A coupler interconnects adjacent sections of soil nail members to extend a length for a soil nail to be installed. The coupler includes a plurality of projections extending from the exterior surface of the coupler. The projections serve multiple purposes. One purpose is to center the soil nail within a drilled hole. Another purpose is to provide mixing for selected amounts of drilled material to remain within the hole, and/or evacuation of drilled material to be removed from the hole. Another purpose is to create a drilled hole with varying diameters in response to different geological layers encountered during drilling. The coupler with projections therefore serves as a secondary drill bit implement. The size of the projections can be altered to selectively enlarge a desired portion of a drilled hole. The invention further includes a soil nail assembly and a method for installing a soil nail assembly including couplers with projections.