in fig4 an additional fixation of the jacket tube 6 by means of a pin or bolt 20 is moreover indicated for a simple connection between adjacent jacket tube elements 6 u2032 and 6 u2033 which are indicated in fig6 and 7 a sleeve shaped element 21 is each provided with projections or elevations 22 protruding towards the interior of the jacket tube 6 being indicated which engage in respective depressions or recesses 23 of the jacket tube to ensure the safe connection of adjacent jacket tube elements 6 u2032 and 6 u2033 said projections or elevations 22 may be preformed such that the sleeve element 21 has to exhibit an appropriate elasticity when joining adjacent jacket tube elements 6 u2032 and 6 u2033 or they may be formed in the region of predetermined breaking points using a simple tool after the arrangement of the sleeve like element 21 in the region of the jacket tube elements 6 u2032 an 6 u2033 to be connected a plurality of passage openings 24 are indicated in the envelope tube 4 in a spaced apart relationship relative to the drill bit already in the schematic illustrations of fig1 and 2 wherein the material haulage from the region of the drill bit 2 is elucidated by way of fig8 to 12 in addition to the passage openings 24 provided at a distance from the drill bit 2 wherein accordingly offset or depressed regions 25 extending in the longitudinal direction are.