Yielding strata bolt

Abstract

The present invention discloses a rock bolt having a tendon ( 1, 201 ) which is able to yield and thereby control movement of unstable rock strata into which the bolt is installed. The tendon has a portion which is provided with a grout slippage mechanism, preferably in the form of a tube ( 8 ) which surrounds the tendon. A two part grout anchor ( 10, 100, 200 ) is clamped to the tendon. The grout anchor is embedded in grout and is therefore essentially immovable. The tendon passing through the anchor is worked and thereby dissipates energy. The tendon can be either a multi-strand cable ( 1 ) or a solid bar ( 200 ). Various forms of anchor ( 10, 200 ) are disclosed with either complementary recess(es) ( 14 ) and protrusion(s) ( 15 ) or opposed protrusions ( 115 ) which form pinch point(s). A one piece grout anchor ( 300 ) is also disclosed.

1 . A yielding grouted rock bolt to control the movement of unstable rock strata into which the bolt is installed, said bolt comprising an elongate tendon, a portion of said tendon having a grout slippage means, and a grout engaging anchor fitted to said tendon portion and thereby at least partially deforming same, whereby in yielding said tendon portion passes through said anchor and is worked thereby.  
   
   
       2 . The bolt as claimed in  claim 1  wherein said grout slippage means comprises a tube surrounding said tendon portion.  
   
   
       3 . The bolt as claimed in  claim 2  wherein said tendon is formed from metal and said tube from plastics.  
   
   
       4 . The bolt as claimed in  claim 1  wherein said anchor comprises a body engageable with said grout and formed in two parts which are clamped together over said tendon portion to fit said anchor thereto.  
   
   
       5 . (canceled)  
   
   
       6 . The bolt as claimed in  claim 5  wherein said parts include a plurality of complementary protrusions and recesses.  
   
   
       7 . (canceled)  
   
   
       8 . The bolt as claimed in  claim 4  wherein said two parts are substantially identical.  
   
   
       9 . The bolt as claimed in  claim 4  wherein said parts are maintained clamped together by keeper rings shaped to mate with said parts.  
   
   
       10 . The bolt as claimed in  claim 1  wherein said tendon comprises a multi-strand cable.  
   
   
       11 . The bolt as claimed in  claim 1  wherein said tendon comprises a bar.  
   
   
       12 . The bolt as claimed in  claim 1  and having a plurality of said grout engaging anchors.  
   
   
       13 . A two part rock bolt anchor adapted to be fitted to a tendon of a rock bolt, said anchor comprising a body engageable with grout into which said bolt is embedded, and having two parts shaped to be clamped together over said tendon, wherein said tendon moves through said parts in yielding.  
   
   
       14 . (canceled)  
   
   
       15 . The anchor as claimed in  claim 14  wherein said parts include a plurality of complementary protrusions and recesses.  
   
   
       16 . (canceled)  
   
   
       17 . The anchor as claimed in  claim 13  wherein said two parts are substantially identical.  
   
   
       18 - 21 . (canceled)  
   
   
       22 . A rock bolt anchor adapted to be pressed onto a tendon of a rock bolt, said anchor comprising a body engageable with grout into which said bolt is embedded, and said anchor being shaped to be press fitted to said tendon, wherein said tendon moves through said parts in yielding.  
   
   
       23 . The rock anchor as claimed in  claim 22  and comprising a tube having an interior sized to receive said tendon.  
   
   
       24 . The rock anchor as claimed in  claim 23  wherein a portion of said tube is crushed to press fit said tube onto said tendon.