Rock bolt with elongating section

Abstract

A rock bolt device that includes a non-anchoring elongation section that allows elongation of the rock bolt device under tensile load to accommodate rock movement after installation of the rock bolt device.

What is claimed is: 
     
         1 . A rock bolt to be installed with grout to anchor in and stabilize rock, the rock bolt comprising:
 a bolt body having a longitudinal axis and a length along the longitudinal axis between a proximal end of the bolt body to be disposed outside of the rock and a distal end to be disposed in the rock when the rock bolt is installed to stabilize the rock;   a hollow core extending longitudinally through the bolt body and open adjacent the proximal end and the distal end to permit circulation of the grout through the hollow core and around an exterior of the bolt body to secure the bolt body in place with the grout when the rock bolt is installed to stabilize the rock;   the bolt body including at least the following longitudinal sections with relative longitudinal positioning moving along the longitudinal axis in a direction from the distal end toward the proximal end:
 an anchor section comprising first exterior anchor projections to project into and anchor in the grout disposed between an exterior of the anchor section and the rock when the rock bolt is installed to stabilize the rock; 
 a non-anchoring elongation section free of anchor projections on an exterior of the non-anchoring elongation section and having material properties for longitudinal elongation of the elongation section under tensile load following installation to accommodate rock movement in an axial direction of the longitudinal axis; 
 a load absorption section comprising second exterior anchor projections to project into and anchor in the grout disposed between an exterior of the load absorption section and the rock when the rock bolt is installed to stabilize the rock; and 
 a retention section to be disposed outside of the rock when the rock bolt is installed to stabilize the rock; 
   a bearing plate engaged with the retention section of the bolt body and positionable along the retention section to contact a rock surface when the rock bolt is installed to stabilize the rock; and   wherein the bolt body has a tensile load capacity of at least 25 tons and has a pre-installation configuration prior to installation to stabilize the rock and a loaded configuration at a tensile load of 25 tons, and the elongation section has a longitudinal length in the loaded configuration that is at least 15% longer than in the pre-installation configuration.   
     
     
         2 . A stabilized rock adjacent a rock surface, comprising a rock bolt according to  claim 1  penetrating across the rock surface with the anchor section, elongation section and load absorption section disposed in the rock and with the retention section and the bearing plate disposed outside of the rock and with grout disposed between the rock and the exterior of the anchor section and the exterior of the load absorption section engaging the first and second anchor projections. 
     
     
         3 . A method of stabilizing rock, comprising:
 disposing the bolt body of the rock bolt of  claim 1  across a surface of the rock with the anchor section, elongation section and load absorption section disposed in the rock and the retention section disposed outside of the rock;   circulating grout through the hollow core and outside of the bolt body and around the exterior of the bolt body to engage the rock and the first and second anchor projections; and   positioning the bearing plate engaged with the retention section to contact the rock surface.