A New Generation of Back-Reamers for HDD Installations in Cohesive and Fine to Medium Coarse Soils

Thousands of miles of pipelines and cables are being installed in the US using horizontal directional drilling (HDD) each year. However, many technical aspects associated with the HDD process have not been fully investigated to date. Specifically, there are few published studies on the design parameters of reamers used in the HDD process. To date, theoretical work performed on the design and performance of back reamers is very limited, despite reaming being a critical part of the HDD process. Reamer design in the HDD industry has been more of an art than a science, with the majority of designs been developed by trial and error, as a given reamer design is tested in the field and modified numerous times until satisfactory performance is achieved. Reamer design for soil conditions has become stagnant for some time now, and the industry has not seen a major breakthrough in the design of reamers in recent years. The lack of innovation in this area potentially restricts the ability of the HDD industry to increase productivity, reduce costs and enter into new application areas. This paper describes the foundation for systematic approach for the design of reamers, identifying the key aspects that affect their performance in various geological formations, including cutting and mixing capacities, fluid discharge, borehole stability, torque, slurry formation and suspension and transport of the cuttings. Design criteria include shape and optimal orientation of the cutters; length and weight of the reamer; total contact area with the borehole wall; number, area and location of nozzles; and, number and placement of the teeth.