Design and Analysis of a Micro Tunnel Boring Machines (TBM)

Abstract

Tunnel boring machines (TBM) excavate tunnels with a circular cross section through a variety of rock strata. They can be used to bore through hard rock or sand and almost anything in between. Tunnel diameters can range from a metre (done with micro-TBMs) to 19 metres. Tunnel boring machines are used as an alternative to drilling and blasting (D&B) methods. A TBM has the advantages of not disturbing surrounding soil and producing a smooth tunnel wall. This significantly reduces the cost of lining the tunnel, and makes them suitable to use in built-up areas. The key disadvantage is cost. TBMs are expensive to construct, difficult to transport and require significant infrastructure. A tunnel boring machine (TBM) typically consists of one or two shields (large metal cylinders) and trailing support mechanisms. At the front end of the shield a rotating cutting wheel is located. The cutting wheel will typically rotate at 1 to 10 rpm (depending on size and stratum), cutting the rock face into chips or excavating soil (muck). A TBM can cut through rock at up to one kilometre a month. Powerful hydraulic rams force the machine's cutting head forwards as the rock is cut away called the feed. The action here is very much like an earthworm. The rear section of the TBM is braced against the tunnel walls and used to push the TBM head forward. At maximum extension the TBM head is then braced against the tunnel walls and the TBM rear is dragged forward. As tunnels has become one of the most important source of underground transportation like metro rail and other projects, this TBM can be utilized as an easy and effective machine for more better results. Because of their demonstrated capabilities in attaining high rates of advance in civil tunnel construction, the hard rock mining industry has always shown a major interest in the use of TBMs for mine developments. The successful application of TBM technology to mining depends on the selection of most suitable equipment and cutting tools for the rock and ground conditions to be encountered.