Classification of Piles

Piles can be classified according to following basis.

1. Classification of pile with respect to load transmission & functional behavior

• End bearing piles (point bearing piles) – these will transfer the load at the bed rock or layer of firm sand or gravel which has been compacted by displacement and vibration encountered during the driving. The shaft of the piles act as columns carrying the load through the overlaying weak subsoil to firm strata into which the pile toe has penetrated. The load is carried through weak strata and transfers it to a firm stratum on which the end rests.

There are two types of end bearing piles. They are:

• Performed Piles (Timber, PC, Steel, etc.)
• In-situ Reinforced concrete piles
• Friction piles -. If a suitable load bearing strata cannot be found at an acceptable level, particularly in stiff clay soils, it is possible to use a pile to carry this bulb of pressure to a lower level where a higher bearing capacity is found. The friction or floating pile is mainly supported by the adhesion or friction action of the soil around the perimeter of the shaft. These piles transfer their load to the ground through skin friction.

2. Classification of pile with respect to type of material

• Timber – most suitable for below ground water level construction
• Concrete- concrete piles are typically made with steel reinforcing and pre stressing tendons. They are pre-caste so that they can be easily connected together in order to reach to the required length
• Steel – steel piles are suitable for handling and driving in long lengths. But there is a risk of corrosion
• Composite piles -Combination of different materials in the same of pile

3. Classification of pile with respect to effect on the soil

A simplified division into driven or bored piles is often employed.

• Driven piles - A driven pile is a deep foundation that is constructed by driving a concrete, steel or timber pile to support the anticipated loads in competent subsurface material. Driven piles are considered to be displacement piles. In the process of driving the pile into the ground, soil is moved radically as the pile shaft enters the ground. There may also be a component of movement of the soil in the vertical direction. Prefabricated concrete piles are driven using a pile driver equipped with a hydraulic free fall hammer. Prefabricated concrete piles are primarily used in loose soils.

• Bored piles - Bored piles (Replacement piles), a void is formed by boring or excavation before piles is produced. Piles can be produced by casting concrete in the void by using a tremmie pipe. Gravel the ground requires temporary support from casing or bentonite slurry. Alternatively the casing may be permanent, but driven into a hole which is bored as casing is advanced. A different technique, which is still essentially non-displacement, is to intrude, a grout or a concrete from an auger which is rotated into the granular soil, and hence produced a grouted column of soil. There are other types of replacement piles such are Augured, Cable percussion drilling, Drilled-in tubes, Mini piles.

4. Specialty piles

• Micro piles - Micro piles or mini piles are used for underpinning works. Installation of micro piles can be achieved using drilling, impact driving, jacking, vibrating or screwing machinery.
• Tripod piles-The use of a tripod rig to install piles is one of the more traditional ways, and although unit costs are generally higher than with most other forms of piling. The tripod system is easy and inexpensive to bring to site, making it ideal for jobs with a small number of piles. It can work in restricted sites (particularly where height limits exist),
• Sheet piles - Sheet piling is a form of driven piling using thin interlocking sheets of steel to obtain a continuous barrier in the ground. The main application of steel sheet piles is in retaining wall and cofferdams erected to enable permanent works to proceed.

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