Reamer

Reamers come in many different diameters and designs (fly cutter, barrel, hole opener, etc.). Each has a different function and is chosen according to the ground conditions.

Reamer types and choosing for the ground

Reamers fall into three main families according to the ground. The fly cutter advances quickly in soft and medium clay and silt; because its blades let the fluid circulate freely, it is preferred for large diameters. The barrel reamer compacts the hole wall in ground that does not stand on its own, such as sand and gravel, leaves a smooth tunnel and centres the pipe during pullback. Hole openers and rock reamers are heavy tools fitted with cone cutters, designed for hard and weathered rock; they require high torque and high fluid flow.

Stage planning determines the duration and risk of the project. The final hole diameter is chosen at 1.2–1.5 times the pipe diameter; in hard and mixed ground the number of stages is increased, and at each stage torque and pull force are kept within the rig's safe range. After each stage the hole is left full of fluid; the density and viscosity of the fluid are adjusted to carry the cuttings and support the wall. During pullback a swivel is placed between the reamer and the pipe so that the reamer's rotation is not transferred to the pipe.

Deltek keeps fly cutter, barrel and rock reamers from 100 mm to 1600 mm cutting diameter in its Istanbul and Izmir equipment fleet. The reamer type, the number of stages and the drilling fluid recipe are determined together from the geotechnical survey; when these three are set up correctly, the pullback stage of an HDD project is completed without surprises.