Title:
METHOD AND APPARATUS FOR CREATING SOIL OR ROCK SUBSURFACE SUPPORT
Kind Code:
A1


Abstract:
A subsurface support is provided in the form of a soil nail. The soil nail has asperities formed on the outer surface thereof to improve the pullout capacity of the soil nail. The asperities can take a number of forms to include indentations, deformations and threads formed on the outer surface of the soil nail. Optionally, a stinger may be attached to a distal end of the soil nail to further enhance the pullout capacity of the soil nail.



Inventors:
Barrett, Robert K. (Grand Junction, CO, US)
Ruckman, Albert C. (Palisade, CO, US)
Barrett, Colby (Fruita, CO, US)
Application Number:
12/615668
Publication Date:
03/04/2010
Filing Date:
11/10/2009
Primary Class:
International Classes:
E21D21/00
View Patent Images:
Related US Applications:



Primary Examiner:
MAYO-PINNOCK, TARA LEIGH
Attorney, Agent or Firm:
Sheridan Ross PC (Denver, CO, US)
Claims:
1. 1-11. (canceled)

12. A method of installing a subsurface support in the form of a soil nail, comprising: providing a tubular body having a uniform diameter extending along the length of the body, and having a plurality of asperities formed thereon, said asperities including at least two of (i) indentations formed on an outer surface of the tubular body, said indentations extending into the body, but not penetrating a wall of the soil nail, (ii) threaded sections, (iii) deformations changing a cross-sectional shape of the tubular body, and (iv) protrusions; and placing the subsurface support by at least one of excavating the ground and inserting the tubular body, or launching the tubular body from a launching device.

13. A method as claimed in claim 12, wherein: said subsurface support further includes a stinger secured to the distal end of the soil nail.

14. A method as claimed in claim 12, wherein: said tubular body further includes a second set of indentation formed on opposite sides of the soil nail, and said indentations of said first and second sets extending substantially along a length of the soil nail from a proximal end to the distal end thereof.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of co-pending U.S. application Ser. No. 11/460,317, filed on Jul. 27, 2006, entitled “METHOD AND APPARATUS FOR CREATING SOIL OR ROCK SUBSURFACE SUPPORT”, which is a continuation-in-part of copending U.S. application Ser. No. 10/741,951, filed on Dec. 18, 2003, entitled “METHOD AND APPARATUS FOR CREATING SOIL OR ROCK SUBSURFACE SUPPORT”, the disclosures of these applications being hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates generally to subsurface supports placed in the ground, and more particularly, to a method and apparatus for creating a soil or rock subsurface support that can be used in multiple ways to include support for excavations as a passive soil nail in tension, bending and/or shear, support to stabilize sloping terrain as a tieback in tension, support for an above ground structure as a micropile in compression and/or shear, or support for an above ground structure as an anchor in tension.

BACKGROUND OF THE INVENTION

In the construction of buildings, bridges, and other man-made structures, it is well known to place passive supports such as footers, piles, and other subsurface supports for supporting such man-made structures. These types of supports are passive because the earth around the subsurface support must first shift or move to mobilize the available tensile, bending, or shear capacities.

One particular problem associated with subsurface supports which may be made of iron, steel, or other metals is that over time, corrosion takes place which ultimately degrades the ability of the support to provide designed support for an overlying structure.

In addition to providing the above-mentioned subsurface supports, it is also known to provide ground strengthening by driving elongate reinforcing members, referred to as soil nails, into the ground, in an array thus improving the bulk properties of the ground. The soil nails themselves are not used for direct support of an overlying structure; rather, the soil nails are simply used to prevent shifting or other undesirable properties or characteristics of a particular geological formation that is built upon.

In some cases, the earth surrounding or near a man made structure becomes unstable and requires active support, such as by a tieback. Tiebacks are pre-tensioned subsurface supports that are used to restrain any movement of surrounding soil and rock. Tiebacks are similar to passive soil nails in construction, and can be emplaced in a similar fashion as a soil nail. More recently, soil nails and tiebacks have also been used to provide temporary and permanent excavation support and slope stabilization.

The U.S. Pat. No. 5,044,831 discloses a method of soil nailing wherein a soil nail is placed in the ground by being fired from a barrel of a launcher. The soil nail is loaded into the barrel, and pressurized gas emitted from the barrel forces the soil nail into the ground to a desired depth. One advantage of using a soil nail launcher, is that the soil nails can be emplaced with a minimum amount of labor and equipment thereby minimizing environmental impacts as well as providing a simple and economical means of strengthening the ground. Drilling is the traditional way to install soil nails, tiebacks, and anchors.

Although there are a multitude of subsurface supports and methods by which subsurface supports can be emplaced, there is still a need for simple and effective subsurface supports and an environmentally friendly manner in which subsurface supports are emplaced.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method and apparatus are provided to create a subsurface support device that is placed in the ground. In a first embodiment of the invention, the support device of the present invention has many potential uses. In one use, this support device can be used as a passive soil nail. In another use, this support device of the present invention can be used as an active tieback in tension. More generally, for use as a tieback, this support device can also be referred to as a soil or rock inclusion. The term inclusion refers to the ability of the support device to increase the tensile capacity of the rock and soil. In yet another use, this support device can be used as a micropile in compression, bending and shear. This support device, when acting as a micropile, can be physically connected to an overlying structure. In yet another use, this support device can be used as an anchor in tension. For example, this support may be tensioned as by a cable that interconnects the support to a man made structure.

Once emplaced, this support device includes a protective outer member or tube, an inner support member, and a stabilizing mixture, preferably in the form of grout, cement, resin, or combinations thereof which fixes the inner support member within the outer protective member. The stabilizing mixture may also be referred to as a cementious mixture. The outer protective member supports the opening into the native rock and soil, and acts as a housing for the cementious mixture. As discussed further below, the outer member may be perforated thereby allowing the cementious material to exit the perforations and increase the overall tensile and compressive contribution of the support device. The outer protective member also provides a barrier to prevent water or other corrosive materials from contacting the inner support member. The inner support member provides the design tensile and compressive strength of the support. The inner support member may protrude a desired distance above the outer member to connect to an overlying structure to provide support in any desired manner to include bearing/compression, tension, and/or shear. The diameter and length of the outer member and inner member can be selected to provide the necessary support. The outer member and stabilizing mixture provide strengthening support to the inner member. For example, in compression, the forces are transmitted from the inner support member directly to the stabilizing mixture and the outer member. In tension, forces are also transmitted to the stabilizing mixture and the outer member thereby greatly increasing the force necessary to dislodge or pull out the inner member. The method by which the outer member of the subsurface support is emplaced in the ground is preferably by a launching mechanism, such as that disclosed in the U.S. Pat. No. 5,044,831.

In another embodiment of the present invention, the support device is in the form of an improved soil nail including a fiberglass body and a metal tip. The metal tip is preferably made from a single piece of metal, such as a machined ingot of hardened steel. The tip comprises a contacting portion or stinger that makes contact with the ground when emplaced, and a proximal base portion that is received within an opening in the distal end of the fiberglass body thus allowing the tip to be attached to the fiberglass body. The base portion may be attached by a compression fit within the opening of the body and/or may be secured by an appropriate bonding agent, such urethane glue. The size and dimensions of the soil nail can be modified for the intended purpose of use. One common size acceptable for use in many soil stabilization efforts includes a fiberglass body of twenty feet in length and a contacting portion of the metal tip extending approximately six inches in length from the distal end of the fiberglass body. For those applications in which a shorter body is required, the same tip construction can be used, and the length of the body can simply be shortened. Unlike most prior art soil nails, the soil nail of the present invention has a tubular shaped body without projections which allows the soil nail to be emplaced by the soil nail launcher disclosed in the U.S. Pat. No. 5,044,831. The use of a soil nail with a fiberglass body in conjunction with a metal tip provides many advantages. The fiberglass body provides a more cost effective solution than traditional soil nails that are just made of metal. The fiberglass body also is highly resistant to corrosion, even more so than many metal soil nails within corrosion treated surfaces. The weight of the soil nail of the present invention is also less than a metal soil nail, allowing it to achieve greater velocity when emplaced by a soil nail launcher, thus enhancing its ability to penetrate the ground. The strength of the soil nail is not compromised because the fiberglass has adequate strength, and has a greater elastic limit as compared to many metal soil nails enabling the nail to handle even greater tensile and shear loads. Although the soil nail has a relatively smooth outer surface allowing it to be emplaced by a launcher, the surface characteristics of the fiberglass provide excellent adhesion with soil. Additionally, the stinger can be especially designed to handle particular soil or rock formations without having to modify the body of the soil nail. For example, in more dense soil or rock formations, the stinger shape can be modified prior to assembly with the body thus making the soil nail more adaptable for many uses.

Other features and advantages of the present invention will become apparent by a review of the following figures, taken in conjunction with the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of the subsurface support of the present invention in a first embodiment, the support device being emplaced in the ground and providing tensioning support to an overlying above ground structure;

FIG. 2 is a cross-section illustrating an example launcher that may be used to emplace the outer member of the support device;

FIG. 3 is a partial cross-section illustrating a second embodiment of the support device emplaced in the ground and providing compression or bearing support to an overlying structure;

FIG. 3A is an enlarged section of FIG. 3 illustrating one way in which to provide holes or perforations in the subsurface support;

FIG. 4 is a simplified elevation of a plurality of support devices that may be used as passive soil nails or as tiebacks to stabilize a sloping surface, the supports being emplaced in a horizontal orientation;

FIG. 5 is an exploded fragmentary perspective view of a third embodiment of the present invention in the form of an improved soil nail;

FIG. 6 is a fragmentary side view of the soil nail of FIG. 5;

FIG. 7 is a cross section similar to FIG. 2 illustrating the soil of the third embodiment being loaded in the launcher;

FIG. 8 shows an example installation of the soil nail of the third embodiment to reinforce soil near a river or streambed against scouring.

FIG. 9 illustrates yet another embodiment of a subsurface support of the present invention in the form of a soil nail;

FIG. 10 is a cross-section taken along line 10-10 of FIG. 9;

FIG. 11 is a perspective view of a modification of the embodiment of FIG. 9;

FIG. 12 is a perspective view of yet a further modification of the embodiment of FIG. 9; and

FIG. 13 is a schematic diagram illustrating a method of manufacturing the embodiment of FIG. 9; and

FIG. 14 is a perspective view of yet another embodiment of the present invention showing a soil nail with protruding asperities.

DETAILED DESCRIPTION

Referring to FIG. 1, the subsurface support 10 in a first embodiment of the present invention is shown installed in the ground G. The support device includes an outer member, preferably in the form of a steel or iron tube 12 having a selected length and diameter, and having an integral pointed tip 14. The tip 14 can be conical in shape that facilitates emplacement of the outer tube as by a launcher, as discussed below. After the outer tube is emplaced, the stabilizing mixture is placed in the interior chamber of the outer tube. Then, an inner support member that can be in the form of an epoxy coated steel rod or bar is then placed within the stabilizing mixture prior to hardening of the mixture. When the stabilizing mixture cures, the inner support member 16 can provide support to an overlying structure in compression, tension, and/or shear. Depending upon the design requirements of the particular structure to be built, a plurality of subsurface supports may be emplaced at desired locations at the construction site, and each of the support devices can be sized to provide the necessary support.

FIG. 1 also illustrates one example of the manner in which the support device 10 provides support. This one example illustrates use of the subsurface support as an anchor in tension. The subsurface support 10 includes a head or cap 20 that is connected to the exposed upper end of the inner support member 16. This head or cap can be attached by an integral threaded member 21 that is placed into a threaded well formed in the upper end of the inner support member 16. The cap or head 20 then can be used for attachment to the overlying structure. In the example of FIG. 1, a ring 22 attaches to the cap 20, and a cable 24 connects to the above ground structure (not shown). Thus, in FIG. 1, the support device is used for providing tensioning support to the manmade structure. If the device 10 was needed to provide support in compression, the inner support member 16 could be directly connected to the foundation or other base support of the overlying manmade structure, as further discussed below with respect to FIG. 3.

Referring now to FIG. 2, a launching device 40 is shown as a preferred method in which to emplace the outer member of the device 10. The launcher 40 illustrated in FIG. 2 corresponds to the launcher illustrated in the U.S. Pat. No. 5,044,831, this reference being incorporated herein in its entirety. The launcher 40 is shown in its loaded condition with an outer member/tube 12 loaded in the launcher and ready for firing. The outer tube 12 with the pointed end 14 is capable of penetrating the ground upon sufficient impact force. The launcher 40 comprises a barrel 42 communicating with a breach 44. The breach 44 defines an upper chamber 45. The distal or forward end of the outer tube 12 is received within an annular shaped sabot 46, preferably made of a plastics material, which is slidably received within the barrel 42 adjacent the chamber 45. The trailing or proximal end of the outer tube 12 extends through the chamber 44 and projects rearwards from the launcher 40 through an aperture formed in the cap or upper surface 50 of the breach 44. An annual shaped breach seal 52 seals the outer tube 12 with respect to the upper surface 50. A gas inlet tube 54 communicates with the chamber 45 for the admission of compressed gas. A baffle 56 of a larger diameter than the barrel 40 forms an axial projection of the barrel extending into contact with the surface of the ground G. On firing the launcher, compressed gas is forced into the chamber 45 that causes outer tube 12 to be fired into the ground. The baffle 56 includes a locating ring 58 that forms a snug fit around the sabot 46 such that the launcher remains in alignment with the outer tube that is emplaced in the ground. Accordingly, the outer tube when emplaced, remains in coaxial alignment with the barrel 42. As also shown in FIG. 2, the breach seal 52 and sabot 46 may be held in position prior to firing by a plurality of resilient members 60 which exert a separating force between the seal and the sabot.

Although a launcher of a particular construction is illustrated in FIG. 2, it shall be understood that other launcher types and methods can be used to emplace the outer tube within the ground. For example, a launcher that makes use of an explosive charge may be used. Alternatively, a vibratory means may also be used along with some force that helps to ease the outer tube into the ground. As stated above, it is preferable to avoid excavation for emplacement of the outer tube as such excavation is equipment and manpower intensive, and environmentally unfriendly.

FIG. 3 illustrates a second embodiment 10′ of the present invention. The support device 10′ is the same as shown with respect to the subsurface support of the first embodiment, with the exception of a plurality of perforations/openings 30 which may be formed in the outer tube 12. FIG. 3 also illustrates the device 10′ used to support an overlying structure S in compression. More specifically, the device 10′ has its upper end 28 embedded within a concrete foundation F of a structure S. The foundation is shown as extending a distance below ground level G. As also shown in FIG. 3, the plurality of perforations/openings 30 which may be formed in the outer tube allow the stabilizing material 18 to flow out from the openings 30, thus forming external stabilizing structures 32. In compression or tension, these external stabilizing features 32 help to strengthen the connection of the device 10′ to the surrounding soil. When filling the interior chamber of the outer tube with the stabilizing mixture 18, such filling may take place under pressure so that a desired quantity of the stabilizing mixture 18 exits the perforation/openings 30, thereby forming the external stabilizing features 32. In order to completely fill the interior chamber of the outer tube, it may be preferable to commence filling of the chamber from the lower most portion of the chamber. A line (not shown) carrying the stabilizing mixture under pressure can be inserted in the chamber and extend to the lower most end of the support device, and then as the stabilizing mixture fills the chamber, the line may be raised as necessary. Those skilled in the art can envision other ways in which the stabilizing mixture can fill the chamber of the outer tube.

Now referring to FIG. 3A, an enlarged section of the support device 10′ is shown specifically illustrating one manner in which holes or perforations may be made in the outer tube 12. In FIG. 3A, the openings 30 are formed by creating moon shaped cutouts thereby leaving a chad or tab 34. The chad or tab 34 would be pushed away from the exterior surface of the outer tube 12 as the pressurized stabilizing mixture exited the interior chamber of the outer tube. Alternatively, holes could be drilled or punched in the outer tube 12 in order to create an opening by which the stabilizing mixture could flow through. Those skilled in the art can envision other ways in which openings may be formed through the outer tube 12 in order to facilitate flow of stabilizing mixture therethrough to create the external stabilizing features 32.

FIG. 4 illustrates use of the subsurface support of the invention to stabilize a sloping surface. In the figure, three support devices 10 are illustrated and are spaced from one another in a desired arrangement to best support the sloping surface. The support devices are disposed in a horizontal orientation, but it shall be understood that the support devices may be placed at any angle or orientation depending upon the surrounding terrain. The support devices in FIG. 4 would be representative of use of the supports as either passive soil nails or tiebacks.

Additionally, the subsurface support of the present invention can be used in combination at a particular jobsite to support an overlying structure and to stabilize surrounding soil. In this case, one or more support devices can be structurally connected to an overlying structure such as shown in the figures, and one or more additional support devices can be used as soil nails to stabilize the surrounding soil or rock formation. Even in tunnel construction, the support device of the present invention can be used to stabilize the soil or rock formation surrounding the tunnel. In a tunnel, a support device can be emplaced in any orientation to include stabilizing the ceiling/upper surface of the tunnel.

FIGS. 5 and 6 illustrate yet another preferred embodiment of the present invention, namely, an improved soil nail 70 of dual material construction. As shown, the nail 70 includes a contacting portion or stinger 72 that attaches to a fiberglass body 74. The soil nail extends symmetrically along a longitudinal axis A-A. The stinger 72 comprises a conical distal tip 76, and a plurality of axially aligned flanges 78 that extend proximally from the tip 76. Spaced between the flanges 78 are neck sections 80 defining portions of the stinger with smaller diameters. A transition flange 82 interconnects the most proximally located neck section 80 to an intermediate extension 84. A shoulder 86 defines the interface with the distal end of the body 74. A base portion 88 extends from the shoulder 86, and is inserted within the opening 90 formed in the distal end of the body 74. Preferably, the distal end 92 of the body 74 has a flat surface thus providing a complementary flat mating surface with the contacting face 94 of the shoulder 86. As shown, the stinger components are generally smaller in diameter than the diameter of the body 74. Further, the flanges 78 generally have a similar diameter as compared to the large end of the conical distal tip 76. The conical tip 76 and flanges 78 may further include peripheral edges 79 that extend generally parallel to the longitudinal axis A-A of the soil nail. The base portion 88 preferably extends approximately one foot within the opening 90 if the exposed part of the stinger has a length of approximately six inches. If a longer stinger is used, then preferably the base portion extends further into the opening 90 in order to provide adequate support. The base portion may be secured by a compression fitting in opening 90 and/or an appropriate bonding agent can be used.

Referring to FIG. 7, the soil nail 70 is shown as mounted within the soil nail launcher 40 of FIG. 2. The soil nail 70 is emplaced in the same manner as the outer tube 12 described in the first embodiment; however, it being understood that the soil nail 70 is a subsurface support that can also be completely buried within the soil without exposing an upper end thereof.

FIG. 8 shows an example use of the soil nails 70. This figure specifically shows a number of soil nails 70 installed in and around the bed of a body of water, such as a stream or river R to thereby stabilize the soil around the bed. The soil nails 70 have been placed adjacent some abutments A that may be used to stabilize an overhead structure such as a bridge (not shown). Scouring and other types of erosion can be remedied with use of soil nails in this manner. It shall be understood that the soil nail of the present invention can be used in many other applications, and FIG. 8 is simply one example.

FIG. 9 illustrates yet another soil nail embodiment of the present invention. The soil nail 100 of FIG. 9 includes a plurality of surface asperities that improve the pull out capacity of the soil nail. Once a soil nail is in place, it is advantageous for the soil nail to remain in place without slippage or pull out. With respect to the embodiment shown in FIG. 3, pull out capacity is improved after the cementious material exits the location of the external stabilizing features. However, there is also a need to provide a soil nail with improved pull out capacity wherein such features are not activated in a later processing step, but rather, are formed integrally with the soil nail prior to placement. In the embodiment of FIG. 9, the body 102 of the soil nail 100 includes a plurality of dimples or indentations 110 formed in a linear pattern. Referring also to FIG. 10, these indentations 110 preferably do not pass through the entire thickness of the wall of the soil nail thereby maintaining better structural integrity of the soil nail whereas a plurality of holes made in the same linear fashion might otherwise decrease the overall strength of the soil nail such that it may break apart upon being fired from a launcher into the ground, or may prematurely deteriorate in the soil. The surface asperities caused by the indentations enhance the pullout capacity of the soil nail without materially weakening the construction of the soil nail. FIG. 9 also illustrates an optional stinger 104 attached to the distal end 106 of the soil nail. Therefore, as discussed above with respect to the embodiment shown in FIGS. 5 and 6, the stinger may be used to further improve the pullout capacity of the soil nail.

Although the indentations 110 are shown as extending uninterrupted between the proximal end 108 and the distal end 106, it is also contemplated that the indentations could be provided in a discontinuous pattern, a continuous pattern, or combinations thereof. Additionally, while the indentations are shown as being provided in a linear orientation, it is also contemplated that the indentations could be provided in a non-linear or random fashion.

FIG. 11 illustrates a modification to the embodiment of FIG. 9 wherein a combination of surface asperities or features are provided to improve the pull out capacity of the soil nail. In FIG. 11, the soil nail 120 has at least one linear set of indentations 124, as well as being deformed along a linear line L following the path of the indentations 124. The deformed shape of the bar, as well as the indentations each improve the pull out capacity of the soil nail.

FIG. 12 shows yet another modification to the embodiment of FIG. 9. This soil nail is also deformed along a linear line following a path of the indentations 124, but further includes a plurality of threaded portions 126 spaced along the length of the soil nail. The threads also increase the pull out capacity of the soil nail, and are features that can be formed prior to a placement of the soil nail.

FIG. 13 illustrates a method by which a linear set of indentations may be formed on opposite sides of the soil nail 100 in accordance with the embodiment of FIG. 9. As shown, an upper sprocket 112 has a plurality of teeth 114 formed on the outer surface thereof, similar to a sprocket for a bicycle. A lower sprocket 116 with teeth 118 are also provided, and disposed on an opposite side of the soil nail. In order to form the indentations, the bar is orientated so that it passes between the sprockets, and the sprockets then rotate about their respective central axes to form the indentations on the outer surface of the soil nail.

With respect to a method of making the soil nail shown in FIG. 12, a first step may include creating the various sets of threads 126 on the outer surface of the soil nail. In the next step, the indentations 124 can be formed in the manner shown in FIG. 13. Additionally, it is contemplated that the amount of force or pressure provided by one or both of the sprockets 112 and 116 could be increased such that the body of the soil nail is deformed along the path of the indentations.

FIG. 14 illustrates yet another embodiment of the present invention. In this embodiment, the soil nail 130 has a plurality of small asperities formed on the outer surface of the nail. The asperities in this preferred embodiment are shown as small protrusions 132. The protrusions are relatively small in comparison to the tabs 34 shown in the embodiment of FIG. 3A. The protrusions 132 help in increasing the pullout capacity of the soil nail. One method to create the protrusions 132 is to weld small pieces of material to the soil nail. The protrusions 132 can be used with a soil nail that is launched from launcher 40 without concern that the protrusions will create excessive interference which otherwise might deform or break the nail upon being launched. The protrusions can be provided in a geometrically spaced pattern or randomly on the outer surface of the soil nail. One acceptable general size for the protrusions may include those that protrude approximately one-eighth to one-half inch away from the outer surface of the soil nail. Spacing between each of the protrusions may be approximately 4-6 inches.

It is also contemplated that the protrusions 132 could also be combined with the other asperities shown in FIGS. 9-12. Thus, a composite group of asperities could be provided on a soil nail to optimize pull out capacity. A desired combination of the asperities can be tailored to match optimum pullout capacity based on the type of soil and rock formations present.

With respect to launching the soil nails illustrated in FIGS. 9-12 and 14, the launcher 40 illustrated in FIG. 2 can be used without requiring modification.

With the method and apparatus of the present invention, a subsurface support is provided which can be emplaced with a minimum of effort. In one advantage of the present invention, the subsurface support provides an alternative to other anchoring means because the outer tube provides protection to the inner support member from corrosion or other undesirable environmental factors. Depending upon the geological conditions, the outer tube can be emplaced with a launching device that is adapted to account for varying geological formations. For example, ground formations with little rock allows emplacement of the outer tube with a minimum of force while placement of the outer tube into an actual rock formation would require a greater force provided by the launching mechanism. In any case, the particular launching device chosen may have the capability of emplacing the outer tube to the appropriate depth and through various rock and soil conditions. In another advantage of the present invention, an improved soil nail is provided in a two-piece construction. This construction is cost effective yet provides at least the same performance as compared to a soil nail made of a single piece of material.

While the method and the apparatus of the present invention have been provided in various preferred embodiments, it shall be understood that various other changes and modifications may be made within the spirit and scope of the present invention.