GB2117814A

GB2117814A - Tunnel support arch

Info

Publication number: GB2117814A
Application number: GB08308090A
Authority: GB
Inventors: Colin John Macleod
Original assignee: Caledonian Mining Co Ltd
Current assignee: Caledonian Mining Co Ltd
Priority date: 1982-03-24
Filing date: 1983-03-24
Publication date: 1983-10-19
Also published as: EP0092307A1; AU1596483A; GB8308090D0

Description

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GB 2 117 814 A 1

SPECIFICATION

Improvements in and relating to support arches for colliery tunnels

This invention relates to arches for use as 5 members to help to support underground tunnels in, for example, a colliery.

Such arches are usually made of l-section steel and in order for the arches to be positioned in the confined spaces in a mine tunnel, the legs of these 10 arches are normally cut from the crown. Once the crown portion of the arch system has been positioned in the tunnel, the legs are attached thereto by shaped fish-plates bolted through the web of the l-section across the join.

15 This method has the disadvantage that the fishplates are separate components from the crown and legs and there is a risk of loss or delay in assembling the arches.

A method of manufacturing arches for colliery 20 tunnels or the like in accordance with this invention comprises manufacturing the arch (for example, by the process and apparatus forming the subject of our co-pending British Patent Application No. 8038202), forming bolt holes 25 through both flanges of both the crown and leg portions on each side of, and adjacent to, a "cut line" between the crown and leg portions, cutting the legs from the crown along the said cut line (either before or after the holes are formed) and, 30 preferably, bolting a splice plate to the two flanges of either the top of each leg portion or to the bottom of each side of the crown portion.

The invention also extends to a colliery or like tunnel support arch made, for example, in 35 accordance with the method of the invention, which is of l-section or channel section and which has its crown portion separate from its legs, holes being provided through the two flanges of both the crown and upper ends of the iegs adjacent the 40 ends thereof to enable the legs to be spliced to the crown, using splice plates bolted to both flanges of both the crown and leg portions and extending across the joins.

With the arch of the invention, it is possible to 45 fit the splice plates to the arch at the place of manufacture which avoids the possibility of separate plates being lost or having to be assembled in the darkness and dirt of a mine tunnel.

50 The fact that the splice plates are secured to the flanges of the crown section enables the crown and/or legs of the arch to be "nested" or transported from the factory to the colliery. The use of "splice plates" on the flanges also offer 55 anchorage points when the crown is to be transported underground.

When the arch is assembled in the mine tunnel by bolting the splice plates which are attached to the crown (or legs) to the other component 60 portion(s) in position in the mine tunnel, a particularly strong joint is obtained as the distance between the plates is greater than would be the distance between two fish-plates secured to the web of the l-section and the arch joint is enabled

65 to resist both tension and compression forces.

The splice plates may be connected to the flanges either by bolts passing completely across the section adjacent the web, or by shorter bolts on each side which merely bolt one flange to the 70 adjacent splice plate.

The splice plates may be corrugated laterally or longitudinally or may be plain. The plate thickness is calculated according to the size or weight of the steel arch.

75 A further problem with the fish plate joint used conventionally is that extreme stress applied normal to the flange portions that is in the plane of the central web eventually results in a catastrophic failure of the joint by fracturing of the 80 beams web across the web hole nearest the beam end. Tearing of the beam flanges away from the web also occurs. It is highly undesirable in a mine for any roof support to fail without some warning.

A joint member for a tunnel arch according to a 85 further aspect of the present invention comprises an elongate plate at least two bolt holes in the plate spaced apart in the elongate direction, a slot or groove providing an area of reduced strength extending from each bolt hole toward the elongate 90 ends of the plate. The area of reduced strength may extend either parallel or angled to the elongate direction of the plate.

The effect of providing the slot or groove is that when the plate is bolted across the flange portions 95 of adjacent 'I' beams to join the beams together pressure applied to the beams normal to the flange surface results in flanges of adjacent beams tending to move apart. The bolts then tend to move into the area of reduced strength until 100 eventually they start to move down the slot or groove towards the plate ends. Since the mine roof pressure is applied gradually to the beams the movement of the bolts and/or gradual opening of the beam joint can be viewed in time to replace 105 the arch before any failure of joint components ensues.

Preferably the joint member is provided with two pairs of bolt holes, the centres of the holes of each pair being transverse the plate. 110 In order to increase the strength of the area immediately around each hole and to increase the effect of the weakened area extending from the hole it is advantageous to provide an area or areas around the hole preferably from the sides of the 11 5 slot or groove which is of greater thickness than the general plate thickness. The plate is suitably formed to the shape of the beams at the joint, that is normally curved for arches. However the plate may be flat for joints between straight beams. 120 In the case of the weakened area being a slot this provides when using a connecting bolt having a projection from its shank, a useful means for locating the bolt in the bolt hole.

A joining means for joining beams according to 125 the present invention comprises a pair of elongate plates, at least one plate having at least two bolt holes in the plate spaced apart in the elongate direction, a slot or groove providing an area of reduced strength extending from each bolt hole

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toward the elongate ends of the plate, and bolting means for each hole, the beams to be joined having bolt holes in opposed flange portions, the plates being bolted across the beams so as to lie 5 against each flange portion.

Preferably the beams are of T cross-section but it is possible to join channel beams using the same means.

The invention also extends to a tunnel support 10 arch formed from T section beams and which has its crown portion separate from its legs, joining means as defined above being used to join the crown to the legs.

The invention will now be described by way of 15 example, with reference to the accompanying drawings in which:—

Figure 1 is a perspective view of a spliced joint between the crown and leg of a mine arch according to one embodiment of the invention, 20 Figure 2 is a perspective view of a spliced joint according to a second embodiment of the invention,

Figure 3 is a plan view of plate for the joint of Figure 1 or 2,

25 Figure 4 is a cross-section through one of the bolt holes of the plate of Figure 3,

Figure 5 is a plan view of a bolt suitably inserted in part of the plate of Figure 3,

Figure 6 is a cross-section of one of the beams 30 shown in Figure 1 with splice plates in place,

Figure 7 is a side view of part of a spliced joint between the crown and leg portions of a mine arch according to a third embodiment of the invention, and 35 Figure 8 is a plan view of the splice plate for the joint of Figure 7 seen from A.

One kind of colliery arch for supporting a tunnel roof is made of 'I' section beam formed into a general arch shape conveniently made up of three 40 main parts of a crown and two legs, joints between the crown 2 and one of the legs 4 is shown in Figures 1 and 2.

Each upper and lower flange 6 and 8 is drilled with bolt holes 10 close to the beam ends for a 45 typical beam (114 mm) across the flanges and 5" (127 mm) between the flanges the holes are 26 mm diameter and are centred about 60 mm from the beam ends. All subsequent dimensions will be for a joint between such a 50 typical beam.

Either side of the crown beam are secured splice plates 12 and 14 as in Figure 1 or 16 and 18 as in Figure 2. The plates are secured (see Fig. 6) by means of bolts 20 and nuts 22. Tapered mild 55 steel washers 24 between the nut and underside of flanges 6 and 8 ensure the nut acts evenly on the underside of the flange. Normally high tensile steel bolts are used the shank being 22 mm diameter. For some purposes it may be necessary 60 to use mild steel tensile bolts.

To assemble the arch in a mine, the crown is supported on beams extending from previously erected arches. The upper end of the legs are then slid between the plates 12 and 14 and further 65 bolts 20 and nuts 22 with washers 24 are used to bolt the legs to the plates 12 and 14 and thus to the crown.

The plates are carefully constructed and dimensioned to give advance warning of joint failure. One typical plate 30 for a typical beam joint is shown in Figures 3 and 4. This plate is similar to plates 12 and 18 of Figures 1 and 2. The plate has an overall elongate length L of 240 mm, a width C of 120 mm and a thickness T of 12.5 mm (for some larger beams and purposes this may be 15 mm). Holes 32 of a diameter D of 26 mm are punched out of the plate. In the process of punching the hole out an upstanding strengthened area 33 is formed of a height H of about 6 mm. Area 33 extends all round the hole except at a point where a slot 35 is formed in the plate. The slot width W is between 5/8 and 3/8 D and preferably about 12.5 mm and it extends a distance F of 45 mm from the centre of hole 32 toward the elongate end 38 of the plate. The holes 32 are a distance B which is 60 mm from the ends 38 of the plate so that the slots end 15 mm from the ends 38 of the plate. The relationship between F and B has been found to be preferably 3:4 but may be in the range 5 to 7:8.

In the case where the pressure on the arch is greater on the top than on the side the tendency will be for the crown to be forced down relative the legs and the joint will have the tendency to pivot about the inner plate so that the Figure 1 arrangement with the slotted plate outside is preferable. Sometimes however the surrounding forces on the arch press more on the sides of the arch so that the tendency is on the joint to pivot about the outer plate. In the latter case it is preferable to have the slotted plate on the inside as Figure 2. It may, however, be preferable to have slotted plates on either side of the joint.

The shape and alignment of the slot may vary for instance the elongate alignment of pairs of adjacent slots may be angled inwardly towards each other. A groove extending only partly through the plate has been tried. An added advantage to providing a slot is that bolts may be provided as shown in Figure 5 with a projection 40 which engages with slot 35 to prevent the bolt turning in the hole 32. This provision is useful for bolting the outer plates where spanner access to the outer bolt heads is restricted and is such that only one spanner is required for the inwardly located nut.

The shape of the strengthened area 33 can be varied, for example arcuate portions 42 need only be provided on the lateral sides of the holes 32 as shown in Fig. 5.

The plates are curved to the curved shape of the beams at the joint a radius of 7 feet (2.13 metres) being a typical curve.

The provision of slots in the plates has been found to provide an excellent weakened area which has the effect of guiding the bolt shanks down the slots under an arch deforming pressure. The joint whilst opening up still remains an effective joint until a substantial movement of the bolt along the slot has ensued. Their movement and joint opening is easily seen by monitoring staff

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so that plenty of warning is given before arch failure approaches.

A further advantage of these plates is that the arch may be set by what is referred to as a "full 5 arch setting procedure", that is, the arch legs and crown can be coupled together using these plates but the nuts are only fitted loosely enabling the legs of the arch to be pulled inside of their final width and thus set in one piece in their final 10 position.

This method reduces accidents caused by having to work underneath unsupported roof and sides whilst coupling the legs to the crown.

A third embodiment where a simple holed 15 plates is provided is shown in Figures 1 and 8. In this joining method each flange of both the crown 52 and leg portions 54 are drilled with bolt holes 58 adjacent the "cut" line 56 and cut as described in our copending British Patent Application No. 20 8038202 at the place of manufacture. An outer and inner splice plate 60 is secured respectively to the flanges of the crown portion by means of high tensile or mild steel bolts 62 which pass through the holes in the crown web and also through 25 corresponding holes in the splice plates.

Nuts 64 hold the bolts in position together with lock nuts 66 (if required).

The crown and leg portions can now be transported to a mine, the crowns being stacked 30 on top of each other with the edges of the flanges lying across the top of the bolts above the webs and between the flanges of an adjacent crown portion.

When the arches are to be assembled in a 35 mine, the crown portion is firstly positioned and held by beams extending from previously erected arches. The leg portions are then connected to the crown portions by sliding the upper ends of the leg sideways between the pair of splice plates 40 extending out from the crown. Bolts 68 are then passed through the corresponding holes in the splice plates 60 and the holes in the flanges of the leg portion so as to secure the legs to the crown.

Claims

45 1. A tunnel support arch of l-section or channel section which has its crown portion separate from its leg characterised in that holes are provided through the two flanges of both the crown and upper ends of the legs adjacent the ends thereof 50 to enable the legs to splice the crown, using splice plates bolted to both flanges of both the crown and leg portions and extending across the joints.
2. An arch as claimed in Claim 1 wherein at least one splice plate comprises an elongate plate 55 at least two bolt holes in the plate spaced apart in the elongate direction (L), a slot or groove providing an area of reduced strength extending from each bolt hole toward the elongate end of the plate.

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3. An arch as claimed in Claim 2 wherein the area of reduced strength extends parallel or at*arf angle to the elongate direction of the plate.
4. An arch as claimed in any Claim 2 or 3 wherein the plate provided with an area of

65 reduced strength is provided with an area or areas around the hole which is of greater thickness than the general thickness.
5. An arch as claimed in Claim 4 wherein the area or areas of greater thickness extend from the

70 sides of the slot or groove.
6. An arch as claimed in any one of Claims 2 to

5 wherein the area of reduced strength is a slot and wherein the connecting bolts bolting through the bolt holes from which the slot extends is

75 provided with a projection from its shank which when the joint is made engages with the slot to lock the bolt against rotation in the bolt hole.
7. An arch as claimed in any one of Claims 1 to

6 wherein the or each splice plate is provided with

80 two pairs of bolt holes, the centres of the holes of each pair being transverse the plate (Figure 3).
8. A joint member for a tunnel arch comprising an elongate plate, at least two bolt holes in the plate spaced apart in the elongate direction (L),

85 characterised in that a slot or groove providing an area of reduced strength extends from each bolt hole toward the elongate ends of the plate.
9. A beam joining means for joining l-section or channel section beams comprising a pair of

90 elongate plates, each having at least two bolt holes spaced apart in the elongate direction (L) and bolting means bolting the plates to the beams through bolt holes in the plates characterised in that a slot or groove providing an area of reduced

95 strength extends from each bolt hole in at least one of the pair of plates toward the elongate ends of that plate, the beams to be joined having bolt holes in opposed flange portions, the plates being bolted across the beams so as to lie against each 100 flange portion.
10. An arch, joint member or joining means as claimed in any of Claims 2 to 6, 8 or 9, wherein the area of reduced strength is of a width (W) across the plate of less than the bolt hole diameter

105 (D) and preferably between 5/8 and 3/8 the diameter of the hole, and the ratio of lengths of the slot or groove from bolt hole centre (F)

towards the nearest plate extremity to the length from that bolt hole to that extremity (B) is in the 110 range 5 to 7:8 and preferably 3:4.
11. A method of manufacturing a tunnel arch of l-section or channel section and comprising crown and leg portions characterised in that bolt holes are formed through both flanges of both the crown

115 and leg portions on each side of and adjacent a "cut line" between the crown and leg portions, cutting the legs from the crown along the said cut line either before or after forming the holes, and bolting a splice plate to the two flanges of either 120 the top of each leg portion or to the bottom of each side of the crown portion.

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12. A tunnel support arch substantially as
13. A method of manufacturing a tunnel arch hereinbefore described with reference to the 5 substantially as hereinbefore described,

accompanying drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1983. Published by the Patent Office 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.