One of two Herrenknecht Mixshield slurry TBMs, called ‘Wiske’, recently completed a 6km drive under the River Scheldt (River Escaut in French), and a dock waterway, for the 16.2km freight rail link between the two banks of the river to the west of Antwerp. The second, parallel, bore of the Liefkenshoek Tunnel will be completed by TBM ‘Schanulleke’ at the end of July. The TBM will break into the Kruisweg reception shaft on the ‘Right Bank’. These bores will form Belgium’s longest rail tunnels to date.

The various portions of the project are:
• Surface railway between Left Bank Rail Cluster South to existing Beveren rail tunnel
• Renovation and adaption of the cut-and-cover, twin-track Beveren Tunnel to modern requirements under Waslaandkanal
• Access tunnel between Beveren Tunnel and the new Liefkenshoek bores
• The twin Liefkenshoek Tunnel bores under the River Scheldt and the Dock Channel B1-B2
• Cut and cover and open cut ramp on Right Bank Adaptation of existing tunnel under R2 highway

The work is being carried out by the Locobouw consortium is a PPP scheme for Infrabel, the Belgian national rail transport agency. Participants in the scheme are Vinci, CFE and Bam.

Work is carried out 24h a day, seven days a week, to comply with the planned schedule. Around 530 people work on the project including the surface rail-route preparation, cut and cover (4.27km long) and open cut access ramps, and modifications to the existing 1.2km-long Beveren Tunnel.

Some 300 of these are craftsmen and labourers, 80 supervisors, and 150 working for sub-contractors. There is also another short (75m) tunnel to be adapted under highway R2 enabling the new rail link to meet with the marshalling yard at Antwerpen-Noord.

The first Herrenknecht Mixshield to complete its drive (Wiske) was actually launched second, on 26 March 2010 from a shaft at Ploegweg.

The other, Schanulleke, was launched on 8 February 2010 and, as of 17 June, had just crossed under the dock channel, making good progress. Each TBM has a cutting diameter of 8.39m and cutterhead power of 1100kW.

The average TBM progress is about 15m a day, with simultaneous erection of precast concrete segmental lining in 1.8m wide rings totalling 6630 rings. Each ring consists of seven segments and a key. Delivery to the shaft site is by rail from a Max Bogl plant just across the German border. The rail route was specially extended for the project and has a planned capacity of 1200 segments per week.

The maximum daily TBM progress achieved was 45m on 19 April this year. Progress of the first TBM was deliberately slowed compared to the second, to enable preparatory works for the cross passages to be carried out.

Each TBM utilises a computerised, laser-based guidance system manufactured and installed by CAP of France.

The bentonite slurry pressure is monitored in real-time; a control facility that is particularly important under waterways.

The slurry density is controlled from the spoil separation and treatment plant designed and manufactured by MS of France to handle the very fine sand and silt, which can be troublesome. These are separated from the water medium with the aid of filter presses.

Ground conditions
The ground on the tunnel alignment comprises mainly waterlogged loose sand although clay may be encountered in the low part of the face in the middle section of the drives partially under the River Scheldt. These conditions present no problem for the Mixshield TBMs except for the passages under the Scheldt itself and the Kanaaldock (Dock Channel, see below). Fortunately the clay is excavated as lumps and does not become too sticky nor break down into the slurry medium.

Where intervention is required to change cutters and carry out other maintenance, previous experience has shown that these can be very difficult in the high groundwater pressures experienced in the region, even with the possibility of creating a face slurry-cake seal and using compressed air. Project director Alex Vandemeulebroecke explains that the maximum pressure expected on the TBM face is four bar, which is the maximum allowed under Belgian health and safety law so leaving no margin for error. Therefore it was decided to use planned ‘maintenance boxes’ in the tunnel drives consisting of cement/bentonite blocks constructed from the surface. It is then possible to carry out other maintenance work at atmospheric pressure.

Under waterways
Crucial phases of the project have been the TBMs crossings under the River Scheldt and also the channel to dock B1-B2 without any disruption to shipping. The cover under the Scheldt is only about 10m (40m below water level), and 30m below water level under the dock canal (see figure 2). It was decided to place a concrete mat on the bed of the Dock Canal for final cover of 3.5m including the mat. This will not only provide additional protection for the completed tunnels, but also help to prevent pressurised slurry blow-outs when the TBM passes below, with low cover, using the weight of the concrete and diverting the weakest path for pressure loss.

The TBM slurry density and pressures are carefully controlled to prevent such an occurrence. This is aided by a real-time pressure measuring system. In the soft ground and less cover below the waterways, however, these additional precautions were deemed necessary. Tidal effects also have to be taken into consideration as the variations can create up to 0.6 bar extra pressure on the TBM face at Spring high tides.

Dredging International, a CFE subsidiary, dredged silts from the canal between two previously installed walls of sheet piling. The contractor then placed 25000m3 of slow-setting mass concrete in the dock channel in May last year over a four-day continuous period.

This was accomplished using pontoon barges and divers in a tremieing operation away from the bank, and also using four truck-mounted concrete pumps from the bank being fed from four batching plants using 120 truck mixers. Some 240 people were involved in the operation including several divers.

In July, 17,000m3 more of concrete, but this time a rapid-setting mix with steel fibres, was poured in the same way to create two, 2m-thick concrete slabs on top. These act as a counterweight during TBM passage, as previously described, and also act as protection against impact by ship anchors. As can be seen on the section the TBMs bored through the placed mortar as well as the Tertiary sands.

Cross-passages and escape
The second drive allows for the construction of a number of ancillary works including evacuation shafts, cross passages between the bores, and a platform/walkway to facilitate maintenance and the passage of work trains. This ancillary excavation work includes shafts at every 600m for evacuation and 13 cross-passages spaced at every 300m along the tunnel. Each shaft, excavated within diaphragm walls, measures 21 x 6m in plan, and with depths ranging from 28 to 45m. In order to keep out groundwater when connecting with the tunnel bores seven of the shafts use cement bentonite slurry in diaphragm walls installed by Soletanche Bachy, and the other one has been excavated through frozen ground as linked with the cross passages.

Soletanche Bachy, together with Belgian subsidiary Fontec, was also sub-contracted for other retaining walls in cut and cover stretches. In total there are 145,000m2 of diaphragm walls and 95,000m2 of cement-bentonite cut-off walls. These range in depth from 15 to 40m and are generally constructed to penetrate the impermeable clay beneath the rail route. Three trench excavators have been used on a five-day week around the clock.

As has been the case with other crossings under the Scheldt, the soft, waterlogged ground makes the use of carefully controlled ground-freezing procedures necessary. All excavation and lining is carried out in frozen ground and then the ground-freeze connection is shut off for controlled defrosting.

Project director Alex Vandemeulebroecke of Locobouw reported to T&TI that, by 17 June, two of the 13 cross passages had reached this state of completion. Two more have been excavated with the cast concrete lining being installed.

In four more passage locations ground freezing has commenced. The installation of ground-freeze pipes is soon to commence in the remaining five cross-passage positions. Ground freezing employs a brine circuit with the refrigeration unit located in the start shaft or an evacuation shaft.

Operational safety
In addition to the cross-passages and shafts constructed for evacuation, the tunnel design includes a number of other safety features.

The concrete used in construction of the Liefkenshoek Tunnel and renovation of the Beveren Tunnel is fire-resistant by virtue of using a fire-resistant sprayed concrete mix including vermiculite expanding mineral to provide insulation to 380oC. The steel reinforcement bar starts to be heated at 250oC. The pre-cast concrete segments include polypropylene fibres to prevent spalling in a fire. In both cases the lining has been tested according to the RWS curve criteria without destroying the lining.

A fire detection system, to include CCTV imaging, will be installed, together with ventilation to remove any smoke and excess heat. There will also be an automatic ‘hot foam’ extinguishing system, used for the first time in a rail tunnel, and designed by a joint venture (Locofire) of the BAM group and a local specialist fire engineering company AquaSecurity. Similar systems have been used extensively in chemical industry infrastructure.

Stevens, a subsidiary of CFE, is installing electrical cabling.

The project pays careful attention to environmental protection. In tunneling terms this includes the MS slurry recycling plant for spoil separation from the bentonite slurry and controlling water discharge. Where the 6.5km of surface route is disturbing part of a wetlands nature reserve with protected species of frogs and birds, this is has been compensated by a new 54-hectare (133-acre) site at the The Groot Rietveld old farming area in Kallo. Sound absorbent screens have been erected at strategic locations.

As much as possible of the tunnel spoil, and other excavated material, will be used as trackbed fill, material to build noise barriers and dykes, or built into slopes near the track and planted with trees. Locobouw will be responsible for the upkeep of such environmental measures for two years.

All civil engineering works by THV Locobouw are due for completion mid-2013 following commencement in November 2008. The new rail link is scheduled for completion mid-2014, providing a large increase in rail freight capacity to serve the port of Antwerp in linking Waaslanhaven and Antwerpen-Noord direct. Trains will no longer have to make a detour around the junctions at the Kennedy rail tunnel and the rail axis Antwerpen-Berchem to Schijnpoort. It will also free up capacity for more passenger traffic on these routes. Infrabel would like to expand the share of rail traffic in the port to 15 per cent by 2020.

Loading pre-cast segments onto a purpose-designed Metalliance trackless ‘train’ at the start shaft Figure 1, a section along the 6km-long Liefkenshoek bored tunnels Figure 2, A map of the complete 16.2km Liefkenshoek rail route through Antwerp’s western docks Arrival of TBM ‘Bobette’ or ‘Wiske’ to complete the first bore of Liefkenshoek Excavating a cross-passage in frozen ground Installing cross-passage concrete reinforcement cage within a waterproofing membrane layer