In the field of microtunneling Terratest is one of the European leaders, throughout our owned company Eurohinca, providing its own Tunnel Boring Machines and a wide experience in all kind of soil conditions and applications.
T.B.M. is the abbrevation of Tunnel Boring Machine and his definition is equipment capable of digging tunnels to complete section. To restrict a bit this definition we can be divided TBM in several classifications:
- Full face support TBM: TBM able to control the pressure in the front during the excavation. This type of machines can work under cities and cross road, railways, etc.
- Open shields: For stabilize grounds and without any civil construction in the surface.
Depending on the tunnel support
- Segment lining: Can be use in all type of ground and with all type of TBM.
- Metal roof truss: Used only in rock ground and with gripper TBM.
- Pipe jacking: For tunnels with diameter smaller than 3 m.
Depending on the extraction method
- EPB Shield: Extraction with endless screw conveyor.
- Hidroshield: Extraction with pumps.
- Rock TBM, double shield and open shields: Extraction with conveyor belt.
ADVANTAGES OF TRENCHLES TECHNOLOGY
- Less effect on existeng services.
- Lower environmental impact.
- Minimizes spoil and waste generated.
- Compact instalation.
- Increased security for workers. (Works inside a shield)
- Less risk of surface settlements. (Excavation Front is supported)
- Higher outputs. Minor delays.
- Reduced impact on ground water level.
- Server and water supply networks. Collectors.
- Crossings under existing services. (road, streets, railways, rivers, airport runways, golf courses, etc.)
- Sea outfalls. Water release or intake.
- Tunnels with tunnel boring machines.
- Underground corridors.
- Gas and oil pipelines. Drainage and evacuation systems.
- Pipe arching for road or railway crossings.
- Steel pressure pipes.
- Water intake and release for fish farm or desalination plants.
- Water waste pipe and intakes in reservoir dam.
CLOSED FACE TUNNEL BORING MACHINES
The EPB Shields (Earth Pressure Balance) are TBM machines that support the tunnel face with the pressure applied by the excavated soil located inside the excavation chamber; the controlled extraction of the soil from the excavation chamber by means of a variable speed auger allows the adjustment of the pressure applied to the tunnel face.
The excavated material is transported to the launching shaft by conveyor belts or muck wagons.
The EPB Shields were initially designed to bore soft, cohesive ground, (mainly clay), but with the use of foam and polymers it is possible to bore other type of soils as sand or even rock.
The TBM mix shield, or hydro shield, supports the tunnel face by the pressure of the bentonite suspensions injected in the excavating chamber and mixed with the excavated material.
This mixture is crushed in the excavation chamber and is evacuated by hydraulic pumps to the launch shaft where a separation plant separates the excavated material from the bentonite suspension.
The Hidro shield TBM can be used in almost all type of ground, and performs well in sand, rock, under ground water level (Sea outfalls) and it is specially indicated for small diameters.
OPEN FACE TUNNEL BORING MACHINES
OPEN SHIELDS – ROADHEADERS OR EXCAVATION
Open face shields allow a visual contact to tunnel face. The front is excavated by powerful roadheaders or excavators. The extraction of the excavated material is made by muck wagons pushed by locomotives or winches.
Ii is economic and optimal solution for non urban with cohesive soils and above ground water level.
A detailed and comprehensive geotechnical study (including ground investigation, ground water level, type of soil, resistance to simple compression, rock abrasivity, etc…) is the basis for the selection of the appropriate TBM equipment and excavation method.
With complete information it is possible to define the most suitable TBM, cutter head configuration and tools, characteristics of the lining, the alignment of the tunnel, and also, if necessary, preventive measures to be taken, monitoring systems, etc…
Precast concrete elements that are installed inside the tail skin shield of the TBM, building a complete ring that constitutes the final tunnel lining.
The thrust of the machine is made on the last ring installed: this allows to excavate great lengths and curved tunnels alignment.
Prefabricated pipes (concrete, steel, etc…) that form the lining of the tunnel and are installed and from the launch shaft pushing forward the TBM to the ending shaft.
To reduce the friction between the pipe and the ground during the jacking phase bentonite is injected in the overcut. Intermediate jacking staions are necessary for long dstances.