2015-04-17
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1. There is a variety of solutions used for construction of bridge foundations. Some of these solutions are very (высокотехнологичный) while others date back to ancient Rome. The method depends on the depth and speed of the water, as well as on the geological conditions.
2. The experts always carefully investigate (подошва фундамента) conditions because the foundation must work in tandem with the soils to support the bridge. The cost of the foundation investigation using (зондирование), (гидролокация), and borings can be millions of dollars.
3. One of the construction methods is (свайный фундамент). In this case, the foundation consists of long steel, reinforced concrete or wood poles, known as piles. Pile-driving equipment hammer or drives piles into soft soils until the pile ends contact a hard layer. If the piles are driven rather deep, the friction between the pile and the soil can support the load. A multi-span bridge may have hundreds of piles driven in groups consisting of dozens of individual piles.
4. (Фундамент на буровых сваях) are an alternative to pile foundations. In this type of foundation, the workers drive a deep (скважина) by rotary methods using a big auger. Normal shaft diameters range from 15.5 cm to 1.42 m. The hole is cut through soil or rock to the desired depth, and fresh concrete and reinforcing steel are placed into a drilled hole. A drilled shaft is a deep foundation system.
5. Caving soils and water infiltration in drilled shafts require temporary or permanent steel casing placed in the hole to maintain the sides of the excavation. To keep the hole from (обрушение) the workers lower a steel reinforcing basket into it and fill it with concrete or dense clay-water slurry. Slurry keeps the hole from collapsing until the steel and concrete displace it. Drilled shafts can support high (осевые и поперечные нагрузки).
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6. The other type of foundation is (фундамент на естественном основании) that rests on a natural bed. The workers build this foundation at a shallow depth on solid rock or very hard soils. The spread footing requires a suitable rock surface that must be specially created. A solid concrete block is cast directly on the prepared surface.
7. Large cranes working from the shore can build foundations in the small body of water. If the water barrier is vast, special barges are required. In other cases, big steel tubes or boxes known as (опускной колодец) are used. These structures, placed in the water, are pumped out. Cofferdams protect the workers constructing the foundation inside these structures.
8. Where cofferdams are useless, the most (реальный) method of constructing foundations is the caisson. Caisson foundations need soil of adequate bearing strength. Caissons provide protection for the workers against collapse of soil and water (давление). Usually large caissons are used singly and small ones may be used either singly or in groups.
9. Fast moving water can undermine bridge foundations. Engineers have to combat scour by placing piles or other items around the foundations. They deflect and diffuse the (водные течения). However, after each flood, bridges should be closed until divers or underwater cameras inspect the foundations carefully to ensure that they remain safe.
Word combinations: Axial and lateral loads, cofferdams, collapsing, drilled shafts, feasible, high-tech, hdo the workersole, pile foundations, pressure, probing, sonar, a spread footing, subgrade, water currents
