Apparatus and method of blasting undersea rocks

Abstract

 A method and apparatus for blasting undersea rocks uses a chamber (1) having a semi-spherical shape with a flat bottom plate (3), which in operation is placed against the surface of the rocks. The external surface of the semi-spherical container is moulded with a layer of concrete (5).

Description

[0001] This invention relates to an apparatus and a method of blasting undersea rocks.

[0002] It is known to blast undersea reef, rock or the like by drilling holes in to the rocks and then to fill the holes with explosives or alternatively by attaching explosives to the external surface of the rock. In the former method, the equipment required is very expensive but yet the efficiency of underwater operation is very low. Furthermore, during the operation of blasting, the whole area surrounding the working site must be cordoned off and blocked for a long time and this results in traffic problems and an increase of administrative expenses, and therefore the total cost of project engineering is usually over five times the cost of blasting on land. In the latter method, despite the advantage that the operating time is slightly shorter than the former method, it requires more explosive and can only blast relatively soft rocks. It is less effective in blasting hard reef, rock or silt stone of toughness over N70.

[0003] To overcome the above disadvantages of longer working time, high operation costs and inability to blast hard rocks, the present inventor devised a very effective and improved method capable of blasting hard, and tough underwater rocks in a much shorter period of time which is disclosed in Chinese Patent No: 6280. In the prior method, a container having a conically shaped chamber for explosive is used made of materials of high strength but having a comparatively weak bottom made, for example, of wooden board, plastics, paper board, or the like soítllat when the container filled with explosives and attached to the surface of the rocks to be blasted, the force of explosion is directed to the target to thereby achieve better results. Such a method can shorten the operating time by 50% and save more than 40% of the costs. However, it has been found that the blasting pressure generated by such apparatus tends to disperse into the surrounding water and the impact upon the rocks is greatly reduced. This is because the conical shape of the container has a comparatively weak resistance strength against the force of explosion inside the container.

[0004] The present invention seeks to provide an apparatus and method of blasting undersea rocks in which the foregoing difficulties are substantially mitigated.

[0005] According to one aspect of this invention the apparatus comprises an explosive chamber having a member of arcuate cross-section made by casting material of high strength and a substantially flat bottom plate sealed to the arcuate member by securing means, the external surface of the arcuate member being moulded with a layer of reinforcement material, such as concrete.

[0006] According to a further aspect of this invention a method of blasting rocks and particularly undersea rocks comprises placing the apparatus according to said one aspect with the flat bottom plate in contact with the rocks and detonating the apparatus to provide a high explosion effect.

[0007] The apparatus and method of the present invention have the effect of simultaneously controlling and delaying the pressure generated by the explosion inside the container due to the arcuate cross-section of the upper part of the explosive chamber which has a higher tensile strength than the conical shape of the known apparatus.

[0008] When in use the present invention is filled with explosive on land and the apparatus is then taken to the predetermined location to carry out the blasting where the apparatus is submerged into the water with the flat bottom plate in contact with the rock. Upon detonation the flat bottom plate is the first to rupture and a highly pressurised blasting force is provided to the rock which has the effect of enlarging the area of the explosion.

[0009] In distinction to the conventional undersea blasting method where it is necessary to drill holes in the underwater rock and then fill the holes with explosives the blasting operation can be carried out with less equipment and more quickly with the present invention. Furthennore, in the conventional method of attaching explosives to the rock surface, the blasting pressure generated tends to disburse into the surrounding water which has a density much less than that of the rock, and the impact force against the rock dissipates almost entirely. Therefore, such a known method has very little efficiency in blasting hard and tough rocks. The present invention overcomes these disadvantages by providing an explosive chamber of material of high strength made by casting with the purpose that the pressure generated from an explosion inside the chamber can be instantaneously controlled and delayed so pressure is enhanced to become a concentrated impact force by the arcuate portion of the chamber guarding and concentrating the explosive force toward the rocks.

[0010] The explosive chamber of the present invention for housing the explosive is made of a single kind of material by casting in a uniform thickness and after being sealed with the bottom plate, it can constrain the blasting pressure of the detonated explosives for a moment to enhance the force of blasting.

[0011] The apparatus of the present invention will now be described by way of example with reference to the accompanying drawings in which,

Figure 1 is a vertical cross-section of the blasting apparatus of the present invention, and

Figure 2 is a bottom view of the apparatus with the bottom plate removed.

[0012] Referring to the figures, an explosive chamber 1 is formed by a semi-spherical, uniform thickness, cast-steel shell 2 having a flat bottom plate 3 secured to the shell by circumferentially disposed bolts 4, and a reinforcing layer 5 of high specific gravity, such as concrete, moulded over the external surface of the semi-spherical shell 2 to increase the weight and stability of the apparatus. A handle 6 is mounted on the top portion of the semi-spherical shell and a tube 7 is provided under the handle and through the concrete layer 5 and shell 2 into the explosion chamber 1 for installation of an electrical ignition wire (not shown) to the explosive (also not shown).

[0013] In operation the explosive chamber 1 is filled with explosive and the bottom plate 3 secured in position by the bolts 4 on land. The apparatus is then taken to the required site and positioned against the rock to be blasted with an electrical detonating wire protruding from the tube 7. On detonating the explosive the force is initially delayed and controlled by the shell and layer 5 and the blast force is then concentrated by the. scmi- spherical shape of the shell to be directed by a bottom plate 3 against the rock.

Claims

1. A blasting apparatus comprising an explosive chamber having a base plate in which chamber the explosive is housed, characterised in that the explosive chamber (1) has a member (2) of arcuate cross-section made by casting material of high strength and a substantially flat bottom plate (3) sealed to the arcuate member by securing means (4), the external surface of the arcuate member being moulded with a layer of reinforcement material (5).

2. An apparatus as claimed in claim 1, characterised in that the member of arcuate cross-section is a semi-spherical shape.

3. An apparatus as claimed in claim 1 or 2, wherein the material of the arcuate member is steel.

4. An apparatus as claimed in any preceding claim, wherein the layer of reinforcement material is made of concrete.

5. An apparatus as claimed in any preceding claim, characterised in that the bottom plate is made of the same material as that of the member of arcuate cross-section.

6. A method of blasting rocks comprising placing an apparatus having an explosive chamber formed partially by a base plate with the base plate against the rock to be blasted characterised in that the apparatus is in accordance with any preceding claims having a flat base plate (3) and a member (2) of arcuate cross-section made by casting material of high strength with the base plate sealed to the arcuate member by securing means (4) and an external surface of the arcuate member being moulded with a layer of reinforcement material, the method comprising placing the bottom plate of the apparatus in contact with the surface to be blasted and detonating the apparatus so as to provide a concentrated impact force.

Drawing