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Tunnel Boring Machine Slurry System of Kosun on Soft Ground

Tunnel Boring Machine Slurry  System

Tunnel Boring Machine Slurry  System of Kosun with more than 20 years experience.
Three main types of tunnel boring machine separators are used in soft ground excavations-
–    Slurry shield TBMs
–    Earth pressure balance machine
–    Open – face type
In soft grounds with pressure less than 7bar, earth pressure balance machines are used. These along with cutting head also comprises tungsten carbide disc cutters, cutting bits and hard disk cutters.

Machine derives its name from the fact that it balances the pressure in tunnel head by use of excavated earth. Rate of excavation and advances through Archimedes screw controls pressure in the cutterhead. Some additives like bentonite may have to be injected to increase the stability.

Kosun Tunnel Boring Machine Slurry System
Tunnel Boring Machine Slurry System

These are also added to make sure that the earth is sufficiently attached to the Archimedes screw thus marinating the pressure in the head and prevent seepage of water in the tunnel.

Slurry shield TMBs are used in cases where the ground is so granular in nature that it cannot form plug in Archimedes screw. The cutting head is feeded with slurry which in turn applies pressure. This even acts as transporting medium as it mixes with excavated earth and is being pumped out in slurry separation units usually located out of tunnel. In this separation unit slurry is processed so that it is recycled and can be used again. This filtration is a multi- staged process. However, filtration of slurry depends on the size of excavated particles.

Thus making this slurry shield tunnel boring machine separation units suit able for clays and silts sized particles as they are smaller than bentonite particle, which makes the slurry. In these instances separation with water can be done which will help form clay cake thus filtering the slurry in the end.

In grounds where the excavated tunnels can stand without support for a little period, open face TMBs can be used. These tunnel boring machine separators are generally used where strength is more than 10Mpa and seepage of water is low. Cross sections of sizes up to 10 meters can excavated with these TMBs.

Cutter head excavates within 150mm of the shield edge. This shield is moved forwards and cut the ground in same circular manner. Pre-casted concretes or graphite iron segments provide ground support. The key spreads the rings until it is tightly fitted against the tunnel made by tunnel boring machine separators shields. Open face TMBs comes in many variations.

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Tunnel Boring Machine Slurry Separation System of Kosun

Tunnel Boring Machine Slurry Separation System

Tunnel Boring Machine Slurry Separation System through muddy water pressure balance model not only can effectively use the mud to stabilize the excavation surface strata, but also prevent the collapse at the same time, through the mud wall formed by the effective prevention of gushing water, and through the simultaneous grouting can be very Good control of the surface subsidence and to avoid the occurrence of segment leakage, which can ensure that the ground environment, ground buildings from the impact of tunnel construction.

Tunnel Boring Machine Slurry Separation System on the shield of environmental protection in the construction of mud treatment has a very important role.

Tunnel Boring Machine Slurry Separation System
Tunnel Boring Machine Slurry Separation System

On hard grounds or rocky grounds two types of TBMs are used. Open type TBMs or Shielded tunnel boring machine separator. Excavation of hard rock is carried out by disc cutter fitted in cutter head of TBMs.

These generate compressive stress that leads to crackers or fractures in the earth. This excavated earth or rock is called muck, which is passed through holes between the cutter head to the conveyor belt and then is exited out of the machine.

Open type tunnel boring machine separator do not have any shield, thus the area behind the head depends on rock for support. Gripper system helps the machine to advance forward. But not every machine can move continuously with the help of gripper like the Wirth machine, in such cases the machine moves ahead with help of thrust gained against grippers.

Open type tunnel boring machine separator do not excrete cement segment behind them like other machines. The tunnel rock is supported by rings beams, shot rete, steel straps, rock bolts, ring steel, etc.
In cases where rocks are prone to fracture shielded hard rock tunnel boring machine separator are used.

These unlike open type excrete concrete segments which support the fractured unstable parts of the tunnel. There are two modes in double shield tunnel boring machine separator.

These use the tunnel walls for grip in stable conditions to move ahead. In fractured rock cases, the thrust of the gripper is used to move forward. This prevents the thrust forces damaging the already fragile walls of the tunnel.

Same method is followed by single shield tunnel boring machine separator but can be useful only in fractured ground cases because the move ahead only after being pushed by the segments of concrete excreted behind in the tunnel.