Ammunition and explosives – Blasting – Terrain clearance
Reexamination Certificate
1999-04-09
2001-11-27
Nelson, Peter A. (Department: 3641)
Ammunition and explosives
Blasting
Terrain clearance
C102S303000, C102S312000, C102S313000, C102S333000
Reexamination Certificate
active
06321655
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 any 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 flyrock control devices for use with small-charge blasting of a material that is near a flyrock restricted area. The method broadly includes the steps of:
(a) determining a flyrock distance requirement for the material to be broken;
(b) determining an uncontrolled flyrock distance produced by the small-charge blast in the absence of a flyrock control device;
(c) comparing the flyrock distance requirement with the uncontrolled (or unsuppressed) flyrock distance to determine whether flyrock control is needed;
(d) if the uncontrolled flyrock distance of step (b) is more than the flyrock distance requirement of step (a), selecting one or more flyrock control devices from a menu of flyrock control devices to produce a desired degree of flyrock control. “Uncontrolled flyrock distance” refers to the probable flight distance of flyrock from the hole. 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 demanding requirements in flyrock 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 menu of flyrock control devices preferably includes at least:
(i) a collar flyrock control device located at or near the opening of the hole and engaged with a sealing member positioned in the hole, the collar flyrock control device having a surface for suppressing or deflecting flyrock,
(ii) a mat positioned on the surface of the material to be broken around the hole opening for deflecting or suppressing flyrock,
(iii) an enclosure substantially surrounding the hole opening for deflecting flyrock, and
(iv) a barrier located between the hole opening and the sensitive area for deflecting flyrock.
The determining step (a) can include a number of substeps to determine the flyrock distance requirement. By way of example, the substeps can include:
determining at least one of (a) a job flyrock distance requirement (i.e., the “job flyrock distance requirement” refers to flyrock distance restrictions that are unique to the specific job, such as imposed by regulatory authorities or by the surroundings of the job, e.g., nearby structures or thoroughfares), (b) a personnel flyrock distance requirement (i.e., the “personnel flyrock distance requirement” refers to flyrock distance restrictions that are generally applied by the operator to protect personnel and are independent of the specific job), and (c) a machine flyrock distance requirement (i.e., the “machine flyrock distance requirement” refers to flyrock distance restrictions that are generally applied by the operator to protect equipment and are independent of the specific job) and
comparing at least two of the job flyrock distance requirement, the personnel flyrock distance requirement, and the machine flyrock distance requirement with the more restrictive being the flyrock distance requirement.
The uncontrolled flyrock distance is typically a function of (a) the degree of pre-existing fracturing of the rock and the type of rock and (b) the energy released by the blast. The function is often construed from the measured results of many shots of the small charge blast being used. In the case of small charge blasting with explosives or propellants, the energy released may be replaced by a mass of the explosive or propellant used.
To control pressure waves such as airblast, the method can include additional steps. Specifically, the steps include:
determining a pres
Branson Jeffrey W.
Gavrilovic Mihailo
Georgiou Peter N.
Mudge Kevin
Tota Edward W.
Nelson Peter A.
Rocktek Limited
Sheridan Ross PCC.
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