Concrete lining shafts is not a new idea. Conventional sinkers have been doing it for years. The first recorded concrete lined shaft, for the coal industry in the US, was in Pocahontas County, VA in 1904.

Until recently, the blind drilling shaft technology has only allowed for shafts up to 8’-10’ in diameter. These shafts are more economically lined with a Hydrostatic Steel Liner. However, with advances in technology, North American Drillers, Inc. is now routinely drilling shafts in the 12’ and 14’ diameter range. Once you get into these diameters steel and trucking costs become outrageous and the only feasible way to line the shaft is with concrete.

Concrete lining a conventional sunk shaft, where you can pour the lining as you go down, is one thing. But in drilled shafts the entire hole is opened before the lining process begins. Designed and built by North American, the SLS-100 is a slip form lining rig which allows us to pour cast-in-place concrete from the surface to the bottom of the shaft one section at a time. Since we use a simple air lift method of circulation to drill these shafts the hole remains full of water throughout the drilling operation and can be dewatered a little at a time during the lining operation. By keeping a head of water on the formation after drilling, there is much less chance for the formations to squeeze reducing the original diameter before the liner is in place.