Concrete Dam Characteristics

1.6. Concrete dam types and characteristics:

Concrete dams are constructed of mass concrete. Face slopes are dissimilar, generally steep downstream and near vertical upstream, and dams have relatively slender profiles dependent upon the type. This group includes all types of concrete dams as,

1-Gravity Dams: The concrete gravity dam is made of roller compacted concrete (RCC) or masonry building and adopted to sites having sound rock foundation. Gravity dams depend on their weight in stability. However, low structures may be founded on alluvial foundations provided with adequate cutoffs. Spillway is a monolithic part of the dam as seen in Figure (2-3) .

Figure (2-5) Gravity Dams

2- Arch Dam: A concrete arch dam is built at sites where the

Flat slab damns and multiple arch dams are the two common types of buttressed concrete dams Figure (2-5) . Figure (2-5) Buttress Dams

A comparison of the general characteristics of concrete dams with those of the embankment dam suggests the following inherent disadvantages for the former.

1. Concrete dams are relatively demanding with respect to foundation conditions, requiring sound and stable rock.

2. Concrete dams require processed natural materials of suitable quality and quantity for aggregate, and the importation to site and storage of bulk cement and other materials.

3. Traditional mass concrete construction is relatively slow, being labor intensive and discontinuous, and requires certain skills, e.g. for formwork, concreting, etc.

4. Completed unit costs for mass concrete, i.e. cost per cubic meter, and are very much higher than for embankment fills, typically by an order of magnitude or more. This is seldom counterbalanced by the much lower volumes of concrete required in a dam of given height.

1.7. Design and Construction of New embankment Dams:

The design and construction of embankment dams is complex because of the nature of the varying foundation conditions and range of properties of the materials available for

(e) Design safety factors : The designing engineer shall use the following minimum safety factors: 1.75 for horizontal shear at base of fill; 1.5 for horizontal shear within the fill due to seepage through the outer face; 1.5 for bearing capacity of foundation soils; 1.5 for protection against shear failure of any circular arc in either inside or outside slope. It is imperative that water pressure distribution be included in the analyses.

Construction phase:

This phase includes preparation of subsequent construction contracts, review of selected construction contracts, site visits, support for claims and modifications, development of operation and maintenance (O&M) manuals, and preparation and maintenance of as-built drawings. Site visits must be made to verify that conditions match the assumptions used in designing the project features.

Operation and maintenance