| 摘要 |
To bore a noncircular hole a conventional tunneling machine is provided with two or more rotatable cutter wheels mounted at the rear of the machine and rotating about axes parallel, but offset relative to, the main boring head of the machine. The main boring head digs the conventional circular bore. The rear-mounted wheels advance with the machine and dig into the circular bore to form the desired cross-sectional shape- D- or horseshoe-shape, etc.
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