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the price of boring rises linearly with depth; bore axis with neutral floating; the possibility to make vertical or inclined bores up to 10 km deep; the possibility to make large diameter bores – even 5 times larger than on the ground compared to today drilling technologies; casing formed on site in the borehole
The decision whether to construct a tunnel using a TBM or using a drill and blast method includes a number of factors. Tunnel length is a key issue that needs to be addressed because large TBMs for a rock tunnel have a high capital cost, but because they are usually quicker than a drill and blast tunnel the price per metre of tunnel is lower. [2]
Directional boring machine. Directional boring, also referred to as horizontal directional drilling (HDD), is a minimal impact trenchless method of installing underground utilities such as pipe, conduit, or cables in a relatively shallow arc or radius along a prescribed underground path using a surface-launched drilling rig.
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Drilling for boreholes was time-consuming and long. As the depth of the holes varied, the drilling of a single well could last nearly one full decade. [4] It was not up until the 19th century that Europe and the West would catch up and rival ancient Chinese borehole drilling technology. [10] [5]
Thus very high surface qualities with bore hole tolerances of IT 9 to IT 7 can be achieved by deep hole drilling processes. Subsequent steps to improve the surface quality of the bore hole can often be reduced or eliminated completely. A further advantage is the low burr formation for trough holes and for over-drilling cross holes. [1]