Ammunition and explosives – Blasting – Mat or deflector
Reexamination Certificate
1999-04-09
2001-12-25
Nelson, Peter A. (Department: 3641)
Ammunition and explosives
Blasting
Mat or deflector
C102S302000, C102S312000, C102S313000, C102S333000, C102S301000
Reexamination Certificate
active
06332401
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed generally to methods and devices for small charge blasting of rock and other materials and specifically to methods and devices for controlling pressure wave emissions and/or flyrock generated by the small-charge blasting process.
BACKGROUND OF THE INVENTION
In civil excavation projects in urban environments, many restrictions are imposed on operators that substantially increase the operator's capital and operating costs. The operator must generally comply with strict requirements regarding not only the transportation, storage and use of explosives but also airblast, noise, and airborne flyrock particles. “Airblast” refers to pressure waves in air emanating from a rapid release of energy (e.g., a blast). Airblast noise is the audible part of the airblast energy spectrum, having frequencies in the range from 20 to 20,000 Hz. Airblast concussion is the inaudible part of the airblast energy spectrum, having a frequency content below 20 Hz. “Noise” refers to pressure waves in air generated by equipment other than the small charge blasting equipment, such as the drill during formation of one or more holes for small charge blasting and/or the impact breaker during removal of fractured material. “Flyrock” refers to rock particles thrown into the air by the rapid release of energy (e.g., blast). Flyrock may be in the form of a shower of small pieces at relatively high velocities (20 to 50 m/s typical), which typically originate from the collar region of the drill hole. Flyrock may also be in the form of larger pieces of rock at relatively low velocity (1 to 10 m/s typical), which typically originate in the mass of rock excavated from the crater formed by the blasting event.
Existing drill and blast methods may be inapplicable in many applications as a result of these restrictions, even though the blasting methods are the most cost effective method for the specific application. For example, small charge blasting which commonly has a lower seismic and airblast signature, cause less flyrock, and have lower operating costs compared to conventional drill and blast techniques, can nonetheless generate airblast, equipment noise, and/or flyrock levels that exceed the maximum permissible levels in many applications. “Small charge blasting” refers to any excavation method where relatively small amounts of an energetic substance (typically a few kilograms or less) are consumed for each hole in a rock fracturing sequence.
SUMMARY OF THE INVENTION
Objectives of the present invention include providing a drilling and blasting methodology for excavating rock, particularly hard rock, in airblast, noise, and/or flyrock restricted areas, such as urban settings, and providing a methodology and apparatus(es) for use with small-charge blasting techniques for controlling and/or suppressing airblast in airblast restricted areas, controlling and/or suppressing equipment noise in noise restricted areas, and/or for controlling and/or suppressing flyrock in flyrock restricted areas.
These and other objectives are addressed by the methodology and apparatuses of the present invention. In a first embodiment, a method is provided for selecting one or more pressure wave suppression devices for use with small-charge blasting of a material that is near a pressure wave (i.e., an airblast and/or noise) restricted area. The method broadly includes the steps of:
(a) determining one or more pressure wave level requirement(s) at corresponding selected distance(s) from the material to be broken;
(b) determining a corresponding unsuppressed pressure wave level(s) at each selected distance produced by the excavation equipment in the absence of a pressure wave suppression device;
(c) comparing the pressure wave level requirement(s) with the corresponding unsuppressed pressure wave level(s) to determine a desired amount of pressure wave suppression;
(d) comparing the desired amount(s) of pressure wave suppression at one or more distances from the material to be broken with an amount of pressure wave suppression for each of a plurality of pressure wave suppression devices; and
(e) thereafter selecting one or more pressure wave suppression devices based on the comparing step (d) to produce the desired amount(s) of pressure wave suppression. As used herein, a “pressure wave level requirement” refers to the maximum permissible pressure wave emission levels and is often expressed as a maximum allowable pressure wave emission level at a specified distance from the blasting site (e.g., the location of the energetic substance used in the small charge blasting process). The method provides an operator with versatility in meeting the unique requirements of each job and a relatively low cost and simple excavation technique that complies with the often demanding requirements in pressure wave restricted areas.
The process is particularly applicable to small charge blasting techniques using controlled fracturing to break the material. Generally, controlled fracturing is performed by drilling a hole in the material to be broken, inserting a sealing member, which can be a stemming bar, a gas injector barrel, or other pressurizing device, into the drill hole, and releasing a pressurized working fluid rapidly into a portion of the drill hole, usually the bottom portion. “Sealing” refers to partial or total blockage of the hole to inhibit the escape of the fluid from the drill hole. “Sealing member” refers to any downhole device capable of sealing a pressurized working fluid in the bottom of a hole, including without limitation loosely consolidated or unconsolidated particles such as sand, gravel, rock fragments, and the like, and a solid material such as grout, a stemming bar, a gas injector barrel, and the like. The pressurized fluid is typically generated by combustion of a propellant or explosive source, by an electrical discharge into a conductive fluid, or by compression of the working fluid. The fractured material is thereafter removed from the face by an impact breaker and mucking equipment. Because of the relatively low weight of the energetic substance used to generate the working fluid and the relatively low pressure wave and flyrock emissions, equipment and personnel commonly remain in the area of the hole during the small charge blast.
The plurality of pressure wave suppression devices and their performance capabilities can be listed in the form of a menu from which any number of appropriate devices can be selected. The plurality of pressure wave suppression devices preferably includes at least one of, more preferably at least two of, and even more preferably at least three of:
(i) a downhole pressure wave suppression device located in a hole in the material for directing flow of the working fluid through one or more nonlinear pathways and/or for contacting at least a portion of the working fluid with a thermal energy absorbing material having a plurality of heat transfer surfaces, and/or for attenuating the noise generated by downhole equipment (e.g., a drill),
(ii) a collar pressure wave suppression device located at or near the opening of the drill hole in communication with the drill hole for directing flow of the working fluid through one or more nonlinear pathways, for contacting at least a portion of the working fluid with a thermal energy absorbing material having a plurality of heat transfer surfaces, and/or for attenuating the noise generated by the downhole equipment,
(iii) a mat positioned on the surface of the material to be broken around the hole opening for directing flow of the working fluid through one or more nonlinear pathways in the mat and/or for absorbing thermal energy from the working fluid by contacting the working fluid with a plurality of heat transfer surfaces,
(iv) an enclosure substantially surrounding the hole opening for containing the equipment noise and/or working fluid (i.e., the pressure waves) and impeding the discharge of the noise and/or working fluid into the ambient atmosphere,
(v) a barrier located between the hole opening and the pr
Branson Jeffrey W.
Gavrilovic Mihailo
Georgiou Peter N.
Tota Edward W.
Watson John D.
Nelson Peter A.
Rocktek Limited
Sheridan & Ross P.C.
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