Pick Arm Anchor Assembly

In mining and tunneling operations, roof bolts with expansion shell type anchors are used extensively. The expansion shell type anchors have proven to be ineffective in tunnel strata or mine roof strata composed of soft rock formations; consequently they contribute to unsafe working conditions in tunnels and mines. Where the pressure exerted through the expansion shell to the wall of the bolt hole exceeds the compressive strength of the rock formation, the yielding rock strata decreases the load bearing capacity of the roof bolt assembly.

The pick arm anchor assembly provides a means by which the anchoring point of the pick arm can be deeply imbedded into the wall of the bolt hole, providing a more effective anchor for the roof bolt in soft rock formations.

The conventional anchor assembly employs a threaded wedge nut to advance down the threaded stem of a roof bolt as the bolt is rotated (tightened) and engage and expand an outer expansion shell unit (or the wings thereof) into the walls of a bolt hole, and the maximum expansion of the conventional expansion anchor is limited to one half (1/2) or less of the diameter of the anchor assembly. The anchoring ability is based on the friction created between the expansion shell wings and the wall of the bolt hole, by transverse thrust forces of the anchor and the transverse stress resistance of the rock strata of the wall of the bolt hole.

Reference is made to the following U.S. Pats., believed to disclose the state of the art as presently utilized in mining and other operations:

No. 691,921 1902 Wheeler;

No. 3,022,700 1962 Dempsey;

No. 3,139,730 1966 Williams.

The pick arm anchor assembly uses an off-center bias slanted thrust wedge to force the pick arm (with a sharp pointed configuration) into the interior wall (rock strata) of the bolt hole. The off-center bias design permits greated depth of penetration by the pick arm than that of a symmetrical expanding shell for a given hole diameter. Although the pick arm anchor assembly has a friction surface on a backup wing to grip the interior of the bolt hole, the pointed part of the pick arm is designed to penetrate the rock strata exposed in the interior of the bolt hole. Penetration of the rock strata by the pick arm utilizes the longitudinal stress resistance of the rock to assist in the anchoring function. The back up wing utilizes the transverse stress resistance of the rock strata to assist in the anchoring function. The pointed configuration of the point of the pick arm allows a unit of thrust applied through the roof bolt stem and in turn through the bias thrust wedge to the pick arm to be concentrated in a much smaller surface area of the bolt hole wall than is possible from the wings of a conventional expansion shell anchor. The greater anchoring ability in soft rock formations provides for safer working areas where the pick arm anchor is employed.

FIG. 1 Partial sectional view of the pick arm anchor assembly installed in a bolt hole in connection with a conventional expansion type roof bolt anchor assembly. This view is before the assembly is tightened, or anchored in the bolt hole.

FIG. 2 A partial sectional view of the pick arm anchor assembly with a conventional type expansion shell anchor, after the assembly has been tightened or anchored in place in the bolt hole wall.

FIG. 3 A frontal sectional view of the pick arm anchor assembly

FIG. 4 A top view of the bias thrust wedge

FIG. 5 A top view of the wedge shaped backup wing

FIG. 6 A top view of the pick arm

FIG. 7 A perspective view of the bias thrust wedge

FIG. 8 A perspective view of the pick arm

FIG. 9 A perspective view of the backup wing (from the back side)

FIG. 10 A perspective view of the elastic band or sleeve

FIG. 11 A perspective view of the stabilizer

FIG. 12 A perspective view of the pick arm anchor assembly

FIG. 13 A partial sectional view of the pick arm and thrust wedge in an alternate configuration of a multiple pick arm anchor assembly

FIG. 14 A top view of the threaded base nut

FIG. 15 A front sectional view of a conventional expansion shell type roof bolt anchor assembly and the threaded end of a mine roof bolt.

FIG. 16 A diagram of the rock stress resistance to a pick arm installed in place in the wall of a bolt hole.

FIG. 17 Alternate configuration of dual pick arm assembly (sectional view)

The pick arm bolt hole anchor assembly consists of a bias thrust wedge (7), a pointed pick arm (8), a wedge shaped backup wing (9), a stabilizer (12), a threaded base nut (10), and an elastic band or sleeve (11). When the pick arm anchor is used in connection with a conventional expansion shell type anchor assembly and assembled to a mine roof bolt, the stabilizer (12) is inserted over the threaded end (6) of a mine roof bolt stem, prior to the attaching of the conventional expansion shell type anchor (FIG. 15) to the mine roof bolt hole stem (6). The bail (5b) of the conventional expansion shell assembly (FIG. 15) should be removed from the expansion shell assembly prior to assembly on the stem (6) of the roof bolt. After the conventional expansion type shell assembly (FIG. 15) is attached to the roof bolt stem (6), the threaded base nut (10) is threaded to the top of the roof bolt stem (6), the pick arm (8) is then attached with the feet (8D) beneath the base of the threaded base nut (10), the bias thrust wedge (7) is then placed on the end of the stem (6) of the roof bolt so that the concave surface (7E) is in contact with the threaded end (6) of the roof bolt stem, the backup wing (9) is then attached with the feet (9C) beneath the base of the threaded base nut (10), the assembly is then held together with an elastic band (11). The complete assembly (pick arm anchor and conventional expansion shell) is then ready to be inserted into the roof bolt hole (2) and tightened in the hole. As the stem of the roof bolt (3) is turned, it tightens the conventional expansion shell (FIG. 15) within the hole, as it tightens, the wedge nut (5A) advances down the stem (6) of the roof bolt, at the same time the pick arm bolt hole anchor (7) (8) (9) (10) is activated by the outward motion of the pick arm (8) and the backup wing (9) caused by the thrust of the bias thrust wedge (7) which is thrust upward by the end of the roof bolt (6) after the conventional expansion shell (FIG. 15) has engaged or locked into the interior wall (2) of the bolt hole. When the conventional anchor engages the wall of the hole (2) the bolt hole stem (6) advances upward into the hole, activating the pick arm assembly (FIG. 1, FIG. 2). The upward force of the end of the bolt (6) against the concave surface of the thrust wedge (7E) exerts pressure transversely to both the pick arm (8) and the backup wing (9) causing the pick arm point (8A) to be forced into the rock strata exposed in the interior of the bolt hole (2) and the backup wing (9) to be tightly forced against the interior surface of the bolt hole (2), the feet of the pick arm (8D) and the feet of the backup wedge (9C) being held against the base of the threaded base nut (10) prevent the pick arm (8) and backup wing (9) from advancing upward in the hole as the end of the roof bolt stem (6) advances upward in the hole. The stabilizer (12) fits snugly against the interior wall of the bolt hole (2) and prevents the pick arm assembly (FIG. 1, FIG. 2) from rotating in the hole as the roof bolt stem (6) (3) is turned to tighten the assembly in the hole. The bail (5B) of the conventional expansion shell (FIG. 15) is unnecessary when used in connection with the pick arm assembly (FIG. 1, FIG. 2.) and should be removed prior to attachment of the pick arm anchor (FIG. 1, FIG. 2) to the end of the roof bolt stem (6). By variation in the angle of slope (FIG. 1,x) of the coplanar slope surface of the pick arm (8B) and the thrust wedge (7A) both the depth of penetration and the rate of penetration of the point of the pick arm (8A) into the wall of the bolt hole (1) can be controlled. The pick arm anchor may be used with a mine roof bolt (6) without the conventional expansion shell assembly (FIG. 15), and as an alternate employment, a plurality of pick arms in one assembly (FIG. 13), or as another alternate employment a dual pick arm anchor assembly (FIG. 17). FIG. 16 is a diagram showing the transverse (15) and the longitudinal (16) thrust of a pick arm in relation to the transverse (13) and longitudinal (14) stress resistance of rock strata in a bolt hole wall. Preferred material for construction of the invention is steel (except the elastic band) in conformance with ANSI/ASTM Specification F432 "Roof and Rock Bolts and Accessories".