ABSTRACT
Practical experience in mines has shown that for certain applications mine roof stabilization with roof bolts is still too rigid and that more yieldable systems were required. Industry has succeeded in supplying a yielding roof bolt with sliding nut. Rock mechanics scientists and engineers have still however to develop an analytical method to explain and calculate the behaviour of highly yielding roof supports. This chapter highlights some important steps on this way in this direction. Yieldable roof bolts which shall control a rock mass during deforming-to-failure or in its post-failure state cannot be considered independently: Rock mass, roof bolt and lining act as a composit unit. Typical is the Dywidag threadbar with a continuous, coarse thread, hot rolled onto the bar during fabrication. A screw-on anchorage device allows the placing of the anchor like a conventional roof bolt. It may even be tightened with an impact wrench.
