Patent Publication Number: US-2018030684-A1

Title: Arched cut-and-cover structure and method of its construction

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage application of International Patent Application No. PCT/CH2016/000011, filed on Jan. 21, 2016, which claims priority to Swiss Patent Application No. CH 200/15, filed on Feb. 13, 2015, each of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to the general art of bridge, tunnel and geotechnical engineering—and to the particular field of the design of overfilled structures such as arched cut-and-cover structures or tunnels. In particular the invention relates to a cut-and-cover structure providing a tunnel or tunnels for rail or road traffic or pipe lines, conveyor belts or cables. Further, the invention relates to a method for the construction of such cut-and-cover structures. 
     BACKGROUND 
     Frequently, earth overfilled structures—in cast-in-place or precast reinforced concrete—are used for cut-and-cover traffic tunnels. These allow a railway line (or a light rail line, or other traffic line, or pipe line, conveyor belt or cable line) to be covered with soil material in such a way that the original landscape can be restored and used in the same way as before construction, without any noise and other impact on the neighbouring areas. 
     Bridges across and over the rail line can be built in the same manner as cut-and-cover tunnels, in the form of short lengths of such a tunnel.
 
Examples of prior art cut-and-cover tunnels and overfilled arch bridges are disclosed in U.S. Pat. Nos. 3,482,406 and 4,458,457 as well as in the European Patent 1,495,191, B1. It is well known that—due to the working space required for the formwork on the outside of the structure—these types of cut-and-cover tunnels and bridges exhibit large excavation and backfilling volumes, leave large footprints at the original ground level and usually require expensive foundations in reinforced concrete as well as costly waterproofing measures.
 
     SUMMARY OF THE INVENTION 
     The principle goals of the design of new cut-and-cover tunnels are to reduce construction costs and construction time as well as to limit the impact of construction activities on the environment. 
     These goals are met according to the invention by a cut-and-cover tunnel structure. 
     Providing an arched shaped excavation surface that leads to an arched lower part of the structure supported directly by the excavation surface allows to simplify the construction by omitting certain presently used construction stages and/or components of the structure which until now have caused the high costs of usual designs. 
     The present invention shows that one of the expedient methods to reduce costs is to limit the required volume of excavation and backfilling and to use most preferably unreinforced concrete for the lower part. The term “unreinforced concrete” means—in the context of the present invention—that no metallic reinforcement is placed on the excavation surface prior to pouring the concrete. It does however encompass the use of concrete being mixed with non-metallic reinforcing material such as a reinforcing fibrous material like polypropylene or carbon fibers or fibers made of other plastic material. Supporting the lower part of the structure directly on the excavated soil further also means that no waterproofing material is placed between the lower part and the excavated soil. Thus, waterproofing membranes are replaced by less expensive, technically equivalent or superior measures such as waterproof concrete. This is the preferred structure and method. It is, however, possible to include a waterproof membrane between the lower concrete part and the excavation line. In this way, it is also possible to significantly speed up the construction process. The claimed and preferred technology significantly reduces the overall costs of cut-and-cover structures in the form of tunnels or bridges. This is especially useful for high speed or conventional railway (or light rail) lines. 
     In a first embodiment, the cut-and-cover concrete tunnel structure can be a single tunnel structure. The present invention is particularly useful in a cut-and-cover concrete tunnel structure which is a tunnel structure separately housing two tunnels and comprising a single lower concrete part, a central wall and two upper parts supported, on the inner side, by the central wall. This leads to a very economic structure especially suitable, for example, for long stretches of high-speed rail or other lines. 
     The cut-and-cover concrete tunnel structure, according to the present invention, is designed such that the lower part functionally becomes an arch. Design, analysis and experience show that such an arch structure—though unreinforced—can reliably take all the loads from the upper part of the structure as well as the earth pressure and almost any possible water pressures acting on it. The reason for this is that the arched structure—and the soil or rock on which it rests—ideally interact with each other. In the case of concrete platforms within the lower part of the structure such as for railways, slots are provided in order to create a true arch within the unreinforced lower part of the tunnel. 
     The unreinforced arch extending away from the center of the base of the lower structure may rise to a level up to six meters above that base level, and the upper part of the structure may be provided with curvature radii between 4 m and 8 m, whereby the longer axis of the ellipse is vertical or near vertical and slightly inclined away from the central wall. It can be seen from these dimensions that even very large cut-and-cover structures can be provided by the present invention. 
     A preferred embodiment of the presently described cut-and-cover structure is a two tunnel structure. Each of the two tunnels contains rails, a rail support structure, platforms and the required tunnel equipment. It is clear for the skilled person that each of the two tunnels can easily provide a sufficiently large air volume suitable for high speed train operation. 
     Preferably, the lower part of the structure contains at least two drainage pipes collecting water from inside the tunnels and/or rare ground water leaks penetrating through the lower part of the concrete structure. The drainage pipes and the inspection manholes, of each of the two tunnels are strictly separated from each other to prevent air overpressure from train operation, spilled liquids or smoke originating in one of the tunnels, from reaching the adjacent tunnel via the drainage system. 
     In further preferred embodiments of the cut-and-cover concrete tunnel structure, at least one separate service and cable tunnel is provided. In particular, the service and cable tunnel is arranged on top of the central wall or it is provided on the side of or on both sides of the upper structure, at the platform level. A service and cable tunnel may as well be provided on one side or on both sides within the lower part. The service and cable tunnel is preferably a cast-in-place or a precast reinforced concrete construction. 
     In yet a further preferred embodiment of the cut-and-cover concrete tunnel structure having two tunnels, the central wall between the tunnels comprises emergency connection openings between one tunnel and the neighboring tunnel, said openings being closable and openable by doors—in particular sliding doors—on both sides of the center wall, thus forming a lock between the doors. Such a preferred embodiment allows operation and maintenance personnel to change from one tunnel to the adjacent one—without ever giving up the strict separation of the two tunnels. These openings also allow personnel to shelter in case of passing trains. In another preferred embodiment, pressure wave relief measures in the form of at least one duct running parallel to the main tunnel and connected to it are provided, the duct having openings to the outside for controlled pressure relief to the outside. 
     It is further a goal of the present invention to provide a method of construction for a cut-and-cover tunnel which reduces construction costs and construction time as well as limits the impact of the construction activities on the environment. 
     This goal is met by a method of construction of a cut-and-cover concrete tunnel structure for rail or road traffic or pipe lines, conveyor belts or cables, with a lower concrete part and an upper concrete or steel part of the structure, wherein the lower part of the structure is constructed preferably in unreinforced concrete and is poured directly against a partly horizontal, partly inclined (and approximately circular or elliptically shaped) excavation line/surface. 
     Providing a partly arch shaped excavation surface leads to an arched lower part of the structure—resting directly on the excavation surface (and on the construction road pavement). 
     The present invention thus simplifies and even omits certain presently used construction stages and/or parts of earlier designs which until now have contributed to their high costs and long construction phases. 
     The present invention also shows that an expedient method to reduce costs is to limit the required volume of excavation and backfilling and to use unreinforced concrete, whereby the term “unreinforced concrete”, means, in the context of the present invention, that no metallic reinforcement is placed on the excavation surface prior to pouring the concrete. It does however include the use of concrete being mixed with reinforcing material such as a reinforcing fibrous material from plastics or carbon. The invention may as well include providing a metallic reinforcement on the excavation surface instead of using unreinforced concrete. Supporting the lower part directly on the excavated soil further means that no waterproofing material is placed between the lower part and the excavated soil. It is, however, possible to add a waterproofing membrane. Thus, waterproofing membranes are replaced by less expensive, technically equivalent or superior measures. In this way, it is also possible to significantly speed up the construction process. The claimed technology significantly reduces the overall costs of cut-and-cover structures in the form of tunnels or bridges. This is especially useful for high speed or conventional railway (or light rail) lines. 
     Preferably, excavation for the deepest part of the cut proceeds in two stages, providing, in the first stage, a horizontal or slightly inclined base (for a construction road) as well as slopes on either side of the base, starting from the ends of the base, and—in a second stage—creating the detailed curved excavation lines against which the lower part unreinforced concrete is directly poured, this pour closely following the detailed excavation procedure along the tunnel axis—and providing a functionally arch-shaped lower part. Preferably, the upper part is constructed in reinforced (cast-in-place or precast) concrete or steel (such as corrugated steel) and is placed on and supported by the lower part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantageous features and applications of the invention can be found in the dependent claims as well as in the following description of the drawings illustrating embodiments of the invention. In the drawings, reference numbers designate the same or similar parts/components/procedures throughout the several figures of which: 
         FIG. 1  shows schematically a first step of constructing an embodiment of the invention having two exactly or approximately parallel rail tunnels; 
         FIG. 2  shows a following construction step of the embodiment of  FIG. 1 ; 
         FIG. 3  shows a next step of constructing the lower part of the structure of this embodiment; 
         FIG. 4  shows schematically another step in which a central wall is built; 
         FIG. 5  shows schematically the addition of an upper part of the structure; 
         FIG. 6  shows a first backfilling step for the cut-and-cover structure according to the preceding Figures; 
         FIG. 7  shows schematically the two tunnel embodiment after the last overfilling step; 
         FIG. 8  shows a detail concerning the internal drainage of two railway tunnel structures according to the embodiment of the preceding Figures; 
         FIG. 9  shows schematically a type of formwork used for the step shown in  FIG. 3 ; 
         FIG. 10  shows an example of the cut-and-cover tunnel structure in the form of a single railway tunnel; 
         FIG. 11  shows an example with two railway tunnels and a central cable and personnel ancillary tunnel; 
         FIG. 12  shows an example with two cable and personnel ancillary tunnels, one in each railway tunnel; and 
         FIG. 13  shows an example with pressure attenuation ducts for high-speed railway tunnels. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 to 7  illustrate the construction procedure for an embodiment of the invention with a cut-and-cover structure  10  providing two separated tunnels  11  and  12 .  FIG. 1  shows the first stage of the excavation and the construction of a temporary road  5  at the lowest excavation level. The excavation is shown in solid lines, while the yet to be constructed structure  10  (or tunnels, respectively), are shown in dotted lines, together with the clearance for the trains. As well shown in dotted lines is a prior art excavation profile  16 . The maximum allowable slope of the excavation profile  6  of the present invention, will in each practical application be determined from the geotechnical properties of the subsoil or rock present. The steeper the slopes, the smaller the volume of excavation and the lesser the need of backfilling and overfilling and the narrower the footprint of construction at the surface. As said before, dashed lines  16  in  FIGS. 1 to 7 —parallel to the actual excavation lines—indicate the excavation and backfilling lines for conventional cut-and-cover tunnels. 
     As a next step shown in  FIG. 2 , and immediately before pouring the concrete for the lower concrete part  2  of the tunnel structure, the final excavation of the lowest stage is fine shaped (line  6 ′) such that it coincides with the outer line of the lower part of the concrete structure that shall be attained. Then a type of formwork  7  of which an example is shown in  FIG. 9  is placed above the basis (in this case the temporary construction road  5 ) of the excavation and the side slopes of the excavation and the concrete is poured in the space between excavated soil and the formwork. No reinforcement is placed beforehand on the soil or rock. It is possible, however, to add a metallic reinforcement that is placed on the excavation line prior to pouring the concrete. As well, preferably no waterproofing means are placed on the soil before pouring the concrete. Thus, instead of the usual steel reinforced concrete, no reinforcement is preferably used for the lower concrete part  2  of the structure, thus eliminating, at the same time, also the lean concrete layer otherwise necessary for positioning the reinforcement. A type of reinforcement that may be present—but is not understood in the present invention by the term “unreinforced concrete”—is a non-metallic reinforcement mixed into the poured concrete itself, such as carbon or polypropylene fibers. But it has to be stressed that the structure according to the present invention will work as well with no reinforcement at all, greatly simplifying and speeding up construction and reducing the costs. 
     In prior art practice, waterproof membranes usually are laid out on the excavation line before the (reinforced) concrete for the lower part of the structure is poured, and, quite often, drainage measures (directly outside the tunnel structure) are installed. In the construction according to the present invention, these measures are usually eliminated, thus allowing to pour the concrete directly on the final excavation line. Omitting the reinforcement as well as the waterproofing membrane has been shown to be feasible with the present invention. 
     Unreinforced concrete structures are relatively rare in modern civil engineering since—for the normally used rectangular structures—the bending moments and shear forces are of such magnitude that steel reinforcement is required for the structure to sustain the tension and shear present in such primarily rectangular designs. In arched structures, however, the bending moments and shear forces are significantly lower and, additionally, arched structures exhibit axial compression forces that reduce the bending tensions and thus contribute significantly to their carrying capacity, without reinforcement. Thus the partly horizontal, partly inclined (and approximately circular or elliptically shaped) excavation surface providing an arch-like lower concrete part  2  of the structure allows a large part of the simplification and cost reduction aimed at by the present invention. 
     Moreover, by the steps shown, the time during which the excavation profile is left open and unprotected is very short, such that the lowest stage steep cuts in most types of subsoil remain stable until they are covered, supported and consolidated by the placement and compaction of the fresh concrete. 
     Unreinforced concrete—especially in a changing dry/moist environment—is extremely durable, even more so than reinforced concrete since, when reinforced concrete should ever suffer damage, this is mainly due to steel reinforcement corrosion. Unreinforced concrete survives thousands of years, as the mortar (which is nothing else than fine concrete) in old Roman stone or brick vaults clearly shows. As explained, the last stage excavation for the lower part of the structure (line  6 ′) is executed in arch form, and it is congruent with the outside shape of the tunnel structure. The concrete for this part  2  is poured using only the inside formwork  7  to produce the required concrete arch shape and thickness. 
     The construction procedure is particularly time saving since the formwork (and with it the concrete pour) closely follows the last excavation stage. Slip forming can be used (similar to slip form pavement or slip form concrete tower construction) whereby the excavated soil surface is left without support only over a very limited time/distance along the tunnel. The lower concrete part  2  in the form of the unreinforced concrete arch effectively supports the freshly cut subsoil and, after hardening, provides a solid and durable, continuous foundation over the full width of the tunnel. Design, analysis and experience show that such an unreinforced arch can reliably take all the loads from the upper part of the structure as well as the earth pressures and almost any possible water pressures acting on it. This reinforced lower concrete part  2  (or arch  2 , respectively), in the lower part of the structure does not need any membrane or other measures for effective waterproofing—even under groundwater. The reason is that even if this unreinforced concrete structure develops bending cracks, the structure remains waterproof because all cracks stop at the compression zone of the concrete section—the latter being waterproof as such—if suitable concrete quality and concrete curing standards are observed. 
     Concrete shrinkage can lead to cracks going through the entire thickness of the concrete, and such cracks are not waterproof, in contrast to bending cracks. Concrete shrinkage does not produce any cracking circumferentially, since the tunnel structure is free to shrink in that direction. To avoid leakage due to cracks perpendicular to the tunnel axis (caused by concrete shrinkage and temperature effects in the longitudinal direction), sealed shrinkage/work joints are preferably provided at intervals of between 5-10 m along the tunnel axis. 
     The upper part of the structure is built according to established practice for the construction of earth overfilled reinforced arched structures. 
     In the shown example with two tunnels, a central wall  4  is built as shown in  FIG. 4 . The central wall (together with the upper part arches effectively separates the two tunnels from each other (see also  FIG. 5 ). Apart from the vertical loads, it has to sustain some bending (from differences in the horizontal forces applied to it by the two reinforced concrete arches, as well as from tunnel air pressure differences and potential accidents in the tunnel). Depending on the quantitative assumptions for these loadings, the central concrete wall needs to be reinforced—or it can even stay partly or entirely unreinforced: while the central wall is not an arch nor is it embedded in soil, it is in fact, vertically “prestressed” by the weight of the overburden; the large axial forces in the central wall generate considerable bending resistance. It, therefore, can be built without reinforcement unless the bending moments (due to differential outside water pressures or inside accident effects) are beyond the bending capacity of the “prestressed” wall. 
     After the construction of the central wall  4 , the upper part  3  of the cut-and-cover structure  10  will be added. The upper part  3  of the entire structure  10 , in this example, is an arched, reinforced concrete structure—cast-in-place or precast. This upper structure can in the alternative be made of corrugated steel sheets. In the case of high overfills, the most economical shape of this arch is not a circle, but an ellipse with its long axis vertical (or near vertical); for shallow overfills, it is also elliptical, but with the long axis about horizontal. 
     From the viewpoint of the entire tunnel structure and its stability, controlled, well compacted backfill  8  ( FIG. 6 ) of the structure in the upper part  3  of the tunnel is required only up to about 80% of the total tunnel height. The rest ( 9  in  FIG. 7 ) of the fill needs compaction only to avoid large settlements at the surface of the fill—if this is required. 
     The shape of the “inverse arch” (in the lower part of the tunnel structure), at first sight, does not look like an inverse arch.  FIG. 5  shows the boundaries  2 ′ of a “virtual arch” indicated with dashed lines, within the actual concrete dimensions of the lower part  2 . In a 1-dimensional-design calculation, linking the center points of the concrete thickness would not generate a clean arch axis, but rather a succession of concrete beams or blocks. In order to create a “true arch” (from a design calculation viewpoint), slots  20  can be introduced (shown in  FIG. 9 ) which are preferably filled with an elastic soft watertight material and which force the lower concrete part  2  into a functionally true arch shape. These slots are also introduced and modeled in the 2 dimensional calculations, of course. 
     As mentioned above, the present invention enables eliminating all drainage provisions on the outside and around of the structure. The reason for this is that the special design of the proposed concrete structure economically sustains not only the earth pressures and the live loads, but also all potential water pressures—including asymmetrical ones. The design according to the invention, therefore, is not dependent on measures that reduce water pressure. (Buried arch structures, as analysis and experience prove, are quite insensitive to water pressures. 
     In a preferred embodiment, inside drainage provisions, the design of which deviates from the usual setup inasmuch as their main drainage pipes and shafts are strictly separated from each other, are provided. Thus, in case of an accident in one of the two tunnels—involving spills of dangerous fluids—smoke or even explosion pressure waves cannot reach the other rail tunnel. In  FIG. 8 , an enlarged section of the lower concrete part  2  is shown wherein drainage pipes  18  and  19  are shown that are completely separate between each of the two main tunnels. Each drainage pipe is connected to grooves/gullies in the respective tunnel to provide inside drainage provisions to cope with water brought into the tunnel in rainy weather by the trains, and tunnel washing water. These provisions (in the form of grooves/gullies) are indicated with item numbers  8 . 1  to  8 . 4  in  FIG. 8 . The strict separation of the drainage of the two tunnels  11  and  12  prevents air overpressure from train operation, spilled liquids or smoke originating in one of the tunnels from reaching the adjacent tunnel via the drainage system. The cut-and-cover tunnel structure or the method in particular is a rail tunnel having a rail bed resting on lower concrete part  2  wherein water accumulating under the bed is caught by an array of draining geotextiles  8 . 5  and is conducted to the upper side of the rail bed, thus preventing a potential uplift of the rail bed. 
     It is sometimes argued that concrete structures (such as the present one) should be provided with special waterproofing measures (to avoid the penetration of water from the ground into the inside space of the tunnel). The usual reasoning is that unreinforced concrete can develop cracks when subject to bending moments. Experience and design calculations, however, show that bending cracks in an arched structure—such as the lower part of the proposed cut-and-cover tunnel, which is also subject to axial compression forces—are and remain waterproof, since these cracks never extend through the full thickness of the concrete structure. In the lower part of the cut-and-cover tunnel, the largely prevalent loading is the always present overfill (traffic on the overfill as a load case being insignificant, compared to the overfill weight) and, therefore, tension occurs only on one side of the cross section. 
     Cracks penetrating through the entire thickness of the concrete may occur due to concrete shrinkage (the tendency of the hardened concrete to slightly reduce its volume when the excess water evaporates). Such shrinkage cracking in the arched structure proposed in this invention can occur only perpendicular to the tunnel axis (since the concrete structure is free to contract in the circumferential direction, by virtue of the arch shape of the tunnel). Several technical measures serve to reduce such cracking perpendicular to the tunnel axis, such as by two week curing after concreting (keeping the concrete surfaces continuously wet) and by providing shrinkage joints (at intervals of between 5 to 10 m along the tunnel axis). These joints must be sealed, to remain waterproof even when the concrete shrinks. As a result, the individual 5 to 10 m long stretches of the lower part of the tunnel structure will experience no or only extremely limited leakage and—as experience has shown in the case of concrete structures without special waterproofing, even when under the groundwater level—this small potential influx of water usually disappears quickly under railway operation, due to the continuous air exchange together with the heat introduced in the tunnel by train operation. Finally, waterproofing the lower part of the tunnel would be of very limited use anyway because, in rainy weather, water will drop from the trains so that inside drainage provisions have to be provided anyway (shown as a preferred example in  FIG. 8 ). 
       FIG. 10  shows an embodiment of the cut-and-cover structure  10  being a single railway tunnel. The explanations given above for the embodiment with two parallel railway tunnels  11  and  12  apply mutatis mutandis as well for this embodiment. Same reference numerals depict same elements or elements with the same function. 
     In preferred embodiments, in order to house cables running alongside the tunnel, ancillary small tunnels or service and cable tunnels, respectively are provided. In the embodiment of  FIG. 11  such a tunnel  13  is shown on top of the central wall.  FIG. 12  shows two such ancillary tunnels  14  on rail level, one in each rail tunnel  11  and  12 , respectively. These ancillary service tunnels are separated from the main tunnels and allow permanent safe access to the cables and other tunnel equipment even under train operation. Should there be a cable fire, personnel inside the cable tunnels would be warned by fire detectors and would use the emergency exits, while the cable fire would remain contained and extinguished independent of train operation.  FIGS. 11 and 12  thus show two different solutions for separate technical space housing cables and other equipment, running alongside the entire tunnel, providing continuous access for personnel to these cables. In this manner, service work on the cables and the splicing stations can be performed during train operation and incidents such as cable fires cannot jeopardize the trains. The solution presented in  FIG. 11  also allows access to the drainage system, via shaft  35  and slightly inclined shafts  34  down from the inner platforms levels to the drainage pipes. 
     High speed rail tunnel structures have to satisfy a number of special requirements: First, they have to provide an inside air volume sufficient to limit the inside air overpressure (created by high speed trains) to levels acceptable for train operation. Arched structures according to the invention are ideally suited to provide large clearances at small additional costs—smaller than in the case of prior art rectangular structures. Further, to mitigate the micro pressure waves emanating from the portal under high speed train operation, openings in the tunnels are provided (in the near portal zone) that, via small separate parallel ducts connected to the outside, reduce the sharp pressure waves generated by the trains. In the vicinity of the tunnel portals, they have to be designed such that the micro pressure waves emanating from the portals are limited to allowable levels in the neighboring areas. One of the means to achieve this is to enlarge the tunnel continuously as it comes closer to the portal (so called “trumpet design”). Another method is to provide openings to the outside which relieve the micro pressure waves at the portals.  FIG. 13  shows two small adjacent parallel tunnels or “ducts”  15  and  16 , respectively, running alongside the main tunnels  11  and  12  in the vicinity of the portals which, on the one hand side, are connected to the main tunnel at certain intervals by connections  25  and, on the other hand, are open to the outside by vents  26  at certain intervals, thus providing micro wave pressure attenuation in the area around the tunnel portals. 
       FIG. 11  exhibits additional proposed measures to optimize the safety for service personnel and for tunnel equipment, in the improbable case of an accident: Exits  31 , for example every 200-400 m, are provided from one traffic tunnel to the next, in the form of openings in the central wall that are normally closed with solid sliding doors  29  on each side. If the thickness of the central wall is about 0.80 m or more, the two sliding doors  29 —one on each side of the wall—create a small lock between them, allowing to change from one tunnel to the other without creating a connection between the two tunnels&#39; air volumes. 
     A cut-and-cover concrete tunnel structure  10  is provided with a lower concrete part  2  and an upper concrete or steel part  3  of the structure. The lower concrete part  2  of the structure is constructed most preferably in unreinforced concrete, poured directly against and supported by a partly horizontal, partly inclined and approximately circular or elliptically shaped excavation surface  6 ′. The upper part  3  is arch shaped, constructed in reinforced (cast-in-place or precast) concrete or steel, and is of circular, elliptical or partly elliptical shape. This cut-and-cover structure allows a more efficient and less costly tunnel construction. 
     It is to be understood that while certain embodiments of the present invention have been illustrated and described herein, it is not to be limited to the specific embodiments described and shown. 
     While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.