrete around the rails and their sleeper blocks. Three vibrator units work the two sides and the centre.
“The concrete is very controllable because it only flows when you put in energy,” explains Silbermann. “We did some expensive experiments for nearly a year to get that mix right.”
Behind the placer follows a machine like an ancient rowing galley, with a small set of platforms from each of which a skilled worker trowells a section of the concrete surface to smooth it. Behind that a chemical curing membrane is sprayed on, a particularly important finish in the Gotthard because of the rock temperatures. Ventilation systems create a continuous wind in the tunnels which would quickly dry an unprotected surface.
Curing demands another three days for the slab and its track to bear the loads for the next cycle to go ahead.
This sequencing will continue until the first section is finished, a 16km length of tunnel to Faido. The entire crew and its equipment then moves north to work on the finished sections at Amsteg and Estfeld, and then back and forth as and when the civils contractors hand over their finished lined tunnels.
Test runs begin in 2017.
The new Biasca worksite and depot for the railway installation. Picture Transtec The multi-wagon concreting train
