Abstract:
A hole forming tool is disclosed utilizing compressed gas discharged into a shaped shroud resulting in minimal disturbance to the surrounding ground.

Description:
TECHNICAL FIELD 
   This invention relates to a hole forming tool. 
   BACKGROUND TO THE INVENTION 
   It is sometimes necessary to make a hole in the ground and in an area where the ground surface is soil, or a material having similar mechanical properties to soil. This could be for a variety of reasons including for the creation of a pot-hole to inspect buried services such as electricity, gas and water, or for the inspection of tree roots or buried rock, or for providing a mounting hole for a fence post or for planting trees. 
   Currently, implements such as picks, shovels and crow bars are used to make such holes in the ground. However, these implements are labour intensive and use of these implements often disturbs a larger area than needed and can result in damage to underground services. 
   It has been tried to use water based methods to make holes in the ground. However, these require the removal of the resultant sullage, which can be messy and time consuming. 
   SUMMARY OF THE INVENTION 
   The present invention provides a hole forming tool including a hollow shroud having a ground engaging portion for engaging a soil surface; a compressed gas delivery means including an outlet disposed within the shroud; the outlet is disposed at a position within the shroud so that when the ground engaging portion of the shroud is driven into soil, compressed gas emanating from the outlet disrupts the soil inside the shroud to form a hole in the soil. 
   In this way, a smooth sided hole is formed with the assistance of compressed gas. Minimal disturbance is made to the surrounding ground. The sides of the resultant hole conform with the outer dimensions of the shroud. 
   The tube may be bent at a location spaced from the ground engaging portion to direct the disrupted soil away from the hole. 
   The outlet may be a nozzle including more than one flow path through which compressed gas can emanate from the nozzle. The provision of multiple flow paths assists in the breaking up of the soil by the compressed gas. 
   The ground engaging portion of the shroud may be provided with blunt serrations spaced around its periphery. These blunt serrations serve to assist in the break up of soil whilst causing minimal damage to any underground object that may be struck by the teeth during excavation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is an elevation view of an embodiment of a hole forming tool according to the present invention; and 
       FIG. 2  is a cross section view along the line A—A of  FIG. 1 ; 
       FIG. 3  is an underside view of the nozzle of  FIG. 2 ; and 
       FIG. 4  is a cross section view along the line B—B of  FIG. 3 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 1 and 2 , a hole forming tool  10  is shown including a hollow shroud in the form of steel tube  12 . Tube  12  has a diameter of 100 mm and a length of 1800 mm. Tube  12  has a ground engaging portion  14  that is provided with blunt serrated teeth  16  around its periphery. Tube  12  is bent at a point  18  spaced away from ground engaging portion  14 . Exhaust portion  20  is provided with a rim  22  for receiving a vacuum hose (not shown) by way of a cam lock. 
   Tool  10  includes a compressed gas delivery means including pipe  24  and nozzle  26 . Pipe  24  is made from steel and has a diameter of about 12 mm. Pipe  24  enters tube  12  at a point just below bend portion  18  and is affixed to the inside of tube  12 . At a point about 150 mm from the lower end of tube  12  pipe  24  is bent towards the centre of tube  12 . Pipe  24  is provided with an outlet at its lower end in the form of nozzle  26  which is a screw threaded fit to pipe  24 . Nozzle  26  is disposed in the centre of the bore of tube  12  about 30 mm from the lower end of tube  12 . A locknut (not shown) is used to secure nozzle  26  at the correct position on pipe  24 . The upper end of pipe  24  is provided with a suitable fitting  25  to receive an air hose from an air compressor. 
   Tool  10  includes a pair of handles  28 . 
   Referring to  FIGS. 3 and 4 , nozzle  26  is shown in greater detail. Nozzle  26  includes a threaded portion  27  for affixing to pipe  24 . Nozzle further includes a central flow path  30  of 4 mm diameter and peripheral flow paths  32  which are offset from flow path  30  by angle a. In this embodiment angle a is 25 degrees. Peripheral flow paths  32  have a diameter of 2 mm and are equally spaced about central flow path  30 . 
   To form a hole with tool  10 , the tool  10  is stood on the ground at about 90 degrees to the ground in the position where the hole is to be made. Compressed gas in the form of compressed air at about 100 PSI is applied to fitting  25 . By grasping handles  28 , the tool is rotated in alternate directions through an angle of about 60 degrees about the central upright axis of tube  12 . 
   As a result of the rotation of tool  10 , blunt serrations  16  break up the soil and, as the tool descends into the soil, the compressed air emanating from nozzle  26  excavates the ground in the region of nozzle  26 . The soil which is excavated is broken down and forced upwards and out of exhaust end  20  by the compressed air. A hose may be attached to rim  22  is run to a drum, which traps soil leaving exhaust end  20 . 
   For heavy soil, a vacuum pump may be used to assist in drawing excavated soil out of exhaust end  20 . The vacuum pump may be connected directly to a hose attached to rim  22 , or may be attached to draw air from the drum, if used. In the case of wet material the connection between the tool  10  and the vacuum pump may be filtered. 
   During excavation the tool is continued to be rotated in alternate rotational directions through 60 degrees to assist in the excavation and to help locate any solid object in the ground. 
   It can be seen that the invention described herein provides a convenient low impact tool for forming holes in ground with reduced manual effort and with minimal disturbance to surrounding ground and to buried objects. 
   Nozzles of different configurations to the nozzle illustrated may be employed depending upon the physical characteristics of the soil structure to be excavated. 
   The shroud employed in the above described preferred embodiment is in the form of a steel tube which completely surrounds and encloses the nozzle. It is not strictly necessary to completely enclose the nozzle and an open section shroud could be employed. The important factor is that the shroud defines the outer dimensions of the formed hole. 
   Similarly, alternative arrangements to blunt serrations at the ground engaging end of the shroud can be employed. The important factor is that the ground engaging portion of the shroud assists with cutting into the ground to define the outer dimensions of the hole to be formed whilst minimising damage to underground objects. For instance, resilient plastic fingers could be used instead of blunt serrations. 
   Whilst the invention has been described above with reference to forming a hole in soil, the tool can be used to form a hole in any substance that has similar mechanical properties to soil. 
   Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated. 
   Finally, it is to be appreciated that various alterations or additions may be made to the parts previously described without departing from the spirit or ambit of the present invention.