PC-Strand tendons or Prestressed Concrete (PC) strands, commonly referred to as cable bolts, have become a major rock reinforcement device for underground mining and civil applications. The most common configuration is a 1+6 strand designates a center king-wire, with 6 outer wires wound around it to form a 15 mm (0.6 in) diameter cable. The capacity of which approaches 30 tons but the performance is largely dependent on the anchorage medium and the ability of the system to transfer stresses back into the rock mass while reinforcing and suspending the immediate roof. Recent developments to improve the transfer mechanisms of the PC-strand via the anchorage medium by imprinting the individual wires with uniquely designed deformations. These deformations have resulted in improved anchorage and subsequent cable bolt performance. This paper will describe the numerical modeling simulations that were undertaken to refine and optimize the designs that were evaluated in a series of laboratory and field experiments. The indented PC-strand is being introduced to underground coal mines for several different ground control applications.
Maintaining safe underground openings has always been a challenge in underground mining and civil applications. Intrinsic systems, installed into boreholes drilled with conventional mining equipment, started with wedge systems and slowly evolved into the mechanical anchor (shell) systems that are still used in some applications today (Fig 1). In the 1970’s resin systems were introduced that utilized a threaded or headed rebar bolt. These bolts could be forced into a borehole that broke a cartridge that contained polyester resins that would be mixed and cured to form mechanical interlocks along the borehole walls. While the primary bolting system used in underground mines remains the headed rebar system accounting for over 65% of the nearly 100 million bolts installed in the U.S. annually .