Abstract: A channelling machine for cutting a preliminary groove around the working face of a tunnel being excavated. A guide and drive track assembly comprising at least two guide rails and a drive rail displaceable into the immediate proximity of the working face. The guide and drive track assembly is disposed entirely inside a hollow support frame of cross-section complementary to that of the tunnel being excavated. The guide and drive track assembly also includes a back-up rail likewise disposed inside the support frame. Another guide and drive track assembly may be provided symmetrical to the first. The machine is braced against the walls by a plurality of front and rear hydraulic cylinders which also adjust the alignment of the machine in the tunnel. The machine is mounted for displacements on a cradle.