WO2000036274A1

WO2000036274A1 - An underground support pack

Info

Publication number: WO2000036274A1
Application number: PCT/ZA1999/000138
Authority: WO
Inventors: Johann Smit; Petrus Nicolaas Erasmus
Original assignee: Grinaker Construction Limited
Priority date: 1998-12-14
Filing date: 1999-12-14
Publication date: 2000-06-22
Also published as: AU2060500A

Abstract

The invention provides a support component which includes a beam and two yielding elements at spaced locations on the beam, to be used in a support pack which is formed from a plurality of the support components, the support components being arranged overlying one another to form, at least, four outer columns wherein each column is defined by a stacked array of yielding elements alternating with ends of beams. The invention also extends to a support pack which includes a plurality of support components wherein the beams are positioned to overlie one another in a cross-shape to form a central column surrounded by the four outer columns.

Description

AN UNDERGROUND SUPPORT PACK

BACKGROUND OF THE INVENTION

This invention relates to a support pack of a type which is suitable for use in an underground location, and to a support component for use in a support pack of this type. More particularly the invention is concerned with a support structure which may be of a type referred to as a crib, or pack, suitable for use in an underground excavation wherein

the spacing between the roof or hanging wall and the floor or footwall is relatively large.

This use is given by way of example only and is non-limiting.

Substantial roof heights are encountered in certain mines such as underground coal mines. Supports which have been developed for other applications, for example

underground gold mines, are often not suitable for use in coal mines due to a variety of factors. For example, in a coal mine there is a need for a relatively slender structure which can be erected rapidly with minimal labour and which does not occupy an excessive

amount of space. Another factor is that a high roof height requires time consuming and

labour intensive construction of support structures.

A support should exhibit active load generation capabilities of at least approximately 50

tonnes and should be capable of up to 50% closure, depending on mining conditions, yield

loads and similar aspects.

The support structure should also be of a nature which, at least to the extent possible, allows for lateral movement between the roof and the floor without significant adverse effects.

The strata from which coal or any other desired ore is excavated are often relatively soft

and the support structure should be capable of yielding, as closure takes place, without

punching into the strata. For example in a coal mine bumps which take place in pillars created during mining operations, can give rise to rapid increases in loading and the support must be capable of rapid closure under these conditions.

Another factor is that the material which is used in the construction of a support of this kind

should not be combustible.

Timber cribs have been used as supports in coal mines. Such supports do however

support combustion and depending inter alia on the location of a mine can be expensive

to transport, for example if the mine is far from natural resources. Due to the high

excavation heights which may be encountered in coal mines the slendemess ratio of an elongate support may be such that it will fail catastrophically under load i.e. it will buckle

without yielding significantly. On the other hand the provision of timber support structures,

although overcoming the buckling problem, can be labour intensive and space consuming.

As an alternative to timber it is known to make use of precast cementitious blocks which

are stacked one over the other in a particular pattern to form a support structure. The cost

of the structure can be considerable. For example depending on the sizes of the blocks

each layer in this type of support may call for four or more blocks and this, apart from being relatively expensive, is also labour intensive to erect. Another disadvantage is that the support structure can fail under shear load conditions.

In another approach use is made of a steel pipe which is filled with lightweight concrete off-site. The pipe is then manoeuvred to an installation location using mechanised means

and is then vertically oriented. A gap between an upper end of the pipe and the overlying

roof is filled with timber to provide a degree of preloading.

This type of composite elongate support does provide a good yield characteristic but it is

expensive to produce and, as the installation is mechanised, the cost of installation is high.

It is also not easy to allow for differing roof heights.

SUMMARY OF INVENTION

The invention provides in the first instance a support component which includes a beam

and two yielding elements at spaced locations on the beam.

The yielding elements may be located at any convenient locations on the beam member

and preferably are near or at respective opposed ends of the beam.

The elements may be weaker in compressive strength than the beam. Thus, when the

elements and the beam are placed under equal compressive loading, the elements may

deform or yield to a greater extent than the beam. The elements and the beam may be provided in kit form, e.g. to be assembled on site.

The elements may be engaged with the beam in any appropriate way. For example the

elements and the beam may have inter-engaging formations or the elements may be fixed to the beam using straps or suitable fasteners. The elements may also be adhesively

bonded to the beam. Another possibility is to form the elements integrally with the beam.

In another form of the invention each yielding element is fixed to a beam using fastening

devices of any appropriate kind e.g. straps, sheet material or the like.

The beam may be of a first material and the elements may be of a second material. The

materials from which the beam and yielding elements are made may be of any appropriate

type. In one example of the invention the beam is made from timber of a first type and the elements are made from timber of a second type. Alternatively the beam is made from

timber with a grain which extends in one direction and the yielding elements are made from

the same type of timber with a grain which extends in a transverse direction, the directions

being such that, as stated, under compressive loading, the elements yield before the

beam. The beam may otherwise be made from, or include, a steel bar, rod or pipe.

If the beam includes relatively slender elongate components such as steel bars, rods or pipe then ends of the beam may be attached to yielding elements such as timber,

cementitious, plastic or polymeric blocks, or be made from any other suitable material.

In a different form of the invention the beam and the elements are made from cementitious materials. Preferably use is made of a lightweight cementitious aggregate or matrix which may, optionally, be reinforced by the addition of fibres or reinforcing components. The beam may for example include longitudinally extending reinforcing rods, fibres, wires, etc.

In one example of the invention the reinforcing components include mesh which may be metallic or of a suitable fibre.

The cementitious material may be of any appropriate hardness, density and composition,

the intention being to achieve a desired and substantially predetermined yield characteristic under load.

Depending on the construction each beam may be formed with locating formations and each yielding element may include a complementary formation which is engageable with

a respective locating formation.

The invention also extends to a support pack which is formed from a plurality of support

components, each support component being of the aforementioned kind, the support

components being arranged overlying one another to form, at least, four outer columns

wherein each column is defined by a stacked array of yielding elements alternating with ends of beams.

The support components may be arranged in successive pairs with the components in

each pair being substantially parallel to and spaced from each other, and with an upper pair of components overlying a lower pair of components and being displaced through 90°

relatively to the lower pair of components, each yielding element being sandwiched between ends of adjacent upper and lower beams thereby to defined the said columns.

The support components may be arranged overlying each other in a cross-shape, viewed in plan, and forming the four outer columns which, viewed from the side, are continuous

and each column being defined by a respective said stacked array.

The pack may include a central column which includes a succession of gaps and bridging

sections which extend to the outer columns.

The gaps may be air gaps or be formed by material which yields easily.

The invention also extends to a support pack which includes a plurality of beams

positioned overlying one another in a cross-shape, when viewed in plan, a plurality of yielding elements, each yielding element being positioned between opposing ends of a

respective pair of superimposed, parallel beams, the yielding elements and the said ends

of the beams forming four outer columns, and the beams and the yielding elements being

so dimensioned that a central column is formed, between the outer columns, by central

sections of the beams, at least some of the sections being spaced from each other by

gaps. The gaps may be air gaps.

The invention further extends to a support pack which includes a plurality of spaced

columns, means interconnecting the columns at spaced locations, and each column

including a plurality of yielding elements and relatively harder components positioned

between at least some of the elements. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of examples with reference to the accompanying

drawings in which: Figure 1 to 7 respectively illustrate different support components according to the

invention;

Figure 8 illustrates a yielding element which may be incorporated in any of the components

shown in Figure 1 to 7;

Figure 9 illustrates a support structure, in the nature of a crib structure, which is erected

using support components according to the invention;

Figure 10 is perspective view of a support pack which is made from a plurality of

components, each of which is of the type shown in Figure 4;

Figure 11 is a cross-sectional view through the pack of Figure 10 taken on the line x - x;

Figure 12 illustrates a further modification according to the invention; and Figures 13A, 13B and 13C are graphs of load versus yield for different support packs of

the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 of the accompanying drawings illustrates a support component 10 according to

a first form of the invention which includes an elongate beam 12 and two yielding elements

14 and 16 respectively.

The beam 12 is made from wood or concrete of any appropriate mix. The concrete may for example be a lightweight cementitious mixture and include internal steel or other reinforcing 18.

The yielding elements 14 and 16 are blocks which, in plan and in this example, are square

in outline. The blocks could have any other suitable shape and could for example be

circular or rectangular. Each yielding element is made from a lightweight cementitious

matrix of an appropriate composition.

Merely by way of example, without being limiting, each yielding element has the following dimensions: length of side = 300mm; height from 50 to 150mm. Each yielding element is

formed from a cementitious composition which includes the following materials: cement;

suitable fillers e.g. sand or fly ash; extenders e.g. slagment or fly ash; air; steel or fibre

reinforcing. The density of the cementitious mixture used in each yielding element is in

the range of from 400kg/m³ to 1000kg/m³ and its strength is in the range of from 1 ,6MPa

to 8,0MPa.

Again merely by way of example, and without being limiting, the length of the beam is of the order of from 600mm to 1200mm and it is made from a cementitious mixture with the

following composition: cement; suitable fillers e.g. sand or fly ash; extenders e.g. slagment

or fly ash; air; steel or fibre reinforcing. The density may range from 800kg/m³ to

1200kg/m³, and the strength from 3,0MPa to 12,0MPa.

The strength of the beam is greater than the strength of the yielding element. The reinforcing 18 may include steel rods or wires in any appropriate configuration.

In the arrangement of Figure 1 the yielding elements 14 and 16 are adhesively fixed to the beam using any appropriate adhesive or grout.

Figure 2 illustrates a support component 20 according to a second form of the invention

which, in many respects, is similar to the component 10. In this instance however the

beam is formed with two recessed formations 22 at respective ends of its upper surface

24 and each yielding element 14, 16 is formed with a respective downwardly facing

projection 26 which is complementary in shape to the recessed formation.

As is indicated in dotted outline, each yielding element may include a recessed formation 28 on its uppermost surface and the beam 12 may include a complementary projection 30

on its lowermost surface. Again it is possible to fix the yielding element to the beam using

a suitable adhesive.

Figure 3 depicts a component 32 wherein use is made of plastic straps 34 to secure the

yielding elements 14 and 16 to the beam 12. The straps are applied using commercially

available strapping machines which exert a predetermined tension on the straps before

tying the straps in a non-releasable manner.

Figure 4 illustrates a support component 36 wherein a beam 12 is formed integrally with upstanding formations 38 at its opposed ends. The formation 38, in effect, form the

yielding elements 14 and 16 which, in the other examples, are separately formed and then attached to the beam. Although an integral construction may be resorted to, it is to be

noted that those sections which form the yielding elements 14 and 16 may have a different composition from the respective underlying sections designated 40. This may be achieved

for example by casting an appropriate cementitious mixture, which makes up the elements 14 and 16, over a precast beam 12 which has a different composition from the composition of the yielding elements.

Figure 5 illustrates a composite structure wherein a support component 42 includes an elongate steel rod, pipe or bar 44 with concrete blocks 46 and 48 attached to opposed

ends of the pipe or rod etc. In this instance opposed ends of the pipe are embedded in

the blocks 46 and 48. Yielding elements 14 and 16 which are separately formed are

attached to the blocks 46, 48 respectively, again making use of an adhesive, or straps of the kind shown in Figure 3, or in any other way. For example plastic sheet material may

be wrapped around each yielding element and the underlying block.

Figure 6 shown a precast beam 12 which is made from a lightweight cementitious matrix of such a nature that a depression 49 can be stamped into the beam, once it has set,

without fracturing the tie member. The depression is shaped to receive a portion of a

yielding element 16 which, once located in the depression, is peripherally reinforced at its

mating edges by the surrounding material of the beam.

A downwardly facing surface of an overlying beam, not shown, is similarly shaped to

engage with an upper surface of the element 16. Figure 7 illustrates a support component 50 according to a variation of the invention. In

this instance the beam 52 has a shallow U-shaped cross-section and yielding elements

54 and 56 are fixed to the beam. The thickness 58 of an end section of a beam is the same as the thickness 60 of a yielding element. The thickness 58 is greater than the

thickness 62 of a central section of the beam by an amount 64.

Figure 8 illustrates a yielding element 14 which is formed with a vertically extending passage 66 and which is internally reinforced by means of a steel mesh 68 which is bent into the form of a cage which is embedded in the cementitious matrix 70. The mesh is

positioned so that it is close to an outer surface of the element. This type of construction may be adopted for any of the components shown in Figure 1 to 7. The passage 66 promotes a controlled collapse, and hence yield, of the element under load while the mesh

68 confines the element, in a peripheral or circumferential sense, and prevents

uncontrolled lateral expansion or disintegration of the element under a compressive load.

As is indicated by a dotted line 72, centrally positioned reinforcing could be used in place

of the confining mesh.

Figure 9 illustrates a crib type support structure 74 which is constructed using support components of the kind shown in any of Figures 1 to 7.

A lowermost layer of the crib structure includes two components 10A and 10B respectively

which are parallel to and spaced from each other by a distance which is substantially equal to the length of the beam 12. An overlying pair of components 10C and 10D is placed over the components 10A and 10B. The components 10C and 10D are parallel to and spaced from each other and are displaced through 90° relatively to the components 10A and 10B. Ends of the beams 12C and 12D lie respectively on the underlying yielding elements 14A

and 14B, and 16A and 16B, respectively.

The erection of the crib is continued in the illustrated manner with successive pairs of

support components being displaced through 90° relatively to the immediately underlying pair of support components, until such time as the structure 60 reaches a required height

which is as close as possible to the opposing surface of the overlying roof. At this juncture prestressing elements are inserted between the opposing surfaces of the structure 74 and

the overlying roof, particularly at the four corners of the crib structure. For example use may be made of grout filled bags which are pressurised in order to prestress the four columns of the crib structure. This is mentioned merely by way of example and the scope

of the invention is not confined in any way in this regard.

The structure 74, in essence, provides four columnar type supports designated 76, 78, 80 and 82 respectively at its four respective corners. Each columnar support includes a

stacked array of yielding elements which are respectively sandwiched between opposing

upper and lower ends of adjacent beams. The columnar supports are braced in that each columnar support is anchored to adjacent columnar supports by means of the respective

beams which extend at right angles to each other from the various columnar supports.

The crib type structure thus provides columnar supports which are anchored to each other in a lateral sense. Problems which would otherwise arise with slendemess ratios are therefore eliminated or, at least, significantly reduced. The area which is encompassed by the structure 74 is not filled with support material and the stability which is obtained by making use of a structure which extends in the horizontal plane is not accompanied by a corresponding increase in the quantity of material which is required. The crib structure is hollow inside and the transversely extending tie members provide a "slatted" configuration which reduces the amount of material required for lateral stability and which does not

significantly impede the passage of air which might for example be required for ventilation purposes. Without limiting the scope of the invention, the height to width ratio of the crib

structure may be at least 4: 1.

The skeletal crib structure thus reduces material requirements.

Each yielding element may be designed to provide a required yield characteristic. This makes it possible to customise the yielding characteristic, within limits, to the actual installation conditions. The support is active and provides continuous and controlled

yielding, without buckling, for at least 50% of the height of the structure.

The crib structure 74 may be constructed using any of the components shown in Figures 1 to 7. With the Figure 2 embodiment the formations 28 and 30 engage with

complementary formations in, and are used for correctly positioning, transversely

extending support components.

The blocks 46 and 48 in the Figure 5 version could have similar characteristics to the

material of the beam, immediately underlying the yielding elements, in any of the other versions.

To a substantial extent the yield characteristic of the structure 74 is determined by the characteristics of the yielding elements 14 and 16. These elements are designed to yield,

in a controlled manner, before the material of the beam yields. Thus, as shown in Figure 8, each yielding element may for example include cavities or recesses to promote yielding and may be reinforced using fibres or steel or any other material.

Referring again to Figure 4, the beam 12 has a thickness 88. Each element 14 and 16 has a thickness 90 which is greater than the thickness 88. The beam has a width 92 (see Figure 10) and the elements 14 and 16 are spaced from one another by a distance 94. The distance 94 is slightly greater than the width 92.

A plurality of the beams are used in the manner shown in Figure 10 to erect a cross- shaped support pack 96 in an underground excavation, not shown. In Figure 10 the pack

is shown in perspective in order to illustrate the principles of this form of the invention. A component 10A is laid on a foot wall and, at a central region, the component 10A is then

flanked by elements 98. Each element 98 is substantially similar to one of the elements 14 (or 16) and one element is located on one side of the component 10A, at a central

region, and the other element is located on an opposing side of the support component

A second component 10B is then positioned on the elements 98, transversely to the component 10A. The beam 12B of the second component passes between the elements 14A and 16A of the first component. However as the thickness 90 of the element is greater than the thickness or height 88 of the beam 12A, the beam 12B, where it traverses the beam 12A, does not contact the beam 12A and a gap 100 (see Figure 11 ) is formed

between an undersurface of the beam 12B and an upper surface of the beam 12A. A third component 10C is then laid over the components 10A and 10B and the beam 12C of the third component is directly superimposed over the beam 12A of the first component although it is separated therefrom by the elements 14A and 16A. The beam 12C is

however directly in contact with the beam 12B.

The process continues in this way and the support pack 96 is erected to a desired height.

As is evident from an inspection of Figure 10 the support pack has a cross-shaped form,

in cross-section, and includes four outer columns 102, 104, 106 and 108, and a central column 110. Each of the columns 102 to 108 includes a stacked alternating array of end sections of beams 12 and yielding elements 14 and 16. The central column 110, on the other hand, is defined by overlying central sections of transverse beams with gaps 100

between each set of adjacent pairs of beams.

The pack of Figure 10 has a number of significant benefits. It provides significant areal

support with a highly effective use being made of the material which is used in construction

of the pack. The four principal load-bearing columns 102 to 108 can, to a significant extent, yield independently from each other but they are, nonetheless, linked to one

another through the medium of the transversely extending beams. The central column 110 has a plurality of air gaps 100 in its height. Consequently when closure between the

hanging wall (roof) and foot wall takes place, the air gaps are firstly closed, in a vertical direction, before the central column 110 is capable of taking a significant compressive load. To a considerable extent therefore the pack can yield in a manner which initially allows loading on the pack to be substantially uniformly distributed over the full area of the

pack. As further yielding takes place the central column 110 takes up an increasing

proportion of the load which is carried by the pack for, as noted, the gaps of the central

column are gradually closed as the pack yields.

Figure 4 shows the distance 94 materially greater than the width 92. Normally this is not the case and the distance 94 is only slightly greater than the width 92 with the result that the central column 110 effectively forms an inner boundary to the outer columns which significantly supports the outer columns.

The situation should be contrasted with what occurs when the central column does not

include yieldable sections ie. the air gaps 100. Under these conditions if two outer columns yield to different extents than a substantial torsional or bending force is exerted

on the beams which can sever the beams and cause premature failure of the pack.

Each beam 12, at its central region between the elements 14 and 16, could be made from a more yielding material than the outer sections of the beam or, alternatively, each beam

could include a filler of a relatively soft yielding material which fills the space which

otherwise would be occupied by the air gaps 100 in the central column.

Figure 12 is a side view of a support component 120 according to another form of the

invention. The component includes a beam 124 and yielding elements 126 and 128 respectively. The beam is formed in its upper surface with recesses 130 and lower surfaces of the yielding elements include projections 132 which are complementary in shape to the recesses. Upper surfaces of the yielding elements include recesses 134 which are substantially similar to the recesses 130. Similarly, lower surfaces of the beam include projections 136 which are similar to the projections 132.

It has already been pointed out that the yielding elements may be attached to the beam

in any appropriate way and that for example use may be made of adhesive, bonding agents, fasteners, shrink wrapping, straps and the like to secure the yielding elements to the beam. Alternatively or additionally the beams and the elements are formed with

complementary inter-engageable formations, as is shown in Figure 12, to provide a physical interlock between the various components. The arrangement shown in Figure 12 has the advantage that transporting and storage requirements are facilitated for the elements are engaged with the beams on site while a support pack is being constructed.

The yield characteristic of a support pack of the invention can be designed to meet different requirements. The yield characteristic can be altered by changing the materials from which the beams and the yielding elements are made. The cross-sectional

dimensions of the beams and the yielding elements can also be altered as well as the

relative thicknesses of the beams and elements.

Figures 13A, 13B and 13C illustrate three graphs of load versus yield, obtained for packs of the type shown in Figure 10. In the graph, in Figure 13A, the size of each air gap in the central column is essentially zero. In the graphs in Figure 13B and 13C respectively the air gaps are increased in size. In the first case the entire pack yields with a substantially constant characteristic. In the second case the pack yields with a first characteristic and then, as the air gaps close, the pack yields with a second characteristic. In the third case,

by choosing the density and strength of the beam and of the yielding elements appropriately and by varying the amount of steel reinforcing included in the beam and in

the yielding element, a yielding curve results which initially has a fairly flat characteristic

and which thereafter increases as closure takes place. As has been stated the beam, and the yielding elements, can be made from timber, or different types of timber, or any other suitable material. It is preferred though to make use of a lightweight cementitious mixture or mixtures, with suitable reinforcing, for this type of material enables the support components to be made with a consistent quality and with predictable and reliable characteristics.

Claims

1. A support component which includes a beam and two yielding elements at spaced locations on the beam.

2. A support component according to claim 1 wherein the yielding elements are

located at respective opposed ends of the beam.

3. A support component according to claim 1 or 2 wherein the yielding elements are

weaker in compressive strength than the beams.

4. A support component according to any one of claims 1 to 3 wherein the beam and

the elements are made from cementitious materials.

5. A support component according to claim 4 wherein the beam and the elements are

separately formed and then engaged with each other.

6. A support component according to claim 4 wherein the beam and the elements are

integrally formed.

7. A support component according to any one of claims 4 to 6 wherein the beam and the elements are reinforced.

8. A support component according to any one of claims 4 to 7 wherein the beam includes longitudinally extending reinforcing.

9. A support component according to any one of claims 4 to 8 wherein the yielding

element includes reinforcing mesh.

10. A support pack which is formed from a plurality of support components, each

support component being according to any one of the claims 1 to 9, the support components being arranged overlying one another to form, at least, four outer columns wherein each column is defined by a stacked array of yielding elements

alternating with ends of beams.

11. A support pack according to claim 10 wherein the support components are arranged in successive pairs with the components in each pair being substantially parallel to and spaced from each other, and with an upper pair of components overlying a lower pair of components and being displaced through 90° relatively to

the lower pair of components, each yielding element being sandwiched between ends of adjacent upper and lower beams thereby to define the said columns.

12. A support pack according to claim 10 wherein the support components are arranged overlying each other in a cross-shape, viewed in plan, and forming the four outer columns which, viewed from the side, are continuous, each column being defined by a respective said stacked array.

13. A support pack according to claim 12 which includes a central column which includes a succession of gaps and bridging sections, formed by the beams, which extend to the outer columns.

14. A support pack according to claim 13 wherein the gaps are air gaps.

15. A support pack which includes a plurality of beams positioned overlying one another in a cross-shape, when viewed in plan, a plurality of yielding elements, each yielding element being positioned between opposing ends of a respective pair of superimposed, parallel beams, the yielding elements and the said ends of the beams forming four outer columns, and the beams and the yielding elements being so dimensioned that a central column is formed, between the outer columns, by sections of the beams, at least some of the sections being spaced from each other

by gaps.

16. A support pack according to claim 15 wherein the beams and the yielding elements are made from cementitious materials.