US2130044A - Dam - Google Patents

Description

Sept. 13, 1938 P. SUBKOW ET'IAL DAM Filed Jan. 11, 1936 a 1 An i l. p 3 1 INVENTORS Phi 1' 'ubkow BY Lan fon 8.566101%??? 5 AITTORNEY.

Patented Sept. 13, 1938 UNITED STATES PATENT OFFICE DAM Application January 11, 1936, Serial No. 58,690

5 Claims.

The present invention relates to improvements in dams, levees and like types of water impounding structures and embankments. In particular, the invention relates to structures of the above mentioned type containing layers. of an asphaltic or bituminous concrete. The invention further pertains to the constructions, combinations, arrangements and method herein described and claimed.

In the construction of rock-filled dams which have been developed and used until the present time, it is customary to employ a water-impervious material, such as clay or even concrete. These materials are used to prevent any leakage throughthe dams or levees with the incidental washing away of the finer materials in such rockfilled structures. This, in turn, causes the weakening and even the complete destruction of the dam structure. Obviously, the lack 'of clay, as the water-impermeable material, may make the construction of such dam structures impractical or even dangerous. On the other hand, such water-impervious material. usually comprising approximately the upstream one-third of the darn structure, the use of Portland cement concrete as the impervious material is excessively costly,

and often prohibitive.

It is therefore the main object of the present invention to obviate the above mentioned defects. and to provide a structure which is safe and which will withstand the pressures generated by the head of water being dammed. It is a further object of the present invention to provide a dam structure which eliminates the necessity of using.

a large quantity of a water-impervious material, such as clay. It is a still further object of the present invention to provide a safe structure of the above described type which does not require the use of clay as the water-impervious material.

It is still a further object of the present inven- I tion to provide a safe dam or levee structure which does not contain clay or large quantities of other water-impervious materials, said structure having provisions for the draining of any water which may have seeped thereinto, either during or after the construction of said dam or levee structure.

It has now been discovered that dam or levee structures may be constructed by the use of alternate layers of crushed rock or stone and of hituminous or asphaltic concrete.

- a minimum of voids.

approximately 300 lbs. per square inch and an impact resistance of upwards of approximately 2.5 ft. lbs. when mixed with Ottawa sand in amounts sufiicient to exactly fill the voids in the sand. The D grade asphalt referred to in the present specification is a steam refined asphalt having a penetration of 40 to at 77 F., a melting or softening point of F. to F., and a ductility of greater than 100 at 77 F. Although the D grade asphalt'is mentioned in the present specification, it is obvious that other grades and types of asphalts or bitumens may be substituted therefor. Thus, in very hot climates it may be advantageous to employ air-blown asphalts.

To prepare a proper asphaltic concrete it is essential to combine a properly graded crushed stone, a filler and the asphalt in such pro-portions that all the voids are completely filled. For this purpose it is advantageous to first proportion the percentage of steam refined asphalt and filler, such as diatomaceous earth and/or rock dust, as to produce a filled asphalt having the desired physical properties, such as melting point, tensile strength,etc. Then the percentages of a properly graded crushed stone and of the thus obtained filled asphalt should be proportioned so as to fill all .of the vvoids in said crushed stone with the filled asphalt. As an example, a filled asphalt composed of 72% by weight of asphalt and 28% by weight of diatomaceous earth will have the desired properties described hereinabove.

It is preferable to choose a properly graded crushed stone having a maximum density, that is, having a minimum of voids. By carefully proportioning the amount of sand to crushed rock, it is possible to obtain such an aggregate having The preferred aggregate used for admixture with filled asphalt to produce a desirable asphaltic concrete comprises a mixture of hard, clean, sharp crushed stone and clean graded sand having the following specifications:

. Per cent Passing a 200 mesh sieve 6- 8 Passing an 80 mesh sieve 14- 20 Passing a 40 mesh sieve 26 34 Passing a 10 mesh sieve 36- 44 Passing a 3 mesh sieve 54- 64 Passing a screen with in. circular openings 78- 88 Passing a screen with A in. circular openings 95-100 It has been found that an aggregate composed of crushed rock capable of passinga screen having in. circular openings and of the above described graded sand in substantially equal proportions by volume has a smaller percentage of voids than any other combination of these materials, this percentage being approximately 20.5%. Consequently approximately 20.5% by volume of filled asphalt will exactly fill the voids of this aggregate to produce an asphaltic con-'- crete of maximum density.

As stated above, it has been discovered a dam or a levee structure may be constructed by providing alternate layers of crushed compacted stone and of the above described asphaltic or bitumi nous concrete. To provide such a structure a layer of rock fill, for example, of quarry-run stone crushed so that all the. stone will pass through a screen having 4 inch circular openings is first placed on the foundation for the dam structure. Preferably said foundation should be such as to withstand the pressures. For this purpose it is advantageous to first excavate to bed rock. After the laying of the first layer of crushed rock, a layer of the above described asphaltic concrete should be spread thereon, the thickness of such asphaltic concrete being such as will provide a water-impervious layer as well as necessary protection to the dam. This asphaltic concrete layer should preferably be rolled to compact the concrete to conform to the contour of the crushed rock layer as well as to decrease the voids in said concrete. Thereafter, alternate layers of the crushed rock and of the asphaltic concrete should be placed on top of each other as described hereinabove.

In its broadest aspects, the present invention may be stated to comprise a dam or levee construction comprising alternate layers of rock fill and of asphalt, and particularly of rock fill and of asphaltic or bituminous concrete. The invention further resides in a method of constructing structures of the above described type which comprises placing a layer of rock fill on the foundation on which the dam is to be constructed, covering said layer with a layer of asphaltic concrete, and building up said structure by placing on top of said first mentioned layer of asphaltic concrete alternate layers of said rock fill and asphaltic concrete.

The invention still further resides in a method for constructing dam or levee structures, which comprises placing a layer of rock fill on the foundation on which the structure is to be constructed, compacting said layer of crushed rock with or without the addition of a quantity of water thereto for purposes of increasing density of the mass, disposing a layer of asphaltic concrete on the layer of crushed rock fill, compacting said layer of concrete, and building up said structure by disposing on top of said first mentioned layer of asphaltic concrete alternate layers of said compacted rock fill and of asphaltic or bituminous concrete. The invention also includes the provision of a top layer of compacted or rolled asphaltic concrete, said layer covering the upstream side of the structure and preferably ex- 1 tending some distance along the bed of the water course being dammed.

Although the layers may be disposed horizontally, it is sometimes advantageous or preferable to have them tipping downwardly either towards the upstream side of the structure or in the opposite direction. Both types have been found to have their advantages. Thus, if the layers are arranged so that they are tipped downwardly towards the upstream side of the dam or levee structure, the pressure of the water dammed, as well as the earth pressure tend to compact the materials constituting the individual layers, and therefore, to consolidate the dam structure. On the other hand, the tipping of the individual rock fill layers, as well as prevents any blow outs" which may result from seepage of water into the .dam structure followed by a sudden lowering of the level of the impounded water.

The invention may therefore be also stated to reside in a structure of the described type wherein the individual layers of rock and of asphaltic concrete are disposed either horizontally or tipped downwardly towards or away from the upstream side of the structure.

In some instances, and especially when the layers comprising the dam structure are arranged so that they tip downwardly away from the upstream side of the structure, it has been found advantageous to dispose layers of class A stone intermediate a lower layer of crushed rock and the asphaltic concrete layer or membrane thereabove. class A stone presents the advantages .of added free drainage of any water which might have seeped into the dam as through the upstream facing thereof. The arrangement of such a layer of class A stone below an asphaltic concrete membrane prevents the plugging of the voids in such layer by the silt from the quarry-run crushed rock layer disposed above. The interposed asphaltic concrete membrane prevents such downward passage of the silt.

The term class A stone as used in the present specification and claims means a sound hard quarried rock which is free from cracks and/or planes of cleavage. This rock is such that approximately 75% of the mass consists of pieces, each of which weighs about 3 to 10 tons, while the balance consists of pieces weighing approximately 10 to 15 tons each. This class A stone is thus free from any small crushed particles, and

when disposed in the form of a layer, provides a substantially free drainage for any infiltrating water.

The invention therefore may be still further stated to reside in a structure of the described type which comprises a multiplicity of layers of quarry-run crushed rock, interspersed with layers of class A stone and of asphaltic or bituminous concrete, the asphaltic concrete layers or membranes being preferably disposed above the layers of class A stone and below the quarry-run stone layers.

The invention may be more fully understood from the description of the accompanying drawing, in which:

Fig. lis a section of a preferred embodiment of a dam or levee structure constructed according to the present invention; and

Fig, 2 is a sectional view of a modified dam or levee structure.

Referring now to the drawing, and more particularly to Fig. 1, the numeral l0 represents the foundation, such as bed rock on which the dam or levee structure is to be disposed. The lowermost layer ll comprises quarry-run crushed stone, such as for example stone which will pass through a screen having 4 inch circular openings. Above said layer II is a layer I2 consisting of class A stone, this layer being covered by a layer or a membrane l3 of asphaltic or bituminous concrete. Above these three layers are disposed similar layers of quarry-run stone, class A stone, and asphaltic concrete disposed in the same order as the first 3, namely, first a layer ll of quarry-run crushed stone, thereabove layer I 2 of class A, and then a top layer or membrane Such interposition of a layer of I3 of asphaltic concrete. Asis obvious, the sectional lengths of the individual layers gradually decrease from the lowermost to the uppermost to provide the usual trapezoidal section necessary to withstand the pressure of the water dammed, as well as the pressure of the darn itself. As shown in the drawing, the uppermost layer or membrane I3 of asphaltic or bituminous concrete is extended along the upstream inclined face I4 of the dam structure'in the form of a facing or lining I5. In the preferred form said asphaltic concrete facing I5 should also extend for some distance along the foundation on the upstream side of the structure. This is shown in the form of a layer I6 similarly consisting of the asphaltic or bituminous concrete. The purpose of the concrete facing I5 and Iii is obvious since it prevents seepage or infiltration of the water both into and under the dam structure.

The method of constructing a dam or levee structure such as the one represented in Fig. 1

' is as follows: After it is determined that the foundation I is suificiently rigid to withstand the stresses created by the pressures generated by the water and the dam structure itself, a layer II of quarry-run stone crushed to the size described above, is placed on said foundation Iii. If desired, a quantity of water, experimentally determined to afford maximum density to said layer after compaction, may be added, and the mass should then be compacted as by rolling. The thickness of this layer of quarry-run stone depends on the type and size of structure being constructed. After the compaction of the quarry-run stone layer, a layer I2 of the above described class A stone is placed on the first mentioned layer, the class A stone being similarly rolled. The thickness of the layer of this stone also depends on the various factors entering into the design of the structure. Thereafter, the asphaltic or bituminous concrete is spread on top of layer I2 to form an impervious membrane I3. This membrane is also compacted as by rolling. The compaction eliminates the voids in the membrane and also causes the lower face of the membrane to conform to the contour of the surface of the stone layer I2. The dam structure is then built up as described above by spreading and compacting the next layer I I of quarry-run stone, then of class A stone I2 and finally amembrane I3 of the above described asphaltic or bituminous concrete. The thickness of the last mentioned membrane also varies on various technical factors.

The above described building up of the dam structure is continued until the proper height is attained. Obviously, the sectional lengths of the individual layers should gradually be decreased so as to produce a structure having a trapezoidal cross section. After the structure has been built up to the desired height, and the uppermost layer or membrane I3 has been reached and is being spread, the upstream face of the dam is covered by a facing or lining I5 which lining should be extended as at I6 along the bottom or bed rock III. The main function of this lining is to protect the dam from infiltration or seepage of water and the thickness of layer I5, I6 should be designed accordingly. As with the previous membranes I3, facing I5, I6 should also be compacted to decrease the voids in, the asphaltic concrete.

The advantages of thistype of construction primarily reside in the elimination of the necessity of using clay; in the adaptability of using all of the material forming quarry to produce the quarry-run stone layers II; in the fact that the water impervious asphaltic membranes are flexible enough to yield in cases of settlement, thus preventing cracking and the resultant leak age; in'the provision of layers which permit'the free drainage of any infiltrating water; and, where the individual layers are slightly tipped downwardly in the direction away from the upstream side of the structure, in the prevention of any blow-outs which may be caused by seepage of water into the dam followed by subsequent sudden lowering of the level of the water being dammed.

In the modification shown in Fig. 2, the structure consists of alternately disposed layers of quarry run stone 2i and of membranes 23 of asphaltic concrete. This type of dam is constructed without the use of the class A stone. Another modification of the structure shown in this figure resides in that the individual layers 2i and 23 are tipped downwardly towards the upstream side of the structure. The dam is built up on bed rock or similar foundation 20 in the manner described hereinabove with reference to the description of the structure shown in Fig. 1. As in the case of that structure, the top surface of the dam, as well as the upstream face 24 thereof, are covered with a facing or lining 25, 26, extending downwardly along said upstream face 25 and some distance outwardly along the surface of the foundation 20. This lining 25, 26 after compaction prevents infiltration of the impounded water. In view of the fact that the dip of the individual layers 2 I, 23 of the dam shown in Fig. 2 prevents the free drainage of any water which may'have filtered thereinto, it is necessary to provide the downstream slope of the dam with a lining 28 of asphaltic concrete.

One of the main advantages of this type of an arrangement resides in that the specific positioning or dip of the layers of stone and of the water impervious concrete permit the water pressure, as well as the pressure created by the dam itself, to cause the consolidation of the entire dam, thus further safeguarding it from destruction. Furthermore, the tipping of the water impervious flexible asphaltic membranes 23 insures against leakage of the water through the dam.

It is to be understood that the specific disclosures herein made are merely illustrative of the generic invention, and are not to be considered as limiting, since many variations may be made within the scope of the claims hereof by those skilled in the art.

We claim:

1. A water impounding structure which comprises alternately disposed compacted layers of rock fill and of asphaltic concrete, said layers being arranged so that, the structure has a gradually decreasing sectional width from the bottom of said structure to its top.

2. In a structure according to claim 1, wherein the top and sectional sides of said structure are provided with a layer of asphaltic concrete.

3. In a structure according to claim 1, wherein the top and sectional sides of said structure are provided with a layer of asphaltic concrete and wherein said layer on the upstream side of said structure extends a distance along the bottom on which the structure is disposed.

4. In a structure according to claim 1, wherein the individual layers of rock and of asphaltic concrete are tipped downwardly towards the updownstream side of the water impounding structure, whereby a. greater consolidation of the structure is obtained.

PHILIP SUBKOW. LAWTON B. BECKWITH.

Images