ABSTRACT: Dynamic rock anchors are interior fixtures developed by the author which promise to be a revolutionary development in the field of ground control. The fixtures are designed to be placed in the ground with modern roof bolting equipment, such as the type used in the American coal mining industry. They are composed of a plastic formable anchor tube which serves to fasten a buttress deformed rod which is thrust and turned into the plastic and in turn clamps the roof plate to the rock surface. Plastic tubes 10 to 16 inches in length provide sufficient anchorage to exceed the yield strength of steel rods 5/8, 3/4 or 7/8 inches in diameter.
This paper presents field testing and early work done on the device over the last seven years. Results of pull tests, creep tests, laboratory testing in concrete, and field testing under natural rock conditions demonstrate the uniqueness and effectiveness of this new support system.
A second development which uses the dynamic rock anchor in conjunction with a resin cartridge to provide a stiffer anchorage system is also discussed. These products will be manufactured and marketed by Ingersoll-Rand Co. under the trademark of DYNA-ROK and DYNA-ROK PLUS anchors.
DYNA-ROK anchors have resulted from an extensive research effort. From 1981 to 1984 the author did what he terms "dirty" research to separate various anchor devices and systems. This resulted in the selection of the plastic deformable anchor as being the best candidate for success.
Once testing proved that the anchor was feasible, tests were conducted at the Spokane Mining Research Lab. This resulted in a refinement of effort as electronic readouts could be made of the torque, anchorages achievable, and plate loads.
In 1986 an agreement was finalized with Ingersoll-Rand Co. which did further refinement, research and development in their labs. Ingersoll-Rand is the licensed manufacturer of the product. DYNA-ROK and the DYNA-ROK PLUS are registered trademarks of Ingersoll-Rand for these products.
To install DYNA-ROK fixtures, modern mechanized roof bolting equipment typical to the American coal mining industry is used. The concept is simple. The hole is drilled, the tube inserted and the fixture thrust and torqued to tension the rod and seat the roof plate. The rock surrounding the anchor is strengthened by active spiral thrust vectors from the buttressed rod through the plastic and into the rock.
It is a long point anchor system with the anchor extending over sufficient length so that loads against the rock are not great. The plastic anchor tube eliminates stress concentrations which cause creep and slippage in other systems. It is a cost competitive, productive system which should find wide acceptance in coal mines, potash mines, salt mines and essentially any formations in which small boreholes can be drilled.
The DYNA-ROK Anchors
The DYNA-ROK is designed to be used in a nominal one inch diameter hole. Anchorage can be achieved using 5/8", 3/4" or 7/8" diameter roof bolt rods.