AN IMPROVED LOAD SUPPORT SYSTEM

FIELD OF THE INVENTION

[0001] This Invention relates to an improved system for load support between a hanging and a foot wall of a mine.

BACKGROUND OF THE INVENTION

[0002] An example of a typical preload device Is that described in South African patent no. 1998/07928. This device has an inflatable pressure vessel body with a one-way valve through which water is introduced Into the body in inflation of the device. The device is placed atop a timber elongate prop in a conventional timber prop and preload device system (hereinafter referred to as a "load support system"). The system is then installed between the hanging and foot walls of the mine to provide load support to the hanging wall by inflating the device.

[0003] it is practice that the preload device is installed with very little if any space is left between the device and the hanging wail. When the preload device is inflated, expanding axiaily, the timber prop accommodates for this expansion by compressing. On inflation of the preload device, therefore, the load support system becomes a rigid system with little potential for energy adsorption outside of the timber prop. The timber prop becomes the limiting component of the system.

[0004] This is a problem as timber is a natural product and the load yielding capacity of the wood, before failure, will vary greatly between props. This variability is a result of variability In the growing parameters (temperature, soil, elevation and rainfall) of the trees providing the timber.

[QOGSJFor safety reasons, a load support system cannot be designed around the relatively high average load before failure value. The load support array within a mine is only as good at its weakest point and approximately half of the support systems will fail below the average load. And so, because of the high variability in load support, and to take into account another variable being the mine specific closure rates (rate of closure between the hanging and the foot wall), a standard is adopted to mitigate against the safety issues of this variability. This standard is the 90% confidence level i.e. 90% of the poles of a particular diameter, say 18cm, will achieve a significantly below average peak load level before failure.

[0006] In application, the load support specification of the typical load support system will be set at this 90% confidence level. If a higher 90% confidence level is required, a larger diameter timber prop will be required, at concomitant cost. The cost could be reduced by increasing the spacing between the support system installations with the larger diameter props. However, this solution is not always possible because of the jointing, and therefore block formation, in the hanging wall.

[0007] The invention at least partially solves the aforementioned problems.

SUMMARY OF INVENTION

[0008] In one aspect, the invention provides a preload device which includes: a pressure vessel body which includes; an outer dished component which comprises an outer base wail and an outer sidewall circumscribing the outer base wall; and an inner dished component; with an inner base wail and an inner sidewaii circumscribing the Inner base wail and which inner dished component is received in the outer dished component to provide a socket, bordered by the inner cylindrical sidewaii, in which an end portion of a prop is received; with the inner sidewaii contiguous with the outer sidewaii along a sealed join line to seal an interior of the body; a pressure releasing inlet valve extending through a wail of the body through which a hydraulic fluid is passed to inflate the body; wherein the outer base wail is profiled to define a first plane against which a hanging wall abuts; wherein the inner base wall, within the socket, is profiled to define a second plane on which an end of the prop finds support; and wherein the first plane is spaced from the second plane in an axial direction of the prop.

[0009] At least one of the outer or the inner base walls may have a plateaued profile atop which the first plane or the second plane respectively is defined.

[0010] Alternatively, at least one of the outer or the Inner base walls may be formed with at least one ridge, the apex of which defines the first plane or the second plane respectively. [0011] The at least one ridge may be an annular ridge.

[0012] Further alternatively, at least one of the outer or the inner base walls may be formed with a plurality of conical protrusions, the apices of which define the first plane or the second plane respectively.

10013] The first plane may be spaced from the second plane by between 1u-30mm, Preferably, the first plane is spaced from the second plane by 20mm.

[0014] The pressure releasing inlet valve may be a valve as described in South African patent no. 2003/6369 or 2005/8691 which specifications are herein incorporated by reference.

[0015] The Invention also provides a load support system which includes an elongate timber prop which extends between a first end and a second end and a preload device which has a pressure vessel body which comprises an outer dished component with an outer base wall, which is profiled to define a first plane against which a hanging wall abuts, and an outer sidewali circumscribing the outer base wall, and an inner dished component, which is received in the outer dished component to provide a socket adapted to receive a first end portion of the prop, and which has an inner base wall, which is profiled to define a second plane which is spaced from the first plane and on which the first end of the prop finds support and an inner sidewali circumscribing the inner base wail, with the inner sidewali contiguous with the outer sidewali along a sealed join line to seal an interior of the body, and a pressure releasing inlet valve extending through a wall of the body through which a hydraulic fluid is passed to inflate the body. [0016] At least one of the outer or the inner base walls may have a piateaued profile atop which the first plane or the second plane respectively is defined.

[0017] Alternatively, at least one of the outer or the inner base walls may be formed with at least one ridges, the apex of which defines the first plane or the second plane respectively.

[0018] The at least one ridge may be an annular ridge.

[0019] Further alternatively, at least one of the outer or the inner base wails may be formed with a plurality of conical protrusions, the apices of which define the first plane or the second plane respectively.

[0020] The first plane may be spaced from the second plane by between 10-30mnv Preferably, the first plane is spaced from the second plane by 20mm.

[0021] The pressure releasing inlet valve may be a valve as described in South African patent no. 2003/6369 or 2005/6691 which specifications are herein incorporated by reference.

[0022] The invention extends to a method of providing load support between a hanging wall and a footwail of a mine excavation which includes the steps of:

(a) providing a preload device which has a pressure vessel body which comprises an outer dished component with an outer base wall which is profited to define a first abutment plane, and an outer sidewail circumscribing the outer base wall, and an inner dished component, which is received in the outer dished component to provide a socket, and which has an inner base wall which is profiled to define a second abutment plane, which is spaced from the first abutment plane, and an inner sidewa!l circumscribing the inner base wall and which inner sidewall is contiguous with the outer sidewali along a sealed join line to seal an interior of the body, and a pressure releasing inlet valve extending through a wall of the body;

(b) providing an elongate timber prop which extends between a first end and a second end;

(c) engaging the preload device with the timber prop by placing a first end portion of the prop into the socket provided by the preload device with the first end engaging the inner base wall on the second abutment plane;

(d) placing the timber between the hanging wall and the fooiwai! with the second end of the prop engaged with the footwail and with the hanging wail lying adjacent to, or in contact with, the outer base wali of the preload device on the first abutment plane; and

(e) inflating the preload device in a first step, with hydraulic fluid input through the inlet valve, in which the outer and inner base walls are pushed into spaces defined between the base wails and first and the second abutment planes respectively.

[0023] The method may include the additional step, after step (e), of inflating the preload device in a preload step in which the outer wail in the first abutment plane is pushed into load bearing contact with the hanging wall and the inner wali in the second abutment plane is pushed into load bearing contact with the first end of the prop. [0024] From another perspective, the invention provides a preload device which includes a pressure vessel body which includes an outer dished component with comprises an outer base wall and a first sidewall circumscribing the outer base wall, and an inner dished component with an inner base wall and an second sidewall circumscribing the inner base wall, which inner dished component is received in the outer dished component to provide a socket, bordered by the inner sidewall, to receive an end portion of a prop in use, an arched wall continuous with either the first or the second sidewall that joins the first sidewail to the second sidewall along a sealed join line to seal an interior of the body, and a pressure releasing inlet vaive extending through a wall of the body through which a hydraulic fluid is passed to inflate the body, wherein the inner base wall and the outer base walls align on a separation plane and wherein at least the inner base wall or outer base wall is formed with at least one spacing formation, within the socket, which protrudes from the separation plane.

[0025] The spacing formation may be an annular ridge or fold, a raised circular or plateaued formation or the like.

[0026] The pressure releasing inlet valve may be a valve as described in South African patent no. 2003/6369 or 2005/6691 which specifications are herein incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The various aspects of the invention are described with reference to the following drawings in which: Figure 1 is a view in perspective of an embodiment of a preload device according to the invention;

Figure 2 is a view in plan of the preload device of Figure 1;

Figure 3 is a cross sectional view of the preload device through line 3 - 3 of Figure 2;

Figures 4A to 40 are, respectively, cross sectional views of other embodiments of the preload device of the invention, in each case illustrating the spacing between a first plane of the outer base wall and a second plane of the inner base wail; and

Figures 5A and 5F diagrammatica!ly and sequentially illustrate the steps of a method of providing load support between a hanging wall and a footwali in accordance with another aspect of the invention;

Figure 6 is a graph illustrating load deformation curves of a typical load support system of the state of the art; and

Figure 7 is a graph illustrating load deformation curves of a load support system in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0026] In one aspect of the invention, a preload device 10 is provided. This preload device is used in a load support system, employing a method of providing load support between a hanging wall and a footwali of a mine excavation, in accordance with other aspects of the invention.

[0029] The preload device 10 is shown, in various embodiments, in Figures 1 -3. Common to the embodiments, the device includes a pressure vessel body 12, which 9

Is made from ductile sheet metal such as a suitable mild steel typically having a thickness of between 1.0mm and 2.5mm, and a pressure releasing inlet valve 14 which penetrates the pressure vessel body.

[0030] The pressure vessel body 12 comprises an outer dished component 16 and an inner dished component 18. Each component Is circular in plan. The outer component 16 has an outer base wall 20 and an outer cylindrical sidewall 22 upstanding from the base wall 20. Likewise, the inner component has an inner base wall 24 and an inner cylindrical sidewall 26 upstanding from the base wall 24. With complementary shape and size, the inner component is received in the outer component. A peripheral portion 28 of the Inner sidewall 26 arches outwardly to meet a top edge 27 of the outer sidewall on a circular join line 30. In joining the two components (16, 18) together, the sidewa!is are welded together along this join line to seal the pressure vessel body 12.

[0031] The inner base wall 24 and the outer base wall 20 abut or lie adjacent one another on a separation plane which is shown as a line designated 36 on Figures 3, 4A and 4C.

[0032] In the assembled preload device 10, the inner dished component now provides a prop locating socket 32, the use of which will be describe below. The socket is defined within the inner sidewall 26.

[0033] The pressure releasing inlet valve 14 can penetrate the pressure vessel body 12 through any wail. Typically, the valve is located through the outer sidewall 22 or the peripheral portion 28 of the inner sidewall 26. The valve all can be a valve as described In a specification to South African patent no. 2003/6369 or 2005/6691 which is incorporated in reference. What is common to these valves is that they are adapted to aliow one-way hydraulic fluid input into the pressure vessel 12 to inflate the vessel but then to allow fluid ejectment from the vessel, as a pressure release mechanism, when the pressure within the vessel reaches a predetermined maximum. An exterior portion 37 of the valve body is adapted to serve as a quick- connect connector for a fluid input hose connector (not shown).

[0034] In Figure 1, a first embodiment of a preload device 10A of the invention is shown. In this embodiment, both the outer base wall 20 and the inner base wall 24 are shaped with a spacing formation (respectively designated 38A and 40A) which, in this example, are each a protruding or bulging circular formation. They rise in opposed directions from the separation plane 36. Thus, the shape of the spacing formation 38A of the outer base wall 20 mirrors the shape of the spacing formation 40A of the inner base wall 24 about the separation plane 36.

[0035] Each spacing formation has an inclining portion 42 and a flat surface 44. In profile, each spacing formation of this embodiment takes on a plateaued shape. Atop each formation a first plane and second plane (illustrated with dotted lines and designated 46 and 48 respectively), respectively, are defined.

[0036] Figures 4A to 4D illustrate the other embodiments of the preload device, respectively 10B, 10C, 10D and 10E. The embodiments differ in that the inner and outer base walls (24, 20) are differently configured, taking on different shapes and differing profiles. In device 10B and 10C, only the inner base wall 24 has a spacing formation being, respectively, a circular protruding formation 40B and an annular ridge 40C.ln device 10D, each base wall (20, 24) has a mirrored annular ridge (38D, 40D). In device 10E the outer base wail 24, solely, Is formed with an annular ridge 38E.

[0037] However, what is common to all the embodiments Is that they have a first plane 48 and a second plane 48 which are defined by the particular shape profiles of the respective base wails. In the embodiments where each of the base wails are formed with spacing formations (38, 40), it is the maximum lateral planar extent of these spacing formations that defines each of these planes. In the embodiments where a base wall is not formed with a spacing formation, the base wall surface defines the respective plane. The first plane 46 is separated from the second plane 48 by a separation distance (designated X). Preferably, this distance is 20mm.

[0038] In use of the preload device 10, and as will be described below in greater detail, the first plane is a hanging wall abutting plane and the second plane is a prop- end supporting plane.

[0039] The preload device is used with a timber prop 50 in a load support system 52 that provides support to a mine excavation between a hanging wall 54 and a footwall (not shown). The timber prop has an elongate body 56 that extends between a first end 58 and a second end (not shown). Hereinafter, in the context of a load support system 50, the preload device 10 also will be described as "the engineered component ^* and the timber prop as "the natural component".

[0040] The load support system 52 is used in a method of providing load support between a foot wall and a hanging wail. In describing the method, reference is made to Figures 5A and 5F. [0041] A first end 58 of the timber prop 50 is engaged with the preload device, in this case a preload device 10A, by inserting a first end portion of the prop Into the socket 32 of the device. The end 58 of the prop will engage the inner base wall 24 of the preload device on the second or prop-end engaging plane 48. The system 52 is now assembled and is placed between the foot wall and the hanging wall 54, with the hanging wall lying adjacent to or slightly spaced from the first plane 48 or in contact with the outer base wall 20 on the first plane. This is illustrated in Figure 5A. in this configuration, the hanging wall 54 is spaced from the first end 58 of the prop 50. The spacing formations (38A, 40A) provide spaces 60 which are defined between the planes (46, 48) and the profile of the respective base walls (20, 24).

[0042] Figure 5B illustrates the next step of the method. The preload device 10A is inflated into the spaces 60 by introducing a pressurised fluid stream from a source (not shown) through the pressure releasing inlet valve 14. Importantly, this initial inflation step occurs without significant load being placed on the timber prop, in effect, inflation of the preload device into these spaces gives load absorbing capacity to the load bearing system without bringing the natural component, with its inherent structural variability, into play. As a consequence, the separation distance X remains more or less the same between the two steps. In contrast, in a typical installation, there are little or no spaces as the base walls are not formed with spacing formations and any inflation of the device almost immediately bears on the timber prop, compressing the prop and stiffening the system.

[0043] Figure 5C illustrates the further inflation of the preload device 10A, after the initial inflation step. In practice, this step is not a discrete step but is continuous with the preceding inflation step. With no spaces 60 left to inflate, this step is characterised In that the preload device pushes on, and slightly axiaiiy compressing, the prop in preload. The arrows indicate this load and the direction. The arrows indicate this load and the direction. The prop compression distance is designated Y, The preload inflation step ensures that the load support system 52 is expanded into secure placement between the wails of the excavation and will not topple.

[0044] When the hanging wall 54 and the footwaB start to close, the compressive load (illustrated with directional arrows in Figure 5D) caused by this movement will be adsorbed and dissipated by compression of the preload device 10A and ejectment of hydraulic fluid through the valve. This fluid stream is designated 62. Little or no load is placed on the timber prop at this stage. These naturally occurring stages are illustrated in Figure 5D and 5E.

[0045] Eventually, the preload device 10 fully compresses, bringing the base walls (20. 24) into contact. At this stage, the load absorbing capacity of the engineered component is exhausted. Any load of further rock wall closure wiil transfer through to the natural component as illustrated In Figure 5F.

[0046] The highest rate of rock wall closure, at a locality lying in the vicinity of an excavation face, occurs in the immediate aftermath of a blast event at the excavation face. As the excavation faces advances, the closure rate at this locality drops off significantly. The need for a reliable, invariable, load support system is required during the time of this high-rate-of-closure phase. This phase coincides with a relatively high density of mine workers working within the locality. The reliability of the support system is less important during the following iow-rate-of-closure phase as the loads produced are less and the workers have advanced with the excavation face.

[0047] The load support system 52 of the invention provides reliability of support during the high-rate phase by ensuing that the engineered component is almost exclusively load absorbing. As the preload device, with Its pressure releasing valve, is engineered, there is little variability in performance. This is in contrast to the underlying natural component. Therefore, by having load absorbing capacity built into the preload device, with the spaced configuration of the base walls, the preload device can absorb the energy during the high-rate phase. The bottoming out of the preload device can be designed to coincide with the end of the high-rate phase, by adjusting the spacing distance X. Load produced during the low-rate phase is then absorbed by the natural component.

[0048] In effect, the load support system 52 brings reliability through the introduction of an engineered component. The failure risk associated with the high variability of the natural component is thus mitigated, at least during the high-rate phase of rock closure. Statistically, the increased reliability of the system of the invention is displayed in a relatively narrow load distribution curve as opposed to a broad load distribution curve for a timber prop alone.

[0049] Put another way, by reducing the variability in the performance of an elongate load support system, as is provided by the invention, the confidence level (either the 90% confidence level or a de-rated confidence level) for the system is increased. Because of this reduction in variability, the load support system 52 with a lower mean performance, at say 20mm of deformation, when compared to a typical system (higher mean performance but much higher variability) can have substantially the same confidence level as the typical system. This effect is shown in the graphs of Figure 6 and 7. The graph of Figure 6 shows a load-deformation curve for a timber prop load support system using standard 18-20cm diameter props, whilst the graph of Figure 7 shows a load-deformation curve of a load support system of the invention. In this system 15-18cm diameter props were used.

[0050] The extent to which the variability reducing effect would translate into increased confidence, and therefore performance, is surprising, made more so by the fact that this increased confidence was achieved with timber props in the 15- 18cm diameter range cm. There are obvious cost benefits to this along with a reduction in the overall load support system, another benefit In a confined mine excavation.