The Variable Density TBM
Technological advances in mechanized tunnelling are constantly pushing back the limits of what is possible. Herrenknecht developed the Variable Density TBM to enable safe tunnelling in heterogeneous, variable and highly permeable soft geologies. The machine’s design has proven itself over the past ten years, successfully coping with highly complex project parameters – and several current projects are showing that it has even greater potential.
Metro Lyon
Mastering Extremes
A Herrenknecht Variable Density Tunnel Boring Machine (TBM), operated by experienced miners at Implenia France, excavated a metro tunnel through some extremely challenging geology in Lyon. There was no need for the costly and time-consuming process of stabilizing the ground – heterogeneous, highly permeable ground, with a layer of granite in the alignment − before work could begin. A superior technology for mechanized tunnelling in highly complex heterogeneous geology.
Spotlights
Jobsite
Experiences
Variable Density TBM technology offers a number of advantages. Depending on the circumstances in each specific project, the technology can help to protect the environment, reduce the overall budget or enhance the jobsite logistics.
groundwater protection
High Speed 2, London
MACHINEDATA
- January 2022: 6 Herrenknecht tunnel boring machines (4 x Variable Density TBMs, 2 x EPB Shields) for 56.5 km of tunnel
- Section C1 Chiltern
- Contractor: Align JV (Bouygues Travaux Publics, Sir Robert McAlpine, VolkerFitzpatrick)
- 2 x Variable Density TBMs (Ø 10,240 mm) each driving 16 kilometers of tunnel
- In contrast to EPB Shields, with Variable Density TBMs there is no need to use conditioning materials to enhance conveyance of the excavated material and counteract clogging. As a result, using Variable Density TBMs significantly reduces the risk of groundwater pollution in the vicinity of the tunnel.
PROJECTDATA
- Client: High Speed Two Ltd.
- Application: Rail
- High-speed rail link between the North of England and London
- A total of 100 kilometers of tunnel
recycling
High Speed 2, London
MACHINEDATA
- January 2022: 6 Herrenknecht tunnel boring machines (4 x Variable Density TBMs, 2 x EPB Shields) for 56.5 kilometers of tunnel
- Section N1 Long Itchington Wood Green Tunnel
- Contractor: Balfour Beatty VINCI Joint Venture
- 2 x Variable Density TBMs (Ø 9,920 mm and 8,560 mm) for a total of 8.76 kilometers of tunnel
- Using a separation plant generates not only reusable slurry but also material with a low water content which can therefore be transported cost-effectively and subsequently repurposed.
See for further information Herrenknecht separation technology
PROJECTDATA
- Client: High Speed Two Ltd.
- Application: Rail
- High-speed rail link between the North of England and London
- A total of 100 kilometers of tunnel
Optimal logistics
Grand Paris Express
MACHINEDATA
- January 2022: 21 Herrenknecht tunnel boring machines (17 x EPB Shields, 4 x Variable Density TBMs) for a total of around 96 kilometers of tunnel
- Line 15 South Lot T2A Villejuif Louis Aragon – Crétail L’Echat
- Contractor: Horizon Joint Venture (Bouygues Travaux Publics, Soletanche Bachy France, Soletanche Bachy Tunnels and Bessac)
- 3 x Variable Density TBMs (Ø 9,830 mm and 7,710 mm)
- First Variable Density TBMs in Europe
- Two of the three machines start from a common shaft in the direct vicinity of the River Seine where, given the restricted volume of downtown space, a single high-performance separation plant processes the slurry from both TBMs. The efficient separation process reduces the water content of the excavated material for disposal, helping to cut the cost of transportation by barge along the Seine.
See for further information Herrenknecht separation technology
PROJECTDATA
- Client: Société du Grand Paris
- Application: Metro
- 200 kilometers of track, around 90% underground
- Four new fully automated metro lines with 68 stations
- Efficient links between the municipalities surrounding the city
“It is now common knowledge that Variable Density TBMs make it possible to tunnel through many different types of ground. However, they also allow you to process the excavated material in the separation plant so that some of it can be reused. As awareness of the need to reduce our impact on the planet grows, this will soon be a key factor in people’s choice of TBM type.”
François Renault,
Tunnel Technical Director, Vinci Construction Grand Projets, Hampton Roads Bridge
Tunnel Expansion
“The major geological challenge the project posed was the need to avoid settlement. The final
Denis Vialle,
outcome was very good indeed.”
Technical Director, Implenia France, Lyon Metro Line B
Spotlights
New terrain of feasibility
New Developments
Variable Density TBMs have successfully overcome extremely challenging project conditions at around 15 jobsites. Herrenknecht engineers are constantly optimizing the machine design in close cooperation with the Group’s customers. Together, machines and miners are progressively pushing the envelope so that new subterranean lifelines can be opened up for freight and passenger transportation.
Spotlights
New terrain of feasibility
Hampton Roads Bridge Tunnel Expansion
- USA, Norfolk (VA)
- Client: Virginia Department of Transportation
- Application: Road, 2 x 2,440 m
- Contractors: Hampton Roads Connector Partners Joint Venture (Dragados USA, Vinci Construction Grands Projets, Flatiron Constructors and Dodin Campenon Bernard)
- The largest ever Variable Density TBM: Ø 13,990 mm
- The first Variable Density TBM with an accessible cutting wheel for safe tool changes under atmospheric pressure conditions
- Shorter, more compact screw conveyor mean less material stress and wear and reduced engineering complexity in the back-up area
- François Renault, Tunnel Technical Director, Vinci Construction Grand Projets: “It is now common knowledge that Variable Density TBMs make it possible to tunnel through many different types of ground. However, they also allow you to process the excavated material in the separation plant so that some of it can be reused. As awareness of the need to reduce our impact on the planet grows, this will soon be a key factor in people’s choice of TBM type.”
Spotlights
New terrain of feasibility
Grand Paris Express
- France, Paris
- Client: Société du Grand Paris
- Application: Metro
- 200 kilometers of track, around 90% underground
- Four new, fully automated metro lines with 68 stations
- Efficient links between the municipalities surrounding the city
- January 2022: 21 Herrenknecht tunnel boring machines (17 x EPB Shields, 4 x Variable Density TBMs) for a total of around 96 kilometers of tunnel
- Line 18 Aéroport d’Orly – Versailles-Chantiers Orly Airport-Versailles Lot 1
- Contractors: Vinci/Spie Batignolles Joint Venture
- 1 x Variable Density TBM (Ø 9,130 mm)
- 2 km tunnelling in Variable Density mode for maximum settlement safety with very fine-grained sand below the groundwater level in the densely populated downtown area
- 4 km tunnelling in cost-effective EPB mode
- Easy conversion from Variable Density to EPB mode
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