FOUNDATION PILES TYPES BASICS AND TUTORIALS

DIFFERENT TYPES OF FOUNDATION PILES TUTORIALS
What Are The Different Types of Foundation Piles?


It used to be possible to categorize the various types of pile and their method of installation, using a simple division into ‘driven’ or ‘bored’ piles. This is adequate in many situations, but does not satisfactorily cope with the many different forms of pile now in use.

A more rigorous division into ‘displacement’ or ‘non-displacement’ piles overcomes this difficulty to some extent, but some piles are installed by a combination of these methods and their description may require qualification.

In the displacement (generally driven) pile, soil is displaced radially as the pile shaft penetrates the ground. There may also be a component of movement of the soil in the vertical direction.

Granular soils tend to become compacted by the displacement process, and clay soils may heave, with little immediate volume change as the clay is displaced.

Piles of relatively small cross-sectional area, such as steel ‘H’ section piles or open pipe piles, are termed ‘low displacement piles’, and the effects of compaction or soil heave are reduced. This can be advantageous if long lengths of pile are to be driven through granular deposits, if the piles are at close centres, or if clay heave is a problem.

In the non-displacement (generally bored) pile, lateral stresses in the ground are reduced during excavation and only partly reinstated by concreting. Problems resulting from soil displacement are therefore eliminated, but the benefit of compaction in granular soils is lost and in all soils spoil is produced which may be costly to remove from a site, especially if it is contaminated.

The displacement of the soil by a pile during installation is therefore a fundamental property, and its recognition in any classification of pile type is clearly advantageous. Little-used types such as pre-formed screw piles can also be covered by the (low) displacement classification, whereas they could not be correctly termed ‘driven piles’.

In a further development of the screw pile that is becoming more frequently employed, especially on contaminated sites where it reduces or eliminates the production of spoil, a hollow screw-form auger is rotated into the ground and the bore filled with concrete as it is back-rotated out or retracted without rotation.

The two main categories of pile types may be classified further according to whether pre-formed units are used, and whether the pre-formed unit is used as temporary support for the ground and withdrawn during concreting or left in place.

For nondisplacement piles, factors such as pile diameter and underreaming are introduced to the classification, as they have a bearing on the method of installation, and particularly

ALUMINUM PRODUCTION BASICS AND TUTORIALS (ALUMINUM IN CIVIL CONSTRUCTION)

PRODUCTION OF ALUMINUM USED IN CIVIL CONSTRUCTION
How Aluminum is Produced? What Is Aluminum?


Aluminum production uses processes that were developed in the 1880s. Bayer developed the sodium aluminate leaching process to produce pure alumina Hall and Héroult, working independently, developed an electrolytic process for reducing the alumina to pure aluminum. The essence of the aluminum
production process is shown in Figure 4.3.

The production of aluminum starts with the mining of the aluminum ore, bauxite. Commercial grade bauxite contains between 45% and 60% alumina. The bauxite is crushed, washed to remove clay and silica materials, and is kiln dried to remove most of the water.

The crushed bauxite is mixed with soda ash and lime and passed through a digester, pressure reducer, and settling tank to produce a concentrated solution of sodium aluminate. This step removes silica, iron oxide, and other impurities from the sodium aluminate solution.

The solution is seeded with hydrated alumina crystals in precipitator towers. The seeds attract other alumina crystals and form groups that are heavy enough to settle out of solution. The alumina hydrate crystals are washed to remove remaining traces of impurities and are calcined in kilns to remove all water.

The resulting alumina is ready to be reduced with the Hall–Héroult process. The alumina is melted in a cryolite bath (a molten salt of sodium–aluminum–fluoride). An electric current is passed between anodes and cathodes of carbon to separate the aluminum and oxygen molecules.

The molten aluminum is collected at the cathode at the bottom of the bath. The molten aluminum, with better than 99% purity, is siphoned off to a crucible.

It is then processed in a holding furnace. Hot gases are passed through the molten material to further remove any remaining impurities. Alloying elements are then added.

The molten aluminum is either shipped to a foundry for casting into finished products or is cast into ingots. The ingots are formed by a direct-chill process that produces huge sheets for rolling mills, round loglike billets for extrusion presses, or square billets for production of wire, rod, and bar stock.

Final products are made by either casting, which is the oldest process, or deforming solid aluminum stock. Three forms of casting are used: die casting, permanent mold casting, and sand casting. The basic deformation processes are forging, impact extrusion, stamping, drawing, and drawing plus ironing.

Many structural shapes are made with the extrusion process. Either cast or deformed products can be machined to produce the final shape and surface texture, and they can be heat treated to alter the mechanical behavior of the aluminum.

When recycling aluminum, the scrap stock is melted in a furnace. The molten aluminum is purified and alloys are added. This process takes only about 5% of the electricity that is needed to produce aluminum from bauxite.

In addition to these conventional processes, very high strength aluminum parts can be produced using powder metallurgy methods. A powdered aluminum alloy is compacted in a mold. The material is heated to a temperature that fuses the particles into a unified solid.