shown in the drawings consists of a tunnelling machine 10 having a cylindrical housing 12 in which a concentric cylindrical cutting head 14 is rotatably mounted cutting head 14 comprises a face 16 a truncated conical side wall 18 and an annular rear wall 20 fixed to the side wall face 16 and side wall 18 are fixed together by a ring 22 concentric with housing 12 face 16 comprises a plurality of fixed blind sectors 24 spaced apart to define aperture 26 between each sector a plurality of radical cutter bars 28 superimposed on sectors 24 adjacent each aperture 26 extend radially from a hub 30 each cutter bar 28 carries a row of cutter teeth 32 and both ring 22 and hub 30 each carry additional cutter teeth 34 and 36 respectively rear wall 20 carries an internally toothed ring gear 40 engaged by a gear 42 driven by an hydraulic motor 44 mounted on an annular base plate 46 fixed to housing 12 plate 46 also carries a bearing ring 48 which cooperates with ring gear 40 to form a cage for bearings 50 on which cutting head 14 rotates a plurality of loading plates 52 are fixed radially in cutting head 14 adjacent ring 22 and extend between sectors 24 and rear wall 20 centred in cutting head 14 is a muck ring 54 which as seen in fig4 consists of a drum 56 axially oriented with the cutting head and having a circular side.