Low density blasting mat and method of utilizing same

A mat assembly including a planar mat body formed to cover a preselected area of a surface region. The preselected area partially defines a volume of ground to be broken by explosion therein. The mat body includes one or more layer elements. The mat body has an engagement surface for engagement with the preselected area. The mat assembly includes a skirt element connected with the mat body having an external portion extending from the mat body, for at least partially restraining matter ejected from the volume of ground upon initiation of the explosion.

FIELD OF THE INVENTION

The present invention is a low density blasting mat and a method of utilizing the blasting mat.

BACKGROUND OF THE INVENTION

In the prior art, blasting mats are typically designed to have the greatest area density possible, taking into account the materials used and other practical constraints. This is because until recently all the explosives used (e.g., ANFO (ammonia nitrate and fuel oil)) in commercial blasting operations are high-velocity explosives, for which a higher-density blasting mat is required in order to achieve an acceptable degree of containment of the matter (gases, dust, and flyrock) ejected from the ground (i.e., rock) that is broken by a high-velocity explosive blast.

The conventional blasting mats are available in a number of sizes, e.g., 20 feet by 20 feet (400 square feet). Typically, the conventional high-density blasting mats are made of pieces of used rubber tires that are held together by steel cables that have been passed through the pieces. The steel cables are used also to keep the pieces compressed, to maintain the high density that is thought to be desirable.

As is well known in the art, the conventional high-density blasting mats have a number of disadvantages. First, due to their relatively high area densities (e.g., usually about 18 kg per square foot (39.7 lbs per square foot)), the conventional blasting mats are difficult to handle at the site, and they are also expensive to ship over long distances. Second, the conventional blasting mats are bulky, and this also makes their shipping difficult, and relatively expensive.

In practice, the conventional blasting mats are often overlain with each other, in order to ensure comprehensive coverage over an entire blast pattern. However, the extent of the overlap is significant, e.g., two to three feet at each end of each mat. Because of the overlap, a greater number of conventional blasting mats are required than would otherwise be needed, in the absence of the overlap.

SUMMARY OF THE INVENTION

For the foregoing reasons, there is a need for a blasting mat that overcomes or mitigates one of more of the defects and disadvantages of the prior art.

In its broad aspect, the invention provides a mat body to be positioned on a surface region. The mat body includes one or more layer elements having one or more abrasion-resistant surfaces. The layer element(s) may include a core of high-strength material, and the abrasion-resistant surface may be provided by a coating over part of the core.

In another of its aspects, the invention provides a mat assembly formed to be positioned relative to a preselected area of the surface region. The preselected area partially defines a volume of ground to be broken by explosion therein. The mat assembly includes the mat body formed to cover the preselected area, and a skirt element connected with the mat body. The skirt element includes an external portion extending from the mat body for at least partially restraining matter ejected from the volume of ground, upon initiation of the explosion.

DETAILED DESCRIPTION

In the attached drawings, like reference numerals designate corresponding elements throughout. Reference is first made toFIGS.1A-1Eto describe an embodiment of a mat body in accordance with the invention indicated generally by the numeral20.

As will be described, the mat body20is formed to be positioned on a surface region22(FIGS.1B,1D). Preferably, the mat body20includes one or more layer elements24, the layer elements24including one or more abrasion-resistant surfaces26. In one embodiment, the mat body20preferably has an area density up to 2.2 pounds per square foot.

The layer elements24may be made of any suitable materials. As will also be described, it is preferred that the layer element24includes a core28of high-strength material and a coating30that provides the abrasion-resistant surface26.

In recent years, low-velocity explosives (e.g., Autostem™) have become available for commercial blasting applications. The inventor has determined that blasting mats with reduced area density may be used to provide adequate protection, where low-velocity explosives are used.

A volume of ground (e.g., rock) is drilled with several holes, in a drill pattern, over a preselected area34of the surface region22that partially defines the volume of ground to be broken by explosion therein. For clarity of illustration, the holes in the blast pattern are identified by reference character “BH” inFIG.1B. The low-velocity explosives are then positioned in the drilled holes “BH”. The velocity of the matter (e.g., gases, dust, and flyrock) thrown outwardly from the preselected area when the low-velocity explosives are detonated is less than the velocity thereof if high-velocity explosives were utilized instead. However, even when using low-velocity explosives, such matter is ejected from the volume of ground that is broken by the explosion. Accordingly, the low density mat body is intended to at least partially restrain such matter, which is ejected from the preselected area virtually instantaneously upon initiation of the explosion.

As noted above, the maximum area density of the mat body may be 2.2 pounds per square foot, or less. This compares well with a typical area density of the conventional blasting mat of about 39.7 pounds per square foot, and there are a number of advantages that result from using the lightweight mat body20, as will be described.

As illustrated inFIG.1Afor exemplary purposes, the mat body20may include several layer elements24, which may be made of different materials. The layer elements inFIG.1Aare identified by reference characters24A-24F for clarity of illustration. Also, the layer elements24B,24D, and24F are shown as extending outwardly past the other layer elements (to which they are adjacent) for clarity of illustration.

Although the layer elements24may be made of any suitable material or materials, it is preferred that composite materials and/or plastics are used, because they can provide sufficient strength and an advantageous low area density that may be used to at least partially contain matter ejected from an explosion of low-velocity explosives. Depending on the material used to form the layer element(s)24, the layer element(s)24may be very thin and compact, which is advantageous because the mat is easy to handle at the site, and the shipping costs of the mat body20are reduced, as compared to the conventional blasting mats. It will be understood that, where there is more than one layer element24in the mat body20, the layer elements24may be positioned relative to each other and secured to each other in any suitable manner.

For example, as illustrated inFIG.1C, the layer element24may include fibers32of a suitable material that form the core28. The layer element24may also include the coating30that may cover one or more sides of the core28. The fibers32may be any suitable fibers, e.g., carbon fibers, Kevlar™ fibers, basalt fibers, or fiberglass fibers. As indicated inFIG.1C, in one embodiment, the fibers32may be woven together before the coating30is applied thereto.

The coating30may be any suitable coating that provides strength to the layer element. The coating30may be an abrasion-resistant coating providing the abrasion-resistant surface26, e.g., if the layer element24is formed to engage the surface region22. For example, the coating30may be a suitable polyurethane coating. Preferably, the abrasion-resistant surface26is positioned in the mat body20so that the surface26may be located adjacent to, and at least partially engaged with, the preselected area34.

It will be understood that the mat body20may have a relatively low area density because of the materials selected to be included in the mat body20. The mat body20may be formed using no compression, or minimal compression, of the elements included in the mat body20.

As noted above, the mat body20may include one or more layer elements24. InFIGS.1D and1E, the embodiment of the mat body20illustrated therein includes two layer elements, identified therein for convenience by reference characters24′ and24″.

In one embodiment, the mat body20is positioned so that its edges are congruent with the perimeter of the preselected area34. This can be seen inFIGS.1B and1D. It will be understood that although the preselected area34as illustrated is generally rectangular in outline, the preselected area34may have any suitable form or shape. InFIG.1D, the reference character “L” designates a length of one side of the preselected area34. It can be seen inFIG.1Dthat the abrasion-resistant surface26may engage the preselected area34.

The mat body20may be secured by any suitable means, in part, to the surface region22. For example, the mat body20, if formed to have corners, may be secured at its corners.

Those skilled in the art would appreciate that the mat body20may be used for purposes other than at least partially restraining matter ejected from ground broken by blasting.

The Applicant's invention preferably includes an embodiment of a mat assembly136of the invention that is formed to be positioned relative to the preselected area34of the surface region22(FIGS.2A-2D). As noted above, the preselected area34partially defines a volume of ground to be broken by explosion therein. For instance, low-velocity explosives may be used to break the volume of ground. As illustrated, the preselected area34has a length “L” along one side thereof.

In one embodiment, the mat assembly136preferably includes a planar mat body120formed to cover the preselected area34. Preferably, the mat body20includes one or more layer elements124defining an engagement surface138(FIGS.2B,2D) for engagement with the preselected area34(FIG.2C). The engagement surface138may be at least partially planar. It will be understood that any suitable number of layer elements124may be included in the mat body120. As noted above, it is preferred that the layer elements are made of suitably strong and relatively low density materials. The mat body120may include a number of layer elements124, which may be arranged in a number of layers that are secured together by any suitable means.

It is also preferred that the mat assembly136includes a skirt element140connected with the mat body120, as will be described (FIGS.2A,2B). Preferably, the skirt element140includes an external portion142extending from the mat body120, for at least partially restraining matter ejected from the volume of ground, immediately following initiation of the explosion. The skirt element140may be at least partially planar.

As can be seen inFIG.2A, in one embodiment, the external portion142preferably is parallel, or substantially parallel, with the engagement surface138.

It is preferred that the skirt element140is partially included in the mat body120. In one embodiment, the skirt element140preferably includes a layer element portion144that is connected with one or more of the layer elements located in the mat body120(FIG.2A). Preferably, the layer element portion is secured to the external portion142.

Those skilled in the art would appreciate that, as the mat assembly136is located to position the mat body120on the preselected area34, when the volume of ground below the preselected area is blasted, then matter that is ejected from the volume of ground immediately following the explosion is directed against the engagement surface138of the mat body120, and also against an underside146of the external portion142(FIG.2B).

It will be understood that the mat assembly136may be moved vertically a small distance off the surface region22following the explosion, due to the pressure of gases released by the explosives. Those skilled in the art would appreciate that such movement, if it takes place, occurs immediately after the explosion is initiated. Those skilled in the art would also appreciate that the extent of vertical movement as illustrated inFIG.2Bhas been exaggerated, for clarity of illustration.

The mat assembly136is shown located on the preselected area34inFIG.2A, prior to initiation of the explosion. As illustrated inFIG.2B, the mat assembly136may be lifted in the direction indicated by arrow “A” off the preselected area, immediately following initiation of the explosion. Those skilled in the art would appreciate that, immediately following the initiation of the explosion, gases, dust and debris, and small pieces of broken rock known as “flyrock” (not shown) may be directed against the mat assembly136, as schematically indicated by arrows “B1”-“B4” inFIG.2B. Immediately following the explosion, the flyrock strikes the engagement surface138and the underside146of the external portion142, before falling to the ground (i.e., onto the surface region22, including the preselected area34).

In an alternative embodiment, illustrated inFIG.3, the external portion142preferably is aligned, or substantially aligned, with the engagement surface138. In the embodiment of the invention illustrated inFIG.3, the mat assembly136is positioned inverted on the surface region22.

The external portion142has an opposed side148(FIGS.2A-2C and3), opposite to the underside146. As can be seen inFIGS.2A-2C and3, the mat body120preferably has a second surface150that is opposite to the engagement surface138of the mat body120. The mat assembly136may be positioned with the second surface150engaging the preselected area34(FIG.3) and with the upper side148engaging the surface region22. Those skilled in the art would appreciate that, in this embodiment, upon initiation of the blast, the matter ejected from the preselected area34is primarily directed toward the second surface150of the mat body120, and a portion of the ejected matter is directed toward the upper side148of the external portion142.

It will be understood that, in the embodiment of the invention that is illustrated inFIG.3, the mat assembly136preferably is located to position the mat body120over the preselected area34. Preferably, the mat body120illustrated inFIG.3is formed to cover the preselected area34.

Another embodiment of the mat assembly236of the invention is illustrated inFIGS.4A-5C. As will be described, inFIGS.4A-4C, the mat assembly236is shown in position over the preselected area34, before the explosion is initiated. In contrast,FIGS.5A-5Care intended to show the mat assembly236immediately after the explosion, when the ejected matter has pushed the mat body220to its position furthest away from the preselected area. It will be understood that the extent of movement of the mat assembly236upwardly (away from the surface region22immediately after the explosion), as illustrated inFIGS.5A-5C, is exaggerated for clarity of illustration.

Preferably, the mat assembly236is formed to position the mat body220thereof relative to the preselected area34of the surface region22. As described above in connection with other embodiments, the preselected area34partially defines the volume of ground to be broken by explosion therein. However, the mat body220preferably is larger than the preselected area34. The preselected area34may be rectangular in plan view, having sides “L” and “W” (FIGS.4A,4B). The blastholes “BH” in the preselected area34can be seen inFIG.4C. The mat body220includes one or more layer elements224.

It will be understood that the mat body220as illustrated inFIGS.4A-5Cincludes two layer elements, which are identified for convenience inFIG.4Bby reference characters224A,224B.

It is also preferred that the mat assembly236includes a skirt element240connected with the mat body220. As can be seen inFIGS.4A and4B, the skirt element240preferably includes an external portion242extending from the mat body220.

As can be seen inFIGS.4A-5C, the mat assembly preferably also includes one or more anchor elements251, for engaging a predetermined part of the mat body220to a preselected location on the surface region22relative to the preselected area34.

The mat body220and the external portion242are configured to at least partially restrain matter that is ejected from the volume of ground, upon initiation of the explosion.

As can be seen inFIG.5A, the external portion242preferably is positioned over the preselected area34. The anchor elements251have inner ends252that are secured to corners “C1”-“C4” of the mat body220respectively (FIG.4C). As can be seen nFIGS.4A-4C, the anchor elements251preferably also include outer ends254that are secured to the surface region22. As noted above, the anchor elements251preferably secure the mat body220in a preselected location relative to the preselected area34. Preferably, the mat body220is located so that an outer edge256of the external portion242is substantially congruent or aligned with the outer perimeter of the preselected area34.

The outer ends254may be secured to the surface region22in any suitable manner. For instance, holes (not shown) may be drilled into the surface region22, and pegs257attached to the outer ends254respectively may be lodged in the holes.

InFIGS.5A-5C, the mat assembly236is illustrated immediately following initiation of the explosion. As noted above, the extent of movement of the mat body220from the surface region due to the explosion has been exaggerated in these views, for clarity of illustration. It can be seen inFIGS.5A and5Bthat, immediately following the explosion, the external portion242is extended between an inner edge254thereof that is secured to the mat body220and the outer edge256, which is located around the perimeter of the preselected area34. It will be understood that the preselected area34may have any shape, e.g., rectangular. For example, inFIG.5A, the preselected area34has a length “L”, and inFIG.5B, the preselected area34has a width “W”.

As illustrated inFIGS.5A and5B, the mat body220may be moved upwardly, i.e., in the direction indicated by arrow “2A”, by matter (e.g., gases, dust and debris, and flyrock) ejected from the volume of ground upon initiation of the explosion. Such upward movement, which is brief, is limited by the anchor elements251. The movement of the ejected matter is schematically represented by arrows “2B1”-“2B4” inFIG.5A. When the mat body220is pushed upwardly, the anchor elements250hold the mat body220in position, or substantially in position, over the preselected area34. Those skilled in the art would appreciate that the upward movement (if any) is very brief, and the mat body subsequently falls down under the influence of gravity.

InFIGS.5A and5B, it can be seen that an inner portion238of a lower side270of the mat body220is located within the skirt element240. The matter ejected from the volume of ground that is blasted is directed toward the inner portion238and an inner side272of the external portion242.

Another alternative embodiment of the mat assembly336of the invention is illustrated inFIGS.6A-6C. The mat assembly336is formed to be positioned relative to the preselected area34of the surface region22. As noted above, the preselected area34partially defines the volume of ground to be broken by explosion therein. The blastholes “BH” drilled in the preselected area34can be seen inFIG.6A. In one embodiment, the mat assembly336preferably includes a planar mat body320formed to cover the preselected area34. It is preferred that the mat body320includes one or more layer elements324(FIGS.6B,6C).

Preferably, the mat assembly336also includes a skirt element340connected with the mat body320(FIGS.6B,6C). As can be seen inFIGS.6B and6C, the skirt element340preferably includes an external portion342extending from the mat body320, and the external portion342is located at least partially transverse to the mat body320.

In one embodiment, the mat assembly336preferably also includes one or more anchor devices358, for engaging a predetermined part359of the external portion to the surface region22at preselected locations “X1”-“X4” (FIG.6A) on the surface region22relative to the preselected area34.

The mat body320and the external portion342preferably are configured to at least partially restrain matter that is ejected from the volume of ground upon initiation of the explosion.

InFIG.6B, the mat assembly336is shown prior to initiation of the explosion, and inFIG.6C, the mat assembly336is shown immediately following the explosion. Such upward movement of the mat body320is limited by the anchor devices358. Upon detonation of the low-velocity explosive in the blastholes “BH”, the mat body320briefly moves upwardly due to the matter ejected by the explosion, and the external portion342is, at that time, briefly pulled taut.

It will be understood that the position of the mat body320relative to the preselected area34, as illustrated inFIG.6C, is exaggerated for clarity of illustration. Those skilled in the art would appreciate that, in practice, there is little upward movement of the mat body320immediately following the explosion of a low-velocity explosive (due to the matter ejected upon such explosion). Immediately following any upward movement, the mat body320would fall mostly onto the preselected area34, due to gravity.

The upward movement of the mat body320immediately following the explosion is indicated inFIG.6Cby arrow “3A”. The matter ejected from the volume of rock immediately following the explosion is schematically represented by arrows “3B1”-“3B4” inFIG.6C. As can be seen inFIG.6C, the mat body320preferably includes an engagement surface338, and the external portion342includes an inner side372thereof. Those skilled in the art would appreciate that the matter (e.g., gases, dust and debris, and flyrock) ejected from the volume of the ground immediately after the blast is initiated engages the engagement surface338and the inner side372.

It will be understood that the mat assembly336is not intended to restrain all of the matter that is ejected from the volume of ground that is blasted. It is preferred that minor amounts of dust and gases that are ejected may be allowed to escape from underneath the mat assembly into the ambient atmosphere. Those skilled in the art would appreciate that allowing some of the gases to escape from underneath the mat assembly336would reduce the stresses to which the mat assembly336is subjected immediately following the explosion.

In one embodiment, the mat body320preferably includes a number of layer elements324, and the layer elements324are arranged in a number of layers. For example, the mat body320as illustrated includes two layer elements,324A,324B (FIG.6B).

It is also preferred that the layer elements324in respective adjacent layers are secured to each other.

As noted above, the skirt element340may be formed so that part of it may be included in the mat body320. For example, the skirt element340may include a layer element portion360that is one of the layer elements324, as well as the external portion342.

Also as noted above, the mat body320may have an area density up to 2.2 pounds per square foot.

The predetermined part359of the external portion342that is secured to the surface region22is distal to the mat body320. As can be seen inFIG.6A, in one embodiment, the predetermined part359preferably is secured to the surface region22only at the four locations (identified as “X1”-“X4” inFIG.6A). It is believed that this arrangement permits some of the gases released by the explosion to escape from beneath the mat assembly, along the outer edge of the skirt element240at locations between the predetermined locations “X1”-“X4”. This is thought to be necessary in order to minimize the stresses to which the mat assembly336is subjected, immediately following the explosion.

In use, the mat body20illustrated inFIGS.1A-1Epreferably is positioned on the preselected area34of the surface region22, as shown inFIG.1B. The sides of the mat body20may be congruent with the preselected area34. The blast pattern is drilled in the preselected area34. It will be understood that the blastholes “BH” are shown inFIG.1Bin order to show that the mat body20is positioned on the blast pattern. Those skilled in the art would appreciate that, after the low-velocity explosive charges are loaded into the blastholes “BH”, the mat body20is positioned on the preselected area34, i.e., over the blast pattern. When the low velocity explosives are detonated, the matter (gases, dust and debris, and flyrock) that is ejected from the volume of rock partially defined by the preselected area is at least partially restrained by the mat body20. As noted above, it is preferred that the lower side of the mat body20, which at least partially engages the preselected area, is formed to be generally abrasion-resistant.

Similarly, in use, the mat assembly136is positioned so that the mat body120is over the preselected area (FIGS.2A,2B). As can be seen inFIG.2C, in which the blastholes “BH” are shown, the mat body120preferably is positioned over the blast pattern. When the low-velocity explosives in the blastholes “BH” are detonated, the matter ejected from the volume of rock partially defined by the preselected area34is partially restrained by the mat body120and the external portion142.

As can be seen inFIG.3, in another embodiment of the method of the invention, the mat assembly136may be positioned so that the opposite side150of the mat body120engages the preselected area34, and the upper side148of the external portion142engages an area of the surface region22that surrounds the preselected area34. Upon initiation of the explosion, the matter ejected from the volume of rock partially defined by the preselected area34is partially restrained by the mat body120and the external portion142.

In another embodiment, illustrated inFIGS.4A-5C, the mat assembly236preferably is positioned over the preselected area34. As can be seen inFIGS.5A and5B, the outer edge256of the external portion242preferably is located around the perimeter of the preselected area34. The mat body220is held in place by anchor elements251, which connect predetermined parts of the mat body220with the surface region22(FIG.4C). The mat body220covers the preselected area34, in which the blastholes “BH” are drilled.

As can be seen inFIGS.5A and5B, when the explosion is initiated, the mat body220is moved upwardly, although its upward movement is limited by the anchor elements251. When the mat body220, the external portion242of the skirt element240is briefly extended (FIGS.5A,5B). The matter ejected from the volume of the ground by the explosion is at least partially restrained by the mat body220and the external portion242.

In another embodiment of the method of the invention, the mat body320is positioned on the preselected area34, and the predetermined part359of the external portion342of the skirt element340is secured to the surface region22at predetermined locations, so that the mat body320is positioned to cover the preselected area34and the blastholes “BH” drilled therein. As can be seen inFIG.6A, for example, the external portion342is secured to the surface region22by at locations identified for convenience by reference characters “X1”-“X4”. The matter ejected from the volume of the ground by the explosion is at least partially restrained by the mat body320and the external portion342.

The mat body20, and the mat assemblies136,236,336, preferably only partially restrain the dust and gases that are ejected from the volume of rock upon detonation of the low velocity explosives. It is also believed that the escape of a small amount of the dust and gases from underneath the mat body20and the mat assemblies136,236,336is preferable, because such escape would limit the stresses to which the mat body20and the mat assemblies136,236,336might otherwise be subjected.

It will be understood that the mat body included in each of the mat assemblies136,236, and336preferably is the mat body20described above. As noted above, the mat body preferably had an area density of 2.2 pounds per square foot or less. The mat body preferably is sufficiently flexible that it can be rolled into a relatively small cylinder, to minimize shipping costs.

It will be appreciated by those skilled in the art that the invention can take many forms, and that such forms are within the scope of the invention as claimed. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.