Hydraulic and earth engineering – Earth treatment or control – Rock or earth bolt or anchor
Patent
1984-07-13
1986-12-30
Husar, Cornelius J.
Hydraulic and earth engineering
Earth treatment or control
Rock or earth bolt or anchor
405258, 405288, 52155, E21D 2000
Patent
active
046326057
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with a method and apparatus for reinforcing and consolidating earth structures such as mine shafts and tunnels.
Where a tunnel or drive penetrates an earth structure it is often necessary to reinforce or otherwise confine the wall surfaces (including the roof) against collapse. Reinforcement or confinement has been achieved by steel or timber shoring members and props or fabricated arch members, but these are expensive and unsatisfactory for modern day mining techniques, particularly given the rates of tunnelling now possible. These are known as "passive" support systems as they only become effective once the earth formation fails and collapse occurs.
Of recent years dynamic support of tunnel surfaces (particularly the roof) has been achieved by the use of devices generally known as rock anchors or roof bolts. A plurality of bore holes are drilled to a desired depth in the roof, generally transversely of the direction of progress of the tunnel. The roof bolts are then inserted into the bore holes and are anchored, either by mechanical means such as wedging or by grouting with chemical or cementitious materials, at their remote inner ends. The end of the bolt adjacent the bore hole opening is screw threaded such that with the aid of a large washer and a threaded nut, the bolt may be tensioned. Tensioning of the bolts in this manner creates zones of compression within the earth structure surrounding the bolts. By carefully selecting the bolts spaced overlapping compression zones can be achieved to create, in effect, a reinforced arch structure.
In earth formations where the mechanical properties of the formation would require very close spacing of bolts, reinforcement is achieved by bolting a steel strap to the wall surface with rock bolts intermediate the ends of the girder. These straps (which may include reinforcing ribs or channels) are generally arranged transversely of the direction of progress of the tunnel and, if required, may include props adjacent the ends of the strap. Such straps may be of any suitable length but, in general, do not exceed six meters as they become too difficult to handle.
With the combination of compression zones and supported zones, a dynamic reinforced arch is thus created.
The use of steel straps in conjunction with roof bolts is generally confined to soft, crumbly or highly faulted earth formations such as coal seams, fragmented rock etc., or areas which may be subjected to high induced stresses as a result of adjacent mining action.
In either of the abovementioned "dyanmic" systems, support or reinforcement against earth formation outbursts is confined to a plurality of adjacent transverse "arches". If the region surrounding one or more of the rock bolts fails, tension in the rock bolt can reduce to zero with the result that the integrity of the reinforced "arch" fails with the likelihood of collapse. Further, if a reinforced "arch" fails or collapses, the stress release in the earth formation can cause adjacent "arches" to lose their integrity with a resultant massive collapse.
Neither of the above systems of earth formation reinforcement permits dissipation of outburst stresses to any substantial degree whereby the outburst can be resisted or supported against collpase. The steel strap may support very small portions of loosened earth formation in the immediate vicinity of the strap but no meaningful support is available between adjacent straps. Steel straps are generally constructed of light gauge steel and obtain a degree of flexural rigidity from being rolled or otherwise formed into a corrugated cross-section, generally conforming to a "W" in shape. These straps do not fully utilize the potential tensile strength of such a relatively large mass of steel. Firstly, it is not known in mining practice to interconnect these straps (apart from patterns of say two lengths at tunnel intersections) to form an elongate tensile member of "substantially continuous" length (hereinafter defined). Thus in use, the ability of the strap to support an earth
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Gearhart Australia Limited
Husar Cornelius J.
Stodola Nancy J.
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