| 摘要 |
A tunnelling apparatus has an annular tunnelling element subdivided into a leading and a trailing chamber. The front end of the leading chamber is open to the material-removing face. A material-removing cutting device is lodged in an opening formed in the transverse wall to remove material from the working face. It can be axially withdrawn from the opening into and if necessary rearwardly beyond the trailing chamber, so as to expose the opening and permit access of an operator to the working face through the opening.
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