Ammunition and explosives – Blasting – Borehole loading
Reexamination Certificate
2000-02-24
2001-12-18
Nelson, Peter A. (Department: 3641)
Ammunition and explosives
Blasting
Borehole loading
C102S312000, C102S324000, C102S333000
Reexamination Certificate
active
06330860
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to blasting with explosives, and more particularly to a rock blasting method for reducing ground vibration and noise of the blast in which an air tube is charged with explosives in a borehole.
BACKGROUND OF THE INVENTION
Heretofore, rock blasting for reducing ground vibration has been undertaken by employing various methods known as deck charge, air-decking, pre-splitting and so forth. In the deck charge, explosive cartridges and stemmings are alternately charged along the borehole. Each explosive charge in the borehole is provided with a detonator and the explosives are detonated by delay blasting to reduce ground vibration. This method is costly since it requires a large number of detonators in order to be fitted with the charged explosives. Further, this method is less effective in reducing ground vibration since the same amount of explosives must be used in each charge layer.
In the air-decking method, explosive and detonator are charged at the lower part of the borehole to leave space above the explosive charge, and a plug is used to retain the stemming material at the borehole collar. The space between the top of the explosive charge and the bottom of the plug is the air deck used in blasting. The air deck space is rapidly occupied by the detonation products. The detonation products move repeatedly in the chamber, impacting the borehole wall until an equilibrium state in pressure is reached. A significant amount of potential energy retained in the detonation products is released and imparted to the rock mass, which forms a secondary loading wave in addition to the primary loading wave generated by the detonation of the explosive charge. When the air deck is longer than a predetermined length, the volume of the fragmented rock mass is increased. In addition, the average fragment size gets smaller and the size distribution becomes more uniform. Numerical modeling of the effects of air decking is described in the article of Liqing Liu and P. D. Katsabanis in journal
Rock Fragmentation
by blasting, Mohanty (ed.) 1996 Balkema, Rotterdam, pp.319-330.
In addition, there is indication that the air-decking may reduce ground vibration from ANFO shots to a certain degree. In a field experiment from an article “Ground Vibration from Single-hole Cast Blasts” of Xiaoning Yang, Brian W. Stump and John D. Smith,
The journal of Explosives Engineering
, March/April 1999, pp. 36-41, slightly reduced ground vibration level (15%) from air-decked shot loaded with ANFO was reported.
However, when the air-decking is adopted in the open large scale blast site, positioning the plug in every borehole at a uniform depth is difficult since the plug is plastic and apt to be moving in the borehole. This results in different length of the air deck in each borehole, thereby degrading the above-mentioned air deck effect. Further, it is difficult to secure constant quantity of air in every air deck since the borehole diameter becomes narrow as drilling bits wear out by use. This also affects the air deck effect.
Another method of producing substantially reduced vibration involves arranging explosive cartridges in a borehole such that they are connected serially by a detonating fuse at spaced intervals to form air space between charged explosives. This method, commonly referred to as pre-splitting, requires use of a large amount of explosive which, upon detonation, produce considerable noise of the blast.
Therefore, the above-mentioned prior art blasting methods have problems in that they are still ineffective either in obtaining quantitative air decking or reducing ground vibration and noise of the blast.
SUMMARY OF THE INVENTION
The present invention provides an improved rock blasting method which method comprises drilling a series of aligned boreholes in a rock body according to a desired drilling pattern; charging the boreholes with explosives and an air tube in a predetermined pattern so as to provide a quantitative air decking in every charged borehole; and detonating the charged boreholes with stemmings on the top of the explosive or air tube.
The air tube is a cylindrical flexible tube having a predetermined width and length to be fitted with the borehole. An air injection port is provided at one end portion of the air tube. The air tube is made in the form of sheets and the diameter thereof, upon inflated, becomes the same as or smaller than that of the boreholes. The air tube and air injection port are made from synthetic materials such as polyethylene, polypropylene, polyester and polyamide.
Preferably, the air tube is inflated by using an air injector of air compressors provided in work sites. In the arrangement, the explosives and air tube are alternately charged along the borehole. Further, the air tube is charged first at the bottom of the borehole and subsequently a detonator is charged above the air tube. A plug may be installed above the top of the air tube charged in the borehole. Furthermore, the explosives and air tube are charged in adjacent two boreholes such that they are located in cross relation between each other so that one air tube may face lateral explosives in adjacent boreholes.
The air tube installed above the top of explosives reduces the length of stemmings charged above the air tube as much as the extent of the air tube. The explosives charged above the air tube is detonated by sympathetic detonation.
REFERENCES:
patent: 2703528 (1955-03-01), Lee et al.
patent: 2858764 (1958-11-01), Hesson et al.
patent: 4419935 (1983-12-01), Shibukawa
patent: 4438699 (1984-03-01), Nitzberg
patent: 4813358 (1989-03-01), Roberts
patent: 4919203 (1990-04-01), Fitzgibbon, Jr.
patent: 5000261 (1991-03-01), Fitzgibbon, Jr.
patent: 5273110 (1993-12-01), Fitzgibbon, Jr.
patent: 5841060 (1998-11-01), Skaggs
“Numberical Modelling of the Effects of Air Decking/Decoupling in Production and Controlled Blasting” by Liu et al.,Rock Fragmentation by Blasting,Mohanty (Ed.) ISBN 90 5410 824X, pp. 319-330.
“Ground Vibration from Single-Hole Cast Blasts” by Yang et al.,The Journal of Explosives Engineering,Mar./Apr. 1999, pp. 37-41.
Advertisement for Vari-Stem of St. Louis, Missouri for “Greater Rock Fragmentation, Less Cost”,The Journal of Explosives Engineering,Jul./Aug. 1999, p. 22.
Nelson Peter A.
Sheridan & Ross P.C.
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