Nature of Business
Total Number of Employees
51 to 100 People
Year of Establishment
Legal Status of Firm
Private Limited Company
Double Shield TBMs in operation
Double Shield TBMs are among the most technically sophisticated tunnel boring machines. They unify the functional principles of Gripper and Single Shield TBMs in one machine. Under stable geological conditions, the combination of methods allows for the installation of concrete segments parallel to tunnelling, achieving very high tunnelling performances. This powerful technology is therefore perfectly suited for excavating long tunnels in hard rock.
Advancing with power
When tunnelling with a Double Shield TBM, a rotating cutterhead equipped with disc cutters is pressed against the tunnel face with a pressure of up to 32 tonnes per disc. Due to the rolling movement of the discs, single pieces – so-called chips – are broken out of the rock. Water jets can cool the cutting tools and reduce dust formation. Buckets installed at the cutterhead take up the excavated material. Due to gravity, it slides to the center of the machine through integrated muck chutes while the cutterhead rotates and then falls through the funnel-shaped muck ring onto the machine belt. At the end of the machine belt, the rock chips are passed on to belt conveyors or transport vehicles and removed from the tunnel.
High speed due to a continuous tunnelling mode
Double Shield TBMs consist of two main components: a front shield with cutterhead, main bearing and drive, and a gripper shield with gripping unit, auxiliary thrust cylinders and tailskin. The main thrust cylinders connect the two parts of the shield. They are protected by the telescopic shield where the shield skins of the front and gripper shield overlap. Thus, Double Shield TBMs are also called telescopic shields. In stable rock, the machine is braced radially against the tunnel with the gripper shoes. This means that the front shield can be advanced independently of the gripper shield using the main thrust cylinders.
The reaction forces during the excavation process are transferred into the rock by the extended gripper shoes. Simultaneously to tunnelling, the segments are installed in the tailskin section. The auxiliary thrust cylinders serve only to secure the position of the concrete segments placed. When the stroke is completed, the gripper shoes are loosened and the gripper shield is pushed behind the front shield using the auxiliary thrust cylinders. Regripping lasts only a few minutes, which means that tunnelling is almost continuous. In ideal rock formations, Double Shield TBMs can also operate without segmental lining.
Multi-mode TBMs in operation
Classic tunnelling shields can reach their technical or economic limits with their specific method when they have to drive through highly variable geologies. Along one tunnel alignment to be excavated, the variable ground can change from stable rock to soft water-bearing ground and vice versa, for example, on longer sections. Such alignments pose the most demanding challenges in tunnel construction. Herrenknecht has developed Multi-mode TBMs for cases like this, ensuring optimum safety and flexibility during the entire tunnelling process. These machines are flexibly designed in terms of support and excavation methods. The tunnelling mode can be adapted to changing ground, requiring relatively short conversion times and incurring only low costs. This means that even tunnels with extremely varying geological and hydrogeological conditions can be constructed safely and cost-effectively using the innovative Multi-mode TBM made by Herrenknecht.
Geology Heterogeneous groundVariable grounds along one tunnel alignment
Gripper TBMs in operation
Herrenknecht Gripper TBMs have proven to be efficient solutions for fast mechanized tunnelling in hard rock on many occasions. Due to the process-typical rock support method without segments, medium to high rock strengths are a requirement for high advance rates. In more fractured geological formations, various systems for immediate rock support behind the cutterhead are installed at the TBM directly.
Uncompromising in hard rock
When tunnelling with a Gripper TBM, a rotating cutterhead equipped with disc cutters is pressed against the tunnel face with a pressure of up to 32 tonnes per disc. Due to the rolling movement of the cutter, single pieces – so- called chips – are broken out of the rock. Water jets can cool the cutting tools and reduce dust formation. Buckets installed at the cutterhead take up the excavated material, which slides to the center of the machine via integrated muck chutes while the cutterhead rotates, and then falls through the funnel-shaped muck ring onto the machine belt. From there, the rock chips are passed on via further belt conveyors or transport vehicles and removed from the tunnel.
Braced directly in the rock
Before each stroke, the Gripper TBM is braced against the previously excavated tunnel using laterally extendible hydraulic cylinders. The laterally mounted gripper plates or gripper shoes are the core element of this machine type, hence the name of the machine. Subsequently, the thrust cylinders are braced against the gripper unit and push the rotating cutterhead against the tunnel face. Several telescopic partial shields stabilize the machine against vibrations during the boring process, thus reducing wear and tear. The invert shield also serves as a sliding shoe for the TBM. Lateral partial shields are pressed against the rock with a stabilizing effect. The roof shield above this unit, often equipped with a finger shield extending backwards, offers protection against breaking rock. After completion of a stroke, tunnelling is interrupted and the gripping unit is moved forward.
Control made to measure
The gripper unit also helps to control the TBM. The main beam is positioned in the center of the machine. The beam is moved vertically and horizontally using the hydraulic cylinders in the area of the gripper unit. This allows for precise control. The current position of the TBM is permanently monitored and adjusted to the specified alignment if necessary.
Securing the machine systematically from the start
Gripper TBMs are open-mode tunnel boring machines and do not have a closed shield skin. Therefore, the tunnelling performance depends on the time required to secure the rock. In difficult geological formations, Herrenknecht Gripper TBMs allow for comprehensive measures to temporarily secure the rock right behind the cutterhead. In the so-called L1* working area, securing is mainly achieved using rock anchors, steel mats and steel arches. Probing and, if necessary, soil conditioning ahead of the machine are possible using additional drilling rigs. Water escaping from the rock is pumped away via a drainage system in the invert section of the machine. The excavated tunnel diameter is permanently supported with shotcrete in the back-up area. All necessary supply facilities are installed there. This often includes, in addition to the installation of permanent shotcrete, the installation of invert segments.
AVN machines in operation
Herrenknecht AVN or Slurry Machines with a cone crusher are all-rounders for safe tunnelling in the diameter range of 0.4 to around 4 meters. These microtunnelling experts show their full potential particularly in non-accessible machine sizes. The slurry-supported excavation concept makes it possible to use these machines in all kinds of ground conditions, ranging from silt to clay to incohesive soils, and further to gravel and rock. Depending on the diameter, this is possible both in pipe jacking and for segmental lining.
Flexible in every aspect
AVN Machines belong to the category of closed, full face excavation machines with a hydraulic slurry circuit. The soil to be excavated is removed using a cutterhead adapted to the respective geology. This makes it possible to use the machines in almost all geological conditions. In soft soils and mixed geologies, standard or mixed ground cutterheads are used, while a rock cutterhead with disc cutters is used for tunnelling in stable rock formations. A cone-shaped crusher inside the excavation chamber crumbles stones and other obstructions to a conveyable grain size while tunnelling and advancing. Afterwards, the material falls through openings similar to a strainer in front of the suction port and is then removed through the slurry line together with the suspension. The excavation diameter can be enlarged using an upsize kit and a modified cutterhead. This means that the AVN Machine can be used to tunnel different diameters and for different types of pipes.
Smooth transport of excavated soil due to variable water nozzle options
In cohesive soils, in particular, keeping the crusher cone clean and avoiding clogging is a special challenge. Based upon years of practical project experience, Herrenknecht has developed a range of water nozzle options, which can cope with different geological requirements. Additional water can be injected to clean the system using high pressure nozzles integrated into the cone crusher. These jets cut loam or clay in the excavation chamber avoiding clogging. The medium pressure nozzles use the standard slurry ports. Changing the size of the nozzles can adapt the suspension pressure and optimize the material flow. A newly developed, optional camera system in the excavation chamber provides the operator with an additional tool to visually monitor wear and tear and verify the situation inside machines with a diameter of more than 1.2 meters.
Pipe jacking over great distances
AVN Machines are often used in pipe jacking operations. The maximum drive length depends on several factors such as skin friction, available jacking force, or the nominal diameter of the jacking pipes. Automatic lubrication systems reduce the friction between pipe skin and soil by injecting bentonite into the annular gap. In the range of diameters that allow man-entry it is possible to use additional hydraulic intermediate jacking stations. These are installed in the pipe string at intervals which are defined specifically for each project. By dividing the pipe string into individual sections, the necessary thrust force is reduced and distributed respectively. This means that the distance between launch and reception shaft can be more than 1,000 meters, depending on the project conditions and the number of intermediate jacking stations.
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Herrenknecht India Private Limited
GNT Road (NH5), No. 11 Alinjiwakkam Village, Attipedu Post Tiruvallur District, Ponneri Taluk,
Chennai-600067, Tamil Nadu, India