Abstract: A grouting rod is formed with a first channel, a second channel (or channels) surrounding the first channel and a third channel which is normally in communication with the first channel. A piston valve is vertically movably received in an upper portion of the third channel. When the piston valve is raised, upper lateral communication holes and upper discharge holes which are formed in the upper peripheral wall of the third channel are closed by the piston valve and concurrently the second channels are permitted to communicate with a lower portion of the third channel through lower lateral communication holes also formed in the upper peripheral wall of the third channel. When the piston valve is lowered, the upper lateral communication holes and upper discharge holes are opened and concurrently the second channel(or channels) is prevented from communicating with the lower portion of the third channel through the lower lateral communication holes.