BACKGROUND OF THE INVENTION Most existing dams, classified according to the materials used to build them, comprise the following types: Earth fill dams-Earth fill dams are the most numerous. Their construction involves the use of materials originating from the excavations required and the use of locally available natural materials, large quantities of soil being moved. Earth fill dams require appurtenant concrete structures to serve as spillways and outlet works. Their principal disadvantage is that during construction or in the operational stage they may be damaged or even destroyed by the erosive action of water should it overtop the dam on account of insufficient spillway or river diversion capacity, the lack of other outlet facilities or operational error.

Rock fill dams-Rock fill dams are built with large quantities of rock of all sizes to provide stability. Suitable foundations are rock or compact sand and gravel. Like earth fill dams, rock fill dams require appurtenant concrete structures to serve as spillways and outlet works and are subject to damage or destruction by the overflow of water in case of overtopping. The rock fill mass buckles and may become actively stressed, cracks being opened in the mass itself or in the waterproofing membrane of the upstream facing, a fact that has troubled technicians in this area.

Concrete gravity dams-Concrete gravity dams are suitable for sites where there is a reasonably sound rock foundation. They need large concrete masses to resist water pressure and hence a good deal of time for construction with consequently increased costs.

Concrete arch dams-Concrete arch dams are suitable for narrow gorges and wherever the foundation at the abutments is solid rock capable of resisting arch thrust. They are the most economical existing dams, since they make full use of the resistance of concrete to compression although their formworks are more expensive, mainly when the arch has a double curve. Sites satisfying these conditions are rarely found nowadays.

Concrete buttress dams-Buttressed dams are built with reinforced concrete on good rock foundations. They require about 30% to 40% less concrete than solid gravity dams, but the increased formworks and reinforcement steel usually offset the savings in concrete.

SUMMARY OF THE INVENTION The dams constituting the subject of this invention are small dams in which a large part of the water pressure is absorbed by generic stays upstream made up of steel cables, bundles of steel strands, cables of composite carbon fibres, polymer fibres, or the like anchored in reinforced concrete buttresses and pylons or reinforced concrete blocks upstream pinned with tie rods to the foundation rock. The upstream water retaining element may be

composed of reinforced concrete slabs, vertical reinforced concrete arches and a reinforced concrete wall in dams of less height without buttresses. The construction of cable stayed dams uses considerably smaller quantities of materials than traditional methods.

Consequently it is less harmful to the environment and construction time is shorter, offering a feasible technical and economic solution in those cases in which it is applicable.

It allows slender dams to be built, practically eliminating the uplift acting on foundations in sites where, in the present state of the art, rock fill dams, concrete gravity dams and conventional buttress dams would otherwise be built.

DESCRIPTION OF THE DRAWINGS The invention will be more fully understand from the following detailed description taken in conjunction with accompanying drawings in which: Fig. 1 is a top diagram view of a generic cable stayed concrete buttress dam; Fig. 2 shows the vertical section A-A of buttress 5 of the dam appearing in Figure 1 ; Fig. 3 shows the vertical section B-B of spillway 13 of the dam appearing in Figure 1; Fig. 4 is a top diagram view of a generic cable stayed concrete multiple arch dam; Fig. 5 shows the vertical section C-C of buttress 5 of the dam appearing in Figure 4; Fig. 6 shows the vertical section D-D of spillway 13 of the dam appearing in Figure 4; Fig. 7 is a top diagram view of a generic cable stayed concrete dam ; Fig. 8 shows the vertical section E-E of concrete wall 36 of the dam appearing in Figure 7 ; Fig. 9 shows the vertical section F-F of buttress 25 of the spillway 13 of the dam appearing in Figure 7; Fig. 10 is a top diagram view of a generic cable stayed concrete buttress dam similar to that appearing in Figure 10 ; Fig. 11 shows the vertical section G-G of buttress 5 of the dam appearing in Figure 10; Fig. 12 shows the vertical section H-H of spillway 13 of the dam appearing in Figure 10.

DETAILED DESCRIPTION OF THE INVENTION For the purposes of a better understanding of this invention, a detailed description follows that makes reference to the attached figures.

Figure 1 shows a schematic view from above of the generic reinforced concrete cable stayed dam formed by buttresses 5 and by slabs 6, with spillway 13 in the centre formed by buttresses 25 at the ends, by buttresses 27 and by slabs 26 in the body of spillway 13. A large part of the water pressure from lake 32 is absorbed by generic stay cables 16 made up of steel cables, bundles of steel strands, composite cables of carbon fibres, polymer fibres or the like anchored upstream to buttresses 5,25, and 27 and to reinforced concrete blocks 17, anchored to rock 2 by tie rods 12, not shown in the figure. Should lake 32 be drained, in accordance with the case, wind pressure is absorbed by stay cables 23, downstream from the dam, of the same type as stay cables 16, anchored to the upper part of buttresses 5 and pylons 20, on both banks of river 29, which are anchored to rock 2 by tie rods 12, not shown in the figure.

Figure 2 shows the vertical section A-A of buttress 5 of the dam appearing in figure 1 with maximum water level MWL. Buttress 5 and slab 6 are restrained at the direct foundation or at cutoff wall 30, which passes through soil layer 1 and is set on rock 2, to which it may be anchored upstream by tie rods 12. Stay cable 16 is pinned upstream to buttress 5 by

adjustable anchorage 34 and to concrete block 17 by fixed replaceable anchorage 35.

Concrete block 17 is anchored to rock 2 by tie rods 12. Wind-bracing stay cable 23 is pinned downstream to the upper part of buttress 5 by fixed anchorage 35 and to pylon 20, shown in figure 1, by adjustable anchorage 34.

Figure 2 also shows a wind-bracing alternative for a dam of lower height with reinforced concrete support 10, which encases stay cables 16 upstream, downstream stay cables 23 shown in figure 1 being eliminated in this case.

Figure 3 shows the vertical section B-B of spillway 13 of the dam appearing in figure 1 with maximum water level MWL and normal water retaining level NWL. Buttresses-27 and 25, seen in side view, and slab 26 are restrained at the direct foundation or at cutoff wall 30, which passes through soil layer 1 and is set on rock 2, to which it may be anchored upstream by tie rods 12.

With further reference to figure 3, stay cable 16 is pinned upstream to buttress 27 by adjustable anchorage 34 and to concrete block 17 by fixed replaceable anchorage 35.

Concrete block 17 is anchored to rock 2 by tie rod 12. Adjustable anchorage 34 of stay cable 16, not shown in the figure, is seen on buttress 25.

Figure 4 shows a schematic view from above of the generic reinforced concrete cable stayed dam formed by buttresses 5 and by vertical cylindrical arches 31, with spillway 13 in the centre formed by buttresses 25 and by vertical cylindrical arches 37. A large part of the water pressure from lake 32 is absorbed by generic stay cables 16 formed of steel cables, bundles of steel strands, composite cables of carbon fibres, polymer fibres or the like anchored upstream to buttresses 5 and 25 and to reinforced concrete blocks 17 anchored to rock 2 with tie rods 12, not shown in the figure.

Figure 5 shows the vertical section C-C of buttress 5 of the dam appearing in figure 4 with maximum water level MWL. Buttress 5 and vertical cylindrical arch 31 are restrained at the direct foundation or at cutoff wall 30, which passes through soil layer 1 and is set on rock 2, to which it may be anchored upstream by tie rods 12. Stay cable 16 is pinned upstream to buttress 5 by adjustable anchorage 34 and to concrete block 17 by fixed replaceable anchorage 35. Concrete block 17 is anchored to rock 2 by tie rods 12.

Figure 6 shows the vertical section D-D of spillway 13 of the dam appearing in figure 4 with maximum water level MWL and normal water retaining level NWL. Buttress 25 and vertical cylindrical arch 37 are restrained at the direct foundation or at cutoff wall 30, which passes through soil layer 1 and is set on rock 2, to which it may be anchored upstream by tie rods 12. Stay cable 16 is pinned upstream to buttress 25 by adjustable anchorage 34 and to concrete block 17 by fixed replaceable anchorage 35. Concrete block 17 is anchored to rock 2 by tie rods 12.

Figure 7 shows a schematic view from above of the generic reinforced concrete cable stayed dam formed by wall 36, by spillway 13 in the centre formed by buttresses 25 and by wall 38.

A large part of the water pressure from lake 32 is absorbed by generic stay cables 16 formed of steel cables, bundles of steel strands, composite cables of carbon fibres, polymer fibres or the like anchored upstream to wall 36, to buttresses 25, to wall 38 and to reinforced concrete blocks 17 anchored to rock 2 by tie rods 12, shown in figure 8. Should lake 32 be drained, in accordance with the case, wind pressure is absorbed by stay cables 23, downstream from the dam, of the same type as stay cables 16, anchored by fixed anchorages 35 to the upper part of wall 36 and by adjustable anchorages 34 to pylons 20, on both banks of river 29, which are anchored to rock 2 by tie rods 12, not shown in the figure.

Figure 8 shows the vertical section E-E of reinforced concrete wall 36 of the dam appearing in figure 7 with maximum water level MWL. Wall 36 is restrained at the direct foundation or at cutoff wall 30, which passes through soil layer 1 and is set on rock 2, to which it may be anchored upstream, by tie rods 12. Stay cable 16 is pinned upstream to wall 36 by adjustable anchorage 34 and to. concrete block 17 by fixed replaceable anchorage 35. Concrete block 17 is anchored to rock 2 by tie rods 12.

Wind-bracing stay cable 23 is pinned downstream to wall 36 by fixed anchorage 35 and to pylon 20 by adjustable anchorage 34, shown in figure 7. Figure 8 also shows a wind- bracing alternative for a dam of lower height with reinforced concrete support 10, which encases stay cables 16 upstream, pylons 20 and downstream stay cables 23 shown in figure 7 being eliminated in this case.

Figure 9 shows the vertical section F-F of buttress 25 of spillway 13 of the dam appearing in figure 7 with maximum water level MWL and normal water retaining level NWL.

Buttress 25 and concrete wall 38 are restrained at the direct foundation or at cutoff wall 30, which passes through soil layer 1 and is set on rock 2, to which it may be anchored upstream by tie rods 12. Stay cable 16 is pinned upstream to buttress 25 by adjustable anchorage 34 and to concrete block 17 by fixed replaceable anchorage 35. Concrete block 17 is anchored to rock 2 by tie rods 12.

Figure 10 shows a schematic view from above of the generic reinforced concrete cable stayed dam formed by buttresses 5 and by slabs 6, with spillway 13 in the centre formed by buttresses 25 at the ends, by buttresses 27 and by slabs 26 in the body of spillway 13. This dam is similar to that appearing in Figure 1, from which it differs by the anchorage upstream of stay cables 16. A large part of the water pressure from lake 32 is absorbed by generic stay cables 16 formed of steel cables, bundles of steel strands, composite cables of carbon fibres, polymer fibres or the like anchored upstream to buttresses 5,25, and 27 and to pylons 21 on the shores of lake 32, anchored to rock 2 by tie rods 12, shown in the figures 11 and 12. Should lake 32 be drained, in accordance with the case, wind pressure is absorbed by stay cables 23, downstream from the dam, of the same type as stay cables 16, anchored to the upper part of buttresses 5 and pylons 20, on both banks of river 29, which are anchored to rock 2 by tie rods 12, not shown in the figure.

Figure 11 shows the vertical section G-G of buttress 5 of the dam appearing in figure 10 with maximum water level MWL. Buttress 5 and slab 6 are restrained at the direct foundation. or at cutoff wall 30, which passes through soil layer 1 and is set on rock 2, to which it may be anchored upstream by tie rods 12. Stay cable 16 is pinned upstream to buttress 5 by fixed anchorage 35 and to pylon 21 on the shore of lake 32, by adjustable anchorage 34. In buttress 5, at the height of anchorage 35, appears the cross-section of horizontal girder 40, which extends along the dam and is also seen in plane view in figure 10 between buttresses 5 and 25 on both sides of spillway 13. Pylon 21 is anchored to rock 2 by tie rods 12. Wind-bracing stay cable 23 is pinned downstream to the upper part of buttress 5 by fixed anchorage 35 and to pylon 20 on the bank of river 29, shown in figure 1, by adjustable anchorage 34.

Figure 12 shows the vertical section H-H of spillway 13 of the dam appearing in figure 10 with maximum water level MWL and normal water retaining level NWL. Buttresses 27 and 25, which appear in side view and slab 26, are restrained at the direct foundation or at cutoff wall 30, which passes through soil layer 1 and is set on rock 2, to which it may be

anchored upstream by tie rods 12. Stay cable 16 is pinned upstream to buttress 27 by fixed anchorage 35 and to pylon 21, on the shore of lake 32, by adjustable anchorage 34. In buttress 27, at the height of anchorage 35, appears the cross-section of horizontal girder 40.

Pylon 21 is anchored to rock 2 by tie rods 12.

There follows a description of the methods of constructing the concrete cable stayed dams, no mention being given of the outlet works and river diversion works that follow the current procedures utilised.

Method of constructing the generic concrete cable stayed dam appearing in figures 1, 2 and 3, which method comprises : - the excavation of the trench for the setting of the direct foundation or cutoff wall 30 ; - the pouring of the reinforced concrete of direct foundation 30 or, in accordance with the case, the pouring of the reinforced concrete cutoff wall 30 along the entire dam; - the pouring of the reinforced concrete of buttresses 5 and slabs 6 of the dam, of buttresses 25,27 and slabs 26 of spillway 13, openings being left for stay cables 16 and 23, in accordance with the case, the dam being shored up or provided with temporary stays; - the excavation of pits for concrete blocks 17 upstream and pylons 20 downstream, when necessary in accordance with the height of the dam, and the pouring of the reinforced concrete of the said blocks 17 and pylons 20; - in accordance with the case, the anchoring upstream of cutoff wall 30 and the anchorage of concrete blocks 17 and pylons 20 with tie rods 12 to rock 2; - the installation of stay cables 16 upstream, using fixed replaceable anchorages 35 in concrete blocks 17 and adjustable anchorages 34 in buttresses 5,25 and 27; - the installation of wind-bracing stay cable 23 downstream, being pinned to buttresses 5 by fixed anchorages 35 and to pylons 20 by adjustable anchorages 34 or for a dam of lower height the pouring of the reinforced concrete of supports 10 upstream, which encase some of stay cables 16 ; Method of constructing the generic concrete cable stayed dam appearing in figures 4, 5 and 6, which method comprises: - the excavation of the trench for the setting of the direct foundation or cutoff wall 30 ; - the pouring of the reinforced concrete of direct foundation 30 or, in accordance with the case, the pouring of the concrete of cutoff wall 30 along the entire dam ;; - the pouring of the reinforced concrete of buttresses 5 and of vertical cylindrical arches 31 in the body of the dam, of buttresses 25 and of vertical cylindrical arches 37 of spillway 13, with placement on the direct foundation or on cutoff wall 30, openings being left for stay cables 16; - the excavation of pits for concrete blocks 17 upstream and pouring of the reinforced concrete of the said blocks 17; - in accordance with the case, the anchoring of cutoff wall 30 and of concrete blocks 17 upstream with tie rods 12 to rock 2 ; - the installation of stay cables 16 upstream, using fixed replaceable anchorages 35 in blocks 17 and adjustable anchorages 34 in buttresses 5 and 25; Method of constructing the generic concrete cable stayed dam appearing in figures 7, 8 and 9, which method comprises:

- the excavation of the trench for the setting of the direct foundation or cutoff wall 30 ; - the pouring of the reinforced concrete of direct foundation 30 or, in accordance with the case, the pouring of the reinforced concrete of cutoff wall 30 along the entire dam; - the pouring of the reinforced concrete of wall 36 of the dam, of buttresses 25 and wall 38 of spillway 13, with placement on the direct foundation or on cutoff wall 30, openings being left in wall 36 for stay cables 16 and 23, as well as in buttresses 25 and in wall 38 for stay cables 16, in accordance with the case, the dam being shored up or provided with temporary stays; - the excavation for concrete blocks 17 upstream and pylons 20 downstream, when necessary in accordance with the height of the dam, and the pouring of the reinforced concrete of the said blocks 17 and pylons 20; - in accordance with the case, the anchoring upstream of cutoff wall 30, and the anchoring of concrete blocks 17 and pylons 20 with tie rods 12 to rock 2; - the installation of stay cables 16 upstream, using fixed replaceable anchorages 35 in blocks 17 and adjustable anchorages 34 in buttresses 25 and walls 36 and 38; - the installation of wind-bracing stay cables 23 downstream, when necessary in accordance with the height of the dam, anchored to wall 36 by fixed anchorages 35 and to pylons 20 by adjustable anchorages 34 or the pouring of the reinforced concrete of supports 10, which encase some stay cables 16 upstream; Method of constructing the generic concrete cable stayed dam shown in figures 10,11 and 12, which method comprises: - the excavation of the trench for the setting of the direct foundation or of cutoff wall 3 0 ; - the pouring of the reinforced concrete of direct foundation 30 or, in accordance with the case, the pouring of the reinforced concrete of cutoff wall 30 along the entire dam; - the pouring of the reinforced concrete of buttresses 5 and slabs 6 of the dam, of buttresses 25 and 27 and slabs 26 of spillway 13, with setting on the direct foundation or on cutoff wall 30, openings being left for stay cables 16, as well as for wind-bracing stay cables 23, in accordance to the case, the dam being shored up or provided with temporary stays; - the excavation of pits for pylons 21 upstream, on the shores of lake 32, and for pylons 20 downstream, on the banks of river 29, when necessary in accordance with the height of the dam, and the pouring of the reinforced concrete of the said pylons 21 and 20; - in accordance with the case, the anchoring upstream of cutoff wall 30 and the anchoring of pylons 21 and 20 with tie rods 12 to rock 2; - the installation of stay cables 16 upstream, using adjustable anchorages 34 in pylons 21 and fixed anchorages 35 in buttresses 5, 25 and 27; - the installation of wind-bracing stay cables 23 downstream, when necessary in accordance with the height of the dam, pinned to buttresses 5 with fixed anchorages 35 and to pylons 20 with adjustable anchorages 34.