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Fill in the gaps with the right word.
1)______ usually consist of a rock toe or a drainage 2)______ of coarse material in which seepage water collects and 3)______ to a point where it can be safely discharged. To 4)______ movement of fine materials from the dam into the 5)______, the drain material is graded from relatively fine on the 6)______ of the drain to coarse near the centre. A 7)______ blanket extends farther under the dam than a rock 8)______ does. If a pervious foundation layer is overlain by a 9)_______ pervious layer, relief wells or drain trench through the 10)_____ layer may be necessary to permit escape of seepage 11)______. Match, translate and answer the following questions. Make abstracts of the texts. a) Zoned embankments b) Diaphragm-type dams c) Rock-fill dams
1) _________ are built of coarse rock, which provides structural stability with a concrete membrane on the upstream slope as a water barrier. Ø Where is a concrete membrane as a water barrier used?
2) __________ have a thin central section of concrete, steel or timber which serves as a water barrier, while the surrounding earth or rock fill provides stability. Thin concrete sections are easily cracked by differential (перепад) earth loads, and it is difficult to obtain a perfectly watertight barrier from timber or steel. In addition, the diaphragm must be tied into bedrock or a very impermeable material is required if excessive seepage is to be avoided. Ø What serves as a water barrier, while the surrounding earth or rock fill provides stability? Ø Thin concrete sections are easily cracked by differential earth loads, aren’t they? Ø Is it difficult to obtain a perfectly watertight barrier from timber or steel? Ø What is required if excessive under seepage is to be avoided?
3) __________ usually have a central zone of selected material to form a relatively impermeable core and outer shells of more pervious material for stability. This construction is widely used in earth dams and is always selected when suitable materials are available. Even though clay is a highly impermeable material it is not always possible to build the best core from this material. The most satisfactory cores are made of clay mixed with sand and fine gravel. Ø Why has this type of dam a central zone of selected material? Ø Is this construction widely used in earth dams? Ø When is this type of dam always selected? Ø Is it always possible to build the best core from clay? Ø What are the most satisfactory cores made of?
69. Fill in the table giving short answers to the questions.
Read the texts again and get ready to speak about the process of construction and main features of one type of dams. Use the information from the previous task. UNIT V SPILLWAYS, GATES AND OUTLET WORKS
Study the following picture. Translate the terms into Russian.
Find the translation of the following terms and memorize their meaning.
Read the text to get the gist of it. Answer the following questions. a) What is a spillway? b) What are the spillways used for?
Text A Spillways In the design of almost every dam there must be a spillway to permit the discharge of water. A spillway is necessary to discharge floods and prevent the dam from being damaged. Gates on the spillway crest, together with sluiceways, permit one to control the release of water downstream for various purposes. A spillway is the safety valve for a dam. It must have the capacity to discharge major floods without damage to the dam or any appurtenant structures at the same time keeping the water level in the reservoir below some predetermined maximum level. An overflow spillway is a section of dam designed to permit water to pass over its crest. Overflow spillways are widely used on gravity, arch and buttress dams. Water flows over the crest of a chute spillway into a steep-sloped open channel which is called a chute, or trough. The channel is usually constructed of reinforced- concrete slabs 10 - 20 in thick. Such a structure is relatively light and is well adapted to earth or rock-fill dams when topographic conditions make it necessary to place the spillway on the dam. A chute spillway may be constructed around the end of any type of dam when topographic conditions permit. Such a location is preferred for earth dams to prevent possible damage to the embankment. The chute is sometimes of constant width. But it is usually narrowed for economy and then widened near the end to reduce discharge velocity. Expansion joints are usually required in chute spillways at intervals of about 30 ft. They should be as watertight as possible. Drains under the spillway are highly desirable. The drains may be rock-filled trenches, clay tile or perforated steel pipes. A side-channel spillway is one in which the flow after passing over the crest is carried away in a channel running parallel to the crest. This type of spillway is used in narrow canyons where sufficient crest length is not available for construction of overflow or chute spillways. In a shaft spillway the water drops through a vertical shaft to a horizontal conduit which conveys the water past the dam. A shaft spillway can often be used where there is no adequate space for other types of spillways. Small shaft spillways may be constructed entirely of metal or concrete pipe or clay tile. The large vertical shaft is usually of reinforced concrete. If space is limited, the siphon spillway may be used. Siphon spillways have the advantage that they can automatically maintain water-surface elevation within very close limits.
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