US PATENT SUBCLASS 405 / 139
.~.~ With auxiliary tunnel

Current as of: June, 1999
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405 /   HD   HYDRAULIC AND EARTH ENGINEERING

132  DF  UNDERGROUND PASSAGEWAY, E.G., TUNNEL {6}
138  DF  .~ Boring {4}
139.~.~ With auxiliary tunnel

DEFINITION

Classification: 405/139

With auxiliary tunnel:

(under subclass 138) Method or apparatus wherein a subsidiary passage is employed in the construction of the main corridor.