A crush module and associated shock load reduction system and method

Abstract

A shock load reduction system (10) for a load support element (26) extending into a body of material (31). The system has a housing (12) with a first load bearing end (18) and an opposite second end (20) and a cavity (22) extending therebetween. A crush module (14) having a longitudinal axis (50) is retained in the cavity (22). The crush module (14) comprises a plurality of axially stacked zones (Zi), each zone having a plurality of cells (62). Each cell has a plurality of cell walls (64). The cell walls (64) of each cell (62) in any one of the plurality of zones are coplanar with respective cells walls in at least one other of the plurality of zones of the module. A load transfer coupler (16) is operably associated with the housing (12) and the crush module (14) and is coupled to a load support element (26). The load transfer coupler (16) initially transfers a shock or impulse load experienced in the body of material (31) to the crush module (14) in a direction of the longitudinal axis (50). If the load is sufficient the load transfer coupler operates to crush the crush module (14) against the first load bearing end (18), thereby reducing the length crush module (14). Thus, the crush module absorbs (14) at least a portion of the shock load impulse energy. Any residual shock load is transferred to the load support element (26).

Description

[0001] A CRUSH MODULE AND ASSOCIATED SHOCK LOAD REDUCTION SYSTEM AND METHOD

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a crush module and associated shock load reduction system and method. The crush module and associated shock load reduction system and method have application in many areas of civil, mechanical and mining engineering including, but not exclusively, in relation to a load support structure or element such as a rock bolt.

[0004] BACKGROUND ART

[0005] The stability of excavations in rock in mining and tunnelling operations is critically important for the safety of workers and for access for recovery of ore or other requirements. In excavations in brittle rock, under high stress due to the depth of workings below the surface, a phenomenon called “seismicity” may occur if the stress or pressure is sufficient to cause fault lines to slip and shear, and / or to cause fracturing and failure of an otherwise intact rock mass in proximity to the excavations. These disturbances are variously called rock bursts, strain bursts, seismic events, or dynamic disturbances. They vary in magnitude and damage, but larger disturbances can suddenly, and usually without warning, eject or displace large volumes of broken rock into the excavations, with potentially high risk to any personnel or equipment nearby.

[0006] The causes of seismicity are very complex and interactive, and to date it is not possible to reliably predict the time, place and magnitude of a seismic event. Some of the mining environment factors influencing seismicity are the stress field, stress changes over time, rock properties, rock defects, rock degradation over time, prior seismicity, prior rock mass damage, and in some cases the type of ground support installed and the quality of the installation.

[0007] Rock burst is the phenomenon that the potential energy of elastic deformation accumulated in a body of rock is suddenly and violently released under certain conditions, causing the rock to burst and eject. The dynamic response characteristics of the adjacent rock mass are mainly presented as slabbing, rock ejection, bursting and spalling, throwing damage of the rock mass, and the like.

[0008] The dynamic damage from a rock burst can include: (1) blocks of rock or rock fragments ejected from the surface of an excavation at high speed, up to or exceeding 6 m / sec, and large ejected blocks can have a mass of several tonnes and a kinetic energy of up to or exceeding 50 kJ; and (2) sudden expansion or bulking or buckling of the volume of rock mass by up to or exceeding 50% as the intact rock breaks into numerous fragments which move and push against each other.

[0009] Various means are used in the industry to attempt to control the likelihood and consequences of occurrence of seismicity. A primary means of control is the installation of ground support systems to the exposed perimeter surface of excavations. Ground support systems may include:

[0010] (a) a rock bolt, i.e. a reinforcing element anchored into a borehole drilled into an excavation surface and provided with means to oppose free movement of loosened rock.

[0011] (b) a screen of mesh or fibrecrete (sprayed concrete with fibres), attached to the rock bolts, as a means of opposing the free movement of loosened rock from between the pattern of rock bolts.

[0012] Seismic events can impose very strong dynamic forces onto the excavation surface. Conventional rock bolts (including solid rods, cable bolts, and tubular bolts) have only limited ability to withstand those forces, because they have limited capability to carry high load, absorb high energy, or elongate sufficiently before rupturing.

[0013] Over about the last 30 years, numerous “dynamic bolts” have been introduced to the mining and civil construction industries in an attempt to overcome the deficiencies of the conventional rock bolt, and they are regularly used in deep mines with seismicity hazard.

[0014] A key rock bolt performance criterion is elongation, i.e. the ability of the bolt to stretch or elongate adequately without loading up to the point of rupture. When a portion of rock mass fails during a seismic disturbance, the rock mass expands in volume and forces the rock bolt installed within that volume to elongate accordingly. The fractured rock pieces move against each other and take up more space, or shearing movement along a fault line or along joint planes causes dilation as the joint plane widens. Also, some rock fragments or larger blocks may gain kinetic energy delivered by the disturbance and attempt to transfer that energy to the rock bolt.

[0015] Conventional rock bolts cannot usually elongate adequately, and they may fail. Dynamic rock bolts are designed with a yielding feature that permits the bolt to yield during the disturbance, to increase elongation, while at the same time developing high load to oppose the rock mass volume expansion, and to absorb or dissipate any kinetic energy that the disturbance might have delivered to rock blocks or fragments.

[0016] A problem potentially affecting any installed rock bolt is shearing. In one scenario, the rock mass strata may shear, i.e. one section of the rock mass moves relative to an adjacent section, along a joint or defect or weakness surface between the sections. If a rock bolt is installed in a borehole that crosses the shear surface, the borehole and the contained bolt can be partly or fully sheared, which initially clamps the bolt against movement, and in the worst case ruptures the bolt. Shearing might render a dynamic bolt non-functional.

[0017] In a second shearing scenario, the use of blasting to create an excavation may produce a zone of loose or partly fractured rock as a layer surrounding the perimeter of the excavation. The layer thickness is variable and very dependent on various factors, but 0.1 m to 1 m may be typical. If a rock bolt is installed in a borehole passing through this fractured zone, the borehole and the contained bolt again can be partly or fully sheared due to movements and adjustments in the fractured zone.

[0018] Embodiments of the present disclosure attempt to reduce, delay, or prevent the dynamic rupture of a rock bolt, including a rock bolt subject to shearing or to an extremely high load pulse.

[0019] The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the disclosed shock load reduction system and method to ground supporting applications.

[0020] SUMMARY OF THE DISCLOSURE

[0021] In one aspect there is disclosed a shock load reduction system comprising: a housing having a first load bearing end and an opposite second end and a cavity extending between the first load bearing end and second end; a crush module having a longitudinal axis and retained in the cavity, wherein the crush module comprises a plurality of axially stacked zones, each zone having a plurality of cells, each cell having a plurality of cell walls, wherein the cell walls of each cell in any one zone are coplanar with respective cells walls in at least one other zone of the module; and a load transfer coupler operably associated with the housing and the crush module and coupled to a load support element, the load transfer coupler arranged to initially transfer a shock or impulse load to the crush module in a direction of the longitudinal axis wherein the load transfer coupler is operable to crush the crush module against the first load bearing end to a second axial length being less than the first axial length wherein the crush module absorbs at least a portion of the shock load impulse energy and wherein any residual shock load is transferred to the load support element.

[0022] In one embodiment the one zone and the at least one other zone are mutually adjacent.

[0023] In one embodiment the cell walls of each cell are coplanar with respective cell walls in every other zone for the full length of the module.

[0024] In one embodiment the cell walls of a cell in a first zone are thicker than the cell walls of a cell in a second zone.

[0025] In one embodiment the crush module is composed of at least one plastically deformable media.

[0026] In one embodiment the at least one plastically deformable media comprises at least one zone, each zone having a cellular structure.

[0027] In one embodiment the cellular structure includes a plurality of cells, each cell having a plurality of cell walls wherein mutually adjacent cell walls join along a common node line that extends substantially parallel to the longitudinal axis of the crush module.

[0028] In one embodiment the cells are arranged so that, across a radius of each zone, at least three cell walls join along each of the common node lines.

[0029] In one embodiment each cell has an even number of walls.

[0030] In one embodiment in each zone some cells have a different number of walls than other cells.

[0031] In one embodiment each cell is arranged so that when the crush module is crushed, walls meeting at a common node line pull apart along the common node line. In one embodiment at least one node line and / or one cell wall is formed with a point of weakness to initiate failure of the cells associated with and along the common node line.

[0032] In one embodiment the point of weakness includes one of (a) a dimple formed at the point (b) a hollow or perforation formed at the point (c) a reduction in wall thickness at the point (d) a slot formed along the node line containing the point, and (e) a change in geometry of a portion of a length of the cell walls including the point.

[0033] In one embodiment mutually adjacent cell walls of at least one cell, where the at least one cell has an even number of walls, are arranged to fold in an alternating manner inwardly and outwardly of the at least one cell.

[0034] In one embodiment each cell wall is configured to fold along a fold line that lies in a radial plane of the crush module.

[0035] In one embodiment the fold line lies midway of a height dimension of a corresponding cell.

[0036] In one embodiment the cell walls are one of: (a) planar and of uniform thickness along an axis parallel to the longitudinal axis; or (b) planar and of varying thickness along an axis parallel to the longitudinal axis; (c) non-linear in shape in a radial or axial plane of the module.

[0037] In one embodiment the shock load reduction system includes a brace or prop located within at least one cell of a zone, wherein the brace or prop bears against two or more cell walls of the cell.

[0038] In one embodiment the brace or prop bears against the two or more walls of the cell midway of a height dimension of a corresponding cell.

[0039] In one embodiment the brace or prop is arranged to bear against alternate walls of a cell.

[0040] In one embodiment the brace or prop is arranged to bear against every wall of a cell.

[0041] In one embodiment each cell in a zone is provided with a brace or prop and the braces or props of mutually adjacent cells are configured to bear on opposite sides of a point or region of a common wall. In one embodiment each brace or prop is integrally formed with a corresponding cell.

[0042] In one embodiment the cells are made of a metal or a metal alloy or foamed metal.

[0043] In one embodiment each zone includes a bottom wall and an opposite top wall wherein the walls extend radially across axially opposite ends of each zone and seal the cells.

[0044] In one embodiment the top and bottom walls are provided with holes.

[0045] In one embodiment the top and bottom walls are made from a plastically deformable material.

[0046] In one embodiment the plastically deformable material is a foamed metal.

[0047] In one embodiment the housing has an elongated body which includes the cavity, and the second end of the housing includes a collar arranged to abut a plate that bears on an outside of the body of material into which the load support element extends.

[0048] In one embodiment the load transfer coupler includes a bearing washer slidably engaged with the housing and located at on an end of the crush module distal to the first load bearing end.

[0049] In one embodiment the load transfer coupler includes a first detachable fastener arranged to bear on the bearing washer and detachably coupled to the load support element.

[0050] In one embodiment the crush module is of an annular configuration with an outer circumferential wall and an inner circumferential wall defining a passage extending parallel to the longitudinal axis.

[0051] In one embodiment the load support element is a rock bolt or a cable bolt that passes through the passage and the housing.

[0052] In one embodiment the housing is in the form of a canister.

[0053] In one embodiment the load support element is a tubular bolt, and the housing is located inside the tubular bolt, and the load transfer coupler includes a bolt and a second detachable fastener wherein the bolt extends through the passage and is connected at one end to the first detachable fastener and at a second opposite end to the second detachable fastener.

[0054] In one embodiment the first load bearing end of the housing is of a frusto-conical shape reducing in outer diameter in a direction from the second end toward the first load bearing end.

[0055] In one embodiment an outer surface of the housing at the second end is provided with a plurality of protrusions to facilitate anchoring of the housing into a settable material.

[0056] In a second aspect there is disclosed a shock load reduction system for a load support element extending into a body of material comprising: a housing having a first load bearing end and an opposite second end and a cavity extending between the first load bearing end and second end wherein the second end of the housing includes a collar arranged to abut a plate located on an outside of the body of material into which the load support element extends; an annular crush module retained in the housing and having an inner wall forming a central passage, an outer wall and a first axial length; and a load transfer coupler operably associated with the housing, the load support element and the annular crush module to transfer a shock or impulse load arriving through the central passage to the annular crush module wherein the annular crush module is operable by action of the shock or impulse load to crush within the housing to a second axial length being less than the first axial length between the load transfer coupler and the first load bearing end.

[0057] In a third aspect there is disclosed a method of absorbing a shock or impulse load between a shock or impulse load source and a load bearing member the method comprising: coupling a crushable module between the shock or impulse load source and the load bearing member wherein the crush module is crushed by application of the shock or impulse load to reduce in length to a maximum extent wherein after additional load is transferred through the crush module to the load bearing member.

[0058] In a fourth aspect there is disclosed a crush module for absorbing a load, the crush module comprising a plurality of end to end stacked zones, each zone comprising a plastically deformable cellular structure having a plurality of connected cells, the cells having a plurality of cell walls that extend in a first direction and optionally a plurality of end walls extending in a direction substantially perpendicular to the first direction that separate mutually adjacent zones.

[0059] In a fifth aspect there is disclosed crush module for absorbing a load, the crush module comprising a plurality of end to end stacked zones, each zone comprising a plastically deformable cellular structure having a plurality of connected cells, the cells having a plurality of cell walls that extend in a first direction parallel to a central axis of the crush module and a plurality of end walls extending in a direction substantially perpendicular to the first direction that separate mutually adjacent zones wherein cell walls of mutually adjacent cells in a zone join along a common node line that extends substantially parallel to the central axis wherein each cell is arranged so that when the crush module is crushed, cell walls meeting at a common node line pull apart along the common node line.

[0060] In one embodiment the end walls are plastically deformable.

[0061] In one embodiment the end walls are made of a foamed material.

[0062] In one embodiment the foamed material is a foamed metal.

[0063] In one embodiment cell walls of mutually adjacent cells in a zone join along a common node line that extends substantially parallel to the first axis.

[0064] In one embodiment the cells are arranged so that at least three cell walls join along the common node line.

[0065] In one embodiment each cell has an even number of cell walls.

[0066] In one embodiment each cell is arranged so that when the crush module is crushed, cell walls meeting at a common node line pull apart along the common node line.

[0067] In one embodiment the cell walls in one of the zones have a height that is different to the height of cells walls in another one of the zones.

[0068] In one embodiment at least one node line and / or cell wall is formed with a point of weakness to initiate failure of the cells associated with and along the common node line. In one embodiment the point of weakness includes one of (a) a dimple formed at the point (b) a hollow or perforation formed at the point (c) a reduction in wall thickness at the point (d) a slot formed along the node line containing the point, and (e) a change in geometry of a portion of a length the cell walls including the point.

[0069] In one embodiment mutually adjacent cell walls of at least one cell are arranged to fold in an alternating manner inwardly and outwardly of the at least one cell.

[0070] In one embodiment each cell wall is configured to fold along a fold line that lies in a plane parallel to the end walls of the crush module.

[0071] In one embodiment the fold line lies midway of a height dimension of a corresponding cell.

[0072] In one embodiment the cell walls are one of: (a) planar and of uniform thickness along an axis parallel to the first axis; or (b) planar and of varying thickness along an axis parallel to the first axis; (c) non-linear in shape in a plane parallel to the end walls of the module.

[0073] In one embodiment the crush module includes a brace or prop located within at least one cell of a zone, wherein the brace or prop bears against two or more cell walls of the cell.

[0074] In one embodiment the brace or prop bears against the two or more walls of the cell midway of a height dimension of a corresponding cell.

[0075] In one embodiment the brace or prop is arranged to bear against alternate walls of a cell.

[0076] In one embodiment the brace or prop is arranged to bear against every cell wall of a cell.

[0077] In one embodiment each cell in a zone is provided with a brace or prop and the braces or props of mutually adjacent cells are configured to bear on opposite sides of a point or region of a common cell wall.

[0078] In one embodiment each brace or prop is integrally formed with a corresponding cell.

[0079] BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Notwithstanding any other forms which may fall within the scope of the system and method as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to the drawings in which: Figure 1 is a longitudinal section view of an embodiment of the disclosed shock load reduction system used in conjunction with a rock bolt in the form of a solid rod and installed near a collar of a bore hole in a rock mass prior to a seismic event causing activation of the shock load reduction system.

[0081] Figure 2 is an oblique projection of the shock load reduction system shown in Figure 1.

[0082] Figure 3 is a longitudinal section view of the embodiment of the shock load reduction system shown in Figure 1 after activation of the shock load reduction system.

[0083] Figure 4a is a view of section A-A of Figure 1 .

[0084] Figure 4b is a view of section B-B of Figure 1 .

[0085] Figure 5 is a plan view of a bearing washer incorporated in the embodiment of the shock load reduction system shown in Figure 1.

[0086] Figure 6a is an oblique projection of a crush module incorporated in the embodiment of the shock load reduction system shown in Figure 1.

[0087] Figure 6b is a longitudinal section view of the crush module shown in Figure 6a.

[0088] Figure 6c is an enlarged view of a portion of a cellular structure formed in one zone of the crush module shown in Figure 6a.

[0089] Figures 7a, 7b, 7c, 7d, 7e and 7f are section views of some of many different possible alternate cell wall profiles of one possible cell configuration in the cellular structure of the crush module.

[0090] Figure 8 is a representation in section view of a sector of one zone of a crush module showing two of many possible alternative cell packing configurations for the cellular structure.

[0091] Figure 9 is a representation in section view of a sector of one zone of a crush module showing a further possible cell packing configuration for the cellular structure. Figure 10 is a representation in section view of a sector of one zone of the crush module of Figure 8 where the zone comprises a hexagonal cellular configuration and holes are formed in opposed radial end walls of the zone.

[0092] Figures 11 a, 1 1 b, 11 c, 11 d, and 11 e depict in plan view alternate configurations of braces or props that may be incorporated in the crush module.

[0093] Figure 12 is a representation of the loading applied to different elements of a prop in a cell of the cellular structure during activation of the shock load reduction system shown in Figure 1.

[0094] Figure 13a is a representation in plan view of a group of mutually adjacent cells in a zone of the cellular structure and showing a designed folding pattern of cell walls in response to the application of a shock or impulse load.

[0095] Figure 13b is a representation in cross-section view and at mid cell height of the designed movement of a subset of cell walls shown in Fig 13a that share a common node line during an initial stage of the application of a shock or impulse load.

[0096] Figure 13c is a representation of the movement of the subset of cell walls shown in Fig 13b subsequent to the initial stage and depicting the cell walls being torn apart along the previous common node line.

[0097] Figure 14a is a representation in plan view of a group of mutually adjacent cells in a zone of the cellular structure and showing a designed folding pattern of cell walls in response to the application of a shock load (and is the same as Figure 13a).

[0098] Figure 14b is a view of section A-A of Figure 14a, showing the zone as having a height H1.

[0099] Figure 14c is a representation in plan view showing a partial folding of the cell walls and rupturing of a prop shown in Fig 14a during an intermediate stage of the application of a shock load to the shock load reduction system and crush module.

[0100] Figure 14d is a view of section A-A of Figure 14a showing the zone as having a height H2<H1 as the zone and corresponding crush module are being crushed. Figure 14e is a representation in plan view showing a complete folding of the cell walls and rupture of the prop shown in Fig 14c at the completion of and at maximum absorption of the shock load by the shock load reduction system and crush module.

[0101] Figure 14f is a view of section A-A of Figure 14e, showing the zone as having a height H3< H2<H1 as the zone and corresponding crush module are crushed to a maximum extent.

[0102] Figure 15 is a longitudinal section view of a portion of another embodiment of the disclosed shock load reduction system used in conjunction with a rock bolt in the form of a cable installed in a rock mass.

[0103] Figure 16 is a longitudinal section view of a further embodiment of the disclosed shock load reduction system used in conjunction with a rock bolt in the form of a tubular bolt installed in a rock mass.

[0104] Figure 17 is a longitudinal section view of yet a further embodiment of the disclosed shock load reduction system used in conjunction with a rock bolt in the form of a solid rod but installed at a toe end of a bore hole in a rock mass.

[0105] Figure 18 is a representation of an embodiment of a portion of the disclosed system in which the housing is formed with a separate collar and elongated body that are mechanically coupled together and where the collar in this case lies within the radius of the borehole.

[0106] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0107] Specific embodiments of the disclosed shock load reduction system and method will now be described by way of example only. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the disclosed shock load reduction system and method. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to pertaining to the absorption of a shock impulse particularly in relation to underground excavations. In the drawings, it should be understood that like reference numbers refer to like parts.

[0108] In one possible broad and general form the present disclosure relates to a crush module that is designed to crush in response to and thereby absorb or dissipate the energy of a shock or impulse load. In one embodiment the crush module is arranged to crush by way of plastic deformation on application of a shock or impulse load. This may result in a reduction of the overall length or volume of the crush module. The idea here is that the crush module provides protection to a load support structure or element by reducing at least some of the shock load and absorbing or dissipating at least some of the energy. It is envisaged that only after the crush module has crushed to a physically maximum extent that an additional higher load can be transmitted through the crush module to the load support structure or element. Thus, the crush module may be arranged in systems and methods intended to operate substantially independently of the load support structure or element.

[0109] In one embodiment the crush module may be arranged to be plastically deformable by virtue of comprising a volume of plastically deformable material, or structure or a combination of plastically deformable materials and / or structures. For example, in one form the crush module may comprise a plurality of stacked zones where each zone comprises a plastically deformable cellular structure. The cells have a plurality of cell walls (for example 3 or more) that extend in a first direction which generally coincides with the direction of application of the load. The crush module may also have a plurality of end walls that extend in a direction perpendicular to the first direction that separate mutually adjacent zones. The load may be a shock or impulse load such as, but not limited to, that which may arise due to seismicity in a rock mass. Further the load support structure or element may be in the form of a rock bolt.

[0110] Some embodiments of the disclosed system and method envisage the coupling of a crush module or crush volume of material between a source of a shock or impulse load and a load support structure or element, such as a rock bolt. The crush module or crush volume of material operates independently of the load support structure or element. The crush module or crush volume of material is designed to reduce in length as it is crushed by the absorption of the impulse. The reduction in the module length is simultaneous with a reduction in volume of the module or material. If used in conjunction with a rock bolt, it is only after the shock load reduction system has been activated and the module has reduced in volume / length to its maximum extent that additional higher load is then transferred onto the rock bolt.

[0111] A schematic representation of an embodiment shock load reduction system 10 incorporating a crush module 14 is shown in Figures 1-5. This embodiment of the shock load reduction system (hereinafter “SLRS 10”) comprises a housing 12, a crush module 14 and a load transfer coupler 16. The housing 12 has a first load bearing end 18, an opposite second end 20 and a cavity 22 extending between the first and second ends 18, 20. The crush module 14 is retained in the cavity 22. In this, but not necessarily every, embodiment the crush module 14 is annular in shape having an inner diameter D1 , an outer diameter D2 and a central passage 24. It is important to note however that in other embodiments the crush module need not be annular in shape and may have no passages or may have multiple passages.

[0112] Prior to activation of the SLRS 10 the module 14 has a first length L1. The load transfer coupler 16 is operably associated with the housing 12 and the crush module 14 to transfer a shock load to the crush module 14. When the shock load is above a predetermined level the crush module 14 is crushed to a second length L2 (see Fig 3) being less than the first length L1. This is facilitated by the load transfer coupler 16, or a part thereof located within the housing 12, moving relative to the housing toward the first load bearing end 18 by action of the shock load.

[0113] In Figures 1-3 the SLRS 10 is shown in use coupled to one end of a load support structure / device in the form of a rock bolt 26 and is installed in a collar 28 of a borehole 30 in a rock mass 31 . An anchor (not shown) at an opposite end of the rock bolt attaches the rock bolt to the rock mass 31 . The housing 12 has an elongated body 32 which includes the cavity 22. The housing 12 (i.e., the cavity 22) is formed with an internal diameter to enable a clearance fit with the rock bolt 26. The housing 12 is formed with radius fillets to reduce stress raiser corners and thus help in avoiding fatigue and poor shock load responses. As the housing 12 will potentially experience high shock loads it may be beneficially fabricated of shock-resistant metal. It is envisaged that predominately embodiments of the SLRS 10 will be formed with the body 32 having a circular exterior cross-sectional shape. Other embodiments are possible in which the exterior cross section is of a hexagonal or elliptical shape, or other non-circular shape. However, this may reduce the cross-sectional area of the housing 12 and the module 14 which is believed to be sub optimal.

[0114] An intermediate portion of the body 32, between the first and second ends 18, 20 has a constant outer diameter. Both ends 18 and 20 are open. The first end 18 of the housing 12 may be formed with a frusto-conical shape reducing in outer diameter in a direction from the second end 20 toward the first end 18. The frusto conical shape may assist in sliding the SLRS 10 into the borehole 30. The frusto-conical shape is not essential and as explained later, other configurations of the first end are possible.

[0115] The first end 18 may be formed as a solid part of the SLRS 10, as shown on the left hand side of Fig 1 at 18a, or with a hollow section as shown on the right hand side of Fig 1 at 18b. If formed with a hollow section a conical washer or brace unit 34 may be installed in the cavity 22 to seat in the hollow frusto conical end 18. In both cases an annular surface 36 is formed on the inside of the cavity 22 against which the module 14 can directly, or indirectly via an optional intervening washer 38, bear. Grinding buttons 39 may be attached to the exterior of housing 12 about the first end 18. The buttons 39 may assist during the installation of the SLRS 10 by cutting or breaking through borehole obstructions. This action may be enhanced by rotating the housing 12 during the installation.

[0116] A collar 42 may be provided at the second end 20 of the housing 12. The collar 42 extends radially outward from the outer diameter of the elongated body 32 of the housing 12. In some embodiments the collar may extend beyond the diameter of the bore hole 30 as shown for example in Fig 1 . In other embodiments the collar 42 may lie within the diameter of the bore hole 30 as shown in Fig .18. The collar 42 is designed to abut or otherwise engage with a plate 40 that lies on the surface of the rock mass 31 . The plate 40 in one embodiment is formed with an upwardly projecting rim 44 which surrounds a hole formed in the plate 40.

[0117] The rim 44 is located over the borehole 30 into which the SLRS 10 is installed. The SLRS 10 may be: (a) inserted into the borehole 30 with the first end 18 first and over a previously installed rock bolt 26; or (b) inserted together with a rock bolt 26 which is simultaneously anchored in the borehole 30. In this event an assembly clip 45 may be placed about the rock bolt 26 to act as a stop for the housing sliding down the rock bolt 26 during the installation process. The insertion of the SLRS 10 is arrested by the collar 42 contacting the rim 44. The combination of the rock bolt 26, anchor and plate 40 constitutes a ground support unit (“GSU”).

[0118] A portion of an interior surface of the body 32 that opens onto end 20 is formed with a screw thread 46. This enables the fitting of a separate small stub component to retain mesh, or enable attachment for proof load testing, or enable other kinds of attachments that a mine operator may consider desirable. One or more slots 48 are formed in the interior surface of the housing 12. The slots extend from the second end 20 toward the first end 18. Each slot 48 slot runs parallel to a central axis 50 of the housing 12. In this embodiment there are two diametrically opposed slots 48 which can be best seen in Fig 4a.

[0119] The load transfer coupler 16 includes a bearing washer 52 with radially extending tabs 54 (see Fig 5) that are received in the slots 48. The bearing washer 52 is made with a thickness adequate to carry applied loads without excessive bending or warping. The tabs 54 are configured to snugly fit inside the slots 48, but with clearance adequate to prevent fouling of the washer 52 in case of small angular misalignment between washer 52 and housing 12. The engagement of the tabs 54 in the slots 48 prevents rotation of the bearing washer 52 relative to the housing 12 during installation yet allows sliding axial movement of the bearing washer 52 relative to the housing 12 when the SLRS 10 is activated.

[0120] The load transfer coupler 16 may also include a fastener / nut 56 that engages the rock bolt 26. If the nut 56 is incorporated, an anti-friction washer 58 may also be included between the nut 56 and the bearing washer 52 to allow tightening for preload application. An optional pretension disk 60 is located about the rock bolt 26 between the bearing washer 52 and the module 14. During installation of the SLRS 10, load is applied for example by the fastener 56 until the pretension disk 60 activates. This provides a positive signal to the installer that the SLRS 10 is correctly installed and in operational condition.

[0121] Embodiments of the annular crush module 14 are shown in Figs 6a-14f. The module 14 is composed of at least one plastically deformable media. In the present embodiment the at least one plastically deformable media comprises one or more annular zones Zi (where i is an integer 1 < i < n). Each zone Zi has a cellular structure 61 . The cellular structure 61 includes end plates 63 that extend transversely across axially opposite ends. The end plates in this embodiment are of an annular configuration with inner and outer diameters commensurate with the inner and outer diameters of the annular crush module 14. The end plates 63 may be made from metal, including foamed metal.

[0122] With reference to Fig 6c in one embodiment the cellular structure 61 of each zone Zi includes a plurality of cells 62. Each cell has a plurality of cell walls 64. The cell walls 64 extend in the general direction of the central axis 50. Moreover, mutually adjacent cell walls 64 join along a common nodeline 66 that extends substantially parallel to the axis 50. In addition, in the presently described embodiment the cells 62 of mutually adjacent zones Zi are axially aligned with each other and have a uniform orientation. That is, the cells 62 in zone Z1-Zn are arranged so that, if the end plates 63 were not present, the cells 62 would stack axially upon each other with coplanar walls 64 running from one axial end of the module to the other. Stated in another way, the cell walls 63 of each cell in any one zone are coplanar with respective cells walls in every other zone for the full length of the module. This is shown for example in Fig 6b where the walls 64k, 64I and 64m of zones Zk, ZI and Zm respectively, are coplanar with each other.

[0123] However, it should be understood that alternative embodiments exist where the cell walls 64 of the of each cell in any one zone are not coplanar with respective cell walls in every other zone for the full length of the module. For example, a module 14 may be formed where the cell walls of two mutually adjacent zones are not coplanar. This could even include for example two zones Zf and Zh having an identical cellular structure where the cell walls of each cell in zone Zf are coplanar with the corresponding cell walls of the zone Zh, but where there is one (or more) intervening zone Zg which has a different cellular structure to the zones Zf and Zh so that the cell walls in the zone Zg are not coplanar with all the cell walls of the cells Zf and Zh. This could also include a situation where the intervening zone (or zones) Zg are void with no cellular structure at all. In such embodiments the height of a void zone Zg may be different. For example, the void zone may be shorter in height than one or both of the adjacent zones Zf and Zh. Also, in some embodiments the cell walls of one zone may be different to that of the cell walls of another zone. The difference may be in thickness, shape or configuration. For example, the thickness of the cell walls in different zones may be different. In one ono limiting example cell walls of a zone closer to the load bearing end 18 may be greater than the thickness of cell walls in a zone further from the load bearing end 18.

[0124] The top and bottom ends of the cell walls 64 join seamlessly to opposed transverse annular end plates 63. The end plates 63 provide control of rotation or movement of the axial ends of the cell walls 64. Ideally the plates 63 prevent rotation of the cell wall 64 ends initially, until failure occurs. Since the ends of the walls 64 cannot rotate, the initial failure mode is designed to be buckling or folding in a region of the middle of the cell walls 64 at a higher stress, compared to the stress if the ends of the walls 64 were permitted to rotate. The end plates 63 may be stronger than the cell walls, so that crushing of the end plates 63 only commences once the crushing of the cellular structure 61 of each zone is essentially complete.

[0125] The cell walls 64 have a height H between opposed transverse annular plates 63, a width W and the cell 62 has a span S which is measured as the distance in a plane perpendicular to the axis 50 between two opposed cell walls 64.

[0126] In some embodiments the ratio of the wall height H to the wall width W may be 3:1 or less, i.e., the wall height H may be up to three times the wall width W. The pattern of cells 62 in each zone Zi is the same. Also, the cells 62 in axially contiguous zones Zi are aligned with each other.

[0127] As shown in Figs 7a-7d the cell walls 64 may be planar (Fig 7a), or profiled (Fig 7b) e.g. corrugated in transverse profile; and / or formed of varying thickness (Figs 7c and 7d). The cells 62 are approximately the same size. This facilitates approximately the same peak crushing load across the whole of each zone Zi. However, some part of the cell walls 64 may be weaker than the remainder to provide an initiation point for crushing. Once commenced, the crushing rapidly spreads to the entire zone Zi. In different embodiments the cells 62 may have three, four, five, six or more cell walls 64. For example, Figs 7a-7d show cells 62 with six walls in a hexagonal configuration, while Figs 7e and 7f show quadrilateral shaped cells 62 with four walls in the configuration of a trapezoid. In Fig 7e the cell walls 64 are planar, though as shown in Fig 7f the cell walls 64 may be corrugated in transverse profile.

[0128] Also, the cells 62 can be packed or configured in any arrangement that generally occupies the available annular space. Some fractional sized cells, such as half-sized cells may occupy positions around the edges of each annular zone. As explained later, cells 62 with an even number of cell walls 64 appear to have superior crush / load absorption characteristics than those with an odd number of cell walls 64. Nevertheless, embodiments of the disclosed system may include modules 14 with cellular structures 61 with cells 62 having an odd number of cell walls 64.

[0129] It is also possible for embodiments of the system 10 to include a crush module 14 with multiple zones Zi in which the cell walls 64 of at least one of the zones has a height that is different to the cell wall 64 height of another zone of the same crush module 14.

[0130] Figure 8 shows two of many possible cellular structures 61Qand 61Hthat may be incorporated in a respective zone Zi. While Fig 8 shows the two different cellular structures in the same plane it should be understood that this is for illustrative proposes only and in practice each zone Zi of the same module would ordinarily have an identical cellular structure. The cellular structure 61Qoccupies a sector of about 30° and this sector structure repeats 12 times to occupy the entire annulus of the zone. The cellular structure 61H, extends for a sector of about 30° and this sector structure repeats 12 times to occupy the entire annulus of the zone.

[0131] Cells 62 of the cellular structure 61Qare quadrilateral in shape, which of course may include square shaped. Here there are three cells 62 between the inner circumferential wall 65 and the outer circumferential wall 67. The cells 62 are arranged so that opposite cell walls 64 lie along common radii. As an inherent result of geometry, the area of the cells 62 in the cellular structure 62Q increases with radial distance from the axis 50.

[0132] In the cellular structure 61H, the cells 62 are either in the shape of a hexagon or the shape of a part of a hexagon. Specifically, along a radius, there are two and a half cells 62 between the inner and outer circumferential wall 65, 67.

[0133] Figure 9 illustrates an alternative configuration of the cellular structure 61Hfor a quarter sector of a zone Zi in which the cells 62 are predominantly hexagonal shape but would include other part hexagonal or irregular shapes to fill the area between the inner and outer circumferential walls 65, 67. Here there are approximately 3.5 cells 62 along any radius. The pattern of cells 62 in the cellular structure 61Hrepeat in segments of about 60°. Thus, starting at the radius that extends along points A-A, the pattern of cells 62 repeats in the clockwise direction at the radius that extends along points F-l.

[0134] Each zone Zi has an inner diameter D1 and an outer diameter D2 which are the same as, and indeed constitute the inner and outer diameters of, the crush module 14. Each zone is closed at radial inner and outer sides by the inner and outer circumferential walls 65 and 67. The walls 65, 67 may be formed separately for each zone Zi as the module 14 is being constructed. Alternately the walls 65, 67 may be formed for all zones Zi in the final steps of construction once the module 14 has been built to the desired length which will accord with a designed number of zones Zi.

[0135] To provide some context and comparison, for a module having an inner diameter D1 of 20.5 mm and an outer diameter D2 of 36.9 mm the thickness or radial length of the zone Zi will be 8.2 mm and for the cellular structure 61Hof Figure 8 in which there are about 2.5 cells along a radius, the zone will have about 93 cells 62, whereas the cellular structure 61Hof Figure 9 in which there are about 3.5 cells along a radius, the zone will have about 141 cells 62.

[0136] In other embodiments the opposite end plates 63 of the zones Zi may be provided with through holes 68 as shown in Figure 10. In this example there is one hole 68 located substantially centrally for each cell 62. This is the case irrespective of whether each cell is of a hexagonal shape or an irregular shape. The holes 68 remove unnecessary metal from the end plates 63 to reduce the metal volume compared to the total volume of the crush module. This may also provide more void space within the module to accommodate cell walls that have broken, folded or otherwise deformed in response to the module 14 absorbing a shock load. Also, the holes 68 would enable a flow of fluid or gel or small particles through the cells 62 and thus the module 14. In the absence of the holes 68 the cells 62 are sealed by the end plates 63.

[0137] In one example the inner diameter D1 may be about 20.5mm and the outer diameter D2 may be about 37 mm. The zones Zi may be in the order of 5mm to 10mm in height. The plates 63 may be about 1 mm thick. A module 14 having a length of 300mm may have between 30 to 60 zones Zi. Multiple thin zones per module 14 may result in multiple high peak loads during failure. Those peak loads are higher if the zone heights are less. There will be an optimum height of each zone to optimise the peak crushing force while still having considerable void available to receive the crushed cells as compressive movement occurs. To assist in controlling the manner in which the module 14 deforms as it absorbs a load the cells 62 may be provided with a prop or brace 70. Figures 11 a-11 e illustrate examples of props 70a-70e (hereinafter referred to in general as “prop 70” in the singular or “props 70” in the plural) respectively that may be used with hexagonal shaped cells 62. In general terms a prop 70 is a small structure positioned at mid-cell height in each cell. The prop 70 has a plurality of elements or spokes 72 that bear against a centre point or line of some or all the cell walls 64 and radiate from a hub 73.

[0138] In Figs 11 a-11 c the props 70 are shown in relation to regular hexagonal cells 62. In Figures 11d and 11e, the props 70 are shown in relation to irregular hexagonal cells 62. In both instances the props join mid points / lines of opposing cell walls 64. In the illustrated embodiments the elements 72 bear against each cell wall 64. But in other embodiments, for a hexagonal cell 62 a prop 70 may have three elements / spokes that could be used for transferring a compressive load only; or a tensile load only; or a cell could be provided with two separate three element props, one for the tensile arms and one for the compressive arms. The elements / spokes 72 meet at or near the centre of the cell 62, so that a tensile or compressive load path can be provided via the elements.

[0139] The props 70 are arrange in a zone Zi so that props 70 in adjacent cells 62 bear on a substantially aligned point or line on opposite sides of the same cell wall 64. When the cells 62 have an even number of walls 64 and module 14 is activated to absorb a shock load ideally the respective cell walls 64 of a cell 62 will alternately attempt to fold into the cell and out of the cell placing sequential elements 72 into alternating tensile or compressive loads. This is illustrated in Figure 12 showing a single hexagonal cell 62 with a prop 70 where sequential elements / spokes 72 are alternately in tension T or compression C.

[0140] When a subset of cell walls 64 attempt to deflect into a space defined by the cell walls 64 of a cell 62 in response to a shock load, they resist each other’s movement by virtue of the prop 70 located in the space between them. A small resisting force applied by a prop 70 in the direction normal to the cell wall 64 is effective to oppose buckling of the wall. As a result, a much larger shock force is required within the wall 64 to initiate buckling or folding than would be required in the absence of the prop 70. Substantial movement may only occur when the prop 70 becomes overloaded and destroyed. Once the prop 70 starts to weaken, the buckling or folding process rapidly moves to completion, destroying the prop 70.

[0141] The crushing of the module 14 in response to the application of a shock load is described in detail with reference to Figures 13a-14f.

[0142] Figure 13a shows three mutually adjacent hexagonal cells 62a, 62b, 62c in the same zone of a module 14. In this embodiment each of the cells 62 is provided with a brace 70 as shown in Figure 12 but for visual clarity the braces 70 are not shown in Figure13a. When absorbing the shock load the module 14 is compressed between the first end 18 and the load transfer coupler 16 / bearing washer 52, crushing down from an initial length L1 (Fig 1) to a final length L2 (Fig 3). This is facilitated by the folding or buckling of the cell walls 64. As described above embodiments of the SLRS 10 and module 14 are arranged so that folding or buckling is controlled with alternate walls of each cell 62 folding inwardly and outwardly of the cell. In Fig 13a arrows are used to show the walls 64 that fold inwardly of a cell 62. This folding when synchronised results in the joined walls of a cell 62 tearing apart along a mutual nodeline 66. To facilitate this tearing, the nodeline may be provided with a point or line or volume of weakness, or a void, or a variation in geometry.

[0143] Figures 13b and 13c sequentially show the progress of crushing of module 14 at the cell 62 level. In these Figures the item number 64x shows in side view a cell wall 64 at mid-height of a cell 62 prior to the application of the shock load. The item number 64y illustrates the same cell walls commencing to deflect or fold inwardly or outwardly as the load increases. At this stage the mutually adjacent cell walls are still joined along the common nodeline 66. As the load on module 14 increases, so does the load on the cells 62 as does the tension in the node lines 66 until a point is reached where the joined cell walls 64 of the respective cells pull apart at and along the common nodeline 66. This is represented in Fig 13c where item 64z shows the pulled apart and detached cell walls of the cells 62a, 62b, 62c and the dashed lines show the original position of the cell walls prior to application of the shock load.

[0144] The body of each cell wall 64 may be slightly variable in thickness with a view to avoiding tearing other than at the node line 66 and encouraging folding of cell walls 64 in the correct direction at their mid-height region.

[0145] The crushing of the module 14 and folding of the cell walls 64 is further illustrated in Figures 14a-14f. Figure 14a is similar to Figure 13a and shows in section view the commencement of deflection in the cell walls in response to the initial application of a shock load where the cell walls deflect from their unloaded position 64xto a deflected position 64y with the node lines 66 still intact. Figure 14b is a view of section A-A of Figure 14a where the walls in their unloaded position 64x is represented by dashed lines. Here it can be seen that the props 70 are positioned at a mid-height level in each cell 62 and the walls 64 are slightly non-planar in a manner to encourage a preferred direction of folding in their mid-height region. Also, there is a conformity in the direction of deflection of the cell walls along the section line A-A.

[0146] Figures 14c and 14d show the folding of the cell walls 64 with increased load on the module 14. The cell walls 64 commence tearing apart from each other along the node lines 66, and the props 70 in the cells 62 rupture indicated by item 70R in these Figures. As the cell walls tear apart, they fold at their mid-height region, with each alternate wall folding inwardly of the cell 62. The cell height reduces from a starting maximum height H1 to an intermediate reduced height H2. This height reduction occurs for all cells 62 in all zones Zi and is reflected in a reduction in the length of the module 14 equal to the sum of the height reductions for each of the zones Zi in the module 14.

[0147] Figs 14e and 14f show the end configuration of the zones Zi when the module 14 has absorbed its maximum designed energy from a shock load or impulse. The zones Zi are now at their minimum height H3 (i.e., H3 < H2 < H1) and the module 14 is at its minimum length. The cell walls 64Z have folded over with an upper half of each cell wall overlying a lower half of the same cell wall.

[0148] As previously mentioned, some part of the cell walls 62 may be formed weaker than the remainder to provide an initial point for crushing and control the direction, synchronicity and initiation of folding. This can be achieved by providing a point of weakness at an intermediate height of the wall on the side opposite to the intended direction of folding. For example, the point of weakness could be weakening dot or dimple or furrow (a defect); and may be located, for example, at or near the mid-wall centre point on the side opposite to the intended direction of folding. As the wall compresses, the local point of weakness forces the load path to shift to the side of the wall without the weakness. The load path in the wall is no longer collinear. Therefore, load on the cell wall initiates slight buckling towards the side of the wall without the weakness, putting the prop 70 into compression. (As an analogy, take a matchstick and cut a nick at mid-height one side. Compress it, and it will buckle away from the cut side.) An additional or alternate way to control the direction, synchronicity and initiation of folding is to shape the cell walls slightly to be convex towards the desired fold side. A load applied on the wall initiates slight buckling, putting the prop 70 on that desired fold side into compression, while the prop on the other side goes into tension.

[0149] Other mechanisms to control the direction, synchronicity and initiation of folding include providing, or otherwise forming a cell wall with, (a) a dimple (b) a hollow or perforation (c) a reduction in wall thickness (d) a slot or other void formed adjacent to or within the nodeline, and (e) a change in geometry of a portion of a length of the cell wall, at a point or region where it is desired for the fold to in initiate. In many embodiments this point or region will coincide with a line bisecting the wall in height.

[0150] Performance of the SLRS 10 having an annular crush module 14 may be enhanced by arranging the cell walls 64 immediately adjacent the inner circumferential wall 65 to fold in a direction away from inner circumferential wall 65, i.e., away from the rock bolt 26. The same mechanisms discussed above for controlling the direction and synchronicity of folding of the cell walls 64 can be applied to the cell walls immediately adjacent the inner circumferential wall 65 to maximise the proportion of these of walls folding away from the rock bolt 26. This purpose of this is to reduce interference with or fouling of the rock bolt 26 as well as enable easy withdrawal and replacement of an activated module 14.

[0151] When the module 14 is activated in response to the application of a shock load the module 14 may be crushed to its minimum length / volume where the material of the module 14 is substantially completely folded or crumped up, forming a denser material, capable of carrying higher loads. This may be conveniently referred to herein after as “densification”. The forming of the end plates 63 from foamed metal in embodiments of the SLRS 10 and module 14 may facilitate an increase in the collapse distance of the module 14 (i.e., maximise L1-L2) during densification. The foamed metal end plates are strong enough to provide the required lateral support to cell walls 64 during the wall peak loading episode, yet during densification, the foamed metal will deform locally to match protrusions or voids among the collapsed folded cell walls 64 and the remains of the props 70. During that process, the load carrying capacity of the crushed module will gradually increase. That load will be similarly gradually transferred to the rod, thereby avoiding or minimising shock loading of the load transfer coupler 16 / bearing washer 52 and the rod 26.

[0152] Thus, in this present embodiment the ability to absorb load is derived from the physical construction of the module 14 including the arrangement of cells 62, walls 64 and zones Zn including the controlled crushing pattern. The module 14 in this embodiment does not use or otherwise rely on the provision of liquids, pastes, foams or gels for bearing and absorbing load transferred from the rock mass, and / or being extruded from holes within the module 14 or cell 62, even if such liquids, pastes, foams or gels are supplied and present within at least one cell. The cells 62 of the module 14 are intended to be devoid of any liquid prior to installation and remain that way except for the possibility of transient liquid flow through the cells 62 in embodiments where the end plates 63 of the zones Zi are provided with through holes 68 as shown in Figure 10. It should be noted that in practice one or more of the cells 62 may also contain various residue(s) remaining from the process of manufacturing the module. However, any such residue is only incidental and is not intended to have, nor has, any material effect on the function and operation of the previously described embodiments of the disclosed system and method.

[0153] The expected sequence of events during a dynamic (non-shearing) disturbance that activates the SLRS 10 and module 14 to provide shock loading protection to a rock bolt 26 may be as follows. • A portion of rock mass 31 surrounding the bore hole 30 in which the SLRS 10 and rod 26 are installed suddenly begins to move into an excavation, placing load on the plate 40.

[0154] • The plate 40 transmits the load to housing 12. This is by way of the engagement of the plate rim 44 with the collar 42 which is designed relatively thick so that it can survive the high transient shock loads and strains.

[0155] • The load transmits to the first (downhole) end 18 of the housing 12, which is similarly designed relatively thick to survive high shock loads.

[0156] • The crush module 14 receives the load and attempts to transmit it to the bearing washer 52 / load transfer coupler 16. However, if the load becomes high enough, crushing of the module 14 occurs. During crushing, further load increase is substantially halted, and displacement of the housing 12 towards the excavation occurs.

[0157] • The bearing washer 52 transmits the load to the nut 56.

[0158] • The nut 56 transfers the load to the rod 26, and thus to a distal end of the rod 26 which is anchored to the rock mass 31 at the toe end of the borehole 30.

[0159] • The anchor transfers the load back into the rock mass 31 .

[0160] • During activation of the crush module 14, the load in the rod 26 is controlled to be about the same as the crush load of the crush module 14. This load is designed to be less than the yield load of the rod 26.

[0161] • When and if the crush module 14 is fully crushed, the load transferred to the rod 26 can increase, and can become high enough to then activate any other yield mechanism that might be a characteristic of that rod 26. For example, the rod may undergo plastic deformation.

[0162] • At the conclusion of the dynamic disturbance, static loading conditions remain. The bolt 26 may shrink in length if it can release elastic energy if the load reduces, and this acts to keep the GSU assembly tight to the rock mass 31 . An optional rubber washer 38 if incorporated within the housing 12 will also attempt to release elastic strain and add slightly to the tightness of the GSU assembly.

[0163] • However, if the rock mass 31 has cracked open and loosened during the dynamic disturbance, then when static conditions return, the tension in the bolt 26 may be less than a desirable tension. If so, the nut 56 may be retightened. A regular quality control action after a significant disturbance will be to retorque the nuts to a proof level.

[0164] In one example the crush module 14 crush distance (L1-L2) may be 200mm or 300mm. Once the module 14 is crushed the rock bolt 26 yield mechanism activation commences. If the designed yield distance capacity of the rock bolt is 250mm then an embodiment of the SLRS 10 combined with the designed yield capacity of the rock bolt may provide a total GSU deformation capacity of 450 to 550 mm.

[0165] A most severe adverse situation for a rock bolt 26 is shearing occurring within the rock mass 31 surrounding the GSU. Shearing is here defined as meaning differential displacement of opposite sides of the rock mass separated by a joint or fault or fracture plane or surface. If a shearing movement intersects a borehole 30, the borehole 30 suffers a dislocation and becomes partly closed. If the shearing distance happens to equal the diameter of the borehole 30, and the shear surface is perpendicular to the axis of the borehole, the borehole becomes totally closed off. A GSU installed in such a borehole is severely clamped or locked, and potentially ruptured, by significant shear. This is more problematic for a solid rod rock bolt than for a cable rock bolt. A solid rod performs poorly when forced to carry load through a sheared zone, while a cable strand wraps to some extent through a partly closed sheared borehole and still operates mostly in tension.

[0166] It is believed that embodiments of the SLRS 10 may operate to minimise the effect on a GSU of a shear in a rock mass 31. The reasons for this are as follows. Assume the housing 12 is positioned closely to the borehole wall in the portion of borehole 30 near the collar. If shearing affects the rock bolt 26 in the borehole 30 more distant from the collar than the housing 12, there is no change to the operation of the crush module 14. The yield distance capacity of the SLRS 10 still applies, even if the rock bolt 26 cannot yield, unless the rock bolt 26 strength is so compromised by the shearing that the rock bolt 26 fails before the crush module 14 is fully crushed.

[0167] On the other hand, if shearing occurs close to the collar, a section of the housing 12 will become deformed or bent by the shearing movement. A section of the crush module 14 will likewise be deformed. However, the crush module 14 is somewhat deformable in the sideways or radial or lateral direction, i.e. the direction perpendicular to the axis of the borehole. This lower sideways resistance is a known property of the cellular structure 61. The crush module 14 deforms locally and conforms to the new deformed geometrical volume available to it. The rock bolt 26 will incur a degree of elastic bending or curvature as it passes through the deformed portion of the crush module at the sheared interval, but this is acceptable.

[0168] The zone or zones Zi of the crush module 14 that undergo shear become non-functional. However, all other module zones remain functional. The functional zones Zi will activate under sufficient stress as the nut 56 and bearing washer 52 are pulled deeper into the borehole 30 toward the annular surface 36 on the inside of the housing 12 at the first end 18.

[0169] Performance of the SLRS 10 may become irregular or compromised if the bearing washer 52 reaches the sheared section of the housing 12 and the bearing washer needs to deform in order to progress further down the inside of the housing 12, and this may or may not occur. If it does not occur, crushing of the crush module ceases, and any further yielding depends on the yield capability of the rock bolt 26.

[0170] In the event that shearing occurs too close to the collar, and the module 14 becomes locked in position, the surface plate 40 can potentially become highly loaded and in extreme cases may be torn off the collar 42 of the housing 12. In that event a stub collar piece that engages to the inside of the collar 42 could be fitted to carry a new plate 40.

[0171] One method of installing a new rock bolt in the form of a rod and an embodiment of the SLRS 10 may be as follows.

[0172] • A borehole 30 is drilled in the rock mass 31 .

[0173] • The surface plate 40 is fitted to the housing 12 so that the rim 44 sits under the collar 42. The first (leading or downhole) end 18 of the housing 12 is tapered so that the surface plate slides 40 on easily during installation. The collar end of the rock bolt is passed through the housing 12 and module 14 through the bearing washer 52 and the nut 56 is engaged on the rock bolt / rod 26.

[0174] • GSU assembly with the SLRS 10 is inserted in the borehole and the distal end of the rock bolt / rod 26 is anchored at the toe of the bore bole 30 by other known means. The GSU is tensioned or preloaded by rotation of the nut 56.

[0175] • If a pretension disk 60 is used, the nut 56 is torqued until the pretension disk 60 activates.

[0176] The depth of the borehole 30 should be greater than the depth of the GSU for example by at least 20mm, or 50mm or more. This is so that the rod 26 does not protrude from the borehole once installation is complete. During tensioning the GSU preload must be less than the initial crushing load of the crush module 14. During the tensioning process, the housing 12 is drawn into the borehole 30 and bears against the plate 40, which bears against the rock surface. The rubber washer 38 if fitted would compress slightly. These factors add to the travel distance of the nut 56 during the tensioning process.

[0177] The rotation of the nut 56 may briefly cause rotation of the housing 12 and the surface plate 40. Once the plate 40 is in sufficiently tight contact with the rock surface, rotation will stop and the anti-friction washer 58 will be activated. During tensioning only the nut 56 rotates. This may provide for better reproducible pretension not dependent on other components. Also, during the pretension process, the anti-friction washer 58 may apply some torsion onto the bearing washer 52. The bearing washer 52 does not rotate due to the tab 54 / slot 48 engagement with the housing 12, to ensure that no torsion is applied to the crush module 14.

[0178] The SLRS 10 can be installed in conjunction with common types of mesh or screen used in mines. If mesh is already in place, the SLRS 10 is installed so that the mesh is positioned between the plate 40 and the rock surface. If mesh is to be added subsequently, a stub collar piece is provided that engages to the inside of the collar 42. The stub collar may be of similar geometry to the collar 42, and supports a plate in the same way, so that the subsequent layer of mesh can be pinned to the rock surface. The stub collar may engage to the collar 42 via threads 46, or via a push-fit mechanism, the latter being irreversible. The stub collar itself can accommodate the similar fixing of a further stub collar, should that be required.

[0179] The above embodiment of the SLRS 10 has been described with the rock bolt in the form of a rod (i.e., a solid metal bar). However, the SLRS 10 is adaptable to other forms of rock bolt including cables and tubular bolts. Figure 15 shows an embodiment of the SLRS 10 used with a rock bolt 26 in the form of a cable 26c. The substantive difference with the first embodiment is that the nut 56 is replaced with a barrel and wedge anchor 56xthat comprises a barrel 56b and a wedge 56w. The wedge 56w fits inside the barrel 56b and can bear against the cable 26c. The anchor 56x is tensioned against the bearing washer 52. No rotation is required but rather a tensioning jack with a suitable dolly configured to enable operation within the confines of the bore hole collar is used to apply the pretension load. When barrel and wedge anchor 56x is used, it can bear directly on the bearing washer 52 without the need for an anti-friction washer 58.

[0180] Figure 16 shows a further embodiment of the SLRS 10 used with a rock bolt 26 in the form of a tubular bolt 26t. The tubular bolt 26t comprises an outer tube that is in frictional contact with the borehole walls. The tubular bolt 26t is normally provided with a ring 75 configured to carry a plate (not shown in Figure 16) to bear against the rock mass at the collar of the borehole 30. In this embodiment of the SLRS 10 the housing 12 is reconfigured to be inverted so that the first load bearing end 18 having the annular surface 36 against which the module 14 is crushed is up-hole (i.e., near the borehole collar) relative to the second end 20. The first end 18 is not tapered as in the previous embodiments. The plate 40 is operably joined to the nut 78 and the rod 76 and bears against the rock mass at the collar of the borehole 30. The ring 75 functions to receive the force applied during installation to drive the tubular bolt into the borehole. During a dynamic disturbance, the rock mass is likely to push against ring 75 with force sufficient to tear it off the tubular bolt 26t, however that has no impact on the operation of the SLRS 10.

[0181] The inverted housing 12 is fixed to the tubular bolt 26t. This may be for example by way of teeth 74 formed on an outer surface of the housing 12 that grip onto an inner surface of the tubular bolt 26t. As one possible alternative the housing 12 may be welded to the inner surface of the tubular bolt 26t. The load transfer system 16 is also modified by the inclusion of a bolt 76 that threadingly engages with the nut 56, and a second nut 78 at the collar end that screws onto the bolt 76 and engages rim 44 of the plate 40. In this way a shock load can be transferred onto the module 14 at its in-hole end to crush the module 14 against the inside of the housing 12 at the first end 18.

[0182] In each of the previously described embodiments the SLRS 10 has been located at the collar or up-hole end of the bore hole 30. But as shown in Figure 17 in alternate embodiments the SLRS 10 may be located at the toe end 80 of the bore hole 30. The housing 12, which is also inverted, may be anchored to the borehole 30 by grout, resin or other means. Teeth 77 on the outer circumferential wall of the housing 12 may assist in anchoring to the toe of the borehole 30. The toe end of the rod 26 passes into the housing 12 and through the module 14, and the pre-tension disk 60 and is retained by the nut 56. The nut 56 is secured to the rock bolt / bar 26, for example by a pin 82, although other fixings techniques may be used. The first end 18 of the housing 12 is squared rather than tapered. The annular surface 36 against which the module 14 is crushed during shock load absorption is formed on the inside of the first end 18.

[0183] While several exemplary embodiments have been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. Examples of such variations include:

[0184] • The module 14 may be formed entirely of foamed metal or a combination of layers / zones of different types of foamed metal. In this regard the sizing and arrangement of voids in the foamed metal may vary along the length of the crush module 14, so that the compressive strength of the foamed metal varies along the module 14. In this way the crushing may therefore initiate at a preferred load, but as crushing distance displacement continues, the crushing load increases.

[0185] • The SLRS 10 could be fitted anywhere along the rock bolt, i.e. provide two shorter rock bolts and configure the SLRS 10 in between.

[0186] • Respective SLRSs 10 could be fitted to the toe and collar ends of the same rock bolt.

[0187] • The SLRS 10 can scale to a range of borehole diameters: common diameters in some hard rock mining are 47mm, 64mm and 76mm.

[0188] • The SLRS 10 can scale to a range of rock bolt diameters. Common in the industry are 20mm for rod diameters and 15.2mm for cable diameters.

[0189] • The SLRS 10 can adapt to a twin-strand cable bolt installation.

[0190] • Crush module 14 can vary in internal cellular construction. Cells 62 can be different geometry and size, with different internal features, and cells 62 can be open or closed and cells 62 may vary in configuration from place to place within the module 14.

[0191] The SLRS 10 need not be circular in cross-section - other shapes are possible, symmetrical and non-symmetrical, although it is believed that the circular crosssection provides a maximised load capacity of the SLRS 10. The housing 12 can be an open framework rather than having a continuous circumferential wall / surface.

[0192] ■ The manner in which the SLRS 10 engages the plate 40 may vary.

[0193] ■ The collar 42 may be formed of various shapes and configurations, as indeed is represented by the differences in profile of the collar 22 on left and right hand sides of the central axis 50 in Fig 1 .

[0194] ■ Optionally, the opening at the top of housing 12 at the collar of the borehole 30 can be provided with a cross bar across its diameter. The purpose of the bar is that in extreme load conditions, if the nut 56 strips from the rock bolt 26 or if the rock bolt 26 ruptures, the rod / nut cannot eject from the borehole at high speed. Instead, the ejecting parts impact the bar and share kinetic energy with the entire SLRS 10 assembly, which will greatly reduce the ejection velocity of the various components.

[0195] • To facilitate the monitoring of movement of components of the SLRS 10 and thus of the rock mass 31 , an inside of the housing 12 may be painted a first colour which may be a bright colour, e.g. neon green. Once the SLRS 10 is installed, the exposed inside surface of the up-hole end of the housing may be spray painted a second contrasting colour. This marks the install position or starting position of the SLRS 10. Once activated, a bright neon green ring will become visible inside the housing. This enables movement to be visually detected and measured inside the collar.

[0196] • The module 14 may be made in shapes other than annular particularly for non rock bolt applications. For example, a cylindrical module without a central hole could be located between two parts that move together once a load sufficient to crush the module is applied. Alternately it is possible for the module to have axially extending recesses along the outer circumferential wall of the module to seat connecting rods that attach at one end to a bearing washer or similar device.

[0197] Embodiments of the SLRS 10 may provide one or more of the following advantages or benefits.

[0198] • There are no moving parts scraping against rock surfaces.

[0199] • The SLRS 10 operation does not depend on frictional interaction. The rock bolt 26 and nut 52 / barrel and wedge anchor 56x are located within the housing 12 / bore hole 30 and are largely protected from impact damage, for example from mining equipment / vehicles.

[0200] Apart from Figure 17 where the SLRS 10 is installed at the toe end of the bore hole 30, there is no dependence on resin or grout.

[0201] The shooting out of part of the SLRS 10 during the application of a shock load causing rupture can be substantially prevented.

[0202] The SLRS 10 is largely able to accommodate shear.

[0203] As the region where the rock bolt 26 is coupled to the SLRS 10 (e.g., by way of the nut 56) is below the rock surface at the collar of the bore hole 30, the rock bolt does not need to protrude from the hole. This allows utilisation of a greater length of the rock bolt for anchorage deeper into the rock mass than would otherwise be the case. The components of the SLRS 10 are easy to make using existing fabrication technologies. Also, there is no reliance on tight fitting or tight tolerances therefore precise and high-cost machining of components is not required.

[0204] Preload or pretension is affected by simply tightening the nut 56 or the barrel and wedge anchor 56x.

[0205] Proof test or limit test of the rock bolt 26 or the crush module 14 or both at any time is possible because there is no need to supply a separate pull ring or other fixture for bolts to be tested. Accordingly, every bolt can be tested if desired.

[0206] Following a proof test, or following activation, the nut 52 / barrel and wedge anchor 56x can be tightened to restore or ensure desired preload.

[0207] The SLRS 10 / housing 12 does not impede any anchoring operations on the rock bolt 26. The rock bolt 26 is free to rotate or shift in any way, independent of the SLRS 10. Only when the anchoring of the distal end of the rock bolt 26 is complete, the nut 52 / barrel and wedge anchor 56x are tightened to seat against the housing, pull the surface plate 40 tight to the rock, and pretension the rock bolt 26.

[0208] Positioning the SLRS 10 at the collar end of the GSU permits direct visual inspection of activation of the SLRS 10, and with appropriate measurements, the consumed capacity of the crush module 14 can be known at any time. The crush module 14 is designed to be the weakest link, so it is possible to easily determine whether the rock bolt 26 is fully functional. The rock bolt 26, being fixed to the anchor at the toe of the borehole, is an absolute reference to enable direct measurement of the actual movement between toe and collar.

[0209] As previously described it is possible to attach mesh or indeed anything else considered desirable to an installed GSU fitted with the SLRS 10. This eliminates the need to drill and install a separate rod or mechanism to pin mesh. • The SLRS 10 operation has no gouging or working of metal on metal.

[0210] • The SLRS 10 does not need grease as coolant for operation.

[0211] • The SLRS 10 and its operation does not provide a source of sparks.

[0212] • The SLRS 10 is independent from rock bolt 26 during a dynamic disturbance. The housing 12 and module 14 have a sliding fit around and do not grip onto the rock bolt 26. Thus, the performance of rock bolt 26 and the SLRS 10 are independent of each other in terms of load response and are summable or additive.

[0213] • The SLRS 10 and rock bolt 26 connection can be retightened if loose.

[0214] • The SLRS 10 can be removed and replaced if the GSU has a threaded collar fixture, e.g. uses a nut 56, as distinct from a barrel and wedge anchor 56x.

[0215] • The SLRS 10 can provide any reasonable combination of module force control and module displacement capacity, and therefore energy dissipation capacity.

[0216] • The SLRS 10 can be adapted to any reasonable combinations of length, internal diameter and external diameter.

[0217] • The SLRS 10 operation is expected to be consistent and reproducible, because it is independent of any property of the rock mass 31 or of the rock bolt 26 to which it is attached. The SLRS 10 is expected to closely meet any reasonable criteria for force, displacement, energy, and momentum transfer.

[0218] • SLRS 10 can be adapted to fit any threaded-end rock bolt rod or cable, also to any cable strand with a barrel and wedge anchor 56x.

[0219] • The SLRS 10 could be adapted to a multi-strand cable GSU.

[0220] • SLRS 10 is not dependent of length of the rock bolt.

[0221] • SLRS 10 is not affected by the usual small variations in drilled borehole diameter.

[0222] It should also be appreciated that the exemplary embodiments of the shock load reduction system and method are only examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. For example, as previously described the collar 42 may lie within or extend beyond the diameter of the bore hole 30. The collar 42 may be formed integrally with the housing 30 and elongated body 32 as shown in Fig .1 . But in alternate embodiments the collar 42 may be formed separate from and mechanically coupled to the elongated body 32. An example of this is shown in Fig 18 where the collar 42 is depicted as a short tube with an outwardly formed abutment surface 43. The abutment surface 43 abuts with a plate 40 that lies on the surface of the rock mass 31 in which is located the bore hole 30. The collar 42 has an external thread that engages with a thread formed on the inner circumferential surface at one end of the elongated body 32. The separate form of collar 42 may be used for all embodiments, irrespective of whether the abutment surface 43 thereof extend beyond or lies within the diameter of the bore hole 30. In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word “comprise” and variations such as “comprises” or “comprising” are used in an inclusive sense, i.e., to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the system and method as disclosed herein.

Claims

CLAIMS1 . A shock load reduction system for a load support element extending into a body of material comprising: a housing having a first load bearing end and an opposite second end and a cavity extending between the first load bearing end and second end; a crush module having a longitudinal axis and retained in the cavity, wherein the crush module comprises a plurality of axially stacked zones, each zone having a plurality of cells, each cell having a plurality of cell walls, wherein the cell walls of each cell in one of the plurality of zones are coplanar with respective cells walls in at least one other of the plurality of zones of the module; and a load transfer coupler operably associated with the housing and the crush module and coupled to a load support element, the load transfer coupler arranged to initially transfer a shock or impulse load to the crush module in a direction of the longitudinal axis wherein the load transfer coupler is operable to crush the crush module against the first load bearing end to a second axial length being less than the first axial length wherein the crush module absorbs at least a portion of the shock load impulse energy and wherein any residual shock load is transferred to the load support element.

2. The shock load reduction system according to claim 1 wherein mutually adjacent cell walls within a common zone join along a common node line that extends parallel to the longitudinal axis of the crush module.

3. The shock load reduction system according to claim 2 wherein the cells are arranged so that, across a radius of each zone, at least three cell walls join along each of the common node line.

4. The shock load reduction system according to any one of claim 1 to 3 wherein the cell walls in one of the zones have a height that is different to the height of cells walls in another one of the zones.

5. The shock load reduction system according to claim 3 or 4 wherein each cell is arranged so that when the crush module is crushed, walls meeting at a common node line pull apart along the common node line.

6. The shock load reduction system according to claim 5 wherein at least one node line and / or one cell wall is formed with a point of weakness to initiate failure of the cells associated with and along the common node line.

7. The shock load reduction system according to claim 6 wherein the point of weakness includes one or more of (a) a dimple formed at the point (b) a hollow or perforation formed at the point (c) a reduction in wall thickness at the point (d) a slot formed along the node line containing the point, and (e) a change in geometry of a portion of a length of the cell walls including the point.

8. The shock load reduction system according to any one of claims 1 to 7 wherein mutually adjacent cell walls of at least one cell, where the at least one cell has an even number of walls, are arranged to fold in an alternating manner inwardly and outwardly of the at least one cell.

9. The shock load reduction system according to claim 8 wherein each cell wall is configured to fold along a fold line that lies in a radial plane of the crush module.

10. The shock load reduction system according to claim 9 wherein the fold line lies midway of a height dimension of a corresponding cell.11 . The shock load reduction system according to any one of claims 1 to 10 wherein the cell walls are one of: (a) planar and of uniform thickness along an axis parallel to the longitudinal axis; or (b) planar and of varying thickness along an axis parallel to the longitudinal axis; (c) non-linear in shape in a radial plane of the module.

12. The shock load reduction system according to any one of claims 1 to 11 including a brace or prop located within at least one cell of a zone, wherein the brace or prop bears against two or more cell walls of the cell.

13. The shock load reduction system according to claim 12 wherein the brace or prop bears against the two or more walls of the cell midway of a height dimension of a corresponding cell.

14. The shock load reduction system according to claim 12 or 13 wherein the brace or prop is arranged to bear against alternate walls of a cell.

15. The shock load reduction system according to claim 12 or 13 wherein the brace or prop is arranged to bear against every wall of a cell.

16. The shock load reduction system according to any one of claims 12 to 15 wherein each cell in a zone is provided with a brace or prop and the braces or props of mutually adjacent cells are configured to bear on opposite sides of a point or region of a common wall.

17. The shock load reduction system according to any one of claims 12 to 16 wherein each brace or prop is integrally formed with a corresponding cell.

18. The shock load reduction system according to any one of claims 1 to 17 wherein the cell walls are made of a metal or a metal alloy or foamed metal.

19. The shock load reduction system according to any one of claims 1 to 18 wherein each zone includes a bottom wall and an opposite top wall wherein the walls extend radially across axially opposite ends of each zone and seal the cells.

20. The shock load reduction system according to any one of 1 to 18 wherein each zone includes a bottom wall and an opposite top wall wherein the walls extending radially across axially opposite ends of each zone and the walls are provided with holes.21 . The shock load reduction system according to claim 19 or 20 wherein the top and bottom walls are made from a plastically deformable material.

22. The shock load reduction system according to claim 21 wherein the plastically deformable material is a foamed metal.

23. The shock load reduction system according to any one of claims 1 to 22 wherein the housing has an elongated body which includes the cavity, and the second end of the housing includes a collar arranged to abut a plate that bears on an outside of the body of material into which the load support element extends.

24. The shock load reduction system according to any one of claims 1 to 23 wherein the load transfer coupler includes a bearing washer slidably engaged with the housing and located at an end of the crush module distal to the first load bearing end.

25. The shock load reduction system according to claim 24 wherein the load transfer coupler includes a first detachable fastener arranged to bear on the bearing washer and detachably coupled to the load support element.

26. The shock load reduction system according to any one of claims 1 to 24 wherein the crush module is of an annular configuration with an outer circumferential wall and an inner circumferential wall defining a passage extending parallel to the longitudinal axis.

27. The shock load reduction system according to claim 24 wherein the load support element is a rock bolt or a cable bolt that passes through the passage and the housing.

28. The shock load reduction system according to claim 26 wherein the load support element is a tubular bolt, and the housing is located inside the tubular bolt, and the load transfer coupler includes a bolt and a second detachable fastener wherein the bolt extends through the passage and is connected at one end to the first detachable fastener and at a second opposite end to the second detachable fastener.

29. The shock load reduction system according to any one of claims 26 to 28 wherein the walls of cells immediately adjacent the inner circumferential wall are arranged to fold in a direction away from the inner circumferential wall.

30. The shock load reduction system according to any one of claims 1 to 26 wherein the first load bearing end of the housing is of a frusto-conical shape reducing in outer diameter in a direction from the second end toward the first load bearing end.31 . The shock load reduction system according to any one of claims 1 to 26 wherein an outer surface of the housing at the second end is provided with a plurality of protrusions to facilitate anchoring of the housing into a settable material.

32. A shock load reduction system for a load support element extending into a body of material comprising: a housing having a first load bearing end and an opposite second end and a cavity extending between the first load bearing end and second end wherein the second end of the housing includes a collar arranged to abut a plate that bears on an outside of the body of material into which the load support element extends;an annular crush module retained in the housing and having: an inner wall forming a central passage for accommodating a portion of the load support member, an outer wall, and a first axial length; and a load transfer coupler operably associated with the housing, the load support element and the annular crush module to transfer a shock or impulse load arriving through the central passage to the annular crush module and the load support member wherein the annular crush module is operable by action of the shock or impulse load to crush within the housing to a second length being less than the first axial length between the load transfer coupler and the first load bearing end.

33. A crush module for absorbing a load, the crush module comprising a plurality of end to end stacked zones, each zone comprising a plastically deformable cellular structure having a plurality of connected cells, the cells having a plurality of cell walls that extend in a first direction parallel to a central axis of the crush module and a plurality of end walls extending in a direction substantially perpendicular to the first direction that separate mutually adjacent zones wherein cell walls of mutually adjacent cells in a zone join along a common node line that extends substantially parallel to the central axis wherein each cell is arranged so that when the crush module is crushed, cell walls meeting at a common node line pull apart along the common node line.

34. The crush module according to claim 33 wherein the end walls are plastically deformable.

35. The crush module according to claim 34 wherein the end walls are made of a foamed material.

36. The crush module according to claim 35 wherein the foamed material is a foamed metal.

37. The crush module according to claim 33 wherein the cells are arranged so that at least three cell walls join along the common node line.

38. The crush module according to any one of claims 33 to 37 wherein the cell walls in one of the zones have a height that is different to the height of cells walls in another one of the zones.

39. The crush module according to any one of claims 33 to 38 wherein at least one node line and / or cell wall is formed with a point of weakness to initiate failure of the cells associated with and along the common node line.

40. The crush module according to claim 39 wherein the point of weakness includes one or more of (a) a dimple formed at the point (b) a hollow or perforation formed at the point (c) a reduction in wall thickness at the point (d) a slot formed along the node line containing the point, and (e) a change in geometry of a portion of a length the cell walls including the point.41 . The crush module according to any one of claims 33 to 40 wherein mutually adjacent cell walls of at least one cell are arranged to fold in an alternating manner inwardly and outwardly of the at least one cell.

42. The crush module according to claim 41 wherein each cell wall is configured to fold along a fold line that lies in a plane parallel to the end walls of the crush module.

43. The crush module according to claim 42 wherein the fold line lies midway of a height dimension of a corresponding cell.

44. The crush module according to any one of claims 33 to 43 wherein the cell walls are one of: (a) planar and of uniform thickness along an axis parallel to the first axis; or (b) planar and of varying thickness along an axis parallel to the first axis; (c) nonlinear in shape in a plane parallel to the end walls of the module.

45. The crush module according to any one of claims 33 to 44 including a brace or prop located within at least one cell of a zone, wherein the brace or prop bears against two or more cell walls of the least one cell.

46. The crush module according to claim 45 wherein the brace or prop bears against the two or more walls of the cell midway of a height dimension of a corresponding cell.

47. The crush module according to claim 44 or 45 wherein the brace or prop is arranged to bear against alternate walls of a cell.

48. The crush module according to claim 44 or 45 wherein the brace or prop is arranged to bear against every cell wall of a cell.

49. The crush module according to any one of claims 44 to 48 wherein each cell in a zone is provided with a brace or prop and the braces or props of mutually adjacent cells are configured to bear on opposite sides of a point or region of a common cell wall.

50. The crush module according to any one of claims 44 to 49 wherein each brace or prop is integrally formed with a corresponding cell.51 . The crush module according to any one of claims 1 to 32 wherein the cell walls in the one zone and the at least one other zone are mutually adjacent.

52. The crush module according to any one of claims 1 to 32 wherein the cell walls of each cell are coplanar with respective cell walls in every other zone for the full length of the module.

53. The crush module according to any one of claims 1 to 32, 51 or 52 wherein the cell walls of a cell in a first zone are thicker than the cell walls of a cell in a second zone

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