solid column explosive charge method for blasting rock

Abstract

A solid column explosive charge method for blasting rock includes a hollow gas-filled core component arranged collinearly in concentrically spaced relation within a vertical borehole, the core component being seated upon a first layer of particulate explosive material, and a first annular portion of the particulate explosive material being arranged concentrically about the core component. The first layer and the first annular portion are in engagement to define a continuous explosive column. A plurality of core components together with associated layers and annular portions of the explosive charge may be arranged in a continuous vertical column, the total volume of the core components being from 10 percent to 25 percent of the volume of the explosive column. A top layer of inert fill material is arranged above the core component to close the upper end of the bore opening.

Description

FIELD OF THE INVENTION

A method for continuous column blasting rock for coal mining purposes and the like includes at least one hollow gas-filled core component arranged vertically collinearly within a vertical bore hole and seated on a first layer of a particulate explosive charge. The core component has a transverse cross-sectional dimension that is less than the diameter of the bore hole, with a first annular portion of the particulate explosive charge arranged concentrically about the core component, said first layer and said first annular portion being in contact to define a continuous explosive column. The volume of the core component is generally 10 percent to 25 percent of that of the explosive column.

BACKGROUND OF THE INVENTION

Brief Description of the Prior Art

The simplest form of blast hole loading is a single column of blasting agent, initiated from the bottom or middle with a cast booster. Single column loading is preferable so long as there are no constraints for powder factor (blasting agent per foot) or constraints on vibration concerns are at issue, it is often necessary to load blast holes using the “decking method” or typical air gap method. Under the “decking method,” layers of air or inert material are positioned throughout the column requiring a separate cast booster for each blasting agent layer. While accomplishing a reduction in powder factor, the blast is less efficient since each individual layer is working on its own versus a single, continuous column of blasting agent. Decking also increases the cost as additional detonators and cast boosters are required.

It is well known in the patented prior art to provide air gaps within vertical explosive charges deposited in a bore hole.

In the Kang patent No. 6,330,860, a rock blasting method is disclosed wherein a series of aligned boreholes are charged with explosives and air tubes arranged in a predetermined pattern. The air tube is formed as a cylindrical flexible tube that is fitted within the bore hole so as to provide a “quantitative air decking” in every charged borehole. Sympathetic detonation is used to continue the explosive reaction throughout the borehole due to the separation in the explosive. The diameter of the air tube is the same as or smaller than that of the boreholes so that the inflated air tube can be easily inserted into the bore holes.

In the Fitzgibbon patent Nos. 4,913,233, 4,919,203, and 5,273,110, inflatable devices or air bags are tightly mounted in engagement with the walls of the boreholes, thereby to support the layers of the explosive charge.

In the Lingens, et al., patent No. 3,782,283, vertically spaced cavities are provided in an explosive device for causing, upon detonation, the defined disintegration of the casing of the explosive device. In the explosive cartridge of the Lawrence patent No. 2,622,528, a plurality of longitudinally spaced cavities are provided that define a column made up of alternating solid sections and annular sections.

The present invention was developed to improve the blasting results produced by a given quantity of explosive charge in a safe, cost-effective manner.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide an improved method for blasting rock for coal mining and the like, wherein a core component having a longitudinal axis is arranged collinearly within a vertical bore hole, the core component being seated upon a first particulate explosive layer and having a transverse cross-sectional dimension that is less than the bore hole diameter, thereby to permit an annular portion of the particulate explosive to be deposited concentrically about the core component, the annular explosive portion being in engagement with the first explosive layer to define a continuous explosive column, the volume of the core component being about 10 percent to 25 percent of that of the explosive column.

According to another object of the invention, a plurality of the core components may be collinearly arranged in longitudinally spaced relation in the vertical bore hole, each core component being concentrically surrounded by an annular explosive portion seated on a layer in such a manner as to form a continuous explosive column in the bore hole.

According to a preferred embodiment of the invention, the hollow core components are cylindrical and are filled with compressed air that is introduced during the manufacture of the hollow core component. Preferably, the container is formed from tubular stock of a heat sealable synthetic plastic material by means of pinching the tubular stock by heat seal means at locations spaced longitudinally of the tubular stock, thereby to define the hollow core components.

A further object of the invention is to provide a core component that comprises an air-filled paperboard tube having end caps, the diameter of said paperboard tube being less than the diameter of the bore hole and the volume of the tube being about 10 percent to 25 percent of the explosive column. In another embodiment, the core component is formed by folding a cardboard blank having end closure flaps, thereby to define an air-filled device that assists in the detonation of the explosive charge.

According to a further object of the invention, the solid continuous explosive column is supported in the bore hole by an inert filler base, and a top stem of inert filler material closes the top of the bore hole over the string of vertically spaced core components.

Typically, the procedure for drilling and blasting of geologic formations is designed to meet or match the most difficult rock strata in the formation. Functionally then, that rock type determines the borehole diameter and hole spacing necessary to ensure adequate breakage for excavation or processing. In many mining operations, the strata to be blasted is made up of multiple layers of various types of rock with a wide range of hardness and/or density. This often times means that boreholes are positioned such that if the hardest seam is adequately broken then other softer formations are over shot.

Though explosives density can be changed in the hole, the single greatest determining factor in explosives energy is pounds of blasting agent per foot of column as determined by the available hole diameter. The use of core component of the present invention allows the blaster to vary the size of the explosive column by inserting smaller diameter pre-inflated core components at specific or random locations.

The benefit of the method of the present invention is to allow maximum energy in the hardest formation and then adjusting the explosive load per foot to reduce the energy in softer rock layers. This explosive conservation system can benefit the blasting operation in numerous ways. The key to the concept is the insertion of pre-inflated or pre-formed devices of various materials including but not limited to rigid or flexible poly tubing, pipe or cardboard as well as heat sealed shaped 1.2 to 10.0 mil pvc, polypropylene or other flexible sheet or tube materials of significantly smaller diameter than the borehole.

When inserted in the explosive column, the smaller diameter core component allows the bulk explosives to build up around the void created by its shape, thus never interrupting the solid column propagation of the charge. Since the column of bulk explosive is not interrupted, the continuous propagation is not dependent on reintroduction of priming, therefore the only limiting factor of the number of core components introduced into the bore hole is the desired pounds of blasting agent per foot of column as determined by the available hole diameter.

The core component does not create a plug or gap in the borehole insofar as the explosive column is continuous.

In accordance with the present invention, the blasting products are selected and applied based on variables including but not limited to rock type, depth of borehole, vibration control, proximity of dwellings or utilities and cost. Charged blast holes typically are so designed to meet the needs of the hardest rock or most stringent vibration criteria. Variability from this objective is then limited by the borehole diameter and explosive type and density. By placing a preformed geometric shape into the bulk explosive column representing a profile from 10 percent to 25 percent of the available volume, benefits may be achieved in economy, environmental effects and blast results. The preformed geometric shape of the core component charged with atmosphere air may be cylindrical, rectangular, triangular or other shapes having three dimensions. The preformed geometric shape may be either rigid in construction or flexible and inflated with atmosphere air, inert gases or blast enhancing gases such as oxygen, acetylene, or other fuels. The core component may be of various lengths either more or less than the length of the explosive column. Furthermore, the core component may be divided into separate units and distributed either evenly or at random locations throughout the borehole.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent from a study of the following specification when viewed in the light of the accompanying drawings, in which:

FIG. 1 is a sectional view illustrating a borehole that is to be blasted by the method of the present invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 1;

FIG. 4 is a perspective view of another embodiment of the core component used by the method of the present invention;

FIG. 5 is a front perspective view of a further embodiment of the core component; and

FIG. 6 is a sectional view illustrating the mounting of the core component of FIG. 5 in a bore hole.

DETAILED DESCRIPTION

Referring first more particularly to FIGS. 1 and 2, a bore hole 2 is drilled downwardly into a layer of rock 4 by a conventional drill bit which normally range in size from 6.75″ to 12.25″. The depth of the bore hole may be on the order of 10 feet to 200 feet, depending on the nature of the blasting of the rock that is to be performed. Deposited into the bottom of the bore hole are a bottom layer 6 of inert material, such as dirt, and a first layer 8a of a conventional particulate explosive charge material, such as ANFO, Blasting Emulsion, or other bulk blasting agents, or nitromannite, for example. A conventional blasting cap, booster, or other explosion igniting device 10 is embedded within the first explosive layer 8a, as is known in the art. In accordance with the present invention, a hollow gas-filled core component 12a is inserted within the bore hole 2 and is seated upon the first layer 8a. The longitudinal axis of the core component is arranged collinearly with the axis of the bore hole 2. In the illustrated embodiment, the core component is cylindrical and has a diameter d₁ that is less than the diameter D₁ of the bore hole, thereby to define an annular space arranged concentrically between the outer wall of the core component 12a and the wall surface of the bore hole 2. A quantity of the particulate explosive charge is then deposited in the bore hole concentrically about the first core component 12a, thereby to define a first annular portion 8b. Additional particulate explosive material is then deposited within the bore hole to form a second explosive layer 8c that is in direct contact with the upper surface of the annular explosive portion 8b. A second core component 12b is then introduced into the bore hole and is seated upon the upper end of the second layer 8c. Additional particulate explosive material is then deposited concentrically about the second core component 12b to define a second annular explosive portion 8d that is in direct contact with the second layer 8c. A further explosive layer 8e is deposited in the bore hole in contact with the upper surfaces of the annular portion 8d and the second core component 8b. A third core component 12c is then seated upon the upper surface of this third layer 8e, whereupon a third annular portion 8f is deposited in the bore hole in the annular space surrounding the third component 12c. Finally, a final layer of particulate material 8g is deposited above the annular explosive portion 8f and the upper end of the third core component 12c, whereupon the upper end of the bore hole is closed by a layer of inner material such dirt to define the top stem closure 14.

In accordance with a characterizing feature of the invention, the outer diameter d₁ of the core component is less than the diameter D₁ of the bore hole, and the volume of the core component is about 10 percent to 25 percent of the column defined by the explosive layers 8a and 8b. It is important to note that the particulate explosive material is deposited in the bore hole 2 in such a manner as to define a continuous solid explosive column extending from the bottom inner layer 6 and the top stem 14.

Referring to FIG. 3, the core components 12 are preferably cylindrical in construction and are formed from a continuous tube of synthetic plastic material, such as polyvinyl chloride, polypropylene, or the like that is heat sealed at its ends to define end closure portions 12d. During the sealing process, compressed air is introduced into the core component from an on-site source.

Referring now to a second embodiment of the invention illustrated in FIG. 4, instead of the core component being formed of a synthetic plastic material as in the embodiment of FIGS. 1-3, the core component 20 may comprise a tubular member formed of paper board, for example. The tubular body 20 is closed at opposite ends by end caps 22 and 24, thereby to define a hollow core component 20 that is filled with air at atmospheric pressure.

According to the embodiment of FIGS. 5 and 6, the core component 30 is formed from a corrugated cardboard blank having panels 30a and flaps 30b that are folded to define a hollow closed core component that has a polygonal cross-sectional configuration and is filled with air at atmospheric pressure. The maximum transverse dimension d₁ of the cardboard core component 30 is less than the diameter D₂ of the bore hole. Similarly, the core component could be formed from wood, ABS, PVC, rubber or other synthetic plastic material.

In accordance with the present invention, the core components can be placed at either pre-planned or random locations in the continuous explosive column. In the illustrated embodiment of FIGS. 1-3, the core component has a length from 3 to 6 feet or other customized length, and thus the number of core components provided in a bore hole varies in accordance with the length thereof. The core components create axial air gaps that do not interfere with the continuity of the column, and therefore, additional priming is not required. The core components are sized to match the specific site needs of a customer, such as occurs in surface coal mining, for example.

By the use of the core components, up to 15 percent of the average explosive load may be replaced. This method allows the hardest rock to be shot with the maximum amount of explosive, while the blaster can selectively reduce the change in areas of the formation that adequately fragment with a lesser amount of energy.

The invention offers the advantages of reducing the overall powder factor, reduction in cost and delay decking, helps to control flying rock, and improves equipment and labor efficiency. The invention permits optimum loading without additional priming, and results in a reduction of vibration without the changing of bit size.

Flexibility is provided to the blasting operation regardless of the drill equipment available or the mining conditions. Besides the obvious savings in the use of the blasting agent, the present invention provides improved blasting results versus traditional air gapping methods. Vibration is controlled by the use of the core components, since the blasting operations reduce the pounds per delay in critical situations without introducing more decks or inert materials. The core component is constructed of cylindrical polypropylene heat sealed on both ends, pre-cut to length and available in a range of diameters and thickness. Each core component tube is pre-inflated prior to delivery to the borehole, or it can be inflated at the borehole site via an individual inflation valve. Inflation at the borehole improves efficiency for shipping, storage, and usage.

The amount of explosives required to blast overburden may be reduced by providing an axial air gap in the explosive column and not requiring the reintroduction of priming or being dependent on the limits of sympathetic detonation. Also, the number of separate delay detonators needed per hole to comply with vibration regulations may be reduced by creating or occupying space in borehole and thereby better distributing the explosive column throughout the borehole. The bulk explosives may be placed closer to the surface of the ground by reducing the amount of explosives in terms of pounds per foot and then allow for the fragmentation of rock close to the surface while reducing the likelihood of fly rock from the blast. The over break in adjacent areas may be reduced by reducing the amount of explosives loaded in the last rows of holes. The efficiency of the hole loading equipment and labor is improved by extending the capacity of the delivery equipment by causing the same volume of explosives to charge more boreholes.

While in accordance with the provisions of the Patent Statutes the preferred forms and embodiments of the invention have been illustrated and described, it will be apparent to those skilled in the art that various changes may be made without deviating from the inventive concepts set forth above.

Claims

1. A method for blasting rock for surface coal mining and the like, comprising: (a) drilling in the rock a vertical bore hole having a given diameter of from about 6″ to about 13″ and a generally vertical axis extending to a depth of from about 10 feet to about 200 feet; (b) depositing into said bore hole a bottom layer (6) of inert backfill material; (c) depositing into said bore hole above said layer of backfill material a first layer (8a) of a particulate explosive charge; (d) folding a cardboard blank having a plurality of panels (30a) and flaps (30b) to define a closed air-filled core component (30), said core component having a length of from between 3 feet to 6 feet, (e) inserting said core component into said bore hole in seated engagement with said first layer of particulate explosive charge, said core component having a cross-sectional dimension that is less than that of said bore hole diameter; (f) depositing into said bore hole about the entire length of said core component a second layer (8b) of said particulate explosive charge, said second layer being in direct engagement with said first layer, thereby to define a continuous explosive column containing said core component, the volume of said core component being about 10 percent to 25 percent of the volume of said continuous explosive column; (g) depositing into said bore hole above said core component a top stem of inert material; and (h) detonating said particulate explosive charge.

2. A method for blasting rock as defined in claim 1, and further including, prior to said top stem depositing step: (i) depositing in said bore hole above said second layer a third layer (8c) of said particulate explosive charge; (j) inserting into said bore hole a second one of said hollow gas-filled core components, said second core component having a cross-sectional transverse dimension that is less than said bore hole diameter; and (k) depositing into said bore hole about said second core component a fourth layer (8d) of said particulate explosive charge, said fourth layer being in engagement with said third layer, thereby to define a continuous explosive column containing said core components in spaced collinearly arranged relation, the sum of the volumes of said core components being 10 percent to 25 percent of that of said continuous explosive column

3. A method for blasting rock as defined in claim 2, and further including: (l) depositing into said bore hole above said second core component and in direct contact with said fourth layer a fifth layer (8c) of said particulate explosive charge, thereby to define a continuous explosive column between said first and said fifth explosive layers.

4. A method for blasting rock as defined in claim 1, and further including (i) introducing into said first layer a booster firing cap for detonating said continuous explosive column.