BACKGROUND OF THE INVENTION [0001]This invention relates to a friction rock bolt.

[0002] A friction rock bolt includes an elongate tubular member of convoluted form which is expanded by means of a pressurised fluid, typically pressurised water, in a radial sense so that an outer surface of the tubular member engages frictionally with a wall of a borehole in which the elongate member is positioned. An advantage of this type of process is that the bolt almost immediately exhibits a full load capacity.

[0003] It is evident that the rock bolt can only be installed if a suitable borehole has been formed. The latter task is carried out through the use of an appropriate drilling machine and, thereafter, the rock bolt is placed in position and pressurised.

[0004] An object of the present invention is to provide a friction bolt which expedites the drilling and pressurization processes.

SUMMARY OF INVENTION [0005] The invention provides a self-drilling expansion friction bolt which includes an elongate tubular member with a bore, a first end and an opposed second end, a sacrificial drill bit mounted to the first end, a connector assembly at the second end which is configured to be connected to a drilling machine and to a pressurised fluid source, a fluid passage between the connector assembly and the drill bit, and a valve mechanism which is operable to allow fluid from the source at a pressure below a first pressure to flow through the fluid passage to the drill bit thereby to flush the drill bit, and to allow fluid from the source at a pressure above the first pressure to flow into the bore thereby to expand the elongate tubular member in a radial direction. [0006] The fluid passage may comprise the bore. Alternatively, the self-drilling expansion friction bolt includes a flushing tube which extends from the valve mechanism to the drill bit and the flushing tube includes the fluid passage, and the valve mechanism is located at a second end of the flushing tube. [0007] Preferably, the valve mechanism includes a valve seat which defines a fluid flow aperture, a valve member and a biasing component which acts on the valve member to bias the valve member away from the seat, and the valve member is movable by pressure of the fluid into engagement with the valve seat when the fluid pressure exceeds said first pressure. [0008]The connector assembly may include a first connector which is configured to be connected to the drilling machine, and a second connector which is configured to be connected to the pressurized fluid source.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention is further described by way of examples with reference to the accompanying drawings in which:

Figures 1 and 2 are schematic representations of different embodiments of a self drilling expansion friction bolt according to the invention;

Figures 3 and 4 are end views of a self drilling expansion friction bolt of the kind shown schematically in Figure 1 depicting the bolt prior to and after pressurization;

Figure 5 shows, in elevation, a self drilling expansion friction bolt according to the invention;

Figure 6 is a view in perspective of an end of a tubular member which is included in a self drilling expansion friction bolt according to the invention;

Figure 7 and Figure 8 are side views in section of one end of a self drilling expansion friction bolt which is similar to the bolt shown schematically in Figure 1 ; Figure 9 illustrates an upper end of a self drilling expansion friction bolt of the kind shown schematically in Figure 1 ;

Figure 10 shows an upper end and a lower end, of a self drilling expansion friction bolt of the kind shown schematically in Figure 2; and

Figures 1 1 and 12 are side views in section of one end of a self drilling expansion friction bolt according to another embodiment of the invention, in different modes of operation. DESCRIPTION OF PREFERRED EMBODIMENTS

[0010]The invention is concerned with a self drilling expansion friction bolt which includes a sacrificial drill bit which enables the bolt to be used for the drilling of a borehole in a body of rock and, once the drilling process has been completed, for the bolt to be installed by internally pressurizing the bolt with a suitable pressurized fluid e.g. water which inflates the bolt in a radial sense. This one-pass approach significantly reduces the time needed for installation of the bolt.

[0011] Figures 1 and 2 schematically depict self drilling expansion friction bolts 10 and 12 respectively according to different embodiments of the invention.

[0012]The self drilling expansion friction bolt 10 includes an elongate tubular member 14 of convoluted form (as is described hereinafter) with a first end 16 and an opposed second end 18.

[0013] A sacrificial drill bit 20 is welded or engaged with a thread connection or in any other suitable way with the first end 16. The nature of the drill bit, e.g. a cross bit or a button bit, is determined according to the ground conditions i.e. the characteristics of the rock in which the bolt is to be installed.

[0014]A connector assembly 22 is located at the second end 18. This assembly includes a first connector 24 and a second connector 28. The first connector 24 is welded to the second end 18. This connector is configured to be connected to a drilling machine (not shown) of a standard type so that drilling action can be imparted to the self drilling expansion friction bolt 10 once the bolt is engaged with the drilling machine.

[0015] The second connector 28 is attached to the second end 18. This connector has a standard construction and it is therefore not described in detail herein. A flow path 30 extends through the connector 28. This connector is designed to be connected to a source of pressurised water, not shown.

[0016] A valve mechanism 34 is mounted to the second end 18. The valve mechanism is in flow communication with the flow path 30. Fluid from the flow path 30 can flow to the valve mechanism 34 and through ports 36 into an interior or bore 38 of the tubular member 14. Alternatively, in a different form of construction, fluid from the second connector 28 can bypass the valve mechanism 34 and flow through the ports 36 into the interior 38.

[0017] The self drilling expansion friction bolt 10 can have two possible forms of construction. In a first form a flushing tube 40 extends from the valve mechanism 34 to a flushing passage 42 of the sacrificial drill bit 20. In a second form of the self drilling expansion friction bolt 10 a flushing tube 40A is positioned inside the interior 38 and extends from the valve mechanism 34 to the flushing passage 42.

[0018]The self drilling expansion friction bolt 10, once connected to a drilling machine via the first connector 24, can be used to drill a borehole into a body of rock. The sacrificial drill bit 20 is adequate for the drilling of a single borehole only and thereafter is effectively non-functional. The drill bit 20 is left in the borehole after the drilling thereof.

[0019] During the drilling process a source of a flushing liquid, e.g. water, is connected to the second connector 28. Water is passed through the valve mechanism 34 via the tube 40 or the tube 40A, depending on the configuration, into the flushing passage 42 in the sacrificial drill bit 20. This water is used to flush detritus produced by the drilling process in a manner which is known in the art. [0020]The flushing water is directed to the second connector 28 at a pressure of 5mPa to 10mPa i.e. the pressure is relatively low. At the end of the drilling exercise the drilling machine is disconnected from the first connector 24 and the pressure of the water supplied to the second connector 28 is increased, say, to 30mPa. At this stage the valve mechanism 34 automatically closes so that water no longer flows through the tube 40 or 40A, as the case may be. Also, by this time, the interior or bore 38 of the tubular member 14 is more than likely filled with water due to the flow of water which took place through the ports 36. In each case, as water no longer flows through the tube 40 or 40A, the interior 38 is pressurised. [0021] As the pressure increases in the interior 38, the convoluted tubular member 14 expands in a radial sense and its outer surface is urged into tight frictional contact with a wall of the borehole in which the tubular member 14 is located. The maximum expansion of the tubular member 14 occurs once the pressure in the interior 38 reaches a value of, say, 30mPa (this is exemplary and non-limiting) and at that time a device used to pressurise the water, e.g. a pump, automatically turns off. The coupling of the water source to the second connector 28 is then released, leaving the friction bolt 10 in position in the borehole and frictionally engaged with the wall thereof. Water can drain from the interior 38.

[0022] Figure 3 schematically depicts in cross section the self drilling expansion friction bolt 10 prior to pressurisation while Figure 4 shows the self drilling expansion friction bolt 10 after pressurisation.

[0023]The tubular member 14, prior to pressurization, has a convoluted shape comprising a "C-section" 14A and an elongate inwardly extending channel formation 14B in its outer surface. The tube 40 is positioned inside the formation 14B. The cross-sectional dimensions of the tubular member 14 are such that the member 14 is initially loosely positioned inside a borehole 48 which is formed by means of the sacrificial drill bit 20. Due to the loose fit the flushing water directed to the sacrificial drill bit 20 can flush effectively.

[0024] The friction bolt 2 shown in Figure 2 has a number of similarities to the friction bolt 10 and, where applicable, like reference numerals are used to designate like components. The friction bolt 12 does not include the flushing tube 40 nor the tube 40A. Instead, the interior 38 of the tubular member 14 is used to direct flushing water from the second connector 28 to the sacrificial drill bit 20. A further difference is that the valve mechanism 34 is not at the second end 18 but, instead, it is positioned at an interface 50 of the sacrificial drill bit 20 and the tubular member 14. Thus flushing water can pass from the second connector 28 into the interior 38 and, via the valve mechanism 34, into the flow passage 42 in the drill bit 20. Once the pressure of the water entering the second connector 28 increases, the valve mechanism 34 closes automatically and the interior 38 of the tubular member 14 is pressurised leading to the radial expansion of the tubular member 14 into frictionai engagement with a wall of a borehole in which the tubular member 14 is located.

[0025] Figure 5 is a view in elevation of a practical embodiment of the self drilling expansion friction bolt 10. Components which are the same as those shown in Figure 1 bear like reference numerals and are not further described in detail. In the self drilling expansion friction bolt 10 shown in Figure 5 the first connector 24 has an outer threaded shape 54 to enable it to be engaged with a drilling machine, as is known in the art. Also a load-bearing washer or plate 56 is located adjacent the first connector 24.

[0026] Figure 6 illustrates the second end 18 of the tubular member 14 with the flushing tube 40 positioned within the elongate channel formation 46.

[0027] Figure 7 shows, in section, a part of the end 18 of the self drilling expansion friction bolt 10, but without the load-bearing plate 56. The tubular member 14 extends into a socket 60 inside the second connector 24 and abuts a plate 62 which acts as a valve seat 64. An aperture 66 is formed in the valve seat 64 and is located so that a lower end 68 of the flushing tube 40 surrounds an exit side of the aperture 66.

[0028JA conical valve member 72 is positioned inside the socket 60 between the second connector 28 and the aperture 66. A spring 74 biases the valve member 72 away from the aperture 66. When water at a pressure of, say, 5mPa to 10mPa, goes through an entry passage 28A of the second connector 28, the force which is exerted by the spring 74 is sufficient to keep the valve member 72 away from the aperture 66 and the flushing water can thus flow through the tube 40 to the sacrificial drill bit 20, in the manner which has been described.

[0029] Once the hole-drilling process has been completed the water pressure is increased. The force exerted by the spring 74 on the valve member 72 is exceeded and, as a consequence, the valve member 72 is displaced by the water pressure to a position, shown in Figure 8, at which a conical end 72A of the valve member 72 is forced into sealing engagement with the aperture 66. The water, which has a high pressure of, say, 30mPa, then flows through small ports 36 in the plate 62 and the interior 38 of the tubular member 14 is pressurised. The pressure builds up in the interior 38 and the tubular member 14 is expanded in a radial sense. At a limiting pressure of, say, 30mPa the tubular member 14 is fully expanded into frictional engagement with a wall of a borehole within which the member 14 is located. A pump (not shown), which is used to pressurise the water, then turns off and the self drilling expansion friction bolt is left in position in the borehole, fully installed.

[0030] Figure 9 illustrates the upper end 16 of the tubular member 14. The flushing tube 40 is in direct fluid communication with the flushing passage 42 inside the sacrificial drill bit 20. The drill bit 20 is of any suitable shape, depending on the ground conditions, and includes outlet ports 80 through which the flushing water can flow, carrying with it rock, dust and particles caused by the drilling process.

[0031] Figure 10 is a view of the first end 16, and of the second end 18, of a practical embodiment of the self drilling expansion friction bolt 12 shown in Figure 2. Like reference numerals are used to indicate like components. The valve mechanism 34 is not shown in detail for it is the same as what is shown in Figures 7 and 8. The valve mechanism 34 is positioned so that the valve member 72 is biased out of engagement with an entry into the flushing passage 42 in a component 20A which is used to connect the sacrificial drill bit 20 to the first end 16 of the tubular member 14. [0032] Water which is fed to the self drilling expansion friction bolt via the second connector 28 flows directly into the interior 38 of the tubular member 14 and then through the valve mechanism 34 to the flushing ports 80 of the sacrificial drill bit 20. Once the drilling process has been completed the water pressure is increased and the valve mechanism 34 automatically closes, shutting off the flow of flushing water to the drill bit 20. The tubular member 14 is then internally pressurised and is radially expanded into direct frictional engagement with a wall of a borehole in which the friction bolt is located.

[0033] Figures 1 1 and 12 show a valve mechanism 34A which differs from the mechanism 34. A conical valve member 84, with a guide pin 86 positioned at a mouth 88 of a flushing tube 90 which is located at a plate 92 inside the bore 38A. [0034] A tension spring 94 draws the valve member 84 away from the mouth 88 to allow water flow into the tube 90.

[0035] When water at a pressure of, say, 30 mPa flows through an entry passage 28A of the second connector 28, the force exerted by the spring 94 is overcome and the conical valve member 84 is displaced to a position shown in Figure 12 at which the conical valve member 84 is forced into sealing engagement with the mouth 88 of the tube 90. The water then fills the interior 38 through ports 98 in the plate 92 thereby to pressurize the tubular member 14 internally and to expand the tubular member in a radial sense.

[0036] Each of the valve mechanisms 34 and 34A displays the characteristic that the valve mechanism moves automatically between an open position (low water pressure) at which flushing of the drill bit takes place and a closed position (high water pressure) at which the tubular member 14 is radially expanded. Arduous conditions exist in underground locations and in some instances a valve, inadvertently, can move from an open position to a closed position. If the valve were then to remain in the closed position it would not be possible to recommence the drilling operation for, without flushing water flowing through the drill bit, it is more than likely that the drill bit would become jammed in the borehole. However, with a valve mechanism (34, 34A) of the kind described, if the valve mechanism does, inadvertently, switch to the closed position then the drilling process is stopped and the supply of water to the friction bolt is interrupted. In most instances the reduction in water pressure, inside the tubular member, is then sufficient to cause the valve mechanism to switch to the open position and drilling can then recommence with flushing water being supplied to the drill bit.

[0037]Tests conducted on the expansion bolt of the invention have established that the bolt can withstand the effects of dynamic loading (due to rock movement) and, depending on the size of the bolt, can absorb a minimum of 27 kilojoules of energy.