FIELD OF THE INVENTION

The present invention concerns a reinforcing element to be used for consolidating an excavation wall, for example the wall or the ceiling of a tunnel in a mine. The invention also concerns a process for the consolidation of an excavation wall which provides for the use of one or more reinforcing elements according to the present invention.

STATE OF THE ART

As is known, in the phase of excavation and tunnelling in mines a consolidation technique is used which involves positioning radially on the ceiling of the excavation a series of reinforcing elements, also called bolts, in order to support the ceiling and the sides of the section thus permitting safe continuation of the excavation. In their basic form the "bolts" are formed of a long-shaped element which is first inserted in a hole made in the excavation wall and internally anchored to the rock via an anchoring system which varies according to type.

A type of bolt commonly adopted involves the use, as a long-shaped element, of a threaded bar which, once inserted in the predefined hole, is anchored to the rock/ground by the injection of an adhesive substance, for example cement mortar or via the use of chemical cartridges. Each reinforcing bolt furthermore comprises a load distribution plate which is constrained against the outer surface of the wall to be consolidated via clamping means traditionally comprising a bolt which is tightened to the free end of the threaded bar. The clamping action constrains the distribution plate against said outer surface forming a compression layer of the excavation wall layers or consolidation of the wall itself.

As is known, during their use the reinforcing elements can be subject to dynamic stress produced, for example, by shifting of the ground around the excavation wall or, in the worst scenario, by seismic movements. In this last hypothesis the reinforcing elements are subject to high frequency cyclic stress. It has been seen that currently, in the majority of cases, said elements do not efficiently withstand dynamic stress. In other words, in the presence of high frequency cyclic stress, almost all the reinforcement elements rapidly deteriorate. This dangerous condition translates into subsidence of the excavation wall. In the case of mines, this represents a particularly critical situation for operator safety. The reinforcing elements currently used for the consolidation of excavation walls do not therefore offer sufficient guarantees of dependability especially in regions subject to seismic phenomena, for example South America.

On the basis of these considerations, the. main aim of the present invention is to provide a reinforcing element which overcomes the above-mentioned drawbacks. In the context of this aim, a first object of the present invention is to provide a reinforcing element which is able to effectively absorb any dynamic stress deriving, for example, from shifting of the ground.

A further object of the present invention is to provide a reinforcing element able to effectively absorb also high frequency cyclic dynamic stress such as that produced, for example, by seismic movements.

A further object of the present invention is to provide a reinforcing element which is made from a reduced number of components which can be easily assembled at competitive costs.

A further aim of the present invention is to provide a process for the consolidation of an excavation wall which is reliable and easy to implement, with competitive times and costs.

SUMMARY OF THE INVENTION

The present invention concerns a reinforcing element for use in consolidation of an excavation wall in the construction of tunnels or similar. The reinforcing element according to the invention comprises a longitudinal bar intended for insertion inside a predefined hole in the wall to be consolidated. The reinforcing element comprises a load distribution plate with a hole for passage of the bar and loading means to constrain the distribution plate against the outer surface of the wall to be consolidated. The distribution plate comprises at least one first metal portion and at least one portion made of elastomeric material positioned between the first metal portion and a surface of the distribution plate suitable for facing onto the outer surface of the wall to be consolidated.

It has been seen that the use of a portion made of elastomeric material advantageously permits absorption of the impact loads which act on the bar and which derive, for example, from earth movements. This preserves the condition of the bar, increasing its dependability and life. The longitudinal bar can be made of metal, composite material (for example fibreglass), para-aramid polymeric fibres like those known as Kevlar ® or alternatively another material.

According to a preferred embodiment of the invention, the distribution plate also comprises a second metal portion positioned opposite the first portion or so that the portion made of elastomeric material is between the two metal portions. In this preferred embodiment the portion made of elastomeric material allows a relative rotation of the metal portions in order to permit better adaptation of the distribution plate to the movements of the ground.

The present invention also concerns a method for the consolidation of an excavation wall of a tunnel which involves the use of one or more reinforcing elements according to the present invention.

LIST OF THE FIGURES

Further advantages will become clearer in the description of a preferred but not exclusive embodiment of a reinforcing element according to the present invention, illustrated by way of non-limiting example in the accompanying drawings in which: - figure 1 is a view relative to a possible application of a reinforcing element according to the present invention;

- figure 2 is an enlargement of detail A of figure .

DETAILED DISCLOSURE OF THE INVENTION

With reference to the cited figures, the reinforcing element 1 according to the present invention can be advantageously used for the consolidation of an excavation wall 8. For the purposes of the present invention, the expression "excavation wall" generically indicates any wall deriving from the removal of material in the soil/subsoil and requiring consolidation to avoid subsidence. The reinforcing element 1 according to the invention is particularly suitable for the consolidation of ceiling walls in tunnels in mines or in road and/or railway tunnels. Figure 1 illustrates a possible application of a reinforcing element 1 according to the present invention. The element 1 comprises a bar 5 made of a metal such as steel, for example. The bar 5 presents a development along a longitudinal axis X which allows the same to be inserted in a predefined hole 4 in the wall 8 to be consolidated. In particular the bar 5 has an outer surface 5B, threaded preferably along its entire length. The length of the bar 5 is chosen so that a first terminal portion (indicated in figure 1 by the reference 5A) emerges in a position external to the wall 8.

Once inserted, the bar 5 is fixed to the inner wall of the hole 4 via the use of fastening means, said expression indicating for example cement mortar or chemical cartridges, in other words, the expression "fastening means" indicates in general any substance, mixture or fastening element normally used in the consolidation of tunnels to fix a portion of a reinforcing element inside a predefined hole.

Again with reference to figure 1 , the reinforcing element 1 comprises a load distribution plate 6 which is operationally located near the outer surface (indicated by reference 8B) of the excavation wall 8. The distribution plate 6 configures a hole 7 with diameter larger than that of the threaded bar 5 to allow the passage thereof. The reinforcing element 1 furthermore comprises clamping means which act on the distribution plate 6 constraining the same against the outer surface 8B of the wall 8 to be consolidated.

The distribution plate 6 comprises a first surface 6A on which the clamping means act which comprise, preferably, a retaining nut 9 screwed to the end portion 5A of the bar 5. The retaining nut 9 can act directly in contact with the first surface 6A or indirectly via the interpositioning of a further element. The distribution plate 6 furthermore comprises a second surface 6B, opposite the first surface 6A, which is designed to face against the outer surface 8B of the excavation wall 8. Preferably the second surface 6B faces onto and rests against the outer surface 8B so as to directly distribute the compression load generated by the clamping means.

According to the present invention, the distribution plate 6 comprises at least one first metal portion 11 and at least one portion made of elastomeric material 12 indicated below also by the expression "elastomeric portion" 12. The latter is at least partly positioned between the first metal portion 11 and the second surface 6B of the distribution plate 6. It has been seen that the presence of the elastomeric portion 12 advantageously permits absorption of the dynamic stress to which the reinforcing element 1 can be subjected during its use. This obviously results in greater dependability and longer life of the element.

Preferably the first metal portion 11 is formed of a first flat steel plate. In particular said plate defines at least partly, and preferably wholly, the first surface 6A of the distribution plate. According to this solution the nut 9 rests only on the surface of the steel plate so that the clamping action does not damage the structure of the elastomeric portion.

Figure 2 shows in further detail the distribution plate 6 of the reinforcing element of figure 1. Said plate preferably comprises a second metal portion 11 B arranged in a position opposite said first metal portion 1 1 with respect to the elastomeric portion 12. In other words according to this solution the portion 12 made of elastomeric material is positioned, at least partly, between the first metal portion 11 and the second metal portion 11 B. In particular according to this configuration, the distribution plate 6 shows a substantially stratiform structure with the two outermost layers consisting of the portions 11 , 1 1 B made of metal 1 1 and with a central layer formed of the elastomeric portion 12.

In the configuration of figure 2, the two metal portions 1 1 ,11 B correctly distribute the axial compression load generated by the action of the closing means. The elastomeric portion 12 permits absorption of increases in the load and at the same time permits a relative movement of the two metal portions 11 ,1 1 B for better adaptation to the movements of the ground.

The second metal portion 1 1B is formed preferably of a second flat steel plate analogously to the first plate. The second flat plate defines at least partly, and preferably entirely, the second surface 6B of the distribution plate 6. Via this solution, the distribution plate 6 can rest on the outer surface 8B of the wall 8 without the elastomeric portion 12 coming into contact with the wall. This solution on the one hand permits improved distribution of the compression load on the wall 8 and on the other preserves the condition of the elastomer.

The first metal portion and the second metal portion 11B, or the first and the second steel plate, are connected to the elastomeric portion 12 during the vulcanisation process by injection of the same. The two flat steel plates can be advantageously positioned inside the mould used for the vulcanisation of the elastomeric material so that they remain securely connected to the elastomeric material at the end of said process. The portion 12 in elastomeric material is made of an elastomeric material with high capacity for absorption of the dynamic stress and impact load. Elastomers chosen from the group consisting of natural rubber, chloroprene rubber, styrene rubber and their mixtures have proved particularly suitable for this purpose. -Preferably the elastomeric material used has a hardness degree in the range between 50 and 80 ShA and preferably in the range between 55 and 75 ShA where ShA indicates the Shore A hardness scale. It has been seen that via the use of elastomeric materials with these characteristics it is possible to preserve the condition of the bar 5 much more effectively than with the traditional reinforcing elements currently used which only have a rigid metal distribution plate. The present invention also concerns a method for consolidating an excavation wall involving the use of at least one reinforcing element 1 according to the present invention. In further detail, the method comprises the following phases:

- provide, on the wall to be consolidated, a hole 4 of diameter sufficient to house the longitudinal bar 5 of the reinforcing element 1;

- insert the longitudinal bar 5 inside the hole 4 so that a terminal portion 5A emerges on the outside of said hole 4;

- fix the longitudinal bar 5 to the inner wall of the hole 4 via fastening means (for example cement mortar, chemical cartridges, etc.);

- constrain the distribution plate 6 of the reinforcing element 1 against the outer surface of the wall, acting on the relative clamping means (nut 9) of the element. The technical solutions adopted for the reinforcing element fully achieve the set task and purposes. In particular the reinforcing element is provided with a distribution plate the structure of which, at least partly elastomeric, advantageously permits absorption and dissipation of the dynamic stress and impact loads to which the reinforcing element can be subjected, for example in the case of seismic movements of the ground. Said characteristic makes the reinforcing element particularly reliable, advantageously preserving the condition of the bar and prolonging the life thereof. The latter can be made of metal or alternatively any other material considered suitable for the purpose. The bar can be made, for example, of composite material, such as fibreglass, or also para-aramid polymeric fibres, for example those commercially known like kevlar ®.

The reinforcing element thus conceived can be modified and varied in numerous ways, all falling within the scope of the inventive concept; furthermore all the details can be replaced by other technical equivalents.

In practice, any materials and contingent dimensions and forms can be used, according to requirements and the state of the art.