GB1323032A - Rock bolt - Google Patents

Abstract

1323032 Rock bolting C I WILLIAMS 19 April 1971 [18 Feb 1970 3 Aug 1970] 21503/71 Heading F2H A rock bolt adapted to be held in a mass of grout placed in a hole in a ground formation, has a threaded end adapted for engagement with a nut 17 and is surrounded by the grout initially in the liquid condition thereof, the peripheral surface of the bolt 12 being formed to define a transverse indentation having a maximum slope with respect to the axis of the bolt, at least on the side of the indentation most remote from the threaded end, of less than fifteen degrees and preferrably about ten degrees. The bolt may be coated to prevent its adhesion to the grout. Helical indentations, Fig. 3 (not shown) may be made by a process similar to thread rolling or a series of annular indentations, Fig. 4 (not shown) by a sequence of rolling operations accompanied by repeated indexing of the rod through the rolling machine. In each case a degree of cold work to the material adjacent the indentations will compensate for the reduction of cross-sectional area. Rolls, Fig. 5 (not shown) for forming a helical pattern may be sufficiently spaced to allow axial ribs to be squeezed out. Another configuration has a wave-like pattern mainly in one axial plane, Figs. 6, 7, 8 (not shown). Preferred relationships between rod diameter, pitch and depth of undulations are indicated. A coating of lubricant on the rod assists its wedging reaction with the hole whilst preventing adhesion to the grout.