NOVELTY - The assembly has a grout tube (340) including a flow channel with a flow axis and a flow opening (341) aligned with a rotary output shaft such that the flow axis are generally aligned with a central axis. A drivable coupler (410) facilitates rotating engagement with a drive socket (326) and connected to a pipe assembly (400). A threaded sleeve (510) of a grout plug assembly (500) is connected to internal threads of the drivable coupler in threaded engagement. A sleeve seal (520) of the grout plug assembly engages the grout tube in sealed engagement.    USE - Grouting assembly for receiving viscous hardening material i.e. grout, and delivering the viscous hardening material to a pipe assembly for delivery to underground soil during placement pipe pilings in ground to act as structural supports and geothermal piles.    ADVANTAGE - The assembly allows a flange to provide a point of contact of the coupler with the drive socket, and the flange maintains coaxiality between a socket unit and the coupler when the coupler is coupled to the socket unit, so that enhanced coaxiality can smooth rotary motion imparted to the pipe assembly by the socket unit through the coupler, and reduces wear between the coupler and the socket unit. The assembly allows pipe pilings that have continuous grouting while the pipe pilings are driven, thus providing improved stability and strength due to emission of the grout from the pipe piling, and hence minimizing manufacturing and installation cost of the assembly. The assembly allows a threaded bottom end to be aligned with an upper threaded bore, thus avoiding cross-threading, binding, need for multiple threading attempts and problems that arises from improper alignment of threaded sections.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a method for inserting and removing a grout plug assembly into and out of a drivable coupler.    DESCRIPTION OF DRAWING(S) - The drawing shows an exploded sectional view of a pipe assembly including a coupler and a grout plug assembly removed from a drive socket.    Drive socket (326)    Grout tube (340)    Flow opening (341)    Pipe assembly (400)    Drivable coupler (410)    Grout plug assembly (500)    Threaded sleeve (510)    Sleeve seal (520)