STOPPINGS

Abstract: A stopping system for an underground tunnel comprises an array of steel cables (8, 8a) tensioned across the tunnel opening (3) and connected at their free ends to earth anchors (4, 5, 6, 7) located in bore holes (1) around the periphery of the opening (3). A fine steel mesh (9) is affixed across the array to cover the opening and hardenable cementitious material is pumped or sprayed onto the steel mesh to form a closure for the tunnel. Additional tension may be applied to the array before application of the cementitious material by tensioning a further cable (14) between the centre of the array and a remotely located earth anchor (13) in a bore hole (11).

Description: STOPPINGS This invention is concerned with a stopping for sealing underground tunnels such as mine roadways, tunnels and the like. In underground mines, particularly coal mines, there is often a requirement to seal a tunnel or roadway for ventilation purposes or simply to seal off an area no longer to be worked. Mine stoppings may be permanent or temporary. Permanent stoppings may be constructed in the form of a brick or concrete wall or they may comprise substantial steel frames having a heavy metal sheeting attached thereto. Such stoppings are very slow and expensive to construct. Temporary stoppings on the other hand are constructed from a variety of materials - often utilizing scrap materials no longer required for other purposes. Generally speaking temporary stoppings are often ineffective or inadequate due to the ad hoc nature of their construction or if a more formalised construction is employed they can often be very expensive to construct. Temporary stoppings may be formed by erecting timber props on either side of a tunnel or roadway and then affixing wooden boards, flexible sheeting and the like thereto to form a support substrate. Wire netting or expanded metal sheet is then affixed to the support substrate and the structure then sprayed with a cementitious grout. When cured or set, the grount forms a rigid reinforced membrane. If there is any movement in the earth surrounding the temporary stopping due to stress relief in the earth mass, such stoppings can be destroyed by movement in the timber props etc. Another more effective but substantially more expensive system comprises a substantial steel frame pre¬ fabricated to suit the dimensions of the tunnel. The frame is attached to the tunnel walls and/or floor and/or roof by tensionable roof bolts. A layer of wire mesh or expanded metal is then attached at its periphery to the steel frame and the entire structure sprayed with a cementitious grout. Often this cementitious grout may include chopped fibreglass rovings to provide additional reinforcement. Although quite effective in operation such stoppings are very expensive to construct. In addition, they suffer the problem that when the cementitious grout is being sprayed onto the wire mesh or the like, flexing of the mesh occurs. As the mesh flexes on impact from the sprayed grout, grout already applied begins to sag or even dislodge from the mesh support. Accordingly the grout must be applied slowly and with great care and usually in excess of theoretical requirements. It is an aim of the present invention to overcome or alleviate the problems of prior art stopping constructions and to provide a simple, effective and inexpensive stopping system and method. According to one aspect of the invention there is provided a stopping system, for underground tunnels and the like comprising:- an array of tensionable members arranged across an opening in an earth mass, said tensionable members being attached at their respective opposed ends by anchor members located within the earth mass; a sheet like support means associated with said tensionable members and extending substantially over the area of said opening; and a layer of cementitious material deposited on said support means and connected at least partially to said tensionable members to form a closure for said opening. Preferably said tensionable members comprise steel wires, rods, ropes, cables or the like or steel strapping. Preferably said support means comprises wire mesh, expanded metal, or metal, timber or plastics lath sheets. Preferably said anchor members comprise grouted rock bolts, mechanical earth anchors or the like. Preferably said cementitious material comprises a sprayable cementitious composition including reinforcement means. Preferably said reinforcement means comprises glass or metal fibres, with or without enlarged ends. Preferably said system includes means for applying tension to said tensionable members, said tension most preferably being applied before deposition of said cementitious material on said support means. According to another aspect of the invention there is provided a method of construction of mine stoppings for tunnels and the like. A preferred embodiment of the invention will now be described with reference to the accompanying drawings in which:- ' FIG 1 shows a front elevation of a stopping system. FIG 2 shows a side elevation of the arrangement illustrated in FIG 1. FIG 3 shows an alternative embodiment of the invention. In FIG 1 bore holes 1 are formed in an earth mass 2 surrounding a mine tunnel or the like 3 at diametrically opposed corners. Earth anchors such as rock bolts 4, 5, 6, 7 or the like are then anchored in the bore holes. Preferably however the earth anchors comprise an elongate substantially U-shaped member fabricated from steel reinforcing rod. The free ends of the U-shaped member are anchored in the borehole by means of a chemical or cementitious grout. A pair of flexible wire ropes or cables or steel strapping 8,8a are then connected at their opposed ends to the diametrically opposed rock bolts 5,7 and 4,6 respectively and then tensioned by any suitable conventional tensioning means.- A sheet of expanded metal or wire mesh 9 having dimensions corresponding substantially to the tunnel opening is placed between cables 8,8a and is secured thereto by wire twitches or the like 10 or in the case where the tensile members are steel strapping, self tapping screws or the like may be used. If required, a further bore hole 11 is formed in the roof 12 of the tunnel behind the wire mesh and anchored therein is a further earth anchor such as a rock bolt 13. A tensioning cable 14 is then attached at one end to cables 8,8a at their intersection and at its other end to rock bolt 13. Cable 14 is then tensioned by a turnbuckle or the like 17 or any other suitable means. As tension is applied to cable 1 , cables 8,8a are further tensioned and the structure is deformed out of plane 15 to form a generally concave front surface • 16. A cementitious grout material containing fibre reinforcement is then sprayed over the concave surface 15 to form a seal for the tunnel. When the cementitious material has dryed o cured, there is formed a very rigid construction sealing off the tunnel. By tensioning the structure before application of the sprayed cementitious material, substantially no flexing of the mesh support occurs and thus the spraying operation may be completed quickly without excess usage of material. The rigid structure is firmly located over the face of the tunnel by the earth anchors and remains in a state of tension. Fluctuations is air pressure causing a pressure differential between the front and rear faces of the stopping do not cause flexure of the stopping wall due to the maintenance of tension on the structure. In practice it has been found that for construction of stoppings in relatively small diameter shafts, it is sufficient to employ steel strapping of the type used in packaging applications. The tensioning/clamping device conventionally used with steel strapping provides sufficient tension in the diagonal straps to support the structure. In larger diameter shafts it may be necessary to employ somewhat heavier duty tensile members such as steel rods or cables and these may be tensioned by turnbuckles or the like. Additional tension may then be provided by the rearwardly extending element as shown in the drawings to provide in use additional resistance to flexure resulting from air pressure fluctuations within the mine shaft. It will be apparent to a skilled addressee that many modifications and variations may be made to the invention. For example., the tensionable members may be arranged in vertical or horizontal array or combinations of vertical, horizontal and angled arrays. The tensionable members ma ' y be tensioned by one or more tensioning cables as described above or the.members traversing the tunnel may include integral tensioning means such as turnbuckles or the like. T e very flexible nature of the stopping construction enables it to be engineered according to load requirements. For example, the tensionable members may comprise say a 6mm diameter steel wire for low stress applciations or a 25mm diameter (or larger) steel cable for high stress applciations. The anchored tensionable members provide a means for simply and inexpensively constructing an anchored support frame of any desirable shape or configuration for a stopping structure. As shown in FIG 3, in another aspect of the invention a sprayed cementitious liner may be anchored to an earth structure by an integral anchoring system. This may be used in conjunction with the stopping system or separately. Liners for tunnels usually comprise one or more layers of wire mesh or the like anchored to the tunnel roof or walls by tensionable rock bolts. The mesh is then sprayed with a cementitious grout which when cured forms a shell-like reinforced concrete construction. Although these rock bolts provide a degree of reinforcing for the earth mass, they also act simply to hold the wire mesh in place prior to the application of the sprayable cementitious liner material. Once the sprayable concrete material has set, it adheres very strongly to the mesh and the face of the earth mass behind it thus obviating the need for the continued presence of the rock bolt anchors. These rock bolt anchors and their chemical grout packages are very expensive and thus there exists a need for a less expensive anchoring system. The present aspect of the invention contemplates an integral anchor for tunnel liners. Prior to affixing a layer of wire mesh 20 to the surface of an earth mass 21 , bore holes 22 are drilled in the earth mass at suitab.ly spaced intervals. The wire mesh 20 is then affixed to the exposed face of the earth mass by simple mechanical anchors 23, wire clips or even rock bolts at widely separated distances sufficient merely to hold the mesh 20 in place. The cementitious grout 25 is sprayed over the reinforcing mesh in a conventional manner except that when an open • bore hole 22 is encountered an elongate spray nozzle is inserted into the bore hole to completely fill the bore hole 22 with cementitious grout. The process is continued to achieve a cementitious liner with integrally formed "spikes" 24 extending into the earth mass at regular intervals. The tensile strength of the cementitious material will be found to be adequate in most cases for the integrally formed anchors. When the nature of the earth mass is such that increased tensile strength is required in the cementitious anchors, this may be achieved by the addition of suitable chemical additives and/or fibrous reinforcement. The fibrous reinforcement may comprise chopped fibreglass rovings or enlarged end glass or steel fibres. Experimental data available shows that the incorporation of enlarged end fibres such as "Fibresteel" {Trade Mark) steel fibres to a cementitious composition will substantially increase the physical properties of the composition and, in particular, tensile strength. In yet another aspect of the invention, pumpable fibre reinforced grout may be utilized to create integral reinforcing elements. For example, in lieu of the present practice of using rock bolts or wooden dowels to reinforce coal mine pillars, it is envisaged that reinforcing elements may be created in situ. After a bore hole is formed in the pillar wall, a grout nozzle is inserted therein and the nozzle is progressively withdrawn while pumping grout into the bore hole. When cured, the fibre reinforced cementitious element adheres to the wall of the bore hole over its entire length thus providing reinforcement for the earth mass.

Claims: THE C LAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. A stopping system for underground tunnels and the like comprising:- an array of tensionable members arranged across an opening in an earth mass, said tensionable members being attached at their respective opposed ends by anchor members located within the earth mass; a sheet like support means associated with said tensionable members and extending substantially over the areaof said opening; and, a larger of cementitious material deposited on said support means and connected at least partially to said tensionable members to form a closure for said opening. 2. A system as claimed in claim 1 wherein said tensionable members comprise steel, wires, rods, ropes, cables or strapping. 3. A system as claimed in claim 1 or claim 2 wherein said sheet like support means comprises wire mesh, expanded metal or metal, timber or plastics lath sheets. 4. A system as claimed in any preceding claim wherein said anchor members comprise rock bolts, mechanical earth anchors or elongate U-shaped members locatable in a bore hole in the earth mass with a chemical or cementitious grout. 5. A system- as claimed in any preceding claim wherein said cementitious material comprises a sprayable cementitious composition containing reinforcing fibres. 6. A system as claimed in claim 5 wherein said reinforcing fibres comprise steel or glass fibres, with or without enlarged ends. 7. A system as claimed in any preceding claim including a tensioning means comprising a tensionable member attached at one end to said array of tensionable members and at its other end to a remotely located earth anchor. 8. A method of constructing mine stoppings comprising:- drilling a plurality of spaced bore holes at suitable locations in the wall of an underground tunnel; affixing in each said bore hole an earth anchor with an exposed terminal connection; attaching to each said terminal connection a tensionable member to form an array of tensionable - members across the tunnel opening; tensioning said tensionable members; attaching to said tensionable members a perforate mesh-like support means over substantially the entire area of the tunnel opening; and applying to said support means a hardenable cementitious material to form a closure wall for • • said tunnel opening. 9. A method as claimed in claim 8 wherein an additional earth anchor is located in a wall of said underground tunnel and a further tensionable member connected between said additional earth anchor and said array, said further tensionable member being tensioned to provide additional tension in said array prior to application of said cementitious material.

Inventors: TUCKER MICHAEL CHARLES, TUCKER, MICHAEL, CHARLES
Applicants: GEARHART AUSTRALIA, TUCKER MICHAEL C, GEARHART AUSTRALIA LIMITED, TUCKER, MICHAEL, CHARLES
Application year: 1985
Main classification: E21F1
IPC codes: E21F17