This invention relates to a tunnelling machine for driving non-circular tunnels. British Pat. Specification No. 1,343,444 discloses a tunnelling machine that has a unit that is swingable about a horizontal axis and is provided with a power rotatable cutter head that cuts solely peripherally by means of drag bits over the entire width of the tunnel. The small tunnel driven has an advantageous non-circular form.
There are many patent specifications showing tunnelling machines for driving tunnels with circular cross-section and having a circular head provided with a large number of free-rolling disc-cutters e.g. U.S. Pat. No. 3,232,670. However, circular tunnels are not always desirable.
In some rock, it is advantageous to use disc-cutters instead of drag bits and attempts have been made to make a tunnelling machine for driving non-circular tunnels by means of disc-cutters, cf. for example U.S. Pat. No. 3,840,271. One disadvantage with such prior art machines is that the advance steps are only of the same magnitude as the cutting depth of disc cutters, so that, if the machine slides backwardly only a little, the advance per hour will be considerably affected.
Another disadvantage is that there will be very few discs in cutting engagement with the rock which makes the advance per hour low.
Accordingly, it is an object of the invention to provide a fast driving tunnelling machine which uses free-rolling cutters to produce a small tunnel of an advantageous shape.
The invention will be described with reference to the accompanying drawings which illustrate by way of example a preferred embodiment of the invention.