TBM drilling

GN solids control can supply equipment for TBM drilling by mud system

There are two main methods : earth pressure balanced (EPB) and slurry type shield machine. Selection of shield method depends on surface conditions¬†,ground conditions, dimensions of the tunnel section,tunnel alignment , boring distanceand construction period. Both are closed-face type shield machines, meaning the “head” part of machine is “closed” and separated from the rear part of machine. The “head” has a working/running chamber filled with soil or slurry between the cutting face and bulkhead to stabilize the cutting face under soil pressure . The EPB type shield machine turns the excavated soil into mud pressure and holds it under soil pressure to stabilize the cutting surface. It have system to cut the soil, mixing system to mix the excavated soil into mud pressure, soil discharge solution system to discharge the soil and control system to keep the soil pressure uniform. Therefore, EPB may not be applicable for the rocky soil that is hard to turn the excavated soil into slurry or sludge. It can be used at ground predominated by clayer soil. The slurry kind shield machine, on the other way, uses the external pressurized slurry to stabilize the cutting face, similar to bored piles or diaphragm walls using bentonite to contain the trench wall. The slurry is circulated to transport the excavated soil by fluid conveyance. Besides having excavation system, the slurry type shield machine has slurry feed and discharge equipment to circulate and pressurize slurry and slurry processing equipment on the ground to adjust the slurry properties.

A tunnel boring machine (TBM), also known as a “mole”, is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They may also be used for microtunneling. They can bore through anything from hard rock to sand. Tunnel diameters can range from a metre (done with micro-TBMs) to 19.25 metres to date. Tunnels of less than a metre or so in diameter are typically done using trenchless construction methods or horizontal directional drilling rather than TBMs.

Tunnel boring machines are used as an alternative to drilling and blasting (D&B) methods in rock and conventional “hand mining” in soil. TBMs have the advantages of limiting the disturbance to the surrounding ground and producing a smooth tunnel wall. This significantly reduces the cost of lining the tunnel, and makes them suitable to use in heavily urbanized areas. The major disadvantage is the upfront cost. TBMs are expensive to construct, and can be difficult to transport. The longer the tunnel, the less the relative cost of tunnel boring machines versus drill and blast methods. This is because tunneling with TBMs is much more efficient and results in shortened completion times, assuming they operate successfully.

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