A maxi-rig is a category of horizontal directional drilling (HDD) rigs used for longer distances, greater depths and larger diameter pipes. The term is used in contrast to mini-rigs and midi-rigs, which are names for smaller categories of this machinery.
Projects using maxi-rigs may be used in large operations requiring significant time and support.
Trenchlesspedia Explains Maxi-Rig
In their Standard Guide for Use of Maxi-Horizontal Directional Drilling for Placement of Polyethylene Pipe or Conduit Under Obstacles, Including River Crossings, the Plastics Pipe Institute laid out design and installation procedures for maxi-HDD projects. The classification of drill rig for this type of work would be considered a mini-rig.
Maxi-rigs are used for the installation of large diameter pipes (16-48 inches). They are rated for more than 100,000 pounds of thrust and greater than 20,000 pounds of torque.