2.5. Read the text.

1. On the basis of word-building chains with the stems “base” and “structure” try to define:

– the most common classification of different categories of dams;

– whether there is any information concerning the main structural components of the rockfill dams in the text and state the paragraphs it is in.

2.6. Translate the text into Ukrainian: text a.

1. Dams may be classified into a number of different categories depending upon the purpose of the classification. It is convenient to consider 3 broad classifications: according to materials comprising the structure, use and hydraulic design.

2. The most common way of classifying the dams is based upon choosing the materials comprising the structure. This classification also usually recognizes the basic type of design such as, for example, concrete gravity dam or concrete arch dam.

3. In discussing the diversity of dams, the specialists point out that earthfill dams are the most widespread among them, principally because their construction involves utilization of materials in the natural state requiring a minimum of processing. Moreover, the foundation requirements for earthfill dams are less stringent than for constructing other types.

4. The classification of earthfill dams includes several types-semi-hydraulic-fill, hydraulic-fill and rolled-fill types – the latter being most economical.

5. Earthfill dams require supplementary structures to serve as spillways. The principal disadvantage of an earthfill dam is that its damaging or even destroying may be possible under the erosive action of water flowing over it if sufficient spillway capacity is not provided. It is also subject to undergoing serious damage or even failure due to animals’ burrowing unless being taken special precautions.

6. It is important to find a way of eliminating the possibility of ruining the dam. To be safe, an earth dam must satisfy four basic requirements: it must not be overtopped by flooding which most certainly cut right through it, seepage under the dam must not be allowed to undermine it, seepage through the embankment must not wash it away and the slopes of the embankment must be so constructed that they will not slip.

7. The rockfill dam has two basic structural components – an impervious membrane and an embankment which supports the membrane. The embankment usually consists of an upstream section of dry rubble masonry and a downstream section of loose rockfill.

8. The impervious membrane is most commonly constructed of concrete: a concrete slab, asphaltic concrete paving or steel plates; or it may be an interior thin core of impervious soil.

9. Like the earth embankments, the rockfill dam is subject to damaging or destructing by water overflowing and so must be provided with a spillway of adequate capacity to prevent overflowing of the dam. The only suitable foundation for rockfill dams are rock or compact sand and gravel.

10. Rockfill dams have enjoyed a fine safety record and up to 2008 none had failed as a result of any structural defects.

11. In addition to improving existing construction technologies, a research is being conducted in Ukraine and abroad for developing fundamentally different types of dams.