PILE FOUNDATION

PILE FOUNDATION

Pile

Pile being a constituent element and basic entity that makes up a pile foundations, but cannot independently serve as a foundation, it is like a columnar entity of pile foundation that is  sometimes fabricated with a wedge shape foot in case of structural and functional consideration, the word foundation means much more than just a structure that transmit loads to the soil but a frame work of systems that are constructed  such that it could withstand any form of  loads which have to be considered in the preliminary stages of design. choosing a foundation design depend on  the bearing strata  that is a soil layer that has the sufficient bearing capacity of load, ground water condition and  the environment  the structure is to be proposed. Piles foundation can be classified in three different ways, classification can be base on material used to fabricate piles, or base on the effect of piles on the bearing and classification base on the method of construction. classification base on material include whether they are manufactured from timber or steel concrete or reinforced concrete, concrete is preferred in most building constructions due to its ability to be used with steel, the use of reinforced concrete in an extensive manner was pioneered by auguste  perret, reinforced concrete used in beams, column and also in foundations to distribute the load from beams to through the columns down to the reinforced concrete pile foundation. Classification base on bearing strata could be divided into friction piles; piles which are held firm in place through frictional forces from the surrounding soil strata, soil might be wet or dry, geotechnical professionals as to take the dry coarse aggregate soil as permissible during test, for safety reasons, since the coarse water logged, secondly the end bearing piles, theses are pile foundation whose piles are driven far below to a point where a bearing capable of withstanding the loads. piles can also be classified base on installation effect on soil, these includes displacement or replacement piles, displacement piles are piles that forced into the ground such that it compact the neighbouring soil in it surrounding or sub soils, these types of piles include precast or piles formed inside a steel tube or concrete shells.

Classification of piles can be base on construction or installation methods these includes, driven piles, they are precast piles which are manufacture off site, then are transported to site for installation they are use for both end bearing and friction piles, the difficulties in transportation of precast piles and the noise during hammering or compaction is discouraging for contractor so it is usually not the best choice, these precast piles can be pre stressed such that  the reinforcement are stretched to reduce the cross sectional area thereby reduces cracks due to tensile stresses, and increase durability ,secondly classification base on installation  include; driven cast-in-place, it is said to be of two types, that which has permanent casing of steel or concrete and the other without permanent, the essence of driving and maintaining a permanent casing is to strengthen the subsoil around the casing ,leaving in place the lining in other to protect the green concrete in shell from the weak strata. the other without a permanent casing is install by driving a steel tube lining with a cast iron shoe into the ground in which after attaining the bearing strata the reinforcement cage is inserted, after which the green concrete is compacted, in that process the tube meant for lining is removed is removed gradually but the cast iron shoe is left underground, the purpose of the shoe is to penetrate the compact stratum.

There are also the jacked piles; they are introduce when there is a confinement of space for working conditions, situations were an existing wall undergoing relative settlement, the only solution might be underpinning.

Piles are manufactured and installed in different ways which include hammering, grouting, vibrating and twisting, hammered piles are installed by pounding the piles (concrete or steel) down to a preset depth in other to set using a drop hammer machine, grouted piles are installed filling the concrete into the prepare reinforcement cage, the filling process must be done with a predetermined pressure and the volume must be controlled to construct a continuous pile without defect. Vibration is used in the installation of precast piles, such that it is driven to displace the bearing strata, twisted piles might be rotated or bolted to, turned into the ground like a screw.

Pile foundation are used in deep foundation because they can be embedded into the ground at a very long distance below the water table, pile is analogous to a pole, the pier, drilled shafts and a caisson.”According to oxford dictionary piles are long slender column usually of, timber, steel, or reinforced concrete”

Component of pile

Individual piles are made of different sections that are basic to the strength and functionality of piles, the component includes: the pile shoe, the pile ring or driving head and the reinforcement cage, piles can be made of different shapes in section such as circular, rectangular, and hexagonal. Pile shoe are made of cast iron pointed and worn on the foot of concrete or timber piles to facilitate stability. the driving head has a point of connection where it can be picked by a machine for installation, or to connect them to beams that are yet to be installed, the reinforcement cage is an internal constituent that react with the concrete to overcome both compression and tensile forces, in case if the pile is made of concrete. In other to provide for structural continuity reinforcement should be extended to the pile cap. through the strata bars protruding from top of cast in place concrete.

The use of pile foundations are expected when the proposed structure is close to a water body flowing, across like a bridge, with a strong lateral forces, situation were te soil is expandable or collapsible with a strong upward forces on site, there is need to reduce excessive settlement and prevent any form of upward forces. Piles foundation works by friction between piles and the neighbouring soil strata, or when it is able to attain a strong end bearing that will permanently hold it firm and should be installed such that standard pile spacing must be adhere to ,for both friction piles and end bearing piles .

Advantages of Pile Foundation.

Piles can easily be fabricated from timber or concrete, piles foundation are best options when the bearing strata is very deep, pile foundation are best choice for structures with large weight and height, pile foundations makes development of bridges, skyscraper, and offshore resident possible relatively cheap price of the stake when compared with the foundation sinks

Pile foundation bearing capacity through the use of a group of piles, which all together makes it stronger other than being monolithically erected.

Pile foundation bearing capacity can reach the hardest strata using drilling machines

Bored piles of different length can be extended through soft compressible or swelling soil, into suitable bearing material; piles can be extended to a depth below frost penetration, and seasonal moisture variation.

Through the use of bored piles, large excavation and subsequent backfilling are eliminated during excavation, during installation of bored piles adjacent soil is not disturbed or remoulded when bored piles are used.

Bored piles are good, due to the absence of vibration such that it will not disturb adjacent structure, bored piles is best for bridge construction and tall buildings

Disadvantage of pile foundation

Pile foundation requires high level of experience and machine operatives to install piles such that a precast pile specialist might not necessarily know how to install bored piles.

Pile foundation requires more monetary resources and time to construct

Pile foundation expose installers or workers to high level risk, since pile foundations are used in offshore, water logged and in water ways, all of the mentioned are risky working site .Pile foundation require high level of accuracy installation with regular geotechnical checks and Supervision of pile foundation construction can be very difficult due to difficulties in site accessibility.

Pile foundations pollute and disturb the underground water table, since it goes beyond to attain it end bearing.

Conclusion

Pile foundation being an engineering idea and innovation, as being a break through to a world of construction, which as being subjected to many advances and new development to make it do more exploit in the realm of construction, it  give opportunities to gross structural development in architecture and help environmental development.