US2685251A

US2685251A - Method of blasting

Info

Publication number: US2685251A
Application number: US95686A
Authority: US
Inventors: Davis Clyde Oliver; Lewis Harold Arthur; Noddin George Adelbert
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1947-12-17
Filing date: 1949-05-27
Publication date: 1954-08-03
Anticipated expiration: 1971-08-03

Description

Patented Aug. 3, 1954 UNITED STATES PATENT OFFICE METHOD OF BLASTING Original application December 17, 1947, Serial No. 792,202. Divided and this application May 27, 1949, Serial No. 95,686

4 Claims.

This invention relates to a novel method of blasting under fluid confinement and more particularly to a novel method of submarine blasting.

This application is a division of our co-pending application, Serial No. '7 92,202, filed December 17, 1947, now abandoned.

Underwater blasting operations are required for such purposes as the deepening of harbors and channels, the removal of rock obstructions, the destruction of sunken objects, and the like. In such work, it is customary to prepare the required number of boreholes spaced at suitable distances apart and to load high strength explosive into each of said boreholes. Heretofore in such blasting, it has been necessary to follow one of two procedures, each of which involved serious disadvantages. One method consisted in spacing the boreholes sufliciently close together, loading each of the holes with explosive, initiating one of the charges by means of an electric blasting cap, and bringing about explosion of the other charges by propagation from hole to to hole. The disadvantage of such a method was that the use of explosives of a high degree of sensitivity was required. As a matter of fact, it has been customary in such work to employ 60% straight dynamite, high strength gelatin, or high strength gelatin primed with 60% straight. The use of high explosives of such an order of sensitiveness is undesirable and unduly hazardous for large scale rock blasting operations where a certain amount of rough handling is necessary. Furthermore, premature explosions on drill barges with consequent loss of life have occurred with these highly sensitive explosives.

A second method practiced heretofore has allowed the use of many types of cap-sensitive explosives but has necessitated the insertion of at least one electric blasting cap into each borehole charge. This has not only been wasteful in its requirements of relatively expensive electric blasting caps but has introduced complications because of the presence of the many cap wires of considerable length, which could readily become tangled or fouled by material floating on or submerged in the water, nearby vessels, etc. A distinct hazard is involved also in the event of electrical storms, not necessarily in the immediate vicinity, which in a number of cases have brought about the explosion of underwater charges with emergent cap wires.

In view of the disadvantages present in previous procedures for submarine blasting, where a plurality of explosive charges is to be fired, it will be apparent that a method that allows the use of relatively insensitive explosives without requiring electric blasting caps leading to each charge will represent a highly desirable advance.

An object of the present invention is a novel method of carrying out blasting operations beneath the surface of or in contact with a dense fluid medium and particularly for underwater blasting. A further object is such a method permitting the employment of relatively insensitive blasting explosives and not requiring electric blasting caps and their wires for the various charges. A still further object is a method for submarine blasting employing a novel type of detonator. Additional objects will be disclosed as the invention is described at greater length hereinafter.

We have found that the foregoing objects are accomplished when we carry out submarine blasting operations by a method comprising introducing a plurality of detonating explosive charges into the desired subsurface blasting positions; locating at least one blasting cap adjacent to each of the explosive charges and in detonating relationship therewith, said blasting cap being free from electrical firing arrangements and adapted to become initiated under the efiect of pressure from the explosion of a nearby charge; locating an explosive priming charge in suitable proximity to said blasting cap; bringing about the explosion of said priming charge; and thereby causing the collapse of the shells of the blasting caps, the initiation of the respective cap charges and the detonation of the main explosive charges adjacent thereto. The detonators or blasting caps adapted to become initiated under the efiect of pressure, as described, may, for example, contain loosely-packed charges of impactignitible mixtures within a portion of the shell, which become fired as a result of the impact of the collapsing walls. The high velocity compressed detonating explosive base charge within the cap will be brought to explosion by the loose charge. A blasting cap of the above characteristics and structure is fully disclosed and claimed in our co-pending application, Serial No. 792,202.

The invention will be illustrated more clearly by reference to the attached drawing, in which Figures 1, 2 and 3 are diagrammatic views of different arrangements of explosive charges under water, adapted to employ the principle of the invention.

In Figures 2 is shown an assembly for underwater blasting using a pressure-responsive detonator. In this figure, Ill represents the surface of a body of water, beneath which, and confined by said body, have been placed explosive charges I? and I3, in boreholes in the rock bottom. Inserted in these charges are pressure responsive blasting caps l4 and I5. An explosive charge I6 has been lowered into a position in proximity to caps M and I5, and an electric blasting cap I? is in detonating relationship with this charge, having insulated cap wires l8. When ready for the blast, the cap wires are thrown into circuit with a source of electric current (not shown) and the charge is fired. The pressure resulting from the detonation of charge l6 brings about the initiation of caps 14 and 5, with consequent detonation of the charges [2 and [3. In this figure, two explosive charges have been shown containing inserted propagation detonators and in position to be exploded under the influence of pressure.

Figure 1 shows another and a preferred assembly of charges for underwater blasting employing the pressure-responsive detonator. In this figure, six explosive charges IS-M, are shown loaded into their respective boreholes in the rock bottom, spaced from one another at reasonably short distances. Into charge i9, an electric blasting cap 25 has been inserted, having insulated cap wires 36. Spaced from charge l9 are the successive explosive charges 20, 2!, 22, 23 and 24, into each of which has been introduced a nonelectric closed detonator of the type described, these detonators being designated by 26, 2'1, 28, 29 and 39 respectively. At the time of firing, the wires from the cap in explosive charge is are connected with a source of firing current and electric blasting cap 25 and charge 19 are brought to detonation. The adjacent explosive charges 2fi24 are not sufficiently sensitive to propagation to be detonated sympathetically from the first charge 49, but the resulting pressure causes the collapse of the walls of cap 26 and the detonation of this and its charge 26 and the subsequent successive detonation of charges 2 l24 by means of the inserted pressure-sensitive detonators. It will be understood that, in the illustration of the invention according to Figure 2, the explosive charges in the different boreholes may consist of single cartridges in each hole or a column or group of cartridges. Where a number of cartridges are present in each hole, a single pressure responsive detonator in the top cartridge may be suificient, the explosion propagating from one cartridge to another, or, if desired, propagation detonators may be present in all or in any chosen number of the cartridges, depending on the sensitiveness of the explosive and the continuity of the column.

Figure 3 illustrates a vertical sprung hole where chambering is desired. The small diameter vertical borehole 3? opens into the enlarged chamber 38, which is filled with water to the level 39. Into this hole have been charged a great number of explosive cartridges or cans, as shown. A priming cartridge 40 contains an inserted electric blasting cap H, the leading wires 42 from which pass up outside the hole. Propagation detonators may be inserted into all or as many of the cartridges as desired. The priming cartridge is fired by connecting the blasting cap wires to a source of electric current and the presence of propagation detonators, adapted to fire under the action of the pressure from the priming cartridge, assures complete detonation of all cartridges and the consequent desired enlargement of the chamber.

The method described in the foregoing will be applicable in blasting operations beneath the surface of a dense fluid medium, and particularly in submarine blasting, for the deepening of harbors and channels, the removal of rock obstructions, the destruction and disintegration of sunken objects, shaft sinking, and the like. It has other sub-fluid applications, however, for example in oil well shooting and in various uses of explosives in the oil production industry. By the words dense fluid medium we intend to in clude all liquids and fiowable solids such as mud, wet sand and all solid-containing mixtures that may be caused to fiow under pressure. The method is applicable, for example, in ditch blasting where the explosion is propagated from cartridge to cartridge by sympathetic detonation through a wet soil medium.

The method of underwater blasting according to the present invention is outstanding in its advantages. The pressure-responsive detonators used are simpler in design and more economical in cost of materials than electric blasing caps. Since only one electric blasting cap is required for a group of shots, this means a very considerable saving, particularly in cap wires and electrical firing means. At the same time the disadvantages are avoided of a large number of sets of cap wires that may become fouled by floating or submerged objects and may constitute a hazard during the occurrence of electrical storms, even at a considerable distance from the place of blasting.

A particular advantage comes from the fact that the method allows the satisfactory and effective use of explosives of a lower order of sensitivity than has been possible heretofore in the usual procedures followed. It has previously been the practice in submarine blasting to employ 60% straight dynamite, in order to assure complete detonation where propagation from hole to hole was desired. This 60% straight dynamite is of a high order of sensitivity and its use in large scale blasting operations is not desirable because of the rough treatment involved and the care required in such handling. Using the method of the present invention, any cap sensitive explosive may be employed and we find highly desirable explosives relatively insensitive to impact such as those high in ammonium nitrate content, for instance over 60% ammonium nitrate, non-nitroglycerin explosives containing solid sensitizers, granulated cast mixtures of ammonium nitrate and trinitroltoluene; blasting agents of the Nitramon type where a cap-sensitive booster charge is required, and many others. With such explosives, having a pressureresponsive detonator inserted in each cartridge or in each group of cartridges, the advantages are obtained of excellent blasting execution, simplicity of assembly, and freedom from the hazards sensitive explosives. It will be understood that, when the term explosive charge is used, this may designate either a single explosive cartridge or a group of cartridges in substantial contact or in detonating relationship with one another.

The invention has been disclosed at length in the foregoing but it will be understood that many changes in details of charges, arrangement of charges, assembly and detonator design may be made without departure from the scope of the invention.

We intend to be limited, therefore, only by by the following claims.

We claim:

1. A method of blasting beneath the surface of a dense fluid medium, which comprises introducing into each of a plurality of desired subsurface blasting positions at least one relatively insensitive explosive charge at such a distance from other said positions that sympathetioal detonation by other charges in said other positions is precluded; locating at least one pressure ignitable detonator in detonating relationship with said charges; placing an explosive priming charge in proximity to said detonators; bringing about the explosion of said priming charge; and thereby causing pressure-induced ignition of the said detonators, the initiation of the respective detonator charges, and the detonation of the explosive charges.

2. The method of claim 1, in which the charges of detonating explosive comprise compositions high in ammonium nitrate content.

3. The method of claim 1, in which the charges of detonating explosive comprise mixtures of ammonium nitrate and trinitrotoluene.

4. The method of claim 1, in which the charges of detonating explosive comprise relatively insensitive ammonium nitrate compositions, said compositions being adjacent to booster charges of ca -sensitive material.

References Cited in the file of this patent UNITED STATES PATENTS 166 of the Du Pont Blasters Handbook, 1939 (cited in the preceding action) is added to the record.

Explosives, by Martin Meyer, published by Thomas Y. Crowell 00., N. Y. 1943, pp. 291, 292. 294, 295, 296. Copy in Scientific Library.

Claims

1. A METHOD OF BLASTING BENEATH THE SURFACE OF A DENSE FLUID MEDIUM, WHICH COMPRISES INTRODUCING INTO EACH OF A PLURALITY OF DESIRED SUBSURFACE BLASTING POSITIONS AT LEAST ONE RELATIVELY INSENSITIVE EXPLOSIVE CHARGE AT SUCH A DISTANCE FROM OTHER SAID POSITIONS THAT SYMPATHETICAL DETONATION BY OTHER CHARGES IN SAID OTHER POSITIONS IS PRECLUDED; LOCATING AT LEAST ONE PRESSURE IGNITABLE DETONATOR IN DETONATING RELATIONSHIP WITH SAID CHARGES; PLACING AN EXPLOSIVE PRIMING CHARGE IN PROXIMITY TO SAID DETONATORS; BRINGING ABOUT THE EXPLOSION OF SAID PRIMING CHARGE; AND THEREBY CAUSING PRESSURE-INDUCED IGNITION OF THE SAID DETONATORS, THE INITIATION OF THE RESPECTIVE DETONATOR CHARGES, AND THE DETONATION OF THE EXPLOSIVE CHARGES.