US1846840A - Dam - Google Patents

Description

l mas -w Feb. 23 11932. s. w. STEWART DAM Filed April 30, 1930 2 Sheets-Sheet l INVENT xk ATTORNEY Feb. 23, 1932. s, w, STEWART 1,846,840

DAM

Filed April 1930 2 Sheets-Sheet 2 Patented Feb. 23, 1932 1 UNITED STATES- PATENT; FFICE srnncnn w. STEWART, or WHITE PLAINS, NEW yonn'assrenon. To annunsnn oo t- STRUGTION COMPANY, IN'C., on NEW YORK, I\1'.Y., A conronarron" on NEW YORK Application filed April 30,

This invention relates to a novel and im proved form'of dam and more particularly to a foundation therefor. The novel features will be best uderstoocl from the following description and the annexed drawings, in which are shown selected embodiments of the invention and in which:

Fig. '1 is a fragmentary I sectional View through a dam lengthwise thereof, and illustrating prior art practice.

Fig. 2 is a View corresponding to Fig. 1 but showing the practice according to one embodiment of my invention.

Fig. 3 is a verticalsectional view through a dam, this section being taken at right angles to the plane of Fig. 2.

Fig. 4. is a view similar to Fig. 3 but'showing a different embodiment of the invention.

Fig. 5 is a View corresponding to Fig. 2 but illustrating the invention as practiced accordingto the embodiment shown in Fig. 4.

Fig. 6 is'a view on the same plane as Fig. 5' but on an enlarged scale. V

Fig. 7 is another View onthe same plane as Figs. 5 and 6 but on a still larger scale, to illustrate the details ofthe construction.

At certain sites selected for the construction of dams there is frequently found an area or areas comprising foundation material not capable of taking the full loading put upon it by thedam structure. Such areas frequently occur at portions of a site. which is otherwise of excellent material for dam construction. Examples of such areas are furnished by rock, which is different in character from the high-grade rock adjacent it or rock which may be broken or have lines of cleavage not capable of resisting the sliding forces put upon it by the weight of the structure; 'a' faulted condition caused by earthquakes or major earth movements; or a deep narrow gorge filled with earth or other soft material which it would be uneconomical to excavate. V

An example of a situation which may be found is shown in Fig. 1, wherein A designates a portion of soft material which may be found in the stream bed across which the dam is being built and which may extend downwardly for a great depth. Adjacent 1930. Serial No. 448,459.

this material may be found a portion B of" broken rock capable of taking more'load than the portionA but still not suflic-iently. good to support the dam structure. On opposite sides of the poor material A and B this uncertainty as to the support from beneath, and usually they are in actual practice far in excess of those for which the founda tion structure was designed, or could be de-. signed economically. The result is, of course,

a dangerous condition which may jeopardize the entire structure. Anothertype of fault is also illustrated in Fig. 1, this fault being exemplified by'theline-of cleavage, F which often occurs with a condition such as shown in Fig. 1, and may, of'course, occur independw ently of the veins of poor foundation material A and B; This plane of cleavage F slopes towards the river bed and represents a fracture underlying a considerable portion of the dam structure. When the dam is under load, there is seriousdanger that the portion of the structure over the plane F will slide toward the river bed under the influence of the lateral forces induced by the weight of the structure over'theseplanes. This condition has been a serious menace to dams constructed under prior art practice and, so far as I know, no successful and economical way of resisting it has been devised.

Referring now to Figs-:2 and 3, I have shown therein one embodiment of the invention in which it is possible to economically build a foundation for a dam superstructure which will overcome the difficulties discussed above. In this form, I span the river bed or portion containing the poor foundation mateif rial A and B by a monolithic plug 1 resting on the material A and B and also on the sound rock C on opposite sides of this material. The top 2 of this plug is formed as an eXtrados of an arch and the theoretical intrados is indicated by the dotted line 3. The plug is so designed thatthearch 4:. disposed between the lines 2 and 3 is normally capable of supporting the superstructure of the dam disposed above it. It is well known that a beam which is short as compared with its thickness, will have an interior arch action and I make use of that principle in this construc tion. The portion of the plug beneath the line 3 will rest upon the material and B and when the load is thrust upon the plug from the superstructure of the dam, the tendency is for the arch to deflect, thus setting up tensile stresses at the under side of the arch. and in the plug beneath the arch. In Fig. 2, I have shown lines ,5 which indicate construction joints and which may be disposed substantially radially of the arch so as to divide the arch into what are in effect a plurality of voussoirs. As the arch deflects, these joints may open up to a certain height, but the structure is so designed that they will not open within the limits of the theoretical arch. At the same time, the material A and B will normally be sufficiently good foundation material to support the masonry in the plug beneath the line 3 and may be good enough to provide some support for the masonry in the arch itself and thus aid the arch in supporting the superstructure ofthe dam. The conrial A and B is ignored, except in so far as r it is considered sufficient to support the concrete below the line 3. r

In order to aid in preventing slides such as might occur along the cleavage plane-F, I provide a plurality of bracing walls 6 eX- tending transversely of the arch or lengthwise of the dam, these walls extending between the buttresses 7 of the superstructure, these buttresses in turn supporting the water bearing member 8. It is preferable to form the extrados of the arch in steps, as indicated in Fig. 2, and to provide sliding joints 9 between the bracing walls and the arch. Otherwise, an additional stress would be induced in the bracing walls by the load and possible deflection of the arch. It is preferable to have the top 10 of each wall in the same horizontal plane and to make each wall substantially continuous to the bearing material on each bank of the stream. The banks may be further braced against lateral movement by pouring monolithic concrete between the ex trados and the bank, as indicated at 11.

Referring now to Figs. 4, 5, 6 and 7, I have shown an arrangement somewhat similar to what has been just described, except that here the arch 12 is separate from the subintradosal concrete 13, this concrete being placed between the intrados 14 of the arch and the bed of the stream exemplified by the top of the material A and B. The arch is car ried completely across the material A and B to solid rock at G and on its extrados 15 it supports the superstructure of the dam, here indicated as buttresses 7 supporting the deck 8. The bracing walls (Sand monolithic concrete 11 may be used here as in the other embodiment, to take up side thrust,as from material above the fault F.

The load on the dam constructed according to this embodiment will cause a deflection of the arch 12, but as this arch is in direct contact with the sub-intradosal concrete beneath it, the tendency to deflect is resisted by this concrete, and the material A and B thus is permitted to carry all of the load that it can. The remainder of the load will be transmitted in direct thrust to the solid material at the abutments of the arch. If the load on the dam is removed, the'sub-intradosal concrete may or may not rise as the load returnsto its initial position. When the dam is again loaded, however, the arch will dew fleet and again come in contact with the upper surface of this sub-'intradosal concrete.

In designing the arch of this embodiment, care should be taken to prevent adhering of the sub-intradosal concrete 1? to the intrados of the arch, because this would prevent the functioning of the structure as designed. The bond between the arch and the sub-intradosal concrete may be prevented by. coating the surface of one or both with some material such as oil or a thin asphalt paint.

In the form shown in Figs. 4, 5, 6 and 7, there must be considered the efiect of back water loading that may occur when a structure of this type is placed in a river bed section. According to this invention, back water is permitted to pass from the extrados to the space between the intrados and the top of the sub-intradosal concrete, whichmay be formed by deflection and subsequent rising of the arch, or by settlement ofthe sub-intradosal concrete. The water may be admitted by means of drain pipes 16 through the arch or by inlets 17 which are here shown in the form of grooves inthe upper surface of the sub-intradosal concrete, which grooves run transversely of the arch. The ends of the pipes 16 are disposed in these grooves which may conveniently be filled with porous material 18. These fillers may be formed of porous mortar which'will permit water to pass lengthwise of the grooves and thus a pressure is permitted. to build up on the intrados of the arch, which pressure will be equal to the pressure from the water on the extrados. This arrangement provides equal pressure on both sides of the arch and therefore will I lighten the weight of the arch barrel to a certain extent. I

I claim z- 1. A masonry dam extending across an area of poor bearing material beneath it and having a foundation formed of an arch extending across said area with its abutments on solid material on opposite sides of said area, a superstructure supported at least in part on said arch, and masonry closing the space beneath the intrados of said arch, whereby deflection of the arch will transfer part of the load on the arch to said masonry and thence to said poor bearing material.

2. A masonry dam extending across a depression in the ground and comprising a superstructure, a foundation supporting said superstructure and comprising an arch extending across the lowest part of said depression, means closing the space beneaththe intrados of said arch, and walls extending from said arch to the material on the sides of the depression to transmit thrust to the arch from said material. a

3. A masonry dam extending across a depression in the ground and comprising a superstructure, a foundation supporting said superstructure and comprising an arch extending across the lowest part of said de pression, means closing the space beneath the intrados of said arch, and masonry disposed between said arch and the material on the sides of the depression to transmit thrust from said material to the arch.

4:. A masonry dam extending across an area of poor bearing material beneath it and having a foundation formed of an arch extending across said area with its abutments on solid material on opposite sides of said area, masonry closing the space, beneath the intrados of said arch whereby deflection of the arch will transfer part of the load on the arch to said masonry and thence to said poor bearing material, and means preventing the sub-intradosal masonry from forming a joint with the masonry in said arch, whereby the arch may act independently of said subintradosal masonry. V

5. A masonry dam extending across an area of poor bearing material beneath it and having a foundation formed of an arch extending across said area with its abutments on solid material on opposite sides of said area, masonry closing the space beneath the intrados of said arch, and means for admitting back water to the space between the intrados of the arch and the top of the sub-intradosal masonry.

SPENCER W. STEWART.

Images