OF REVERSE CIRCULATION
The Technology – Blind boring utilizing reverse circulation starts with a rotary table connected to the reamer body (cutting tool) by a heavy doubled walled rod or “drill string.” The rotary table provides the torque or turning action for the reamer.
To create up flow, the shaft is filled with drilling fluid (water) which is maintained at a constant level throughout the entire shaft development. The water fills both the shaft and the hollow drill string creating two independent columns of water.
Compressed air is injected into the water column of the drill string displacing the fluids and creating a much lighter column.
The heavier water column inside the shaft pushes down and across the development face (bottom of the shaft). The water is then forced through a small opening called a “pick-up” on the reamer body, which displaces the lighter water column in the drill string. The displacement of the lighter drill string fluid results in an upward flow or “reverse circulation.” The volume of fluids being displaced, typically 2,000 to 3,000 gallons per minute, creates a tremendous suction (vacuum) at the pick-up point that literally sucks the cuttings from the development face. The terms “up-flow” and “reverse circulation” refer to the direction of water flowing up the drill string to the surface.
The reverse circulation is maintained by providing a constant level of water in the shaft. This constant level provides both a downward pressure for flow and the added benefit of concentric outward pressure on the shaft wall. Concentric pressure reduces the potential for strata to shift or move and, in turn, increases overall stability.
Once fully developed, the shafts are typically lined prior to dewatering. Depending on application -- and to maximize efficiency -- the final liner is available in steel, concrete or composite material.
Advanced Technology for Reverse Circulation Minimizes Cost