AU593600B2

AU593600B2 - Method and apparatus for excavating soil and the like using a supersonic gas

Info

Publication number: AU593600B2
Application number: AU66595/86A
Authority: AU
Inventors: Aubrey Charles Briggs
Original assignee: BRIGGS Tech Inc
Current assignee: ACB Tech CORP
Priority date: 1986-06-23
Filing date: 1986-12-16
Publication date: 1990-02-15
Anticipated expiration: 2006-12-16
Also published as: FR2600373A1; AU6659586A; FR2600373B1; JPS634130A; EP0251660A1; ATE82027T1; DE3782458T2; ES2035862T3; DE251660T1; EP0251660B1; DE3782458D1

Abstract

A method and apparatus (2) suitable for excavating a soil mass and like granular materials in which pressurized gas, preferably air, is provided in a reservoir and directed through appropriate valve (4) and duct means to a converging/diverging nozzle (50) positioned at the exit of the duct means. The nozzle includes a restricted throat section and a diverging transitional section which terminates in an outlet section. The ratio of the area of the outlet section to the area of the throat section is greater than 1.0 and preferably greater than 1.2 or more, while the ratio of reservoir pressure to ambient pressure is greater than about 1.9 and preferably greater than 3.7, whereby a gas stream having a calculated velocity greater than Mach 1, and preferably in excess of Mach 1.5 or more, is produced. The high velocity gas stream infiltrates the soil mass creating fissures and cavities, then stagnates within the cavities and violoently expands to fracture the mass.

Description

'ii W 593600 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION FOR OFFICE USE Short Title: Int. Cl: Application Number: b6$ Lodged: Form Complete Specification-Lodged: Accepted: Lapsed: Published: *e 4 *4 4 4 g* 4- .4 4C p* 4*4 4.4; 4 4 i Priority: Related Art: This document contains the amendments made under Section 49 and is correct for printing.

TO BE COMPLETED BY APPLICANT Name of Applicant: Address of Applicant: Actual Inventor: Address for Service: .4 .4 .4 t .4 .4 14 4 .4 1 II .4 BRIGGS TECHNOLOGY INC.

4706 Grand Avenue, Pittsburgh, Pennsylvania 15225, U.S.A.

Aubrey Charles Briggs GRIFFITH HASSEL FRAZER 71 YORK STREET SYDNEY NSW 2000

AUSTRALIA

Complete Specification for the invention entitled: METHOD AND APPARATUS FOR EXCAVATING SOIL AND THE LIKE USING A SUPERSONIC GAS The following statement is a full description of this invention, including the best method of oerforming it known to me/us:- 1370A:rk c g~ I ;:i rr

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~9~6 .9 9 Specification My invention relates generally to the excavation of soil and other granular materials by a high velocity gas stream. More particularly, my invention relates to a method and apparatus utilizing a stream of' supersonic gas, preferably air, for the excavation of granular materials such as soil around buried objects. The present invention is particularly suited for excavation in close proximity to and in contact with subterranean utility lines, conduits and the like where conventional mechanical and hand excavation techniques could cause damage to the buried pipes, wires or cables and, in some cases, create explosion hazards.

Heretofore, when excavation has been required in close proximity to ga lines, water and sewer pi.pe, underground power and television cables, telephone lines and the like, it has been necessar-y to convert from the usual mechanized equipment, such as power shovels or backhoes, and employ hand excavation tools such as picks and shovels to con\plete the task. Hand excavation not only results in a 20 dromatic reduction in the material removal rate, but it alsn does not completely solve the problem of inadvertent striking and rupturing of buried utility lines a&v ipes.

Such mishaps result in potentially expensive property damage and troublesome service interruptions. In addition, in the case of natural gas lines, there is alio a continual threat of bodily injury to the workmien resulting from the explosion hazards cirea tdd by the uise of hand tools in and around the cast iron pipes. In such an environment, sparks caused by a collision of the steel digging tools with a pipe or a stone can result in a gas explosion if a leak is present. In an attemipt to overcoie, the reduced excavation rates of hand -2- 9 ~l~4 It 9 It~ t, 9$ j $9 99 9 9 9 *t~ 9 1 j47".

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Sr i-j i! tols, attempts have been made to introduce various mechanized digging aids such as scrapers, power brushes, fluid sprays, and the like to minimize or completely eliminate the hand work. These devices have met with limited success in the field and, at best, are a marginal solution to the dilemma. In operation, the cleaning mechanisms quickly become dull and worn, requiring frequent maintenance and replacement. The soil usually adheres to the cleaning mechanism, reducing its effectiveness; brushes clog and scrapers become caked. In addition, the cleaning mechanism itself can damage the surface of the object being cleaned and a scraper or hoe can gouge or destroy a pipe or valve if 9.

the mechanism controlling the device is inadequate or *9 improperly set. In the case of liquid hydraulic sprays, such as water, the disadvantages re. also manifest. A large supply of water is usually required, which creates a disposal problem at the job site. In addition, the splashing of the water spray must be contained and generally coats surrounding equipment with a layer of mud. In cold weather *o t20 operations, the water must be treated with an antifreeze or S" some other fluid must be employed so as to eliminate icing problems.

o A ONT 0 e 3- I S The converging/diverging nozzle 50 is firmly

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0 90 99 8 99 9 90 9 900999 8 9 9.9.9* 9 89 99 0 9 o 9 98 0 99 According to the'present invention there is provi~ded a method of exczvating ac soil mass or like granular material mass, comprising: providing a reservoir of a gas at a pressure of at least about 1.9 times greater thanan ambient pressure adjacent the soil or material mass; transmitting the gas through a duct means from the reservoir to a nozzle means of a converging/diverging type and accelerating the gas therethrough to produce a gas 3 stream which is substantially free of entrained solids and which exits said outlet at a calculated velocity greater than Mach 1; and directing said gas stream to said soil or material mass, whereby said mass is infiltrated and fractured by said 15 gas stream.

Another aspect of the present invention is a method of excavating a soil mass or like granular material mass, comprising: providing a reservoir of gas at a pressure of between about 2 to 37 times greater than an ambient pressure adjacent the soil or material mass; transmitting the gas through a duct means from the reservoir to a nozzle means of a converging/diverging type including a throat section and an outlet section and 25 accelerating the gas, substantially free of entrained solids, through the nozzle means to produce a gas stream exiting said nozzle having a calculated velocity between about Mach 1 and about Mach 3; directing said gas stream to said soil or material mass; 30 infiltrating said soil or material mass with said gas stream to create fissures and cavities thererin; stagnating said gas stream within said fissures and cavities; and expanding said stagnated gas to ambient pressure whereby portions of said mass are fractured by the forces generated by said expansion.

There is also provided an apparatus suitable for excavating a soil mass or like material mass comprising: 4 '618/KLUI 4

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section. It is also known that the r' r r 4* 4, 4 44 I44 0 *I *d9 04 4 4q04D 4 44 4 v 4 4 4 4 a 4a 4 duct means adapted to communicate with a reservoir containing a pressurised gas at a pressure of at least about 1.9 times greater than an ambient pressure adjacent the soil or material mass; nozzle means of the converging/diverging type positioned within said duct means and having a throat section and an outlet section, each of said sections defining a respective cross-sectional area, and wherein the ratio of said outlet section area to said throat section area is greater than 1.0, whereby said apparatus is adapted to produce a stream of gas, substantially free of entrained solids, at a calculated velocity of greater than Mach 1 when said pressurised gas from the reservoir passes through said nozzle means.

15 The hand-operated embodiment of the present invention incorporates a unique, low-torque trigger valve mechanism which employs the reservoir gas at high pressure as a pilot to assist in opening the valve to the high pressure supply line. The valve body and covers provide a sealed environment against dust, mud and water or other hostile environments making it suitable for the demanding service experienced in the field.

In another embodiment of the present invention, small amounts of liquid water of gaseous CO 2 may be introduced 25 into the device to produce an entrained flow of solid particles within the supersonic air stream to provide an abrasive cleaning action to the high speed jet. In this manner, the advantages of abrasives are gained without the related problems of abrasive wear in a hose and the problem 30 of abrasive contamination.

The present invention in one form also provides a device which is capable of producing supersonic gas streams of various cross-sectioned configurations depending upon the shape of the nozzle employed. Circular or square nozzles are preferred in excavation applications, while a thin, knife-like rectangular nozzle is particularly suited for cleaning operations, such as in cleaning caked substances Sfrom bulk material conveyor belts.

rII ATh4 1 e4, 'C 2; ~ii31/ The method and apparatus of the present invention according to one embodiment provide these advantages and desirable features by employing a reservoir of pressurised gas, preferably air, maintained at about 90-100 psig or higher, the flow of which is regulated through appropriate valve means to a barrel of the device which is fitted with a converging/diverging nozzle at the end of the bore thereof.

The nozzle may possess a circular cross-section or a square or rectangular cross-section, depending upon the shape of the air jet desired. The converging/diverging configuration of the nozzle is critical in the creation of the supersonic air jet in accordance with known principles of fluid mechanics. In nozzles of this type, the boundary conditions of supply pressure and ambient or atmospheric pressure 15 produce a choked sonic flow condition at the throat of the a" nozzle and a supersonic flow in the diverging section. The o" diverging section is flared such that the air accelerates smoothly, without shock waves, to produce a maximum velocity .a and Mach number at the nozzle outlet. The choked flow 20 condition is a

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*rt ~riknown phenomenon and occurs when the fluid mass flow rate attains a maximum value for a given throat area of the nozzle at given upstream conditions of temperature and pressure. The flow rate at the exit of the converging/diverging nozzle thus can be predicted by closely controlling the area ratio of the throat and outlet regions of the nozzle, along with the pressure ratio of the air within the reservoir with that of the ambient pressure, normally atmospheric.

According to the present invention, for excavating most soils, wet clay through dry loam to sand, a gis stream velocity greater than sonic is required and, more particularly, a velocity at least about Mach 2 is preferred since it provides a more efficient digging tool. A nozzle for producing an exit velocity of Mach 2 employs an area ratio of about 1:1.685 outlet area to throat area, and a pressure r S ratio of about 7.8:1, reservoir pressure to ambient presr, sure. Thus, a Mach 2 exit velocity is feasible utilizing a conventional air compressor which usually is capable of .20 generating between 90 to 110 psi reservoir pressure at a sufficient flow rate of, for example, 125 cubic feet per minute of air.

In the hand-operated embodiment of the present invention, a trigger actuated valve, normally spring-biased i to a closed or deactivated position, is provided to pilot the flow of high pressure rese:voir air around the valve to assist in overcoming the force of the pressurized reservoir air which normally maintains the valve in the closed position. The valve member comprises a valve stem positioned within the bore of a valve body or housing having a valve -7-

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r il;l! I" i i an~a head positioned in sealing engagement with a valve seat at an inlet end which is in communication with the pressurized inlet air. The valve also includes a second ed carrying a piston of a larger diameter than the valve head. An air inlet bypass bore is formed within the valve body of the handle member, communicating at a first end with the pressurized air channel upstream of the valve head and communicating at itF second end with an interior space of the valve housing adjacent to the piston. Positioned in a space between the first and second ends of the air inlet bore is a rotatable trigger shaft which has a bore formed through its diameter which communicates with the aforementioned air inlet bore when the trigger shaft is rotated to a firing or activated position. In the activated ic position, the pressurized air from the inlet is fed to the rtf space adjacent to the larger diameter piston causing the t t valve to instantly unseat, permitting the pressurized air from the reservoir to pass through the valve body into the bore of the barrel and thence to the converging/diverging nozzle. The trigger mechanism is spring-biased to return to t1 t S the closed position when the operator releases his grip t It thereon. The trigger shaft is also provided with a vent .4I orifice which communicates with the air inlet bore on the piston side thereof to permit the venting of the by-pass S bore when the trigger is returned to its close position. In addition, an air pressure gauge is also preferably provided orn the excavator device to insure that proper operating air pressure is maintained. The device is also preferably constructed of a noncorrosive and nonferrous material so that the device is rust-resistant and also nonsparking to -8- SI S .render it suitable for use in explosive environments. The barrel may also be provided with an elongated pick elemeot, outwardly projecting beyond the nozzle, to permit the operator to dislodge any stubborn lumps of material during the excavating operation. The barrel of the device may be either a straight length of pipe or it may be fitted with a curved exit section for difficult-to-reach applications.

Other objects and advantages of the present invention will become readily apparent upon reference to the accompanying description when taken in conjunction with the Re following drawings, wherein: Figure 1 is a side elevation view of a a go hand-operated device constructed in accordance with the e present invention; I4 Figure 2 is an enlarged cross-sectional view of the handle and trigger valve assembly of the device of Figure 1; t*t Fi ?ure 3 is a cross-sectional side view of the t 20 handle and valve assembly taken along line III-IlI of Figure 4; Figure 4 is a partial cross-sectional view of the trigger assembly taken along line IV-IV of Figure 2; a Figure 5 is a partial cross-sectional side view of a converging/diverging nozzle in place on a barrel with a j pick-like tip in place thereon; Figure 6 is a partial cross-sectional side view of a nozzle and barrel similar to Figure Figure 7 is a partial side view of a barrel with an angular discharge section; -p 1 11^ k* /2 I Figure 8 is a pictorial representation of the hand operated device of the present invention being used in excavating around a buried utility pipe and electrical line; Figure 9 is an enlarged, partial cross-sectional view taken along line IX-IX of Figure 10 showing the details of a converging/diverging nozzle of the type employed in the present invention; Figure 10 is an end view of the nozzle of Figure Figure 11 is a partial plan view of a rectangular nozzle which may be employed in the present invention; and Figure 12 is an end view of the rectangular nozzle of Figure ii.

1 Referring now to the drawings, wherein like t reference numerals indicate the same parts throughout the tr0 various views, a hand operated device constructed in accordance with the present invention is shown and designated generally by the reference numeral 2 therein. The excavator device 2 is uniquely suited for manual excavation of buried utility lines, such as the utility pipe or conduit ct 22 or the television, electrical, telephone or like cable 22' shown in Figure 8. Referring to Figures 1 and 8, the

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device 2 is operably connected by way of a high pressure air hose 16 to a storage reservoir of high pressure air generated by compressor 20. The air compressor is preferably of a conventional type normally used in construction work and capable of delivering 125 cubic feet per minute of air at a reservoir pressure of at least 90 pounds per square inch gauge (psig) at the outlet. The air hose 16 preferably has a minimum inside diameter of about 1 inch in order to .T

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41 I i -i handle the air volume required for the intended excavating purposes. Device 2 is operably connected to the air hose 16 by way of a conventional quick disconnect coupling 18 which may be threadably fitted to the handle member 10 at the base conduit 24, Figs. 2 and 3. The device 2 further includes a control valve body 4 with a trigger mechanism 12 for controlling the flow of high pressure air therethrough. The device 2 also includes a converging/diverging nozzle fitted wichin a bore 7 of barrel 6 at the outlet end 8 thereof. As will be explained in detail hereinafter, the ratio of the outlet diameter to throat diameter of the nozzle 50, at a given supply pressure of air from the compressor 20, will produce a choked sonic flow condition at S the nozzle throat and supersonic air flow in the diverging section at the outlet of the nozzle 50 which provides the S required energy for excavating. The device 2 also preferably contains a handle 14 for convenient gripping by the operator and also a pressure gauge 21 mounted on the rear face of the S valve body 4 to enable observation of the operating air 20 pressure.

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0 The valve mechanism for regulating the flow of high pressure air through the hand operated excavation device 2 is depicted in Figures 2, 3, and 4. The conduit 24 has a bore 25 which communicates with air hose 16 and with the high pressure air within the reservoir generated by compressor 20. Conduit 24 is fitted within handle 10 and attached to the valve body 4 by way of tt'eads, soldering, or the like to create an airtight fit therewith. Valve body 4 has an internal bore 5 extending therethrough in a generally T-shaped configuration from the inlet end adjacent

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Z77 conduit 24 to the outlet end adjacent the barrel 6. Barrel 6 has a bore 7 which is also in communication with the bore of the valve body. Barrel 6 is rigidly attached to the valve body 4 in an airtight manner by leeve fitting 82 which is secured by way of threaded section 83 to the valve body 4. A pair of 0-ring seals 84 and 86 are provided around the sleeve fitting 82 and the barrel 6 to provide c mechanically strong and airtight seal.

The high pressure inlet air within the bore 25 is sealed-off from the bore 7 of the barrel by way of a valve member 28 which is movably positioned within the bore 5 of the valve body. Valve 28 includes a head portion 30 having a tapered edge which sealably engages the seat 34 of a venturi-type sleeve 32 which is seated within the bore Sleeve 32 has a cylindrical bore formed therethrough which is sealed off when the valve 30 is in the closed position shown in Figure 2. In the closed position, the tapered edge S of the valve head 30 sealably engages tapered valve seat 34 to prevent pressurized air from entering the barel bore 7.

20 A generally cylindrical piston 38 is mounted on valve stem 36 of the valve 28 at the opposite end from che head Piston 38 is slidably positioned within a chamber 80 formed within the upper portion of the valve body 4 and is secured S' to the valve stem 36 by a nut and washer 40. The piston 38 also preferably contains an annular cutout portion 44 formed in the underside thereof to receive a coil spring 42 therein. A cylindrically shaped valve guide 46 is fitted Swithin the valve body 4 and tightly receives the valve stem 36 therethrough. At 0-ring 48 is fitted within Lhe valve guide 46 to prevelt air leakage around the moving valve stem r: 1 1 o .i 1 1 1 1 l h l y 'kkA- 'V X i -i-e .L1-_li: i THE CLAIMS DEFINING THE INVENTION A9E AS FOLLOWS: which slidably moves therein. The coil spring 42 compressively engage, the top of the valve guide 46 and the bottom of the piston 38 within portion 44 to bias the valve 28 and the attached head portion 30 to a closed position against the sealing seat 34 of the sleeve 32. An O-ring 47 is also provided around the periphery of the piston 38 to minimize air leakage therearound.

In the closed position depicted in Figure 2, the valve head 30 is firmly held in place against the valve seat 34 by the high air pressure in the bore 25. By way of example, if the area of the valve head 30 is 1 square inch S and the inlet pressure within the bore 25 is 1QO psig, then a force of greater than 100 pounds is required to unseat the 4 r* valve head 30 to permit air to enter into the bore 7 of the S barrel 6, In order to assist in overcoming the rel-tively large unseating force required to open the valve 28, a control valve is provided which is operated by pilot air pressure from the main air supply withiln the conduit 25. The pilot air flow is controlled by movement of the trigger mechanism 12 which is ported to selectively permit the air to enter or exhaust depending on the position of the trigger S 12. The valve body 4 has a small diameter air inlet bore 62 formed therein which communicates with the bore 5 at one end 4 t thereof and is adapted to communicate with a first end of bore 64 formed in the cylindrical trigger shaft 26. When the trigger is in the deactivated position shown in Figure 2, the bore 64 does not communicate with the bore 62; hences pressurized pilot air is supplied to open the viV the activated position of Figure 3, the trigger Vt T Ni iitegral shaft 26 rotate in a counterclockwise diret. ^13

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6* 06* align the bores 62 and 64 to permit the flow of pilot air therethrough.

The valve body 4 also contains a bore 66 which is formed therein to communicate with the second end of bore 64 uf the trigger shaft when the trigger 12 is in the activated position. Bore 66 communicates with a vertically extending bore 68 also formed within the body 4 which, in turn, communicates with a transversely extending bore 70 which communicates with circumferentially extending grooves 72 which are formed around the cylindrical outer sidewall of the sleeve 32 which, thence, communicate with a bore 74.

Bore 74 communicates with a bore 76, also formed within the S valve body 4, which, in turn, communicates with a passage 78 near the top of the valve body 4. Passage 78 communicates with the chamber 80 above the piston 38 of the valve 28. The surface area of the face of piston 38 which is exposed to chamber 80 is greater than that of the valve head 30. Hence, S when the trigger 12 is in the activated position of Figure 3, pilot air, at line pressure, is supplied through bores 20 62, 64, 66, 68, 70, 72, 74, 76, 78 to the chamber Chamber 80 is likewise contained within an airtight closure by way of a threaded cap 45 and an 0-ring seal 49 affixed to the valve body 4. The pressurized pilot air supplied through the activation of the trigger 12 will cause the immediate downward movement of the valve 28 due t. the unbalanced forces acting on the valve. Movement results from the fact that the surface area of the piston 38 is greater than that of the valve head 30. Downward movement of ialve 28 causes the valve head to unseat and permits the pressurized air from compressor 20 within the bores 2) and 5 to enter into 14 4 6 ii 1- 94.i 9446 1 6 66 6 *6~ I *6 6; L tia .4 0 r* It' I e 44 tIC( 44 I a I I

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I I 4 1I 0I 0~ #004r **0 the bore 7 of the barrel 6 and, thence, to the nozzle 50 and outlet 8 of the device 2.

When the trigger mechanism 12 is deactivated as in Figure 2, the pressucized air within the chamber 80 is vented through the aforementioned bores 78, 76, 74, 72, 68, 66 and, thence, through bores 87 and 88 formed within the trigger shaft 26 which, in turn, communicate with a bore 89 formed within (;he valve body 4. Hence, the pressurized air within the chamber 80 above the piston 38 is instantaneously ventpd to the atmosphere when the trigger mechanism is deactivated to permit the valve head 30 to -o instantaneously move upwardly to seat against the sealing S surface 34 of the sleeve 32 to halt the air flow through the device 2.

r0 As seen in Figure 4, the trigger mechanism 12 and S trigger shaft 26 are biased outwa'cdly in the deactivated position by way of a torsion spring 27 which is attached to the trigger shaft 26. Pressurized air leakage from the bores c' 64 and 70 is minimized through a plurviity of O-rings 33, '20 and 35' which are fitted within slots formed in the periphery of the trigger shaft 26 to sealably engage against S seatig bore 37 forimed within the valve body 4. A pair of Scover plates 29 and 29' are secured to the valve body 4 by way of threaded fasteners 31. The plates 29, 29' seal the trigger shaft 26 and bore 64 of th, valve mechanism against the environment. The only access to the interior of the valve is ithrough the small diameter pilot exhaust port (not shown) which blocks the entry of dust by emitting constant stream of outflowing air which seeps between the inner face Sof the trigger shaft 26 and t e seating bore 37 of the valve 4! s I- 1 1 I 1 1 1 4 k, ,j 1 i r.

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attempt to overcome the reduced excavation rates of hand -2-

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i i ii Ii,, body 4. The valve body 4 also is fitted with a conventional air pressure gauge 21 which is mounted at the rear face of the body 4, operably attached to a bore 23 which communicates with the interior 5 of the valve body to permit the operator to monitor the line pressure when the device 2 is in use. If the pressure drops below a certain value, for example, 90 psig, the operator is alerted to take corrective action to ensure that the air compressor is operating properly.

*a II p 0r 0 It, p 00 p 48 ii 40 a A~ I r The materials of construction of the valve body 4, the internal valve components and trigger assembly, as well as the barrel 6, are preferably of noncorrosive materials such as cast bronze, stainless steel, or high impact plastic. In situations where sparks may create an explosion hazard around natural gas fumes, the barrel 6 as well as the tip 58 may be constructed of a nonferrous, nonsparking material such as bronze. The gripping portions of the device 2, handles 10 and 14, may be constructed of a hard rubber, plastic, hard wood, or like material.

Referring to Figures 5-7, the outlet end 8 of the supersonic excavator device 2 may be provided with variously shaped fitting- suitable for the particular work involved.

Figures 1 and 5 show the outlet end 8 fitted with a pick-like tip 58 to permit the operator to loosen lumps of unusually stubborn material with the sharpened tip thereof.

The barrel 6 may be straight or it may contain a curved or i angled section 60 at the outlet end 8 thereof as shown in Figure 7. The curved section 60 provides additional maneuverability in the device for difficult to reach tunneling applications and in areas beneath pipes and conduits.

i I if,. __J The converging/diverging nozzle 50 is firmly attached, as for example, by silver solder or fine threads, to the end of the barrel 6 such that the inlet end 52 of the converging section of the nozzle smoothly blends with the bore 7 of the barrel. The converging section gradually tapers to a throat section 54 which presents the minimum diameter within the nozzle. The nozzle then gradually increases in diameter to terminate at an outlet portion 56.

The nozzle 50 has a reduced outer diameter section 51 near its inlet end 52, which is snugly received within the bore 7 of the barrel 6. If the pick-like tip 58 is employed, as in 49 Figure 5, the nozzle 50 has a second reduced outer diametel 4*« section 53 formed around the outlet end 56 thereof, to '41 9" permit the attachment of the tip 58 thereto. Attachment can .4 be made by a solder or threaded joint or the like.

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t t In the science of fluid mechanics, it is known that the maximum flow rate for an ideal gas in frictionless adiabatic or isentropic flow (without heat addition or subt t t traction) through a converging nozzle is at a Mach number of 20 one, which occurs at the minimum section, at the throat of the nozzle. The Mach number is defined herein as the ratio of velocity of the air jet at che outlet 56 of the nozzle 50 to the velocity of sound at that point. It is also known that supersonic flow will occur if the nozzle area downstream from the nozzle throat increases, thus forming a converging/diverging nozzle of the type employed in the present invention. Hence, it is known in the field of fluid mechanics' that it is possible to obtain supersonic steady flow -from a gas, such as air at rest in a reservoir, by first passing it through a converging nozzle section and e then a diverging nozzle section. It is also known that the Mach number achieved by an air jet at the outlet of a converging/diverging nozzle is influenced by a number of variables, such as the boundary conditions of pressure, namely, the supply pressure and the ambient or atmospheric pressure, as well as by the ratio of the area of the outlet to the area. of the throat of the nozzle. When the supply pressure reaches a given threshhold value, a choked sonic flow condition is achieved at the throat of the nozzle, indicated as 54 in the drawings. The gas undergoes isentropic expansion from the sonic condition at the throat 54 u to the diverging section 55 of the nozzle wherein the flow S enters the supersonic regime, assuming the pressure and temperature conditions are satisfied.

SIn order to reach the sonic threshhold, it is thus necessary to provide a ratio of the area at outlet 56 to the area of the throat 54 greater than the value 1. Through f I known formulas and sets of calculations, tables have been created which list certain nozzle ratios which are needed to achieve a given Mach value at given pressure and temperature ratios for the isentropic flow of dry air through a convergc ing/diverging nozzle section. Higher Mach numbers are et. achieved as the ratio of the reservoir pressure to local pressure increases and as the ratio of exit area to throat area of the nozzle increases. Table I is illustrative of this principle, for the isentropic flow of dry air, i

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i ~r-x TABLE I Mach No. Po/P A/A* 1.895 1.00 3.675 1.176 7.830 1.685 17.075 2.629 36.644 4.213 75.926 6.739 150.796 10.612 where: Po Reservoir pressure P Ambient pressure at exit SA Area of nozzle at outlet A* Area of nozzle at throat I have discovered that a gas stream, such as air, traveling at a velocity greater than Mach 1 provides a surprisingly effective medium for excavating soil or other granular materials due to its ability to create and infiltrate small fissures and cavities therein. I hypothesize that the supersonic jet penetrates the soil structure until 20 complete stagnation occurs within these local cavities which, in effect, act as reservoirs for the momentary storage of high pressure, decelerated air. The stagnated air must then expand and, in so doing, causes the soil to fracture in tension, its weakest directional attribute.

These local reservoir sites of high pressure provide the energy source for the final fracture of the material in tension end the nearly instantaneous initiation of a pneumatic explosion due to the rapid expansive release of high pressure air to the atmopshere. It is thus understood that the present invention provides a method and apparatus for 11 11

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i- transferring the pressure energy produced by the air compressor 20 to a local excavation site where its destructive power is utilized and further provides, through its large momentum flux, the aforementioned cavities for the instantaneous storage and release of such pressure energy.

In order to illustrate the above principle, a nozzle 50 suitable for use in soil excavation in accordance with the present invention is shown in greater detail in Figures 9 and 10. Nozzle 50 is circular in cross-section and includes an inlet 52 having a bore diameter equal to that of the barrel bore 7 which may, in this example, be about 0.875 inch. The nozzle profile then converges to the throat section 54, with a diameter of, for example, 0.250 inch.

The nozzle bore then gradually expands in the diverging section 55. By way of further example, dimension may be 0.269 inch, where is equal to 0.172 inch. The illustrative nozzle outlet 56 diameter ,is represented by dimension ctl" which is 0.283 inch. Dimension the distance between C rt r the throat 54 and the outlet 56 is, in this example, 0.425 tc ,20 inch. Utilizing a compressor 20 having a flow rate capacity r cc of 0.15 Ib./sec. (120 CFM free air) at a reservoir pressure to ambient pressure ratio (Po/P) of about 4.5, at 70 0

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It it ambient temperature, calculations demonstrate that the above-dimensioned nozzle 50 is capable of producing a supersonic jet of air at a velocity of about Mach 1.64. Once again the calculations are based on the assumption that the fow is isentropic, the flow takes place without friction and without heat addition or subtraction. My tests indicate that a circular nozzle is advantageous over other shapes with respect to the frictional effects in relation to "r i77

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.a9 I t I stand-off distance versus flow decay. I have also determined that there appears to be a threshhold pressure below which many soils are not amenable to efficient excavation. This threshhold pressure appears to be about 80 psig. Dramatic increases in excavation capability result as the reservoir pressure (Po) is increased, with a 25% improvement having been observed in going from 80 psig to 100 psig.

The profile of the supersonic jet can be changed from the above-described circular shape to a square or rectangular shape if desired. Figures 11 and 12 depict a nozzle S 94 which is capable of producing a rectangularly shaped, supersonic air stream which finds application in cleaning flat surfaces, as for example, conveyor belts which transport bulk materials. Nozzle 94 includes a body 95 with e.t S. tapered side plates 102 and 102' with a tapered divider plate 104 disposed therebetween. The plates 102, 102' and t r 104 are held in place by cover plates 101 and 103 which are secured by fasteners 106. As seen in Figure 11, the tapered D t C r plates 102 and 104 form a converging nozzle section 98, a 12b throat at 96 and a diverging section which terminates at outlet 100. An identical nozzle shape is formed adjacent thereto by tapered plates 102' and 104 with a rectangularly shaped jet of air emitted from outlet 100'. In operation, the side by side jets exiting from outlets 100 and 100' would merge together a short distance from the nozzle to provide a single, thin knife-like profile ideally suited for cleaning operations where soil or other caked or lodged matvrials must be removed from flat surfaces. The same ratios of outlet area to throat area apply to the rectan- #-Str L1 gular nozzle 94 as previously discussed in relation to the circular nozzle In still another embodiment of the invention, as shown in Figure 6, a substance which solidifies upon cooling, such as liquid water or gaseous carbon dioxide, may be introduced into the bore 7, ahead of the nozzle through a feed passage 59, shown in phantom lines in the drawing. A water mist or stream of gaseous carbon dioxide from passage 59 is entrained within the air stream and is nearly instantaneously solidified as it passes through the

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converging/diverging nozzle 50' due to the great temperature decrease which naturally occurs as the air stream is S* accelerated through the nozzle. Ice particles or solid CO2 particles are then emitted with the high velocity jet of air to provide an additional abrasive aid in excavating and cleaning applications. As used herein, the terms S* "excavating" and "cleaning" may be used interchangeably with respect to the intended use environment for the invention.

It can be appreciated that carbon dioxide is a unique additive since it presents no residue or disposal problems Safter it desolidifies.

In order to furi.er demonstrate the effectiveness

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r H of the invention, a test was run in the field comparing the manual device 2 of the present invention with conventional hand work using a pick and shovel. For purposes of comparison, three common types of excavation holes were made, namely, a face notch, a vertical hole, and a horizontal tunnel. The results are reported in the percent improvement in the volume of material excavated in the same time period sft lA*4. t nci 'A 0 for the device 2 of the present invention over conventional hand work. These results are set forth in Table II: TABLE II Type of Improvement Excavation Air Jet v. Hand Work Face Notch 260% Vertical Hole 240% Tunneling 327% The test reported in Table II was run at a calculated air jet velocity of Mach 2 with an air compressor S° running at about 100 psig. Hence, from the above results, the advantages of the present invention over commonly employed hand work methods are readily apparent.

4* 4 It is further apparent to those skilled in the art that the hand-operated device 2 can be modified so as to be fitted on a piece of mechanized digging equipment such as a backhoe or the like. It is also understood that apparatus according to the present invention can be incorporated into automated robotic digging equipment, for which the invention 20 is particularly suited. In such applications, it would, of course, be desirable or necessary to modify the valve mechanism from hand-actuated to a pneumatic, hydraulic or like actuation means.

While specific embodiments of the invention have been described in detail, it will be appreciated by those 'skilt~d in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative A only and not limiting as to the scope of the invention which tT i

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is to be given the full breadth of the appended claims and any and all equivalents thereof.

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Claims

1. A method of excavating a soil mass or like granular material mass, comprising: providing a reservoir of a gas at a pressure of at least about 1.9 times greater than an ambient pressure adjacent the soil or material mass; transmitting the gas through a duct means from the reservoir to a nozzle means of a converging/diverging type and accelerating the gas therethrough to produce a gas stream which is substantially free of entrained solids and which exits said outlet at a calculated velocity greater than Mach 1; and directing said gas stream to said soil or material 15 mass, whereby said mass is infiltrated and fractured by said gas stream. a. f 4 4*1* U U i UL Ii 1'4 i i) i 'I 411 25

2. The method of claim 1 wherein the gas in the reservoir is provided at a pressure of at least about 3.675 times greater than the ambient pressure.

3. The method of claim 2 wherein said nozzle includes throat and outlet sections defining cross-sectional areas across said nozzle and wherein the outlet section has a cross-sectional area of at least about 1.176 times greater than said throat section, whereby said gas stream exiting said nozzle has a calculated velocity greater than about Mach

4. The method of claim 1 wherein the gas in the reservoir is provided at a pressuze of at least about 7.83 times greater than the ambient pressure. 4 4 I *44*1 4 Ii II 44 4 I 4 a 4 I 0361s/KLH 25 v a~w 9) i i I C t 'b A 4- S"_ ir rr. II Ill~BLI IA Zt IA *r 4 *r 4 q, The method of claim 4 wherein said nozzle includes throat and outlet sections defining cross-sectional areas across said nozzle and wherein the outlet section has a cross-sectional area of at least about 1.685 times greater than said throat section, whereby said gas stream exiting said nozzle has a calculated velocity greater than about Mach

6. The method of claim 1 wherein the gas in the reservoir is provided at a pressure of at least about 36.644 times greater than the ambient pressure.

7. The method of claim 6 wherein said nozzle includes throat and outlet sections defining cross-sectional areas across said nozzle and wherein the outlet section has a cross-sectional area of at least about 4.213 times greater than said throat section, whereby said gas stream exiting said nozzle has a calculated velocity greater than about Mach 8, The method of claim I wherein the gas in the reservoir is provided at a pressure of at least about

150.796 times greater than the ambient pressure. 9, The method of claim 8 wherein said nozzle includes throat and outlet sections defining cross-sectional areas across said nozzle and wherein the outlet secti64 has a cross-sectional area of at least about 10.612 greater than said throat section, whereby said gas stream exiting srid noz6le has a calculated velocity greater than about Mach w _j L I 's ii 11. The method of claim 1 including the steps of selecting a material which solidifies upon cooling, selected from the group consisting of liquids and gases, introducing said material into the duct means prior to the nozzle means, whereby said material is cooled and solidifies as it passes through the nozzle means and exits said nozzle means as a dispersion of solid particles entrained in the supersonic gas stream. 12. The method of claim 11 wherein the gas is air and the introduced mat-rial is water. 15 *0 a f k C ir' i 13. The method of claim 11 wherein the gas is air, the introduced materia, is carbon dioxide and the ambient pressure is atmospheric. 0* C 0 *000 0000 04i 0* 00 0t 0 OoOOr~o 0 go C 0 o 0* 14. A method of excavating a soil mass or like granular 20 material mass, comprising: providing a reservoir of gas at a pressure of between about 2 to 37 times greater than an ambient pressure adjacent the soil or material mass; transmitting the gas through a duct means from the reservoir to a nozzle means of a conve';ing/diverging typ including a throat section and an outlet section and accelerating the gas, substantially free of entrained solids, through the nozzle means to produce a gas stream exiting said nozzle having a calculated velocity between 30 about Nach 1 and about Mach 3; directing said gaS stream to said soil or material mass; infiltratina said soil or material mass with said gas stream to create fissures and cavities thererin; stygnatin 9 said gas stream within said fissures and cavities; and expanding said stagnated gas to ambient pressure whereby pozrtins of said mass are fractured by the forces generated by said expansion. i -I r i O 1- ls/KLH 27 '4I QJ i: 0 i rr i; I i r-cl Ii;l-i-ii~i~ii-T- ii ii_ li- The method of claim 14 wherein the cross-sectional area of the outlet section of the nozzle means is between about 1 and about 10.6 times greater than the cross-sectional area of the throat section. 16. The method of claim 15 wherein the gas is air and the ambient pressure is atmospheric. 17. The method of claim 14 including the step of introducing a material selected from the group consisting of liquid water and gaseous carbon dioxide, whereby said material is cooled and solified as it passes through the nozzle means and exits said nozzle means as solid particles entrained in the gas stream. .9 0 5 S* a* o 20 25 9• 0 9 30 i 9 ft9 18. An apparatus suitable for excavating a soil mass or like material mass comprising: duct means adapted to communicate with a reservoir containing a pressurised gas at a pressure of at least about 1.9 times greater than an ambient pressure adjacent the soil or material mass; nozz:le means of the converging/diverging type positioned within said duct means and having a throat section and an outlet section, each of said sections defining a respective cross-sectional area, and wherein the ratio of said outlet section area to said throat section area is greater than 1.0, whereby said apparatus is adapted to produce a stream of gas, substantially free of entrained solids, at a calculated velocity >f greater than Mach 1 when said pressurised gas from the reservoir passes through said nozzle means. 19. The apparatus for claim 18 wherein the ratio of the nozzle outlet area to the nozzle throat area is greater than about 1.685 and said reservoir is adapted to contain said gas at a pressure of a least about 7.83 times greater than I. )~03 'lu/KLH r Y'TQ~ 28 4 i i l.ia~ir~pc,, Ii an ambient pressure adjacent the soil or like material mass, whereby said apparatus is adapted to produce a stream of gas at a calculated velocity greater than about Mach 2. 20. The apparatus of claim 18 including passage means for introducing a solidifiable material into the duct means prior to said nozzle means, whereby said material is adapted to solidify and pass through said nozzle, entrained within Raid gas stream. 21. The apparatus of claim 18 including valve means associated with said duct means, adapted to regulate the flow of gas from the reservoir to the nozzle means. 9. 20 3 *9 25 *99e9* 9 9 30 i* 22. The apparatus of claim 21 wherein the valve means comprises a valve body having a bore therethrough, positioned in communication with said duct means and with said reservoir when said apparatus is operably connected therewith, said valve means further including a valve member having a head portion and a piston portion interconnected by a stem, said head portion adapted to seal-off said pressurised gas in said valve bore when said valve means is in a deactivated position, said valve means further including pilot bore means adapted to communicate between the pressurised gas and the piston portion of the valve member when said valve means is in an activated position, whereby said pressurised gas is adapted to pass through said pilot bore means to act on said piston portion to move said valve member and cause said head portion to unseat and permit the flow of pressurised gas through the valve body bore to the duct means. 23. The apparatus of claim 22 wherein the valve means 0includes trigger means including a rotatable cylindrical portion having a pilot port therethrough which is adapted to communicate with said pilot bore means when said trigger means is in an activated position to permit pressurised air 29 r' r, S to flow therethrough to unseat said valve head and adapted to close-off said pilot bore means when said trigger means is in a deactivated position. 24. The apparatus of claim 23 wherein the cylindrical portion of the trigger means also has a vent port formed therein adapted to permit the escape of pressurised air from the pilot bore means to the atmosphere when the trigger means is moved to the deactivated position. The apparatus of claim 18 wherein the duct means and nozzle means are constructed of a nonsparking material. 15 0*0 a 0 09 0 CIC I tt LI I I I C 26. An apparatus suitable to excavating a soil mass and substantially as hereinbefore described with reference to the accompanying drawings. DATED this 15th day of November, 1989 BRIGGS TECHNOLOGY INC,. By their Patent Attorneys GRIFFITH HACK CO. 30 E1 i 'Cj ,I '4 I '1