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FIELD OF THE INVENTION 
   The present invention relates to systems and methods of stabilizing soil, and more particularly, to a soil nail launcher used to emplace soil nails. 
   BACKGROUND OF THE INVENTION 
   In order to stabilize soil and rock formations, it is known to utilize soil nailing in which a plurality of elongate reinforcing members are driven into the ground in an array in order to improve the bulk properties of the surrounding soil and rock. 
   One reference that discloses a device and method of soil nailing includes the U.S. Pat. No. 5,044,831, the disclosure of which is hereby incorporated by reference. 
   Two additional examples of references that disclose soil nailing techniques includes the British Patent No. 1,580,142, and the European Patent 0 239 258. 
   While these references may be adequate for their intended purposes, there is still a need to provide an improved soil nailing device that is easier to maintain, as well as one that is more efficient by having the capability to launch a greater number of soil nails over a period of time. 
   The portion of the soil nailing device that contacts the ground when a nail is being launched is referred to as the shroud or baffle assembly which enables the distribution of pressure away from the barrel of the launcher, and also captures any fragments that are carried through the barrel, such as the sabot or collett which is attached to the distal tip of the soil nail. As time progresses, the baffle may become clogged with soil or other debris, thereby limiting its ability to effectively release high-pressure from the barrel. The baffle may become damaged over time, thereby also changing it pressure-relieving characteristics. The failure to consistently relieve pressure from the barrel as the nail is launched can negatively affect the depth of the launched nail. Therefore, there is a need to provide an improved design for the baffle to ensure it captures fragments launched from the barrel, yet allows effective pressure release from the barrel. 
   Another disadvantage of existing soil nailing devices is that it may take an inordinate amount of time to pressurize the device so that a nail can be launched. One type of soil nailing device includes a barrel having a coaxial arrangement of an inner tube/casing and an outer tube/casing. The annular space between the inner and outer tubes is pressurized, and supplies the motive force for launching the soil nail by release of pressure within this annular space into the breach of the barrel. This annular space is pressurized by a source of compressed gas. Preferably, the source of compressed gas includes a plurality of pressurized containers that are stored on a deployment vehicle that transports and secures the launching device. One limiting factor in how quickly soil nails can be launched depends upon the time in which it takes to adequately pressurize the annular space for the next nail to be launched. Because of the noise associated with the launching of a nail, safety requirements for construction along highways and other roads generally require that traffic be stopped during the launching of a nail. The more quickly the soil nails can be launched, the less disruption for traffic flow and of course the more quickly a job can be completed. Therefore, there is also a need to provide a soil nail launching device that has a shorter cycle time in terms of the number of soil nails that can be launched in a period of time. 
   Additionally, there is also a need to reduce the required pressure to launch a nail, yet still achieving the same depth of penetration for a soil nail that is launched. A reduced pressure requirement will inherently reduce the time to launch successive nails. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In accordance with the present invention, an improved soil nail launching device is provided with two primary improvements. The first improvement of the present invention relates to a construction for the shroud that enables adequate pressure distribution from the barrel after a launch, yet minimizes clogging of the shroud by provision of removable shroud plates, thereby easing maintenance efforts. 
   A second improvement of the present invention relates to an improved barrel construction in which the compressed gas within the annular space between the inner and outer tubes can be more efficiently evacuated into the breach, thereby reducing the actual pressure requirement in the annular space for launching a soil nail to a desired depth. This reduced pressure requirement within the barrel also results in a shorter cycle time for consecutive firing of multiple soil nails at a particular job site. Additionally, the reduced pressure requirement also increases the life of the soil nail launcher by creating less stress on the various seals of the breach and valving that will inherently fail over time and require replacement. 
   With respect to the first improvement of the present invention, the construction of the shroud has been modified by providing the plurality of removable shroud plates attached to a perforated cage. The removable plates are spaced from one another along the cage, yet have parallel side edges that are closely spaced from one another to prevent escape of fragments exiting the barrel. The plates are easily removed from the cage, thereby easing maintenance efforts in replacing damaged plates and to remove debris around the plates. 
   With respect to the second improvement of the present invention, the pathway between the annular gap between the tubes of the barrel and the cavity or chamber within the breach has been improved such that the annular gap can be more quickly evacuated during operation, thereby providing an increased volume of air which pressurizes the chamber within the breach, and therefore increases the force by which the soil nail is driven into the soil. More specifically, a connection between the breach and the barrel has been improved such that there is no constriction as the compressed air travels through that connection and then into the chamber of the breach. 
   Various other features and advantages of the present invention will become apparent from a review of the following detailed description, taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a vehicle that transports and supports a nail launching device, and this Figure also shows a plurality of soil nails that have been emplaced in a sloping surface near a road bed; 
       FIG. 2  is a fragmentary perspective view of the soil nail launching device of the present invention; 
       FIG. 3  is another fragmentary perspective view of the soil nail launching device of the present invention; 
       FIG. 4  is a fragmentary perspective view of a prior art soil nail launching device showing the prior art shroud assembly; 
       FIG. 5  is an enlarged fragmentary perspective view of the soil nail launcher device of the present invention illustrating the improved shroud assembly; 
       FIG. 6  is an enlarged fragmentary cross-sectional view of the shroud assembly of  FIG. 5 ; 
       FIG. 7  is an enlarged fragmentary cross-sectional view of the breach and barrel of a prior art soil nail launching device; and 
       FIG. 8  is an enlarged fragmentary cross-sectional view of the improved barrel and breach of the soil nail launching device of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates the soil nail launching device  10  of the present invention attached to the boom or articulated arm  14  of a deployment vehicle  12 . As shown, a plurality of soil nails N are emplaced in soil S located on a sloping surface adjacent a road bed R. Once all of the nails are emplaced, the protruding ends may be cut to grade. The boom  14  of the deployment vehicle is shown as having two boom segments  16  and  18 , and a number of hydraulic cylinders  20  which are used to articulate the boom to a desired position in order to position the launcher  10 . As also shown, a boom extension  22  interconnects a distal end of the boom segment  16  to the launching device  10 . A boom pivot  24  is provided to enable precise rotational positioning of the launching device  10 . Referring to  FIG. 2 , connection pins  26  of the boom extension are used to connect the extension  22  to the distal end of the boom segment  16 . The boom pivot  24  includes a hydraulic cylinder assembly  30  (partially shown) which can adjust the angle at which the launcher  10  extends with respect to the long axis  23 - 23  of the boom extension  22 . 
   The primary components of the launching device  10  include a barrel  34 , a breach  36  located at one end of the barrel and a shroud assembly  38  located at the opposite end of the barrel. A frame  40  comprising a number of angled plates provide a stable mounting for the launcher components. A front support  42  and a rear support  46  allow the launcher to be placed horizontally on the ground when not in use. The rear support  46  also acts as a housing for valve bank  44 , as described below.  FIG. 2  also illustrates a control box  48  that houses electrical and pneumatic components of the launching device. Various hydraulic and electrical lines have been eliminated in  FIG. 2  in order to clarify viewing of the basic components of the launching device. 
   Now referring to  FIG. 3 , another perspective view of the launching device is provided, as to include illustration of some of the hydraulic and electrical control lines. In this perspective view, the rear support  46  is shown as having a bottom flat surface which enables the breach  36  and the barrel  34  to be placed in a substantially horizontal position. Referring also to  FIG. 1 , the back or rear end of the launching device further includes a nail support bracket  50  and a cylindrical nail housing  52  which holds the portion of the soil nail N that protrudes away from the breach  36  when the soil nail is loaded for launching.  FIG. 3  also illustrates additional details of the breach to include a pair of breach plates  54  that are operated by a pair of control cylinders  56 . Linkage  58  interconnects the pistons of the control cylinders  56  to the protruding ends of the breach plates  54 . An aperture  66  is formed by half circular shaped cut-outs that are formed on the abutting ends of the breach plates  54 . The aperture  66  is sized to receive a soil nail. A breach plate mounting block  60  is used to mount the breach plates to the breach assembly and the block  60  forms the rear portion of the breach  36 . When it is desired to launch a soil nail, the cylinders  52  are operated to separate the plates from one another at the central opening  62  of the mounting block  60 . The forward or front end of the soil nail can then be inserted within the breach  36 , as explained further below. 
   Referring now to  FIG. 4 , the prior art is shown with respect to a prior art shroud assembly  100 . The shroud assembly  100  comprises a base plate  102  that is placed against the ground when the launching device is in operation, a top plate  104 , and an interconnecting plurality of deflectors  110  that form a cylindrical shaped cage. A central opening (not shown) is formed in the base plate to enable a launched soil nail to pass through the opening and into the ground. The deflectors  110  are welded at each end to the respective plates  102  and  104 . The deflectors  110  are angle iron brackets placed in an overlapping arrangement as shown; each bracket is nested in the gap within the adjacent bracket. This overlapping arrangement allows compressed air to escape through the gaps between the adjacent angle iron brackets. This overlapping arrangement also captures fragments that exit the barrel. One problem associated with the prior art is that the angle iron brackets are permanently welded to the plates  102  and  104  and therefore, it is not possible to remove the angle iron brackets  110  to clean the cage. Subsequently, the gaps between the angle iron brackets become clogged, thus sacrificing the pressure relieving capability of the shroud assembly. This loss in pressure relieving capability results in some additional pressure being maintained within the barrel during launching, which sacrifices the depth to which the nail can be launched into the soil. In order to clean debris caught between the adjacent angle iron brackets, this effort is a time-consuming task and must be done frequently in order to maintain optimizing functioning of the shroud assembly. Bent brackets are not be easily replaced and permanent deformation of the brackets also affects barrel pressure. 
   Now referring to  FIGS. 5 and 6 , an improved shroud assembly  38  is illustrated. The shroud assembly according to the present invention also includes a base plate  76 , a top plate  78 ; however, in lieu of the angle iron elements  110  directly attached to the plates  76  and  78 , a cage or cylindrical member  80  interconnects the base plate and top plate. Removable shroud plates  84  are also provided and attach to the cage  80 . As shown, the removable shroud plates  84  are placed in a substantially parallel and side-by-side relationship around the periphery of the cage  80 . The removable plates  84  are secured to the cage by a plurality of fasteners  86 . One or more fasteners are used to secure each removable plate. The orientation of each of the plates is such that they cover a corresponding group of underlying apertures  82  formed in the cage. The removable plates  84  are bent or curved at their opposite side edges  85  thereby forming a U-shape cross-section. Accordingly, the removable plates  84  have opposing side edges  85  that extend closer to the outer surface of the cage, and the interior portion of the removable plates  84  extend further away from the cage as compared to the opposing side edges. In other words, the bend or curve formed in a removable plate  84  is directed radially inwards toward the center of the cage  80 . 
   A slight uniform gap exists between each abutting side edge of adjacent removable plates  84 . With this specific arrangement of the removable plates  84 , venting of the pressurized air within the cage  80  can be achieved, yet debris and fragments exiting the barrel during launching will not escape from the cage. In the event one of the removable plates is damaged or is clogged with debris, the plate can be easily removed. With the use of the removable plates  84 , precise relieving pressures can be maintained which improves the operation of the launching device. 
   Referring to  FIG. 7 , the prior art breach assembly and barrel are illustrated. The barrel  34  includes a concentric arrangement of tubes, namely, an inner tube  142 , and an outer tube  140 . An annular space  146  is defined as the gap or space between the inner and outer tubes. A source of compressed gas  144  carried by line  145  is shown as communicating with the annular space  146  in order to pressurize the annular space. The source of compressed gas  144  may be a plurality of gas containers carried on the deployment vehicle wherein the annular space may be selectively pressurized by a pneumatic switch (not shown) controlled by the operator. The annular space is pressurized to a desired set pressure based upon how much pressure is required to launch the soil nail into the targeted area. Variations in soil density and the presence of rock will dictate the required amount of pressurization within the annular space in order to effectively launch the soil nail to a desired depth. 
   The breach  38  includes a breach block housing  90 , a breach block end plate  92 , and a valve plate area  130 . In  FIG. 8 , to simplify illustration of how gas is allowed to travel from the annular space  146  into the cavity  134  of the breach, in lieu of a valve plate and a plurality of valves being illustrated, the valve plate area  130  is simply illustrated as including an annular passageway  132  interconnecting the cavity  134  within the breach assembly and the annular space  146  located between the outer casing/tube  140 , and the inner casing/tube  142 . 
     FIG. 7  also illustrates a soil nail loaded through the breach into the barrel. The soil nail includes a pointed distal tip  120 , a breach cap  122  which is positioned at the entrance to the breach located at the aperture  66  between the abutting edges of the breach plates, a spacer  124 , and a collett/sabot  126 . The collett  126  further includes a proximal flange or seal  127  such that when a soil nail is loaded, a sealed cavity exists within the breach  38  bounded by the surrounding walls of the breach, the breach cap  122 , and the seal  127  of the collett  126 . The collett  126  and spacer  124  are not launched into the ground, but rather are trapped within the shroud assembly and are broken into fragments as they strike an anvil secured to the base plate as mentioned below. The collett  126 , spacer  124 , and cap  122  are made of a plastic material while the nail is made of a high strength metal such as steel. 
   In the prior art design, the portion of the breach terminating at the barrel includes a flange  150 . The end  148  of the outer tube  140  of the barrel is fitted over the flange  150 , such as by a threaded connection. As shown, by the directional arrows, when the compressed air from the annular space  146  is allowed to travel into the breach cavity  134 , it must first pass through an annular constriction  152  located at the flange  150 . This constriction  152  is defined by the narrowed area between the inner tube  142  and flange  150 . This constriction is smaller in area as compared to the annular space  146 . Because of this constriction  152 , gas cannot be evacuated from the annular space  146  as quickly as if there were no constriction there. 
   The basic operation of the launching device is as follows. First, the compressed source of gas  144  pressurizes the annular space  146  located between the inner and outer tubes  140  and  142 . Once the annular space  146  is pressurized to the set point, then the launcher can be fired by operating valves (not shown) located at the valve plate area  130 , which opens a corresponding plurality of passageways (not shown) between the cavity  134  and the annular space  146 . As mentioned above, the valve plate area  130  is simplified by the illustration of the single annular passageway  132 . As the cavity  134  quickly pressurizes, the soil nail is forced through the barrel as shown by the directional arrow within the bore  160  of the barrel. An o-ring shaped metallic anvil (not shown) is placed around the central opening in the base plate. The anvil has a diameter large enough to allow passage of the soil nail to enter the ground, yet the diameter of the anvil is such that the larger diameter collett strikes the anvil and breaks apart into fragments. Pressurized air is prevented from escaping the cavity  134  by the breach cap  122  that is maintained in its position as shown. The nail passes completely through the breach cap  122  and when enough pressure is relieved in the breach cavity, the breach cap may also be carried along with the spacer to the anvil where they are also fragmented by striking the anvil. 
   Now referring to  FIG. 8  of the present invention, the flange  150  has been eliminated, and a connection is made directly between the outer surface  141  of the outer casing/tube  140  and the interior surface  91  of the breach block housing  90 . By this arrangement, the constriction  152  is eliminated and area  156  defining the open space at the location of the connection between the breach and barrel has a size at least as large as the annular space  146  between the barrel tubes  140  and  142 . Therefore, the annular space  146  within the barrel is able to more quickly evacuate creating greater initial pressure within the cavity  134 . This greater pressure achieved within the cavity causes the soil nail to be propelled at a faster rate through the barrel. The user therefore has the option of either providing less pressure within the annular space  146  to achieve adequate penetration, or may achieve greater penetration of the soil nail with the same applied pressure as compared to the prior art. 
   By redesigning the connection between the breach and the barrel, improved air flow is achieved which allows a more immediate evacuation of the compressed gas into the breach chamber, thereby increasing the speed at which the soil nail can be driven into the ground. This solution is preferable over a complete redesign of the complex valve plate assembly and valving, which otherwise would be a much more complex and expensive redesign effort. 
   By the foregoing, it is apparent that two improvements are provided to an existing soil nail launching device to improve the overall operation and performance. These improvements are achieved without requiring a complete resign of the basic function of the soil nail launching device. 
   Although the foregoing invention has been shown with respect to various preferred embodiments, it should be understood that various other changes and modifications may be made within the spirit and scope of the invention.

Summary:
A soil nail launching device and method are provided wherein the launching device includes an improved configuration for the protective shroud and an improved configuration for a connection between the breach and barrel of the launching device. For the protective shroud, a plurality of removable shroud plates are provided to ease maintenance of the shroud plate, as well as to provide more consistent pressure release after the launcher has been fired. The improved breach and barrel design includes a connection that does not reduce the area of the annular space that is evacuated during firing of the device, thereby optimizing the available volume of air to be transferred to the breach for launching the soil nail through the barrel.