US3811286A

US3811286A - Dam having contoured internal apron

Info

Publication number: US3811286A
Application number: US00307662A
Authority: US
Inventors: A Feiner
Original assignee: Strabag Bau AG
Current assignee: Strabag Bau AG
Priority date: 1971-12-08
Filing date: 1972-11-17
Publication date: 1974-05-21
Anticipated expiration: 1991-05-21
Also published as: CH563502A5; DE2160874C3; GB1376225A; FR2164151A5; JPS5431627B2; JPS4864729A; DE2160874A1; ES404342A1; CA960047A; IT956521B; DE2160874B2

Abstract

In a dam comprising an upright core packing providing a sealing apron, upstream and downstream embankments intimately interengaged with and supporting the core packing, said embankments having different individual settling rates tending to lessen engagement thereof with the core packing, the improvement which comprises the angle of inclination with respect to the horizontal on the downstream side, being less in the upper portion of the core packing than in the lower portion thereof for counteracting the different settling rates and the tendency thereof to lessen said engagement.

Description

United States Patent [191 Feiner [451 May21, 1974 DAM HAVING CONTOURED INTERNAL APRON Inventor: Alfred Feiner, Porz-Westhoven,

Germany Assignee: Strabag Ben-AG, Koln-Deutz, I

Germany Filed: Nov. 17, 1972 Appl. No.: 307,662

Foreign Application Priority Data Dec 8, 1971 Germany 2160874 US. Cl. 61/31 Int. Cl E02b 7/10 Field of Search 4a... 61/31, 30, 32, 33, 35,

References Cited ,UNITED STATES PATENTS Noetzli 61/31 FOREIGN PATENTS OR APPLICATIONS 328,683 5/1958 Switzerland 6l/3l Primary Examiner-Jacob Shapiro Attorney, Agent, or FirmBurgess, Dinklage & Sprung 5 7] ABSTRACT In a dam comprising an upright core packing providing a sealing apron, upstream and downstream embankments intimately interenga'ged with and supporting the core packing, said embankments having different individual settling rates tending to lessen engagement thereof with the core packing, the improvement which comprises the angle of inclination with respect to the horizontal on the downstream side, being less in the upper portion of the core packing than in the lower portion thereof for counteracting the different settling rates and the tendency thereof to lessen said engagement.

20 Claims, 2 Drawing Figures l DAM HAVING CONTOURED INTERNAL APRON BACKGROUND The invention relates to earth dams having an internal sealing apron which extends over the entire longitudinal cross section of the dam in the interior thereof. The sealing apron may be composed of a bituminous material and a mineral skeleton of a concrete-like composition of such fineness that it becomes intimately interengaged with the adjacent darn materials on the water side and on the downstream side.

Such waterproofing sealing aprons or cores, in accordance with German Pat. No. 1,108,620 for example,

have been used successfully in dams up to about 35 meters high. They are constructed by the method disclosed in German Pat. No. 1,170,329 and US Pat. No. 3,299,642 in which the pouring .of the core material and the material adjacent thereto in layers and the simultaneous tampingof the layers assures that the core will betightly gripped between the adjacent dam materials.

Observations and measurements on high dams composed of loose rock 'in the last decade have shown that, in addition to the substantially vertical settling movement, the loose rock also undergoes transverse movements which, especially due to the rising water level, tend increasingly towards'the water side in the middle and upper two thirds of the dam, and shift towards the downstream side only after the maximum water level has been reached. Thus, settling may be in the direction of the arrow 4-in FIG. 1.

These transverse movements are initiated by the greater settling movements of the dam material on the water side in comparison with those of the dam material on the downstream side, owing to the water level variations in the impoundment. The higher the dam is and the lower its degree of compaction, the more these transverse movements tend to have a loosening action in the area of the crest of the dam. This can result in expansion and loosening in the crest area, producing cracks which may sometimes extend several meters down into the interior of the dam.

Bituminous aprons or cut-off walls are disposed perpendicularly within the dam in accordance with the known constructions described above. The perpendicular core wall involves an optimum low consumption of building materials. It is subjected only to slight tensile and bending stresses by the settling movements which take place in the material of the dam. The perpendicular core wall requires, of course, that it be tightly gripped between the dam materials on the downstream side and the water side of the dam to reliably preclude buckling of the core wall under its own weight.

THE INVENTION This tight grip. which is produced by intensive tamping of the'layers of the dam, is nevertheless loosened in the case of relatively high dams in the upper third of the dam. by the loosening action described above, and the higher the dam is the worse this loosening. effect be comes. Although experience has shown that, in the case of dam heights of up to 35 in, no loosening action has been observed which might loosen the grip on the sealing apron or cut-off wall, nevertheless this grip is increasingly endangered in higher dams. In these dams it must be expected that the tight grip on the perpendicular cut-off wall will be loosened, especially on the water side, to such an extend that its stability will be impaired.

The invention is addressed to the problem of preventing the loosening of the grip on the cut-off wall caused by the above-explained loosening up of the materials in, e.g., the upper third of the dam.

This problem is solved in accordance with the invention by the fact that the cut-off wall, at least in the area of the upper third of the dam height, is tilted toward the downstream side of the dam at an angle corresponding approximately to the anticipated transverse movements of the dam materials on the water and downstream sides caused by differences in their settling movements. As a result, the material of the dam is unable to lift away from the cut-off wall as it loosens, and an adequate grip on the cut-off wall is maintained by the weight of the water-side material that is resting on the inclined portion of the cut-off wall.

The transverse movement,- which diminishes towards the foot of the dam, is so slight in the bottom portions of the dam that it can no longer endanger the grip-on 4 the cut-off wall between the downstream-side and the water-side dam materials. Consequently, in further de- Angling the cut-off wall back to the perpendicular, as the base is approached, minimizes the amount of material involved in its construction, not only because a perpendicular cut-off wall has thesmallest structural volume, but also because it can be made relatively thin on account of the favorable stressing of the wall which has been described above.

' Setting the cut-off wall at the other angles described above makes it possible to adapt the orientation of the wall to the geological and topographical conditions prevailing at the subsurface and slope areas of the damsite. Also, the statics of the dam may indicate that a tilt in the cut-off wall is desirable for the most economical utilization-of the dam cross section. In this case both single and multiple angles in the cut-off wall may appear desirable in the lower two thirds of the dam height.

The single or multiple angling of the cut-off wall results in a convexity vaulting toward the water side of the dam, which offers the special advantage that the cut-off wall will be subjected substantially only to compressive stresses under the pressure of the water. In accordance with the invention, the magnitude of the vertex of this vault is made such, by the selection of the angles of inclination of the tilted sections, that under the anticipated settling movements of the dam materials and under the effect of the. water pressure, it will not become convex or bulge towards the downstream side of the dam.

The angle of inclination of the cut-off wall in the upper third of the dam height is generally less than 85 and preferably approximately between 55 and and more preferably 65- 75,-in accordance with another feature of the invention. Such an angle of inclination in this area assures an adequate gripping of thecut-off wall by the downstream dam material and the water side dam material 'due to the weight of the latter, in

spite of the above-described, loosening up of the dam materials. 7 g

The distance between the bend of the cut-off wall and the dam crest, in the upper third of the dam height, from the tilt of the invention to the perpendicular or to positions of different inclination shall not be less than 8 12 m even in the case of dam materials having little settling movement. However, to the extent that this is warranted by the geological nature of the foundation,

it is advisable to dispose the bend at a maximum distance of approx. one-third of the dam height measured from the dam crest, because even in the case of dam materials having greater settling movement a sufficiently firm grip on the inclined section of the cut-off wall in the upper third of the dam height is provided.

Generally, the distance between the bend of the cutoff wall and the dam crest in the upper thirdof the dam height may be the smaller and the angle of inclination of the bend within the above specified limits may be the larger, the smaller the anticipated difference is between the settling movements of the downstream side and the water-side of the dam material; The anticipated settling action of the installed dam material in the dry state (downstream-side of the dam) and that under water (water-side of the dam) may be determined, for instance, by means of the triaxial apparatus'customary in hydraulic engineering; with this apparatus it is possible to apply an desired pressure to material samples in the dry state and saturated with water, to measure the decrease in volume.(settling) occurring per unit time and to determine thereby the difference in settling movement (dry state and wet state). The above data apply to dam heights of more than 30 or 35 meters without upper limit.

The angle in the sealing apron in, e.g., the upper third of the dam in accordance with the invention, exposes the wall at that point to relatively great flexural tensile and shear stresses whichare caused, especially during the construction of the dam and its first year of operation, by relatively great settling movement in the area of the cut-off wall. The bituminous cut-offwall is so composed, with regard to its mineral granular composition and the bituminous binding agent, that its transverse expansion must be inequilibrium within the lowermost section with the deformation of the bodies sup{ porting it on eith erside, even under the heaviest loads. The deformability (plasticity)- f the cutoff wall corresponding to this high stability is,-in further development of the. invention, increased in the upper area of the dam, especially in the areas where the cut-off wall is tilted and in the area'sof the bends in the cutoff wall. It can be increased by up to about 40 percent relative tothe deformability in the bottom section of the cut-off wall as the angle of inclination diminishes from one tilted section'to the next, because an increasing'percentage of the weight of the plastic cut-off wall is taken up by the down-stream supporting body is diminished accordingly.

This provides greater security against the greater stresses to which the inclined sections of the cut-off wall are exposed by the settling movements of the dam, which experience has shown reach their maximum approximately in the area of the middle to uppermost third of the dam height, and diminish further up in accordance with the lower weight.

'4. bitumen type B 45-B 8t) The greater deformability of the inclined sections of the cut-off wall and of the bends therein can be achieved very easily, as is known in the asphalt concrete art for example, by the incorporation of a cut-off wall construction material containing a softer type of bitumen and/or having a different aggregate composition, especially in its mortar of bitumen, sand and tillers.

Thus, by using the different commercially available bitumen types B 45, B 'y, B 80, B 200, B 300, which in accordance with their characteristic numberof 45, 65, etc. are the softer, the larger their characteristic number is, it is possible to greatly vary the plasticity of the bituminous materials made therewith while maintaining, constant the nature and quantity of the mineral constituents mixed therewith (aggregate, sand and fillers). The plasticity of the building materials may be further varied to a large extent by varying the mineral con stituents. Thus, the plasticity of the building materials may be increased by using aggregate in the building material that is round (natural aggregate) rather than sharp-edged (broken) or by admixing with the bitumen a filler that consists of flake-shaped slate powder rather than limestone powder;

The bituminous core material may, for instance, have the following composition:

-60% by wt.

2-755?? 0 MW 2. rock sand or natural sand, O-2mm 30.5-26.5% by wt. 3. filler: slate powder 12-15% by wt.

lf larger settling movements of the'dam material are anticipated, this composition is varied as follows in the zone of the bend of the cut-off wall according to the invention to its upper end:

l. aggregate round (unbroken),

grain size 2-25 or 2-40 4555% by wt. 2. natural sand 0-2 mm 30.5-26% by wt. 3. filler: limestone powder l6-l2% by wt. 4 8.57% by wt.

. bitumen type B 200-8 300 Another means for the absorption of increased flexural tensile stresses and shear stresses, especially in the area of the middle tosuppermost third of the darn height is characterized in accordance with the invention in'that the cut-off wall is made thicker in that area. In this manner its ability to undergo changes of shape can be further increased as required without loss of impermeability. i

The cut-off wall of the invention is preferably made by the method disclosed in German Patent 1,170,329 or US. Pat. No. 3,299,642, in which the cut-off wall material and the adjacent dam materials (on the downstream and upstream sides), separated from one another by dividing plates which are moved on the surface along the line of the dam, are poured simultaneously in layers, graded to the same level and, after the dividing plates have passed, are tamped together, the dividing plates being tilted in accordance with the invention at an angle corresponding to the angle of tilt of the cut-off wall in order to produce the tilted sections of the latter, and being set over laterally from one layer to the next by an amount which will provide the cut-off wall cross section with a smooth, stepless shape.

Thus, the invention is directed to a dam comprising an upright core packing providing a sealing apron, and upstream and downstream embankments intimately interengaged with and supporting the core packing. The embankments have different individual settling rates, and that tends to lessen the engagement of the embankments with the core packing. The invention provides the improvement of making the angle of inclination with respect to the horizontal on the downstream side, less 85 in the upper portion of the core packing than in the lower portion of the core packing for counteracting the different settling rates and the tendency thereof to lessen said engagement. Desirably, the angle of inclination of the upper portion is about equal to the angle of anticipated movement of the embankments based on the different settling rates. Commonly said upper portion is in the upper third of the darn height.

In a further embodiment, at least one further inclined portion below said uppr portion can be provided. Said further inclined portion or .portions have a progressively greater angle or angles of inclination, less than 90, approaching the bottom of the dam.

EMBODIMENTS ,with the cut-off wall of the'invention.

FIG. 2is a diagrammatic representation of the. building method showing a partial cross section of the dam in the areaof the, bend in the sealing apron or cut-off wall.

The dam consists, in accordance with FIG. I, of the dam material on the water side 1, the dam material on the downstream side 2, and the impermeable cut-off wall 3 of bituminous or asphalt concrete which separates thewater-side and downstream-side materials and which extends in the manner of a curtain or apron through the interior of the entire longitudinal cross section of the dam. The upper portion of the cut-off wall, approximately in the uppermost third h3 of the dam height, is inclined, in downstream direction as represented in heavylines, the angle of inclination, B, which it forms with the horizontal running approximately in the direction of the transverse movement of the dam material which is indicated by the arrow 4, and which is to be expected to be caused by differences in the settling movements of the upstream and downstream dam materials. The angle of inclination [3 usually amounts to 55 to 75. Below the angle [3 the cut-off wall is bent downward, as represented by the thick line, to the .perpendicular, or, as represented by the broken lines, to one or more tilted sections whose angles of inclination 7, 8, are more than the'angle of inclination B of the tilted section in the uppermost third of the dam height. This configuration. as it can easily be seen in FIG. 1, results in a vaulting or curvature of the cut-off wall 3 against the water side, i.e., the cut-off wall is convex on the water side, which has the advantage that the cut-off wall will be subjected essentially to only compressive stressed by the water pressure and by the settling move ments of the dam materials. The magnitude of the vertex, V, of the vaulting is made such,'through the selection of the angles of inclination, ,B, 7 and 8, that it will be unable to assume any convexity towards the downstream side of the dam under the anticipated settling movement of the dam materials and the water pressure. The anticipated settling movement can be determined with sufficient accuracy from the settling behavior of the dam materials in the dry state and under water..

In the upper area by of the dam, the deformability of the cut-off wall 3 and of its angled portion K is made greater than its deformability in the lower area Hx by the incorporation of cut-off wall material of greater plasticity at K. The middle portion hz of this area of the cut-off wall, approximately in the middle'to uppermost third of the dam height, in which experience shows that the greatest deformation of the cut-off wall due to settling movements of the dam materials can be anticipated, is preferably given a greater thickness s2 than the thickness s3 of the upper cut-off wall section and the thickness s1 of the lower cut-off wall section, as indicated in dash-dotted lines in FIG. 1. Just as the greater deformability, the greater thickness permits greater deformations in the cut-off wall, without fear of the occurrence of leaks.

The construction of the lower, perpendicular section of the cut-off wallis performed, as shown in FIG. 2, by the method disclosed in German Patent l,l-70,329, or U.S. Pat. No. 3,299,642, in which the cut-off wall material 3 and the adjacent dam materials 1, 2, on the upstream and downstreamsides, separated from one another by

parallel dividing plates

5, 5, which are moved I on the surface along the length-of the dam, are poured simultaneously in layers a, b, etc. scraped to the same level, and tamped together by tamping apparatus following alongthe line of movement of the dividing plates. For the laying of the tilted core wall sections, B, 'y and, the dividing plates 5, 5', as represented in solid lines, are moved along the grade with an inclination corresponding to the angles of inclination [3,7 and and from layer c to layer d they are set over by an amount z which assures the stepless profile of the tilted cut-off wall. The thickening s2 of the cut-off wall may be accomplished by increasing the separation between the dividing

plates

5, 5.

The invention particularly contemplates dams ranging in. height from 35 meters up, without upper limit.

What is claimed is:

1. ln a dam comprising an upright core packing providing a sealing apron, upstream and downstream embankments intimately interengaged with and supporting the core packing, said embankments having different individual settling rates tending to lessen engagement thereof with the core packing, the improvement which comprises the angle of inclination with respect to the horizontal on the downstream side, in the upper portion of the core packing being about equal tothe angle of anticipated movement of the embankments based on the different settling rates, for counteracting the different settling rates and the tendency thereof to lessen said engagement.

greater angle or angles of inclination, less than 90,

approaching the bottom of the dam.

. 4. Dam according to claim 1, the angle of inclination,

of said upper portion being about 55 5. Dam according to claim 2, the angle of inclination of said upper portion being about 55- 75.

6. Dam according to claim 2, the plasticity of the core packing in said upper'portion, being greater than the plasticity of the core packing in the bottom portion thereof.

7. Dam according to claim 3 the plasticity of the core packing in said inclined portions and in the bend at the lower end of the lowermost inclined portion is greater than the plasticity of the core packing in the bottom portion thereof.

8. Dam according to claim 2, the core packing having a greater thickness in the bend in the core packing resulting from inclination of the upper portion, than the thickness of core packing above and below the bend.

9. Dam according to claim 8, the core packing having a greater thickness in the bend in the'core packing resulting frominclination of the upper portion, than the thickness of core packing above and below the bend.

' are leveled to the same grade and compacted, the improvement whichcomprises inclining an upperportion of the core packing toward the downstream side of the dam by steps comprising, in forming said upper portion, inclining said plates to correspond with the inclination of said upper portion and shifting the plates laterally from layer to layer to provide said inclined upper portion.

l1. Dam according to claim 2, the portion below said I upper portion being perpendicular, approaching the bottom of the dam.

l2. Darn according to claim 1, the portion of the core packing below said upper portion being perpendicular or included with respect to the horizontal on the downstream side at a greater angle than said upper portion.

14. Dam according to claim 5,'the portion of the core I packing below said upper portion being perpendicular or included with respect to the horizontal on the downstream side at a greater angle than said upper portion.

15. Darn according to claim 6, the portion of the core packing below said upper portion being perpendicular or included with respect to the horizontal on the downstream side at a greater angle than said upper portion.

16. Darn according to claim 1, the height of the dam being more than 35 meters.

l7. Dam according to claim 12, the height of the dam.

being more than 35 meters.

18. Dam according to claim 13, being more than-35 meters.

19. Dam according to claim 14, the height of the dam being mo'rethan 35 meters. 4

20. Dam according to claim 1.5, the height of the dam being more than meters.

the height of the dam UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,811,286 Dated May 21, 1974 Alfred Feiner a Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

1. Col. 4, line 10, ch ange "B 7" to --B 65--.

2. Col. 8, line 8, (claimdl2, line 3), change "included" to --inclined--.

3. Col. 8, line 13, (claim'l3, line 3) change "included" to inclined; v

4. Col. 8, line 18, (claim "14, line 3) change "included" to --inclined--. I

5. C01. 8 line 23, (claim 15, line 3) change "included" to --'-inc1ined 1 Signed and sealed this lOth'day of December 197A.

(SEAL) Attest:

GIBSON JR. C. MARSHALL DANN z s t i ng Officer Commissioner of Patents FORM PO1050(10-69) UlCOMM-DC BOND-P69 I I. IO'IIIIIIY nllm'm olncl n0 o-au-au

Claims

1. In a dam comprising an upright core packing providing a sealing apron, upstream and downstream embankments intimately interengaged with and supporting the core packing, said embankments having different individual settling rates tending to lessen engagement thereof with the core packing, the improvement which comprises the angle of inclination with respect to the horizontal on the downstream side, in the upper portion of the core packing being about equal to the angle of anticipated movement of the embankments based on the different settling rates, for counteracting the different settling rates and the tendency thereof to lessen said engagement.

2. Dam according to claim 1, said upper portion being in the upper third of the dam height.

3. Dam according to claim 2 and at least one further inclined portion below said upper portion, said further inclined portion or portions having progressively greater angle or angles of inclination, less than 90*, approaching the bottom of the dam.

4. Dam according to claim 1, the angle of inclination of said upper portion being about 55* - 75*.

5. Dam according to claim 2, the angle of inclination of said upper portion being about 55*- 75*.

6. Dam according to claim 2, the plasticity of the core packing in said upper portion, being greater than the plasticity of the core packing in the bottom portion thereof.

7. Dam according to claim 3, the plasticity of the core packing in said inclined portions and in the bend at the lower end of the lowermost inclined portion is greater than the plasticity of the core packing in the bottom portion thereof.

9. Dam according to claim 8, the core packing having a greater thickness in the bend in the core packing resulting from inclination of the upper portion, than the thickness of core packing above and below the bend.

10. In a process for construction of a dam comprising an upright core packing providing a sealing apron and upstream and downstream embankments intimately interengaged with and supporting the core packing, in which the core packing construction material and the adjacent downstream-side and water-side dam materials are poured simultaneously and layer by layer while being separated from one another by parallel dividing plates moved in the direction of the length of the dam, are leveled to the same grade and compacted, the improvement which comprises inclining an upper portion of the core packing toward the downstream side of the dam by steps comprising, in forming said upper portion, inclining said plates to correspond with the inclination of said upper portion and shifting the plates laterally from layer to layer to provide said inclined upper portion.

11. Dam according to claim 2, the portion below said upper portion being perpendicular, approaching the bottom of the dam.

12. Dam according to claim 1, the portion of the core packing below said upper portion being perpendicular or included with respect to the horizontal on the downstream side at a greater angle than said upper portion.

13. Dam according to claim 2, the portion of the core packing below siad upper portion being perpendicular or included with respect to the horiZontal on the downstream side at a greater angle than said upper portion.

14. Dam according to claim 5, the portion of the core packing below said upper portion being perpendicular or included with respect to the horizontal on the downstream side at a greater angle than said upper portion.

15. Dam according to claim 6, the portion of the core packing below said upper portion being perpendicular or included with respect to the horizontal on the downstream side at a greater angle than said upper portion.

16. Dam according to claim 1, the height of the dam being more than 35 meters.

17. Dam according to claim 12, the height of the dam being more than 35 meters.

18. Dam according to claim 13, the height of the dam being more than 35 meters.

19. Dam according to claim 14, the height of the dam being more than 35 meters.

20. Dam according to claim 15, the height of the dam being more than 35 meters.