Expansion Bolt and Mine Roof Reinforcement

This invention relates to an expansion bolt, and more particularly to an expansion roof bolt adapted to hold a pressurizing fluid therein and to expand girthwise upon pressurization of the fluid for anchorage of the bolt in a bore in the roof of a mine for supporting the roof and the method of using it to reinforce the roof.

Various types of anchoring means have been used for supporting the roof of a mine. A widely used anchoring means is the "point-anchored" expansion bolt system comprising a bolt having a head and a threaded shank, and an expansible shell unit on the shank at its end away from the head comprising a shell having a plurality of leaves and a tapered plug threaded on the shank. To anchor the bolt in a bore in the roof of a mine, the bolt with the expansible shell unit thereon is inserted in the bore and the bolt is turned, thereby moving the tapered plug down along the shank into engagement with the leaves of the shell held on the shank against movement therealong for forcing the leaves to move outwardly into engagement with the roof strata. Continued turning of the bolt moves the head up into pressurized engagement with the roof, and tensions the shank for clamping the roof strata together. Among the disadvantages of this system is that it is not effective in relatively soft roof strata, such as that found in uranium mines, and that, over time, the expansible shell unit creeps down in the bore with a resultant decrease in the clamping force applied to the roof strata by the bolt.

Another widely used anchoring means is the so-called "grouted" roof bolt system, such as shown, for example, in U.S. Pat. No. 3,940,941, involving two-component charges of epoxy resin and a bolt having a nut threaded on an end thereof. To install the bolt in a bore in the roof of a mine, charges of unmixed resin are inserted in the bore, the bolt is partially inserted in the bore and rotated to mix the components of the resin, and the bolt is fully inserted in the bore with the nut held in engagement with the roof until the resin sets. On hardening of the resin, the bolt is bonded in place, and pegs the roof strata together. However, "grouted" bolts are more difficult and more expensive to install than "pointanchored" expansion bolts, and provide insufficient load carrying capacity in roof strata having significant fractures and voids in that the resin extrudes into these openings with a resultant decrease in the strength of the bond between the bolt and the roof. Moreover, there is no inspection technique, in general use, to evaluate the integrity of the bond.

Yet another and more recently developed anchoring means is the "friction rock stabilizer" system, such as shown, for example, in U.S. Pat. Nos. 3,922,867 and 4,012,913, involving a hollow cylindrical body of steel open at its ends and split along a line parallel to its longitudinal axis to enable the body to contract girthwise upon being compressed for enabling its insertion in a bore in the roof of a mine of smaller diameter than the diameter of the tube when uncompressed. As the tube is inserted, the compressive force is released and the tube expands girthwise into pressurized frictional engagement with the surfaces of the roof defining the bore. While the body is effective in stabilizing relatively soft roof strata and in retaining its load carrying capacity upon shifting of the mine roof, its load carrying capacity is relatively limited, being essentially equal to the upward force applied to the lower end of the body to insert it in the bore.

Among the several objects of this invention may be noted the provision of an expansion bolt and method of use for anchorage in a hole such as a bore in the roof of a mine; the provision of such a bolt which is adapted to hold a pressurizing fluid and to be expanded girthwise upon pressurization of the fluid; the provision of such a bolt which clamps or compresses the roof strata together; the provision of such a bolt which pegs the roof strata together for substantially the entire portion of the length of the bolt in the bore; the provision of such a bolt which is expanded after being fully inserted in the bore; the provision of such a bolt which is effective in stabilizing relatively soft roof strata; the provision of such a bolt which has increased load carrying capacity for supporting the roof; the provision of such a bolt which applies lateral compressive force to the mine roof counteracting, at least in part, the lateral tension force present in a mine roof due to its tendency to sag; the provision of such a bolt which deforms, upon shifting of the mine roof, to retain its load carrying capacity; the provision of such a bolt having a pressure relief feature to prevent "overloading" of the bolt; the provision of such a bolt which may be readily inspected, after its installation, to establish that it remains in pressurized engagement with the surfaces of the mine defining the bore and thus is capable of supporting the roof; the provision of such a bolt which may be expanded further after its installation to increase its load carrying capacity; and the provision of such a bolt which is simple and economical to manufacture and install.

In general, an expansion bolt of this invention is adapted for insertion in an initial unexpanded condition in a hole drilled in a body (e.g., a mine roof) in which the bolt is to be anchored, and adapted to be expanded girthwise after being inserted in the hole to anchor it in the hole. It has an elongate hollow shank portion constituted by a relatively thin-walled tubular metal member closed at one end constituting its inner end as inserted in the hole and having a head at its other end constituting its outer end. The head is exteriorly threaded for reception of a nut and extends out of the hole when the bolt is anchored in the hole. The tubular member, in its unexpanded condition, is of fluted cross section, and is adapted to hold a fluid under pressure and to expand girthwise under pressure of fluid therein. The head is constructed for delivery of fluid under pressure into the tubular member whereby, following insertion of the tubular member in a hole, fluid under pressure may be delivered into the tubular member to cause it to expand girthwise into pressure engagement with the body within the hole for anchoring it in the hole.

Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.

FIG. 1 is a section through a bore in the roof of a mine showing an expansion bolt of this invention therein, prior to the girthwise expansion of the bolt;

FIG. 2 is a transverse section of the bolt on line 2--2 of FIG. 1;

FIG. 3 is an enlarged longitudinal section of the lower end of the bolt on line 3--3 of FIG. 1; and

FIG. 4 is a view similar to FIG. 1 showing the bolt expanded girthwise into pressurized engagement with the surfaces of the mine roof defining the bore.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Referring to FIG. 1 of the drawings, there is generally indicated at 1 an expansion bolt of this invention comprising a hollow shank portion 3 shown extending up in a drill hole or bore 5 in the roof 7 of a mine, and a threaded portion constituting a head 9 shown extending down out of the bore and having a nut 11 threaded thereon. As best illustrated in FIG. 3, a roof bolt plate 13 and a washer 15 are carried on the head, the washer 15 bearing on the upper or inner face of the nut, the roof bolt plate 13 bearing on the upper or inner face of the washer. With the hollow shank portion 3 anchored in the bore 5, in a manner described hereinafter, the nut 11 may be turned to bring the roof bolt plate 13 into pressurized engagement with the mine roof 7 for supporting the roof.

In particular, the hollow shank portion 3 of the bolt comprises a relatively thin-walled tubular metal member 17, more particularly a a thin-walled tube 17 of suitable deformable material such as a low-carbon steel (e.g., 1016 carbon steel) of a suitable thickness (e.g., one-eighth inch), and of a suitable length (e.g., 3-5 feet long). The tube is crimped and welded closed at one end 18 (i.e., its upper or inner end), as shown in FIG. 1, and is threaded at its other (lower) its or outer end, as shown in FIG. 3, the head 9 being threaded onto the lower end of the tube and closing the tube thereby enabling the bolt to hold pressurizing fluid such as water therein. Upon pressurization of the fluid, the tube 17 is adapted to expand girthwise. To facilitate this expansion, the tube 17 which of a suitable outer diameter (e.g., 13/8-13/4 inch), in its unexpanded condition, is so formed as to be of fluted cross section with a generally circular overall outline. More particularly, the tube has a recess 19 in its outer periphery extending from the closed upper end 18 of the tube down toward but stopping short of the lower end of the tube. When viewed in transverse section, as shown in FIG. 2, the tube is of closed cross section, forming a first portion 20 which is its major portion, in the shape of an arc of a circle and a second generally U-shaped portion 21 bent inwardly to a position within the confines of the circle. Portion 20, being in the shape of an arc of a circle, has a generally cylindrical outer surface.

The head 9 is generally cylindrical, having a circular recess 23 in its upper end and a circular passage 25 of smaller diameter than the recess extending down through the head from the recess to the lower end of the head, a shoulder 27 thereby being formed in the head between the recess 23 and the passage 25. The recess 23 and the passage 25 are internally threaded, the recess receiving the lower end margin of the tube 17 in threaded engagement, with the lower end of the tube engaging the shoulder 27, the passage receiving a threaded plug 29 in threaded engagement.

The plug 29 has an axial hole 31 therein opening into a conical recess in the upper surface thereof constituting a valve seat 33. A threaded adapter of a line (not shown) to a source of fluid under pressure (not shown) is adapted to be threaded on the plug for enabling flow of fluid into the tube 17 via the hole 31 in the plug and the passage 25 in the head. The plug further has a projection 34 of generally square section at its lower end enabling the plug to be turned by a wrench or other suitable tool to advance the plug up in the passage 25 in the head. With fluid held in the bolt, the plug 29, on being advanced up in the passage 25, displaces fluid from the passage up into the tube 17, the plug and the passage thus constituting an expansible chamber means for pressurizing the fluid held in the tube.

A valve member 35 is provided in the passage 25 for holding fluid in the bolt and means, such as a disc 37, is secured in the passage for retaining the valve member in the passage. The valve member 35 has a conical central portion 39 engageable with the valve seat 33 in the plug, a lower projection or stem 41 extending down in the hole 31 in the plug, and an upper projection or stem 43 extending up in the hole in the disc 37, the projections or stems holding the valve member in alignment with the valve seat. The valve member 35 functions as a check valve being movable away from the valve seat 33 in the plug 29 for flow of fluid into the tube 17 and moving into engagement with the valve seat 33 to block fluid flow out of the tube. In addition, the valve member 35 is constructed of a suitable elastomeric material such as natural or synthetic rubber or a low yield strength material such as aluminum, and thus also functions as a relief valve for the bolt in being adapted to be extruded out of the hole 31 in the plug when fluid pressure above a predetermined level is developed in the bolt, such as may occur on shifting of the mine roof and resultant compressive deformation of the tube.

To anchor a bolt 1 of this invention in a bore 5 in the roof 7 of a mine, the bolt, in its unexpanded condition, is inserted into the bore, with the head 9 thereof extending down out of the bore, as shown in FIG. 1. A threaded adapter (not shown) of the line to a source of fluid under pressure (not shown) is threaded on the plug 29, and fluid at a predetermined pressure is introduced into the bolt to expand the tube girthwise into pressurized engagement of its generally cylindrical outer surface with the surfaces of the roof defining the bore for anchoring the bolt in the bore as shown in FIG. 4. The roof bolt plate 13 and washer 15 are positioned on the head, and the nut 11 is threaded up on the head to bring the roof bolt plate 13 into pressurized engagement with the roof 7 for supporting it, the load carrying capacity of the bolt for supporting the roof being a function of the magnitude of the static frictional force between the bolt and the surfaces of the mine defining the bore 5 and thus of the pressure of the fluid in the bolt.

Shifting of the mine roof 7 may affect the load carrying capacity of the bolt. Being deformable, the bolt accomodates most shifts of the mine roof and retains its as-installed load carrying capacity. However, to ensure that the bolt is properly anchored, the bolt may be inspected (monitored) from time to time by measuring the pressure of the fluid. The check valve member 35 is readily opened from outside the head 9 for this purpose. If the fluid pressure is found to be below a predetermined level, the pressure may be increased by reconnecting the line to the source of fluid under pressure (not shown) to the plug 29, or by turning the plug 29 to advance it up in the passage 25. In the event that the shifting of the mine roof causes compressive deformation of the bolt of sufficient magnitude as to increase the fluid pressure above a predetermined relief pressure, the valve member 35 is extruded through the hole 31 in the plug 29 to release the fluid in the bolt.

In certain respects, the expansion bolt of this invention, when anchored, supports the roof in a manner similar to each of the prior art types of anchoring means. Like the "point anchored" mechanical bolt, the bolt of this invention, upon tightening of the nut 11 thereon, effects a clamping of the roof strata. Like the "grouted" bolt system, the bolt of this invention pegs the roof strata together. And like the "friction rock stabilizer" system, the bolt of this invention is effective in relatively soft roof strata, and retains its load carrying capacity on most shifts of the mine roof. However, the bolt of this invention in contrast to the prior art anchoring means has increased load carrying capacity, may be inspected to ensure proper anchorage, and applies a lateral compressive force to the mine roof counteracting, at least in part, the lateral tension force present in the roof due to the tendency of the mine roof to sag.

While the bolt 1 of this invention has been described above and shown in the drawings as being anchored in a bore 5 in the roof of a mine, it is contemplated it could be anchored in a hole in other structures such as the floor or wall of a building. Moreover, while the upper end 18 of the tube 17 is described and shown as being closed by crimping and welding and the head 9 threaded on the lower end of the tube, it is contemplated that the upper end of the tube could be closed by an end cap (not shown) welded or threaded to the upper end of the tube, and the head 9 welded onto the lower end of the tube.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.