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?

Follow-Up

 

69. Fill in the table giving short answers to the questions.

Kinds of dams   Questions	Masonry dams	Embankment dams
Gravity dam	Arch dam	…	Earth-fill dam	…
1. What is a shape of the dam?
2. What does a dam consist of?
3. What is the dam built of?
4. What types of the dam are there?
5. Where is the dam built? What foundation does the dam require?
6. What forces are the most and the least important in the dam?
7. What should the attention be paid to in order to reduce leakage?
8. Choose the best for every kind of dams: a) - the most expensive, b) - less expensive as less concrete is used, c) - usually expensive as well as a gravity dam because of formwork and reinforced steel, d) - less expensive than masonry dams, e) - the cheapest if proper material is available
9. Can you give the examples of every kind of dams? (names)
10. Are there other kinds of dams? What are they? (give as many as possible)

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

Warming-up

 

Study the following picture. Translate the terms into Russian.

 

a) spillway - ________	f) spillway crest - ________
b) cross section - ________	g) tainter gates - ________
c) forebay - ________	h) hydraulic jump - _______
d) tailwater - ________	i) bedrock - ________
e) flip lip - ________	j) stilling basin - ________

 

Reading Task: A

 

Find the translation of the following terms and memorize their meaning.

to narrow	elevation	overflow spillways
to widen	sufficient	chute spillways
the discharge of water	velocity	shaft spillway
the release of water	expansion	siphon spillway
gate	joint	side-channel spillway
safety valve	trench	past(prep.)
appurtenant	clay tile	a trough
flood	a conduit	perforated steel pipe
close limits	steep-slope	a sluiceway
to prefer	to maintain

 

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.

 

Comprehension Check