Arch Dam
Arch dam may be defined as a solid wall curved in plan standing across the entire width of the river valley in a single span. The dam body is usually made up of cement concrete, although rubble and stone masonry has also been used in the past.
This divider will fundamentally be halfway as a cantilever holding divider standing up from its base and incompletely the heap will be exchanged to the side dividers of the gorge, which must be sufficient. The greater the load that will be transferred to the sides of canyon, the greater will be the economy of the dam thickness.
This economy in the dam thickness can be further increased considerably by making the dam body not only curved in plan, but also curved in the section. Such a non-vertical dam is known as double curvature or shell arch dam, because such dams are designed as shell structure.
Simple arch dam which exchange an expansive piece of their stacking by cantilever activity, may likewise be of various kinds, since their powers might be either vertical or cantilever. Depending upon the shape consideration, simple arch dams can be divided into 3 types :
- Constant Radius Arch Dam.
- Variable Radius Arch Dam.
- Constant Angle Arch Dam.
Types of Arch Dams Explained in Detail.
Constant Radius Arch Dam :
A constant radius arch dam is that in which the radii of the outside curved surface are equal to all elevations from top to bottom. The centers of all such circular arch’s called extrodos wall, therefore evidently lie on one vertical line. However the introdos has gradually decreasing radius from top to bottom, so as provided increased concrete thickness towards the base for accounting the proportionally increasing hydrostatic water pressure of the reservoir. The dam body will therefore be triangular in C/S with U/S face vertical and minimum thickness at the top.
Evidently it is only the radii of the introdos which decreases with depth, while the centers of all such circular arch’s continue to lie on the same vertical line, on which the center of extrodos lies. Hence in such dam’s the center of extrodos and introdos as well as the center line of horizontal arch ring at various elevations lie on a straight vertical line that passes through center of horizontal arch ring at the crest.
Such dam is therefore sometimes called as constant center arch dam, although strictly speaking, this center is not at one point but lies at different height and along one vertical line.
Variable Radius Arch Dam :
A variable radius arch dam is the one in which the radii of extrodos curve and of introdos curve may vary at various elevations. Being maximum at the top and certain minimum at the bottom. This makes the focal edges as expansive as could be allowed with the goal that the most extreme curve proficiency might be gotten at all heights.
In typical design of such dam, the down stream face of the dam at the center line is vertical, while at all over locations there is better on both the sides except at the abutments, where again the U/S sides become vertical. If overhangs are permitted, due to availability of stronger foundations then the faces at the crown as abutments may be provided with overhang.
Clearly, since in such dam the focal point of different curve rings at various rises don’t lie on a similar vertical line, it is otherwise called variable radius curve dam. Such dams are preferred for V shaped valley as compared to constant radius arch dam, which may be preferred for comparatively wider U shaped valley.
Constant Angle Arch Dam :
A consistent angle curve dam is an uncommon sort of variable dam in which the focal edges of level curve rings are of same size at all rises. The design of such dam, thus be made by adopting the best central angle 133°34′ and hence such a dam proves to be most economical out of the three types of ordinary arch dams.
Such type of dam cannot be constructed on weak foundations as it involves providing overhangs at abutments for which storage foundations are essential.
Related Article : Reservoir storage zones and its types.