37. Translate the following extracts into English using the vocabulary of the text.

1) Плотина – гидротехническое сооружение, перегораживающее реку для подъема уровня воды в ней, сосредоточения напора в месте расположения сооружения или создания водохранилища. По основному материалу различают земляные, каменные, бетонные, железобетонные, деревянные и другие плотины. Плотины используются также для защиты земель от моря.

2) Водосливные плотины возводятся, чтобы повысить уровень воды в реке или отвести водоток, что обычно необходимо при строительстве электростанций, для обеспечения судоходства или орошения земель.

3) Глухими плотинами (без пропуска воды) перегораживают водоток и создают водохранилища, предназначенные для обеспечения городов водой или электроэнергией либо для ирригационных целей и т.п. У многих плотин этого типа верхняя часть устраивается так, что при необходимости может служить водосбросом.

4) Плотина противодействует напору воды либо собственным весом (гравитационные плотины), либо своей конструкцией, силовые элементы которой обеспечивают устойчивость всего сооружения (арочные, контрфорсные плотины).

38. Read the texts again and make notes under the following headings. Then use your notes to talk about dam classifications.

1. What is a dam?

2. Types of dams.

3. Why are dams built?

4. Forces acting on a dam.

PART 2

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

dead weight	solid rock	adjoining
straight	to pour	a keyway
in plan	a cavity	shear
slightly	a fault	adjacent
to be curved	a grout curtain	a joint
to resemble	heel of a dam	solid
a triangle	to drill	hollow
pressure	a block	to permit
to exert	dimension	access
water stops	to alter	maintenance
inspection galleries	alternately	a gate
a cofferdam	to sprinkle	a valve
to proceed	lateral surfaces	outlets
to complete	asphaltic emulsion	to seep
intercepting drains	adherence	to shrink
overflow dams	low-heat cement	to liberate
non-overflow dams	a crack	to paint

2. Skim the text.

Text A Gravity Dams

The stability of gravity dams depends on their own weight. They use its own dead weight to resist the horizontal force of the water. Gravity dams are usually straight in plan although sometimes they may be slightly curved. The shape of the gravity dam resembles a triangle. This is because of the triangular distribution of the water pressure. The deeper the water, the more horizontal pressure it exerts on the dam. So at the surface of the reservoir, the water is exerting no pressure and at the bottom of the reservoir, the water is exerting maximum pressure.

Generally the base of a concrete gravity dam is equal to approximately 0.7 times the height of the dam. For this type of dams, good impervious foundations are essential.

The Gilboa Dam in the Catskill Mountains of New York State is an example of a "solid" gravity dam.

Gravity dams are classified as “solid” or “hollow”. The solid form is more widely used, though the hollow dam is more economical to construct. Gravity dams can also be classified as “overflow” (spillway) and “non-overflow”.

Before the construction work in a river channel can be started, the stream flow must be diverted. In two stage construction the flow is diverted to one side of the channel by a cofferdam while work proceeds on the other side. After the work on the lower side of the dam is completed, flow is diverted through outlets in this portion while work proceeds in the other half of the channel.

The foundation must be excavated to solid rock before any concrete will be poured. After excavation cavities or faults in the underlying strata are sealed with concrete or grout. Frequently a grout curtain is placed near the heel of the dam to reduce seepage and uplift. Grout cement and water sometimes mixed with a small amount of fine sand is forced under pressure into holes drilled into the rock.

The Gilboa Dam in the Catskill Mountains of New York State is an example of a "solid" gravity dam.

Concrete for the dam is usually placed in blocks depending on the dimensions of the dam. On large dams the maximum width of a block is usually about 50 ft. Maximum height of a single block is usually about 5 ft. Sections are poured alternately so that each block can stand several days before another one is poured next to it or on its top. After individual sections are poured, they are sprinkled with water and so protected from the drying. After the forms are removed, the lateral surfaces of each section are painted with an asphaltic emulsion to prevent adherence of adjoining sections. Keyways are provided between sections. They carry the shear from one section to the adjacent one and make the dam act as a monolith. Metal water stops are also placed in the vertical construction joints near the upstream face to prevent leakage. Inspection galleries to permit access to the interior of the dam are formed as the concrete is placed. These galleries may be necessary for grouting operations, for inspection and maintenance of gates and valves and as intercepting drains for water which seeps into the dam.

When concrete sets, a great deal of heat is liberated and the temperature of the mass is raised. As the concrete cools, it shrinks, and cracks may develop. To avoid cracks, special low-heat cement may be used. For obtaining best results the temperature of the concrete mix should be between 50 and 80 ⁰ F.