US2960859A

US2960859A - Explosion-resistant structure

Info

Publication number: US2960859A
Application number: US720318A
Authority: US
Inventors: Jr Frank Abraham Loving
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1958-03-10
Filing date: 1958-03-10
Publication date: 1960-11-22
Anticipated expiration: 1977-11-22

Description

Nov. 22, 1960 F. A. LOVING, JR

EXPLOSION-RESISTANT STRUCTURE Filed March 10. 1958 ill 71 I3 INVENTOR FRANK ABRAHAM LOVING, JR.

ATTORNEY States Pate EXPLOSION-RESISTANT STRUCTURE Frank Abraham Loving, Jr., Wenonah, N.J., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Mar. 10, 1958, Ser. No. 720,318

8 Claims. (Cl. 73-35) The present invention relates to an explosion-resistant structure. More particularly, the present invention relates to a structure whereby undesirable effects of the detonation of an explosive charge, i.e., noise, air blast, and missiles, can be eliminated.

The number of industrial applications other than blasting involving the use of explosives is rapidly increasing. Such applications include the joining of metal elements, for example by the method described in US. Patent 2,367,206 (Davis, to du Pont, January 16, 1945) and the use of explosives to emboss a metal. surface, which method is fully described in US. Patent 2,604,042 (Cook, to Imperial Chemical Industries, July 22, 1952). More recently, a U.S. Patent (2,703,297, MacLeod, March 1, 1955) has issued on a method for explosively hardening manganese steel. The explosive charges used in the aforedescribed applications may vary from a few grains to a hundred pounds. In all cases, adequate precautions must be taken to protect personnel and surroundings from any harmful or annoying effects of the actuation of the explosive, which precautions, of course, also must be taken in the experimental testing and developing of explosives.

Among these effects is included the noise characteristic of the explosives detonation. Although the noise per se is seldom hazardous, it is frequently annoying to the point of being intolerable, especially when the industrial or testing site is in a populated area. Very often, the noise produced in the operations results in delays and stoppage of the operations due to complaints concerning the noise. This problem naturally could be resolved by conducting the operations in a remote and isolated location. However, this solution of the problem is not only inconvenient but also unfeasible in many industrial areas.

The other effects encountered in the use and testing of explosives, namely air blast, i.e. the airborne pressure pulse, and missiles, definitely constitute safety hazards. In order to protect personnel from such hazards, resort often is made to the construction, at the industrial or testing site, of massive barricades to contain the explosion. Large barricades capable of withstanding the explosion of charges weighing up to 10 pounds are exceedingly expensive. Moreover, although they may be designed to arrest missiles and the air blast adequately, the barricades usually fail to prevent the objectional noise.

As is well known in the art, the noise, air blast, and missiles can be eliminated effectively by the detonation of an explosive under several feet of a liquid such as water. The liquid, which is highly compressible at explosion pressures, efficiently absorbs the explosion energy which then is transmitted to the earth or other surrounding medium with a minimum effect on nearby surface installations. Moreover, as pointed out in the afore-mentioned MacLeod patent, the confinement afforded by the liquid often produces beneficial results in the operation.

Since natural reservoirs of water, i.e. small ponds or lakes, generally are unavailable to the tester or operator,

2,960,859 Patented Nov. 22, 1960 artificial reservoirs must be constructed. The use of small pits in the earth filled with water or another liquid is unfeasible because of the destruction of the earthen walls due to the explosion. The use of liquid-filled tanks of conventional steel or concrete construction is equally unfeasible because of the very damaging effects upon the steel or concrete walls due to the underwater pressure pulse. Because of the high absorption in the liquid, e.g. water, of the energy from the explosion, at a given distance the underwater pressure pulse is many times more destructive than is the corresponding airborne pressure pulse. Although the use of a resilient material such as rubber would overcome some of the disadvantages inherent in a conventional tank of steel or concrete, the fabrication of a rubber tank is impractical not only because of economic factors but also because the preparation of a rubber tank of sufficient stiffness to hold its shape in the required sizes is diflicult if not impossible. Thus, the very characteristics which make a liquid an eflicacious protection medium also make extremely difiicult and expensive the construction of a tank or reservoir which will withstand the underwater explosion pressure.

Accordingly, an object of the present invention is the provision of an efiicient means for the containment of the noise, pressure pulse, and missiles produced by the actuation of an explosive. Another object of the present invention is the provision of an explosion-resistant structure of simple and economical construction wherein a liquid, for example water, is used as the protective medium. A further object of the present invention is the provision of a Water-filled structure for the containment of noise, pressure pulse, and missiles from an explosion, which structure is resistant to damage from the underwater pressure pulse resulting from the explosion and thus can be used over and over again.

I have found that the foregoing objects may be achieved when I provide, as a reusable explosion-resistant structure for the testing and use of explosives, a pit within the earth, a reversibly expandable, i.e. capable of expanding and then returning to its original position, cylindrical liner within the pit, a fill of dense noncohesive material between the walls of the liner and the vertical earthen walls of the pit, the fill extending from the bottom of the pit to occupy a portion of the space within the liner, and a body of liquid disposed within the liner and pit.

In accordance with the structure of the present invention, the reversibly expandable cylindrical liner comprises a plurality of rigid overlapping elongated elements, for example steel plates, interconnected in laminar form by a plurality of spaced, movable guiding and retaining means.

In order to illustrate the invention more completely, reference now is made to the accompanying drawings in which: 7

Figure l is a side view showing partially in section the explosion-resistant structure of the present invention.

Figure 2 is an end view of a segment of reversibly expandable cylindrical liner for use in the structure, the liner being constructed in accordance with one embodiment of the present invention, and

Figure 3 is an end view of a segment of a reversibly expandable cylindrical liner for use in the structure, this liner being constructed in accordance with another embodiment of the present invention.

Referring now to the figures in more detail, in Figure 1 showing the structure, 1 is the earths surface, 2 represents the earthen wall of a pit formed in the earth, 3 is a reversibly expandable cylindrical liner disposed within the pit, 4 is dense, noncohesive material filling the space between the liner 3 and the vertical walls 2 of the pit and extending from the bottom of the pit to occupy a portion of the space within the liner, and 5 indicates the level of the liquid within the liner and pit. Liner 3 consists of a number of curved metal, e.g. steel, plates 6. Platesfi a re arranged to overlap in laminar form and are cted by tie-rods 7, .the ends of which areenlar ged rm stop elements ,8. The tie-rods 7 are inserted in centralapertures' in lugs 9 and which are welded onto t is s s l In Figure 2, the segment of the cylindrical liner shown eo'rresponds in form to the liner illustrated in Figure l, '6 being the plates, 7 the tie-rods, 8 the stop elements, and 9 and 10 the lugs. In this embodiment, the plates over-lap to form an inner series of plates and an outer series of plates. The edges of adjacent plates 6 in the er layer approach each other in the region of the center oniqn of a plate 6 of the outer layer of plates, a slight gap being left between the adjacent plates 6. At sp cedtnervns, a'lug 9 is welded on the contacting surrace'ar'th central portion of the plate 6 of the outer layer, "this'lug9 'thus being positioned in the gap between theadjacent plates 6 of the inner layer. A slightly"shorter lug'10' is welded to the noncontacting surface of 'eachfof the adjacent plates 6 of the inner layer, the lug 10 being attached a slight distance from the lateral edge of "thepla'te. "Through the apertures in these three :iu'gs' is passed the tie-rod 7, and then the appropriate stops 8 are fastened to each end of the tie-rod 7. This series of three lugs 10, 9, 10 and the tie-rod 7 is repeated for every set of adjacent plates in both the inner and outer layers of plate. The layers of steel plate, therefore, are held snugly together, the gaps between the plates in one layer being positioned near the center of the plates in the other layer.

".In the embodiment illustrated in Figure 3, the plates overlap in a manner such that every plate 6 on both its interior and exterior surface contacts another plate 6, the central portion of each plate 6 remaining free of contact with any other plate. Iral, noncontacting portion of each plate 6 is fastened a lug l0, and a lug 9 is provided, on the noncontacting surface, adjacent the edge of each plate 6. Through this lug 9 on the edge of every plate and thence through the adjacent lug 10 provided on the central portion of the next plate is passed the tie-rod 7 in the apertures provided in the lugs. The stops 28 then are fastened to the ends of the tie-rod. This series of two lugs and a tie-rod is repeated circumferentially around the liner and at given intervals along the vertical surfaces of the liner.' Thereby, the plates are held firmly together.

In operation, the explosive charge is actuated below surface of the liquid in the liner, and the resulting internal pressure pulse forces the plates outwardly, the lugs sliding freely over the tie-rods, to a point of ex;

' pansion dependent upon the size of the charge and the eoinpressihility of the dense fill material and the earth. The disengagement of tie-rods from the lugs, of course, is preven ted by the stops. After the internal pressure pulse; is dissipated, the dense fill, having a density exeeeding that ofthe liquid within the liner, expands against thelinercausing' anexternal pressure which forces the plates' together until they arrive at substantially their original position. As is obvious,- the high-pressure forces generated by the explosion are'dissipated in compressing the dense fill and the earth against which the liner is expanded. Thus, the enormous forces which would crack, deform, or fragment a conventional structure are expended harmlessly in the structure of the present invention.

The following example serves to illustrate a specific embodiment of the structure of the present invention. However, it will'be understood to be illustrative only and not as limiting the invention in any manner.

Example A pit about 16 feet in diameter and about 12 feet in depthwasdug in the earth "The cylindrical liner (1O feet in diameter and 10 feet in length) was of the form shown in Figures land 2 and was constructed from l6 curved steel plates each about 4 feet in width and 10 feet in length, the thickness of each plate being A1 inch. The tie-rods were A-inch-diarneter steel rods, and the lugs were 3-inch x 3-inch inch steel blocks welded to the plates and drilled to receive the tie-rods. The liner was suspended in the pit. In the annulus between the earthen walls of the .pit and the outside of the liner poured dense, noncohe siv'e-fill material eonsisting of a mixture of about two parts of sand to one part of gravel, the fill material extending from the bottom of the pit to occupy a portion roughly approximate to one-fourth of the depth within the liner. Then, water was introduced into the liner and seeped into the fill, the water level being slightly below, i.e. about 1 foot below, the earths surface.

In testing this structure, numerous explosive charges were detonated-below the surface of the water. The charges .varied in weight up to twenty pounds, and in no shot did any damage occur. to the structure. In the shot made with the 20-pound charge, the liner expanded from its original diameter of about 10 feet to a diameter of about 12 feet but returned int-act to its original shape and size. In contrast, a" water-filled solid steel shell /2 inch thick and 10 feet in diameter will be permanently deformed, i.e. expanded irreversibly, by the underwater detonation of a At-pound charge. I

As has" been illustrated, the liquid-filled structure of the present invention may be exposed over and over again to the forces from the detonation of an explosive charge. ln'order to provide such a reusable structure,

. the use of a reversibly expandable liner within an earthen To each side of the cen- .pit and the use of noncohesive derisefill are critical. 8'] means of this combination, the enormous pressures from the detonation, which would act detrimentally against a conventional rigid steel tank, are expended harmlessly by working against the liner and the compressible. fill and earth. Because the liner is reversibly expandable and thus can move readily when high internal and external forces are applied to it, no damage to the liner is incurred. The dense noncohesive fill, which absorbs most of the energy from the explosion, presents during the duration of the internal pressure pulse a uniform backing against which theliner' expands, which uniform backing, in contrast to many types of earth, prevents distortion'or rupture of the liner. When the internal pressure is dissipated, the fill material flows back freely against the liner, forcing it inwardly.

The exact arrangement of the rigid elongated elements of the reversibly expandable liner is not critical so long as the elements overlap'to present a continuous laminar surface when the liner is in the normal position. The two illustrated embodiments of the liner construction are easily fabricated and are eflicient in operation. Therefore, these forms constitute preferred embodiments of the liner of the present invention. The exact form of the movable guiding and retaining means, or fasteners, used 'aso is not critical, the only requirement of the fasteners being that they are capable of moving freely to' permit unhampered expansion of the rigid elements. The combination of lugs and tie-rod exemplified QOIISll? tutes the preferred fastener, since these components are readily available and simply installed and yet at the same time allow the necessary movement. The substitution of other forms of a movable fastener, however, is completely Within the scope of the present inventiorn For example, a coil springcould be attached to the lugs 153 of Figure 1 and threaded through lug 9, or the spring could be attached to lugs 9 and 10 of Figure 3.

A wide variety of materials of construction may be used for both the rigid elements and the fasteners. The prime requisites'to be considered in the selection Of the material for the rigid elements. are that it be of sufiicient strength to support the assembled liner and of sgfiicient toughness to resist shattering due to the explosion forces. Any ductile metal will serve adequately as the material of construction of the rigid elements. For minimum cost and simplicity of construction, I prefer to use steel, for example standard steel plates, as the material of the rigid elements. Therefore, for ease of assembly, the use of steel for the fasteners, e.g. the lugs and tie-rods, is preferable.

The dimensions of the liner, and also the pit, are dictated to some extent by the size and configuration of the explosive charges to be tested or used in the structure. For example, a structure of relatively small overall dimensions is adequate when the charges employed are small, i.e. of a few pounds or less, whereas when larger charges are employed, the structure correspondingly must be larger. Although the exact ratio of pit diameter to liner diameter is not critical, 1 have found that the annulus of fill material between the liner in normal position and the pit walls generally should be at least 2 feet in width, in order to supply the proper uniform backing for the liner. Thereby, the pit generally should have a diameter at least 4 feet greater than the liner diameter.

As afore-mentioned, the use of standard steel plates in the liner construction simplifies fabrication. The exemplified plates were 4 feet in width, but, of course, elements of greater or lesser Width may be used depending on the over-all size of the structure, which as previously explained is to some extent dependent upon the size of the charges used. The only factor limiting the width of these elements is that they must not be so narrow as to unlap during expansion of the liner. The thickness of the rigid elements of the liner naturally is governed by the principles upon which the construction of a cylindrical structure is based. The liner must have rigid elements of a certain minimum thickness to withstand the external pressure resulting from the difference in density between the material outside the liner and that within the liner. For example, when the rigid elements are of steel, the ratio of the thickness of the rigid elements to liner diameter (I.D.) must be at least about 1 to 1000. Hence, due to the two-layer construction of the liner, the ratio of maximum Wall thickness to liner diameter (I.D.) must be at least 1 to 500. The larger this ratio, the thicker and stifier the wall will be and the more durable the structure. Thus, only economic considerations limit the extent to which this ratio is increased. When other materials of construction, e.g. aluminum, are used, handbook values of course are available for the determination of the wall thickness required.

As is obvious, with the exception of the afore-d-escribed general requirements, the exact dimensions of the liner components and the specific construction material are not essential to the present invention but are selected on the basis of practicality as governed by the fundamental principles of engineering.

The composition of the fill material is dictated by two essential properties. That is, the fill material must be of greater density than that of the liquid within the liner, and, secondly, this material must be noncohesive, ie it must not be permanently compressed during the expansion but must be capable of flowing freely back against the liner and settling firmly against it after the expansion. A wide variety of dense, noncohesive aggregate materials fit the above-listed prerequisites and, thus, can be used satisfactorily as the fill material. Although the exact composition used, therefore, is not critical to the present invention, experiments have shown a mixture of two parts of sand and one part of gravel gives excellent results, and, thus, on an economic basis, the use of this com sition is preferred.

A bottom-less liner, rather than a tank, has been purposely employed in the structure of the present invention. Thereby, no deformable obstacle is placed in the path of that portion of the pressure pulse traveling downwardly. In most cases, the liquid lost from the pit through seepage into the earth is negligible, and, in any case, some replacement of the liquid during use is required. In very porous soil, excessive seepage may be arrested by adding fine sand, coal ashes, oatmeal, or the like to the dense fill material. Thus, the absence of a bottom in the liner constitutes no drawback.

For economics, availability, and satisfactory performance, water in most cases will be used as the liquid filling the liner. However, other liquids, e.g. a glycol, act in a similar manner, and the use of these other liquids is equally feasible.

Although the invention has been described in detail in the foregoing, it will be apparent to those skilled in the art that many variations are possible without departure from the scope of the invention. I intend, therefore, to be limited only by the following claims.

I claim:

1. A reusable explosion-resistant structure for the testing and use of explosives which comprises a pit in the earth, a reversibly expandable cylindrical liner disposed in said pit, said liner consisting of a plurality of rigid overlapping elongated elements interconnected in laminar form by a plurality of spaced, movable guiding and retaining means, noncohesive fill material occupying the annulus between the earthen walls of said pit and the outside surface of said liner and extending from the bottom of said pit to occupy a portion of the space within said liner, and a body of liquid disposed within said liner and said pit, said noncohesive fill material having a density greater than that of the filling liquid.

2. A structure according to claim 1, wherein the rigid elements of said cylindrical liner are arranged in two layers such that a gap separates the lateral edges of adjacent elements in each of said layers, said gaps in one layer of said rigld elements being positioned near the center of said rigid elements in the other layer.

3. A structure according to claim 1, wherein said rigid elements of said cylindrical liner are so arranged that every element on both its exterior and interior surfaces contacts another rigid element, said surfaces of the central portion of each of said elements remaining free of contact with any other of said elements.

4. A structure according to claim 1, wherein said movable guiding and retaining means consists of a plurality of centrally apertured lugs through which is threaded a tie-rod.

5. A structure according to claim 1, wherein said rigid elements and said movable guiding and retaining means are of a ductile metal.

6. A reusable explosion-resistant structure for the testing and use of explosives which comprises a pit in the earth, reversibly expandable cylindrical liner disposed in said pit, said liner consisting of a plurality of rigid, overlapping, elongated steel elements interconnected in laminar form by a plurality of spaced, movable guiding and retaining means, the ratio of the thickness of said rigid elements to the inner diameter of said liner being at least 1 to 1000, noncohesive fill material occupying the annulus between the earthen walls of said pit and the outside surface of said liner and extending from the bottom of said pit to occupy a portion of the space within said liner, and a body of liquid disposed within said liner and said pit, said noncohesive fill material having a density greater than that of the filling liquid.

7. A structure according to claim 6, wherein said liquid is water.

8. A structure according to claim 6, wherein said fill material is a 2/1 mixture of sand and gravel.

References Cited in the file of this patent UNITED STATES PATENTS 1,427,166 Parton Aug. 29, 1922 2,699,117 La Prairie Jan. 11, 1955 2,798,633 Cornell July 9, 1957