GB2058878A

GB2058878A - Mine Tunnel Supports

Info

Publication number: GB2058878A
Application number: GB8013672A
Authority: GB
Original assignee: Caledonian Mining Co Ltd
Current assignee: Caledonian Mining Co Ltd
Priority date: 1979-09-25
Filing date: 1980-04-25
Publication date: 1981-04-15

Abstract

A support structure suitable for supporting the walls and/or roof of a tunnel comprising at least two supports and lagging boards, the supports (2) being spaced apart and each having one or more flanges for positioning the ends of the lagging boards, the lagging boards being positioned between the supports to form a roof and/or walls of the tunnel, the support structure including ties (4) extending between adjacent supports and positioned between adjacent lagging boards, the lagging boards each having a longitudinal recess along each major edge to accommodate said ties whereby each lagging board is held in place between the supports by said ties, the support structure including means to stress the lagging boards in the longitudinal direction and maintain the stress and means (10, 12) to stress the lagging boards in the transverse direction and maintain the stress. <IMAGE>

Description

SPECIFICATION Mine Tunnel Supports This invention relates to a system for supporting the roof and walls of tunnels and is particularly applicable to mining operations.

In coal mining, the conventional support system involves the erection of metal arches spread at intervals of a few feet and the insertion between these arches of sheets of corrugated iron, wooden planks or slabs of concrete, to assist in supporting the walls and roof. The system is expensive because of the large amount of steel used per unit length of tunnel. The system is wasteful of ventilation energy and efficiency because of the irregular tunnel profile through which the air has to pass. Because the system is not airtight, a great potential hazard is present where spontaneous combustion is a problem.

Hand packing of the space behind the supports is employed which inevitably leaves voids which can become filled with inflammable gases and which are almost impossible to ventilate. Distortion and failure of the supports, which occurs mainly as a result of strata pressure, is further aggravated by deterioration of the strata which occurs on prolonged contact with air.

Our copending Patent Application No.

7,900,882 (Serial No. 2,018,334) describes and claims a support structure suitable for supporting the walls and/or roof of a tunnel comprising at least two supports and lagging boards (as defined herein), the supports being spaced apart and each having one or more flanges for positioning the ends of the lagging boards, the lagging boards being positioned between the supports to form the roof and/or walls of the tunnel, the support structure including ties extending between adjacent supports and positioned between adjacent lagging boards, the lagging boards each having a longitudinal recess along each major edge to accommodate said ties whereby each lagging board is held in place between the supports by said ties, the support structure including means to stress the lagging boards in the longitudinal direction and maintain the stress.

The support structure of that Application is designed so that any external pressures upon the support structure are evenly distributed over a wide area and are not confined to a single support. It is therefore possible to use lighter supports and lagging boards than with conventional support systems whilst maintaining the safety standards.

In the preferred embodiment disclosed in Application No. 7,900,882, the ties comprise struts, the ends of which are bent over at right angles and engage in slots provided on the supports. Thus the system may be readily built up by alternately fitting a lagging board and strut in place. The use of ties or struts holds the lagging boards in place and any cracking or breakage of a lagging board will not result in the lagging board falling into the tunnel.

After assembly of the lagging boards and ties the support structure is stressed in the longitudinal direction, e.g. by the provision of bolts or wires extending between adjacent supports which may be tightened to urge the supports towards each other.

The above described support system has proved to be very effective and is considerably lighter than conventional systems. However, we have now found that the system may be modified in order to increase its effectiveness.

Therefore according to the present invention there is provided a support structure suitable for supporting the walls and/or roof of a tunnel comprising at least two supports and lagging boards (as defined herein), the supports being spaced apart and each having one or more flanges for positioning the ends of the lagging boards, the lagging boards being positioned between the supports to form a roof and/or walls of the tunnel, the support structure including ties extending between adjacent supports and positioned between adjacent lagging boards, the lagging boards (as defined herein) each having a longitudinal recess along each major edge to accommodate said ties whereby each lagging board is held in place between the supports by said ties, the support structure including means to stress the lagging boards in the longitudinal direction and maintain the stress and means to stress the lagging boards in the tranverse direction and maintain the stress.

The term "lagging boards" used herein means any suitable slab of material suitable as an infill between the supports, including wooden planks, iron sheeting and concrete slabs. Preferably lagging boards are concrete slabs which may comprise plain concrete, a mixture of concrete and fibres or concrete slabs having one or more layers of mesh for lightness and strength.

It has been found that by stressing the lagging boards in both the longitudinal and transverse directions a rigid structure is achieved which dissipates external forces over a wide area of the support structure. This may readily be achieved by providing a gap between two adjacent lagging boards and forcing a wedging element into the gap in order to urge the two lagging boards further apart and thus providing compression force to the lagging boards on either side of the wedging element.

In a preferred embodiment a gap of several inches is provided between two lagging boards forming the roof of the tunnel and the wedging element is inserted into the gap and forced into position. Any external force applied to the roof of the tunnel will merely serve to force the wedge further into the gap thereby increasing the compression forces generated thus dissipating the force over a large area of the support system.

According to one embodiment of the invention the wedging elements are made of wood and are inserted vertically, apex downwards into the gap and forced into position, e.g. by hammering. Such wedges are effective if properly inserted.

According to a preferred embodiment of the invention, the wedging element is provided with a locking means to secure the wedging element in position thereby maintaining the compressive forces in the support system. The use of such a locking means also facilitates correct insertion of the wedging element. The wedging element may conveniently take the form of a triangular metal plate welded vertically with apex uppermost, to the edge of the support member. When the lagging boards and struts are placed in position the struts on either side of the gap bear against the sloping sides of the wedging element The locking means may comprise a metal plate which is vertically slideably mounted with respect to the wedging element, having limbs which will bear against the struts on either side of the gap.The locking means is forced vertically downwards forcing the struts downwards and apart over the sloping surfaces of the wedging element thereby effecting a wedging action. The locking means is then secured, e.g. with a bolt passing through the wedging element, thus maintaining the wedging action.

In certain tunnels it is desirabie to provide an artificial roughness to the roof to prevent the build up of layers of methane in the tunnel roof which is highly dangerous and may lead to explosions. In the case of wooden wedging elements, suitable baffles may simply be nailed to the projecting end of the wedge.

The invention will now be described with reference to the accompanying drawings, in which: Figure 1 represents a metal support for use in the invention depicting the position of a wedging element and baffle, Figure 2 represents a side view of a support structure with the lagging boards omitted in the interests of clarity, Figure 3 represents a front elevation of a wedging element and locking means attached to a support, and Figure 4 represents a side view of Figure 3, partly in section.

The support structure comprises a series of metal supports 2 generally having a T crosssection. The supports may be formed in three pieces which are fastened together by fish plates 6.

Whilst the supports generally have a T crosssection certain supports which are subjected to high loading may be modified by welding a metal strip to the stem of the T, thereby increasing the rigidity and load bearing capacity of the support.

The metal strip need not be sufficiently wide so that the cross-section becomes an I girder and may be about half the width of the T. Also the metal strip need not be continuous and it has been found that a series of spaced strips is effective, e.g. 50 mm strips welded at 250 mm intervals.

Adjacent supports are interconnected by struts 4 which may be formed of tubular metal and each end is turned over and engaged in slots formed on the support. Lagging boards, not shown, provided along the major edges with a longitudinal groove to accommodate the struts 4, are positioned between the struts to provide the tunnel cladding.

The lagging boards are stressed longitudinally by the provision of bolts or wires extending between adjacent supports, e.g. from the fish plates, which are tightened when all the lagging boards are in position.

The lagging boards and struts are arranged to provide a gap 8 in the tunnel roof into which is inserted a wedging element 10 which is forced downwardly, e.g. with a hammer. The insertion of the wedging element generates compression forces in the transverse direction of the lagging boards to provide maximum rigidity for the support structure. A baffle 12 may be readily attached to the projecting end of the wedging element to provide artificial roughness in the tunnel roof to prevent methane roof layering.

Referring to Figures 3 and 4, the support 2 includes a series of metal strips 3 welded at intervals along its length as described above. At the top of the arch the support is provided with a pair of wedging elements 12 welded to the ends of the arms of the T as viewed in cross-section.

The wedging elements 12 are triangular in shape and welded with the apex uppermost. When the struts 4 and lagging boards 5 are assembled the struts 4 on either side of the gap bear against the sloping sides of the wedging element 12 as shown by the solid lines in Figure 4.

A locking means 14 in the form of a metal plate is vertically slidably mounted on the wedging element 12 by means of a bolt 16 which is welded to the wedging element and projects through slot 1 8 in the metal plate. The locking means may be secured by nut 20. The locking means 14 includes two limbs 22 which extend across the gap between the two struts 4. The locking means 14 is urged downwards forcing the struts along the sloping surfaces of the wedging element to effect a wedging action, the struts 4 and lagging boards 5 adopting the position shown in dashed outline in Figure 3. The nut 20 is then tightened and the assembly locked in position under compression.

The arrangement of Figures 3 and 4 is particularly advantageous. Firstly, it ensures that the support system is correctly assembled in that if rock particles become trapped between adjacent lagging boards during assembly forcing them apart the last struts will not fit into position and the system must be reconstructed. Also and effecting wedging action is simple to achieve as a hook or similar tool may be inserted in the slot 18, downward pressure applied and the nuts 20 tightened. Furthermore it is readily possible by visual inspection to ensure that each wedging means has been utilized.

A full discussion of the various support structures will be found in our copending Application No. 7,900,882 (Serial No.

2,018,334). In each embodiment transverse stresses in the lagging boards may be generated in an analogous manner to that described above in order to provide maximum rigidity in the support structure.

Claims

1. A support structure suitable for supporting the walls and/or roof of a tunnel comprising at least two supports and lagging boards (as defined herein), the supports being spaced apart and each having one or more flanges for positioning the ends of the lagging boards, the lagging boards being positioned between the supports to form a roof and/or walls of the tunnel, the support structure including ties extending between adjacent supports and positioned between adjacent lagging boards, the lagging boards (as defined herein) each having a longitudinal recess along each major edge to accommodate said ties whereby each lagging board is held in place between the supports by said ties, the support structure including means to stress the lagging boards in the longitudinal direction and maintain the stress and means to stress the lagging boards in the transverse direction and maintain the stress.

2. A support structure as claimed in Claim 1 in which the supports are metal and have a T crosssection.

3. A support structure as claimed in Claim 1 or Claim 2 in which the ties comprise struts, the ends of which are bent over at right angles and engage in slots provided on the supports.

4. A support structure as claimed in any preceding claim in which the lagging boards are stressed in the longitudinal direction by tensioning bolts or wires connecting adjacent supports.

5. A support structure as claimed in any preceding claim in which the metal supports are in three sections secured together by bolted fish plates and the fish plates of adjacent supports are connected by tensioned hanger bolts to stress the lagging boards in the longitudinal direction.

6. A support structure as claimed in any preceding claim in which the means to stress the lagging boards in the transverse direction and maintain the stress comprises a wedging element which is force-fitted between two adjacent lagging boards.

7. A support structure as claimed in Claim 6 in which the wedging element is inserted between lagging boards forming the roof of the tunnel.

8. A support structure as claimed in Claim 6 or Claim 7 in which the wedging element is inserted with its apex directed towards the interior of the tunnel.

9. A support structure as claimed in any preceding claim in which the wedging element comprises a wooden wedge.

1 0. A support structure as claimed in any preceding claim in which the wedging element includes locking means.

11. A support structure as claimed in any one of Claims 1 to 7 in which the means to stress the lagging boards in the transverse direction comprise a triangular metal plate welded along one side thereof to an edge of the support member with an apex of the triangular plate directed towards the outside of the tunnel and a locking means adapted to bear against ties and/or surface of lagging boards forming the exterior of the tunnel, urging said ties and/or lagging boards inwardly against the triangular plate to effect a wedging action.

12. A support structure as claimed in Claim 11 in which the locking means comprises a metal plate, slideably mounted with respect to the tiangular plate, said metal plate having limbs which bear against the ties and/or lagging boards, the locking means including means to immobilize said metal plate with respect to the triangular plate.

13. A support structure substantially as herein described with reference to the accompanying drawings.