fig1 shows a drilling machine using the drilling tool in accordance with the invention . the tool 12 is guided in the trench by a guide beam 14 of constant profile and preferably of rectangular right section . the tool 12 is fastened to the bottom end 14 a of the beam . the guide beam 14 serves to transmit thrust forces and traction forces to the tool 12 . it also serves to protect the pipes feeding the tool with hydraulic binder , together with the pipes powering the motors that drive rotation of the cutters . the guide beam 14 is connected by guide and drive means 16 , 18 to a vertical mast 20 . the mast is supported by a tracked vehicle 22 having installed thereon a system 24 for generating hydraulic power . it will be understood that by causing the guide beam 14 to move upwards and downwards , the tool 12 is caused to move vertically in the soil so as to make a panel of a trench by drilling the soil and mixing the drilling cuttings with the hydraulic binder . fig2 shows the guide beam 14 with the drilling tool proper 12 secured to its bottom end 14 a . the drilling tool is constituted by two pairs of cutters 26 & amp ; 28 and 30 & amp ; 32 , with the cutters in a given pair being on a common axis and with the axes of rotation of the cutters being parallel and substantially horizontal in use . as explained below , according to an essential characteristic of the invention , the motors for driving rotation of the cutters 26 to 32 are disposed inside the cutters themselves , thereby avoiding any need to provide an external motor for driving the cutters . more precisely , the pairs of cutters 26 to 32 are connected to the bottom end 14 a of the guide bar by a support structure given overall reference 34 . in a variant , the support structure 34 may be fitted with scraper systems 36 that serve , when the soil is sticky , to remove the soil that adheres to the cutters between their teeth 38 . with reference now to fig5 , there follows a description in greater detail of the support structure 34 of the tool . the support structure 34 is constituted firstly by a plate 40 that , in the particular embodiment described , consists of two half - plates 42 and 44 interconnected by a triangular part 46 connecting the two half - plates 42 and 44 to a mounting pad 48 used for securing the support structure 34 to the bottom end 14 a of the guide beam . the pad 48 is naturally substantially horizontal and thus orthogonal relative to the half - plates 42 and 44 . as shown in the figures , the mounting pad has substantially the same dimensions as the horizontal right - section of the guide portion 14 . the bottom ends 44 a , 42 a of the half - plates are fitted on each of their faces with pairs of coaxial cylindrical bushings 50 , 52 and 54 , 56 . these bushings have axes x , x ′ and y , y ′ that are orthogonal to the two half - plates 42 and 44 and that serve firstly for mounting the hydraulic motors and secondly for guiding rotation of the drum on which the cutters proper are mounted . as is well known , the guide bar 48 a , in horizontal right - section , is of dimensions that are very small compared with those of the drilling tool 12 and thus compared with those of the drilling performed by the tool . more precisely , the depth l ′ of the pad 48 ( see fig5 ) is less than half the length h of the axis of a pair of cutters 26 to 32 ( see fig4 ). the width l of the pad 48 ( see fig5 ) is less than one - third of the length l of the drilling tool 12 ( see fig4 ), where “ length ” designates its maximum dimension in a horizontal plane . preferably , the top edge face 44 b , 42 b of each half - plate presents a first portion 44 c , 42 c that is substantially horizontal and short in length followed by a downwardly - sloping portion 44 d , 42 d , thereby constituting the sides of a triangle of apex that would be disposed towards the pad 48 . also preferably , the edge faces 42 b , 44 b of the half - plates 42 and 44 are chamfered , as can be seen more clearly in fig4 . more generally , the top edge face of the plate 40 is of a shape that makes it easier to raise the drilling tool through the mixture of cut soil and hydraulic binder that is contained in the trench . as already mentioned , the motors for driving rotation of the cutters are preferably hydraulic motors . under such circumstances , the power fluid feed pipes are constituted by holes such as 58 and 60 made in the thickness of the half - plates 42 and 44 . the top ends of the pipes 58 , 60 open out into orifices such as 62 that are formed in the pad 48 for connecting the pipes 58 and 60 to the power fluid feed pipes that are located in the guide bar 14 . under some circumstances , when the soil is sticky , scraper systems 36 are fastened on either side of the central triangular part 46 of the support means 34 . these scraper systems 36 comprise scrapers such as 64 that are interleaved between the rows of teeth 38 , 38 ′, 38 ″ of the cutters so as to remove the soil that might adhere to the cutters between these teeth . it should be observed that the scraper systems 36 present a profile that makes it easier to raise the drilling tool through the mixture of drilling cuttings and hydraulic binder . fig4 shows the cutters 30 to 36 mounted on the bushings 50 to 56 . firstly there can be seen the hydraulic motors such as 70 , which motors are fastened within the bushings 50 to 56 . the outlet shafts from the motors 70 are connected mechanically in rotation and in translation to drums such as 72 having the cutters 30 to 36 together with their teeth 38 , 38 ′, and 38 ″ mounted thereon . the ends of the hydraulic fluid feed pipes 58 and 60 are connected by any suitable means to the system for feeding power to the hydraulic motors 70 . it will be understood that when it is desirable to raise a drilling tool that is in a trench that is filled with a mixture of drilling cuttings and hydraulic binder , the only portions of the tool that oppose this upward movement are those constituted by the support plate 40 and possibly by the scraper systems 36 . the pad 48 is located in line with the guide bar 14 and therefore does not constitute an obstacle to raising the drilling tool . the half - plates 42 and 44 are of small thickness and they have top edges 44 b , 42 b of profile that facilitates raising the tool , as explained above . in a particular embodiment , the drilling tool presents a width h in the direction of the axes of rotation x , x ′ and y , y ′ that is equal to 800 millimeters ( mm ) and a length l in the direction orthogonal to these axes of 2800 mm . if consideration is now given to the support plate 40 , its long dimension is 2200 mm and its thickness e is equal to 60 mm . furthermore , the fastener plate 48 is rectangular in shape with sides having dimensions of 600 mm and 300 mm . it will be understood that during upward movement , the fastener plate 48 does not constitute an obstacle to such movement since it is in line with the guide bar 14 . consequently , a length of only 1600 mm of the support plate 40 needs to be taken into consideration . thus , the area opposing upward movement is 1600 mm × 60 mm = 96 , 000 square millimeters ( mm 2 ). this section should be compared with the horizontal projection of the tool assembly , which projection presents an area equal to 2800 mm × 800 mm , which is more than 2 million mm 2 . the area opposing upward movement is thus less than 5 % of the area of the tool . during upward movement , the cutters are caused to rotate and therefore do not oppose such movement . when a cutting tool is fitted with pairs of cutters having axes that present a width of 500 mm , this ratio is slightly less than 10 %. in general , the ratio between the areas is preferably less than 10 %. more generally , and preferably , the thickness e of the support plate 40 is less than 15 % of the width h of the tool in the direction of the axes of rotation x , x ′ and y , y ′. more preferably , the ratio is no greater than 10 %. this value for the ratio depends on the dimensions of the cutters . the larger the cutters , the smaller the ratio can be made . the means forming the plate 40 have a minimum thickness of 50 mm to 60 mm in order to ensure the plate presents sufficient strength and in order to make it possible to provide internal ducts therein for powering the motors .