GB2160914A - Mine chock construction - Google Patents

Abstract

Chockpieces for use in constructing mine chocks are fabricated each from two mutually separate timber blocks 10 which are glued between laterally spaced timber plate members 12. Each block is made from two sub-blocks 10A and 10B glued together. In use, the blocks are loaded end-on to the timber grain to attain high early strength, and the plate members are disposed with their general plane upright. The upper and lower block faces are recessed by distance S with respect to the adjacent plate member edge faces so that early local indenting of the plate member edges under loading effects interlocking of the chockpieces. The chockpieces are tension-banded by band 14 at each end. The banding serves to retain the plate members with the blocks so to extend the stabilising function of the plate members on the mine chock during the rupture phase. <IMAGE>

Description

SPECIFICATION Mine chock construction This invention relates to mine chocks, and to chockpieces for use in constructing mine chocks.

Conventional timber mine chocks used in strata control underground consist of a plurality of solid timber pieces (chockpieces) of generally square cross-section arranged with the timber grain generally horizontal in a stack configuration defining at least four supporting columns at the points of overlapping intersection of the chockpieces. Such a configuration is achieved by using two chockpieces in each layer of the stack. A stack having three chockpieces in each layer provides nine supporting columns.

Timber shortages have caused attempts to be made to construct mine chocks from other materials and some success has been achieved using cellular concrete products incorporating wire cages or frames. Nevertheless, many operatives concerned in the industry still prefer the traditional timber products, not only for their particular suitability in terms of load/yield characteristic, but also because the timber products are less prone to damage during transit and handling and are less harsh on operatives in the handling of the chockpieces. Accordingly, there is currently a potential market for mine chockpieces which possess some of the favoured properties of conventional timber products and which can be produced economically.

Advances in geological studies have brought a greater understanding of certain aspects of strata control in mining, resulting in a possibility of specifying more accurately than hitherto what would be the ideal load/yield characteristic of a mine chock in any given location. Accordingly, the same potential market as above mentioned exists for mine chockpieces and a system of mine chock construction whereby a desired load/yield characteristic of a mine chock can be more closely achieved than hitherto.

An object of the present invention is to provide a mine chockpiece for mine chock construction for the potential market as outlined above.

According to the present invention, there is provided a chockpiece for use in constructing a mine chock, comprising at least two mutually separate support blocks arranged for defining elements of supporting columns when said chockpiece is used in conjunction with other similar chockpieces to construct a mine chock, and at least one plate member of elongate rectangular configuration interconnecting said support blocks, the support blocks being secured to mutually spaced face portions of the plate member, and the support blocks being made of timber.

Further, according to the present invention, there is provided a mine chock when constructed using chockpieces each as aforesaid.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a perspective view of part of a chockpiece in accordance with the present invention; Fig. 2 is a side elevation showing part of a mine chock in accordance with the present invention and yielding under compressive loading; Fig. 3 is a graphical representation of the relationship between load and yield in two different mine chocks each in accordance with the present invention; Fig. 4 is a perspective view showing a modification of the chockpiece of Fig. 1; Figures 5, 6 and 7 are respectively progressive illustrations in the course of loading in a mine chock in accordance with the present invention, illustrating the manner of yield of the chockpiece shown in Fig. 4;; Fig. 8 is a perspective view showing a modification of the chockpiece of Fig. 4; and Fig. 9 is a side elevation showing part of a mine chock constructed using chockpieces each as shown in Fig. 8.

In Fig. 1 of the drawings, only one end portion of the mine chockpiece is shown; and it should be taken that the other end is identical with that illustrated. The chockpiece of Fig. 1 consists of two support blocks 10 (one not shown), each of which comprises two sub-blocks 1 OA and 1 OB which are bonded face-to-face on the interface indicated by reference numeral 11 using a timber adhesive. In the interests of safety and with reference to regulations pertaining to fire hazard, the adhesive includes a fire retardent substance. It is advantageous to manufacture each support block 10 in two or more sub-blocks. This reduces the effect of splitting failure in any one sub-block and improves the overall performance of the chockpieces in respect of consistency.Moreover, the sub-blocks being smaller are more readily available from sawn timber pieces.

The support blocks 10 are interconnected by a pair of plate members 1 2 the latter being glued using the same timber adhesive to the adjacent faces of the support blocks 10 on the interfaces indicated by reference numeral 1 3.

Typical dimensions for the mine chockpiece are as follows Lc = 750mm T = 10mum W = 125mm Lb = 175mm D = 125mm where Lc is the length dimension of the chockpiece, W is the cross-sectional width, D is the cross-sectional depth, T is the thickness of each plate member, and Lb is the length dimension of each support block.

An appropriate timber for the manufacture of the chockpieces is a softwood, for example spruce.

In the chockpiece of Fig. 1, the grain direction of each of the sub-blocks 1 OA and 1 OB is parallel with the intended direction of loading.

That is to say that the support blocks 10 are loaded end-on to the timber grain.

When the chockpieces described above are used in the construction of a mine chock, the chockpieces are assembled in known manner so that the support blocks 10 form supporting columns. The plate members 1 2 are disposed with their general planes upright and thus may serve to retain loose filler material within the body of the mine chock.

The presence of the plate members 12, in addition to locating the support blocks 10, and in addition to serving as filler retaining walls, also influence the load/yield characteristic of the mine chock since they effect some control or stabilization of the behaviour of the support blocks 10 when these are loaded to the point where visible rupturing of the timber grain occurs. This is illustrated diagrammatically in Figure 2 of the drawings in which the plate members 1 2 are shown to have split lengthwise and to have parted from the support blocks 1 0. In practice, a more complex configuration occurs, but generally the load/yield characteristic is as shown by the chain dotted graph in Fig. 3.Thus, the chockpieces of Fig. 1 tend to yield relatively rapidly once the timber elements begin to rupture; and the influence of the plate members 1 2 tends to be lost relatively early in the load bearing phase of the mine chock.

A modification of the Fig. 1 chockpiece is illustrated in Figs. 4 to 7 of the drawings in which the same reference numerals are used for like components.

The chockpiece of Fig. 4 is provided (at each end) with an external binding means in the form of a tensioned steel band 14 such as is popularly used in tying packages on an industrial scale. In known manner, the band 14 is applied by means of an automatic banding machine which secures the band 1 4 by means of a clip 1 5. A fire retardant adhesive is used at the interfaces between the plate members 1 2 and the support block 1 0.

In Fig. 5, the appearance in end view of the chockpiece is shown prior to significant load ing. In Fig. 6, loading of the order of 50 tons has been applied and it can be seen that the vertical portions of the band 14 are bowed from the sides of the chockpiece due to the vertical compression. Rupturing of the timber components is not yet visible. In Fig. 7, loading of the order of 90 tons is applied and it can be seen that the plate members 1 2 have split longitudinally and are displaced outwards, but retained by the band 14. Thus, the plate members effect stabilising control over the behaviour of the chockpiece for a much greater portion of the rupture phase.

The performance of the banded chockpiece is illustrated by the broken line graph in Fig. 3.

In a modification of the chockpiece of Fig.

4, two or more bands 14 are applied to each end of the chockpiece. This further extends the effective stabilised portion of the rupture phase.

It is envisaged that the binding means may be effected by virtually any form of sleeving or banding by means of which the rupturing plate members are contained so that they continue their stabilising effect on the support blocks forming the supporting columns in the mine chock.

In a further modification of the Fig. 1 and Fig. 4 embodiments, a single plate member extends between the support blocks, the end portions of the single plate member being clamped between the sub-blocks.

In a further modification of the Fig. 4 embodiment, the binding means may take the form of a band disposed horizontally, that is to say around the vertical axis of the support column. In this case, the or each plate member must be apertured to permit passage of the binding means therethrough.

By providing an external binding means, the use of glue at the interface between the support blocks and the plate members may be dispensed with. This influences the behaviour of the chockpiece by allowing some independence of movement at these interfaces during the rupture phase.

A modification of the Fig. 4 chockpiece is illustrated in Figs. 8 and 9 in which the same reference numerals are used for like components.

In Fig. 8, the vertical dimension of the support blocks is less than that of the plate member so that the upper and lower faces of the support block 10 lie respectively below and above the upper and lower edge faces of the plate members 1 2. Thus, when the chockpieces are initially assembled with the plate members abutting edge-to-edge, the support blocks 10 are vertically spaced. The amount by which the upper and lower faces of the support blocks 10 are recessed is represented by dimension S in Figures 8 and 9. Thus, in an initially assembled mine chock, the support blocks 10 are mutually spaced by a distance equal to 2S as is shown in Fig. 9.

Under progressive loading, edge portions of the plate members 1 2 will be locally indented or deformed until the vertical spacing between the support blocks 10 is reduced to zero.

Thus, initially the mine chock will yield relatively easily, and then the load/yield characteristic will alter in a marked fashion when the support blocks take up the loading. In the initial stages of loading, the local indenting of the plate members 1 2 effectively locks the chockpieces in place. In later stages of load ing the vertical disposition of the side plate members 1 2 favourably influences stability of the mine chock in tending to maintain the support blocks is columnar alignment.

An external binding means 1 4 is used in conjunction with the chockpieces having the recess S. In tensioning the binding means 14, the bands bite into the exposed land on the plate members 1 2 and thus lie close to the support blocks 10. This effects mutual spacing of the bands as between adjacent chockpieces during chock building and thus mitigates difficulty caused by bands sliding against each other.

It is to be understood that the recess feature described with reference to Figures 8 and 9 may be used independently of and without the feature of the external binding means.

In all of the embodiments herein described, it is preferable that the moisture content of the timber used lie within the ranges normally described as "stable". Thus, undue dryness of timber should be avoided and a moisture content in the region of 1 2 to 15% minimum be attained.

Claims (14)

1. A chockpiece for use in constructing a mine chock, comprising at least two mutually separate support blocks arranged for defining elements of supporting columns when said chockpiece is used in conjunction with other similar chockpieces to construct a mine chock, and at least one plate member of elongate rectangular configuration interconnecting said support blocks, the support blocks being secured to mutually spaced face portions of the plate member, and the support blocks being made of timber.

2. A chockpiece according to claim 1, in which the support blocks are disposed with the timber grain thereof extending generally parallel with the intended direction of loading.

3. A chockpiece according to claim 1 or 2, wherein each said support block comprises two or more sub-blocks bonded face-to-face.

4. A chockpiece according to any one of the preceding claims, wherein the or each plate member is of timber with the grain direction thereof extending generally parallel with the length dimension of the chockpiece.

5. A chockpiece according to any one of the preceding claims, comprising two said plate members mutually laterally spaced with the support blocks secured therebetween adjacent the opposite ends of the plate members.

6. A chockpiece according to any one of the preceding claims including an adhesive disposed at interfaces between the support blocks and the or each plate member.

7. A chockpiece according to claim 6, wherein the adhesive includes a fire retardent substance.

8. A chockpiece according to any one of the preceding claims, comprising external binding means disposed to retain the or each plate member with the support blocks.

9. A chockpiece according to claim 8, wherein the external binding means comprises one or more tensioned bands.

1 0. A mine chock comprising a plurality of chockpieces each as claimed in any one of the preceding claims.

11. A mine chock comprising a plurality of chockpieces each as claimed in any preceding claim dependant from claim 5, the general plane of each plate member being generally parallel with the support column axis.

12. A mine chock according to claim 11, wherein the vertical dimensions of the support blocks and of the plate members respectivelly are such that the support blocks are mutually vertically spaced when the chockpieces are initially assembled with the plate members abutting edge to edge.

1 3. A chockpiece for use in constructing a mine chock, substantially as hereinbefore described with reference to and as shown in Fig.

1 or Fig. 4 or Fig. 8 of the accompanying drawings.

14. A mine chock comprising a plurality of chockpieces each as claimed in claim 1 3.