Read the text to have a clear idea of building materials and construction technologies for piers and foundations. Go down the word list and take note of professional terminology.

Bridges are designed, first, to carry their own permanent weight, or dead load; second, to carry traffic, or live loads; and, finally, to resist natural forces such as winds or earthquakes. All bridges need to be secure at the foundations and abutments. In most cases, bridge piers are made of concrete and reinforced concrete. Steel piers are used for flyovers and trestle bridges but not so frequently. The commonly used concrete pier may be subdivided into three groups according to construction technologies:

1. Monolithic or in situ concrete piers (fig. 13.1a). The concrete is poured against the falsework in situ. The falsework determines the pier shapes and dimensions.

2. Precast piers (fig. 13.1b). The piers are made of prefabricated concrete blocks.

3. Composite piers. They are used on a large scale and built from the precast concrete units and in situ concrete.

The methods of building foundations may be rather various and depend on geological conditions, ground strength, pier types and sizes, loads from the spans and piers. Where the soil is especially weak, wooden or steel piles are driven to support the foundations. After the concrete piers and abutments have hardened sufficiently, the erection of a concrete or steel superstructure begins.

Foundations are subdivided into two large groups: shallow foundations (fig. 13.1d) and deep foundations (fig. 13.1e, f, and g).

Shallow foundations are usually designed as monolithic ones on the natural bed. This technology is rather cheap and simple, but it is suitable for solid rock only (fig. 13.1d). The construction of shallow foundations begins with trench excavation. Rather deep trenches, excavated in a dry place for the flyover abutments or piers, viaducts or trestle bridges, demand a watertight enclosure or a sheet piling. The same is done if a trench is excavated in a river (fig. 13.1d) because the bed must be pumped dry to permit the pier construction. A sheet piling is made of metal bars driven to the calculated depth, into the ground, by a pile driver. Horizontal framing components are constructed of heavy timber, steel, or a combination of the two, hold the vertical piles in place. The structure must be able to resist the horizontal forces from the surrounding body of water when the inside water is pumped out of it. Then they place concrete against the casing, spread and compact it.

As a rule, the reinforcement is weak in tension but protects concrete from shrinkage cracks during its setting. The most difficult work is to pour the concrete for the foundations constructed in the river. Despite working water pumps, some water enters the trench, and the builders have to use additional grouting mortar (fig. 13.1d) to consolidate the soil in the water. Then they place the foundations.

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