Decide whether the following statements are true or false according to the text.

1) Gravity dams use its own dead weight to resist the vertical force of the water.

2) The shape of the gravity dam resembles a triangle.

3) The shallower the water, the more horizontal pressure it exerts on the dam.

4) At the surface of the reservoir, the water is exerting maximum pressure.

5) At the bottom of the reservoir, the water is exerting no pressure.

6) For gravity dams, good pervious foundations are essential.

7) The solid form of the gravity dam is more widely used.

8) The hollow dam is less economical to construct.

9) The construction works on a gravity dam may be divided into two stages.

10) The foundation must be excavated to solid rock before any concrete will be poured.

11) After excavation cavities or faults in the foundation are sealed with concrete or grout.

12) A grout curtain is placed near the top of the dam to increase seepage and uplift.

13) The maximum width of a block is usually about 50 ft and maximum height of a single block is usually about 5 ft on medium-height dams.

14) Block are sprinkled with water and so protected from the drying.

15) The lateral surfaces of each block are painted with an asphaltic emulsion to prevent adherence of adjoining sections.

16) Metal water stops are also placed in the vertical construction joints near the downstream face to prevent leakage.

17) Inspection galleries are formed after the concrete has been placed.

18) Water never seeps into the dam.

19) To avoid cracks, special low-heat cement may be used.

20) For obtaining best results the temperature of the concrete mix should be between 10⁰ and 26.6⁰ C.

Answer the following questions.

1) What does the stability of gravity dams depend on?

2) What do gravity dams use to resist the horizontal force of the water?

3) Are gravity dams usually straight or rectangular in plan?

4) May they be slightly curved or convex?

5) The shape of the gravity dam resembles a square, doesn’t it?

6) What does horizontal pressure depend on?

7) Is water exerting no pressure at the surface of the reservoir?

8) Is water exerting minimal pressure at the bottom of the reservoir?

9) What is the base of a concrete gravity dam equal to?

10) Is good impervious foundation essential for the gravity dams?

11) What is the classification of gravity dams?

12) What type of a gravity dam is more widely used?

13) What type of a gravity dam is more economical to construct?

14) What must be done before the construction work in a river channel can be started?

15) What is the flow diverted to one side of the channel by?

16) What happens when the work on the lower side of the dam is completed?

17) What must be excavated to solid rock before any concrete will be poured?

18) What is sealed with concrete or grout after excavation?

19) Why is a grout curtain placed near the heel of the dam?

20) What does the size of blocks depend on?

21) Are block poured alternately?

22) Why are individual sections sprinkled with water?

23) When are the lateral surfaces of each section painted with an asphaltic emulsion? Why?

24) What is provided between sections? Why?

25) Are metal water stops also placed in the vertical or horizontal construction joints near the upstream face?

26) Do inspection galleries permit access to the interior of the dam?

27) When are inspection galleries formed?

28) What may these galleries be necessary for?

29) When may cracks develop?

30) What may be used to avoid cracks?

31) Can you name the most famous gravity dams in the world?

Make a plan of the text and then write a short summary of it.

Match the meanings of the terms with their definitions.

outlet, valve, inspection, joint, cracks, interior, gate, maintenance

1) _______ slides across an opening, often folding into a smaller space as it is opened.

2) _______ is a device which allows air or liquid to enter, or be prevented from entering.

3) _______ are long narrow spaces.

4) _______ is the process of looking at carefully in order to discover information, especially about quality or correctness.

5) _______ is the process of keeping (a road, machine, building, etc.) in good condition.

6) _______ is a way, especially a pipe or hole for liquid or gas to go out.

7) _______ is the inside part of something.

8) _______ is a place where two things are fixed together.

Choose the odd word.

1) to liberate / to restrict / to discharge / to release / to free

2) to preserve / to protect / to attack / to defend

3) to permit / to allow / to let / to admit / to prohibit

4) access / exit / path / entrance / entry / admission

5) surface / covering / exterior / top / inside

6) to form / to build / to destroy / to create / to make / to construct

7) to accumulate / to leak / to seep / to escape / to pass / to discharge

Match the words with their synonyms.

Find in the text the opposites of the following words.

Fill in the correct prepositions, then choose any five items and make sentences.

1) to be straight ___ plan; 2) to exert pressure ___ a dam; 3) ___ the surface of a reservoir; 4) ___ the bottom of a reservoir; 5) to divert water ___ outlets ___ one side of a channel; 6) to be sealed ___ concrete; 7) to force ___ pressure ___ holes; 8) to place ___ blocks; 9) to paint ___ emulsion; 10) to act ___ a monolith.

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

Read the text carefully paying attention to the words in italics. Answer the following question.

Can arch dam be constructed on any site?

Text B                                                                  Arch Dams

An arch dam is built in a convex arch facing the reservoir, and owes its strength essentially to its shape, which is particularly efficient in transferring hydraulic forces to supports. In the arch dams, stability is obtained by a combination of arch and gravity action. If the upstream face is vertical the entire weight of the dam must be carried to the foundation by gravity while the distribution of the normal hydrostatic pressure between vertical cantilever and arch action will depend upon the stiffness of the dam in a vertical and horizontal directions. When the upstream face is sloped the distribution is more complicated.

The same forces which act on gravity dams also act on arch dams, but their relative importance is different. Because of the narrow base width of arch dams, uplift forces are less important than for gravity dams. However, internal stresses caused by ice pressure and temperature changes may become quite important in arch-dam design.

The simplest approach to arch analysis is to assume that the horizontal water load is carried by arch action alone. Most early arch dams were designed on this basis.

Arch dams must be built on solid rock foundation. Seams and pockets in the foundation and abutments are grouted in the usual manner. Since the cross-section of an arch dam is relatively thin care must be taken in the mixing, pouring and curing of the concrete in order to secure its resistance to seepage and weathering. Concrete is placed by techniques similar to those utilized for gravity dams, usually 5-ft lifts, although I0-ft lifts may be also placed at the upper part of an arch where the section is very thin. A layer of mortar is usually placed between lifts to ensure better bond. Small arch dams are provided with only radial construction joints, while large arch dams have circumferential joints as well. All joints must have keyways and in order to prevent leakage water-stops must also be provided. To minimize temperature stresses, the closing section of the dam is poured only after the heat in the other sections is largely dissipated.