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Types of Piles:
There are a number of piles available for use in the market. Now we will be having a discussion on these types one by one.
Drilled Piles:
These piles are those piles which are installed by the method of boring in the ground or by using the method of drilling. There are some other names given to this type of piles and they are caissons, drilled piers, drilled shafts, Cast-in-drilled-hole piles, cast-in-suite piles. These kinds of piles are having larger diameter than any other piles and usually fit for hard or dense strata. For the drilling purpose the drilling machines are used. The boring methods for this can be dry method and wet method depending upon the soil. These piles can be further classified as-
a) Augercast Piles:
This pile is also known as CFA pile. In this up to the required resistance or depth the ground is drilled with the help of auger which is having a hollow stem. There is not any requirement of casing.
After this within the stem of auger the cement grout mixture is pumped. During this whole process the withdrawing of the auger is done slowly. As they cause minimal disturbance, they can be best suitable for environmentally sensitive sites and those sites which are also noise sensitive in nature. There is an expensive waste disposal in forming this pile so they are not appropriate for contaminated soil. But when there is not any other alternative than using augercast pile, it may be reduced by CMC ground improvement method.
This is particularly used in warehouses, bridge abutments, residential buildings, petrochemical plants and highway embankments.
b) Under reamed Piles:
These are mechanically formed piles and they have a larger base usually of 6m in diameter. They usually have an inverted cone type of form and stable soil is best suitable for this. These piles can provide very high load bearing capacity.
Specialty Piles:
a) Tripod Piles:
It is one of the most traditional ways of forming piles. The cost of pilling is generally higher in this kind of pilling. As it is inexpensive and easy to install, so those sites which include less number of piles generally make use of tripod piles. It is also reliable in nature, can work in restricted sites and also capable for all ground conditions.
b) Micropiles:
Micropiles or maniples’ are particularly used in underpinning. They are usually made up of steel and generally having diameter of 60 to 200 mm. For installation of these piles there are a number of methods used. They are jacking, impact driving, drilling, screwing and vibrating machinery.
All those areas which require low headroom or some smaller projects, generally use Micropiles.
c) Soldier piles:
These piles are mainly constructed from wide flang steel which is having H section. The spacing among the two sections is 2 to 3 m and they are drawn near to the excavation.
They are best suitable in those conditions in which well constructed walls may nnot give subsidence result. These conditions can be soils above the water table, over-consolidated clays, free draining soils like sands.
d) Sheet piles:
When thin sheets of steel are interlocked in order to form a continuous barrier in the ground are known as sheet piles. Retaining of wall is their most widely used application. To establish sheet piles, t-crane, vibration hammer and crawler drilling machines are used.
e) Suction Piles:
In order to secure floating platforms under water, these particular piles are used. In this usually a tubular pile is inserted into the seabed and then after sucking the water out of that tubular pile a pump is used. As the pump is continuously sucking the water outside, the pile gets inserted deeper down inside the soil.
Depending upon the soil type, the proportions of the pile are adjusted. The height of the pile may be short and even half of the diameter if the sand is having good holding capacity and is hard to penetrate. Similarly the height can go up to 8 times the diameter if clay is present beneath the construction.
These piles cannot be used in case of gravel sea beds.
f) Adfreeze Piles:
The primary structural foundations in those areas where there is a continous frozen ground adfreeze piles are used.
The strength of the pile is derived from the bond of the pile with the frozen ground. The pre-drilled hole in which the pile is genarally kept is 1.5-3.0 dm and this is larger than the diameter.
To fill the space between the frozen ground and the pile a slurry mixture of soil is used. It gives the shear strength to the construction.
The main problem coming in the construction of adfreeze piles is Global warming. As due to this the frozen ground may become damp.
End Bearing Piles:
As given in the website these kind of piles usually become very hard, a kind of impenetrable material for the rocks. Their maximum carrying capacity is derived from the resistance of the stratum which is placed at the toe of the pile.
Settlement reducing Piles:
These piles are usually used to reduce the differential settlement up to an appropriate level and therefore placed below the central part of the raft. It reinforce the soil and thus prevent the dishing of the raft placed in the center.
Friction Piles:
Skin friction or adhesion is their main source for obtaining the carrying capacity. This is happened when the pile cannot penetrate the soil easily and thus stratum is used to enable penetration.
Tension Piles:
Structures such as tall chimneys, transmission towers and jetties can be subject to large overturning moments and so piles are often used to resist the resulting uplift forces at the foundations. In such cases the resulting forces are transmitted to the soil along the embedded length of the pile. The resisting force can be increased in the case of bored piles by under-reaming. In the design of tension piles the effect of radial contraction of the pile must be taken into account as this can cause about a 10%-20% reduction in shaft resistance.