Patent ID: 7591329

Claim:
An auger for making a borehole that presents in an inside wall a groove that is substantially helical, said auger comprising: a hollow cylindrical core having a longitudinal axis and a bottom portion; at least one helical blade mounted on an outside face of the core and extending over at least a substantial fraction of a length of the core; a movable cutter gouge suitable for taking up an active position in which the gouge projects outside a volume defined by a periphery of the blade and a retracted position in which the gouge is disposed inside said volume; displacement means for displacing said gouge from said retracted position to said active position, comprising: an additional hollow tubular member mounted to move in said core in translation along said longitudinal axis and disposed at least at a bottom end of said core; and control means for causing said gouge to be positively displaced from said retracted position to said active position in response to the translation of said additional hollow tubular member moving relative to at least the bottom portion of said hollow core; and a supply system to deliver grout or concrete through said hollow cylindrical core and said hollow tubular member, wherein the core of said auger comprises a top portion and the bottom portion that is movable in translation relative to said top portion over a predetermined length, said gouge being mounted on said bottom portion, wherein said additional member comprises a tubular part secured to the bottom end of the top portion of said core and penetrating inside said bottom portion of the hollow core, and wherein said control means are mounted on said tubular part in such a manner that displacement of said bottom portion of the core in translation relative to said tubular part causes the gouge to be displaced from said retracted position to said active position.