A casing for use in excavation of a borehole

摘要

This invention relates to a casing (20, 256) for use in excavation of a borehole by an apparatus directing a high velocity fluid against the material to be excavated, the borehole having a predetermined diameter, comprising: a tubular portion (22, 266) of diameter to be moved within the borehole as it is excavated to maintain the diameter of the borehole; a portion (24, 260) secured at an end of said tubular member for passage of the apparatus for excavation within the tubular portion to direct the high velocity fluid at the excavation site, a seal (29, 262) provided in said portion to seal against said apparatus; and a discharge portion (26, 264) to discharge material excavated by said apparatus from the site of excavation along the interior of the tubular portion for disposal. <IMAGE>