Multiple-point anchored rock bolt

Abstract

A rock bolt includes an elongate metallic body having a first end and an opposed second end, a threaded portion at the second end, for attaching thereto and locating thereon, a nut and a bearing plate, a mechanical anchor at, or at least partially located on, a first end portion of the body and a first resistive anchor, located between the threaded portion and the mechanical anchor.

1 . A rock bolt for being grouted in a borehole in a rock which includes an elongate body of a suitable steel material having a first distal end and an opposed second proximal end, a threaded portion at the second end, a mechanical anchor or a composite anchor at, or at least partially located on, a first end portion of the body, a second anchor integrally formed on the body, between the threaded portion and the mechanical or composite anchor, a first stem portion between the mechanical or composite anchor and the second anchor, and a second stem portion between the second anchor and the threaded portion, wherein the first and second stem portions have a smooth cylindrical surface, and wherein the second anchor is adapted to exceed the diameter of the body in at least one radial direction to be locally anchored in a grouted borehole and is adapted to be harder than the stem portions. 
     
     
         2 . A rock anchor according to  claim 1  wherein the mechanical anchor is an expansion shell-type mechanical anchor which is actuated to radially expand into frictional engagement with the walls of the borehole. 
     
     
         3 . A rock anchor according to  claim 1  wherein the composite anchor includes an expansion shell-type mechanical anchor component and an integrally formed anchor component which is adapted to exceed the diameter of the body in at least one radial direction, wherein the mechanical anchor component and the integral anchor component are consecutively serially positioned on the rock bolt body. 
     
     
         4 . A rock anchor according to  claim 1  wherein the second anchor is positioned on the body between 400 and 700 mm from the second end. 
     
     
         5 . A rock anchor according to  claim 4  wherein the second anchor is positioned 600 mm from the second end. 
     
     
         6 . A rock bolt which includes an elongate cylindrical body having a first end and an opposed second end, a threaded portion at the second end for attaching thereto, and locating thereon, a nut and a bearing plate, a mechanical anchor at, or at least partially located on, a first end portion of the body and a first resistive anchor, located between the threaded portion and the mechanical anchor. 
     
     
         7 . A rock bolt according to  claim 6  wherein the mechanical anchor is an expansion shell-type anchor. 
     
     
         8 . A rock bolt according to  claim 6  r wherein the first resistive anchor is integral with the body, formed by adapting a section of the body, between 400 mm and 700 mm from the second end, to exceed the diametric dimension of the body at least in one radial direction. 
     
     
         9 . A rock bolt according to  claim 6 , further comprising a second resistive anchor located between the mechanical anchor and the first resistive anchor. 
     
     
         10 . A rock bolt according to  claim 9  wherein the second resistive anchor is consecutively serially positioned relatively to the mechanical anchor. 
     
     
         11 . A rock bolt according to  claim 10 , further comprising a first and a second stem portion, each of which is adapted to elongate under tensile load and each of which is defined between the second resistive anchor and the first resistive anchor and the first resistive anchor and the threaded portion respectively. 
     
     
         12 . A rock anchor according to  claim 2  wherein the composite anchor includes an expansion shell-type mechanical anchor component and an integrally formed anchor component which is adapted to exceed the diameter of the body in at least one radial direction, wherein the mechanical anchor component and the integral anchor component are consecutively serially positioned on the rock bolt body. 
     
     
         13 . A rock anchor according to  claim 2  wherein the second anchor is positioned on the body between 400 and 700 mm from the second end. 
     
     
         14 . A rock anchor according to  claim 3  wherein the second anchor is positioned on the body between 400 and 700 mm from the second end. 
     
     
         15 . A rock bolt according to  claim 7  wherein the first resistive anchor is integral with the body, formed by adapting a section of the body, between 400 mm and 700 mm from the second end, to exceed the diametric dimension of the body at least in one radial direction. 
     
     
         16 . A rock bolt according to  claim 7 , further comprising a second resistive anchor located between the mechanical anchor and the first resistive anchor. 
     
     
         17 . A rock bolt according to  claim 8 , further comprising a second resistive anchor located between the mechanical anchor and the first resistive anchor.