A pile foundation is a long slender foundation member made of timber, structural steel or concrete which might be cast-in-situ or driven at place.
It acts as a structural member to transfer the load of the structure to a required depth in deep foundation to carries the load which may be vertical or lateral or lateral plus vertical.
Introduction to pile foundation:
Pile foundations consist of piles which are dug into the soil, these foundations transfer the building load to the bearing soil with better load carrying capability.
These foundations are useful in areas with unstable upper soils that can be bad for large buildings.
When pile foundation is preferred:
- The superstructure has a heavy weight and its distribution is uneven.
- The topsoil has poor bearing capacity.Compressible or weak upper soil layer.
- The construction is located near the bed of the river, where there is a danger of water filtration.
- When subjected to uplifting forces.
- Surface has soil erosion.
Types of Pile Foundation:
Classification based on material:
A pile foundation made of tree wood about 30 cm in diameter is used as a heap, the trunk should be strong, durable and straight.
The head of the pile is covered with a steel cap to avoid scattering or spreading of the wood in the event that the pile is hammered into the ground.
An iron shoe is provided at the other end to facilitate insertion and avoid damage to the pile.
Pile foundation made of concrete are commonly used for deep foundation, these piles are either pre-cast concrete piles or reinforce cast-in-situ piles.
Precast concrete piles are mostly circular or octagonal with a tapered edge to one side.
These are mostly pre-stressed piles with a length of over 10 meters, they can sustain a larger hearing pressure than a pile of wood.
A required diameter and depth in the ground is drilled into the concrete piles, the reinforcement cage is then lowered into the hole and concreting is done.
Concrete piles can be used practically for every types of foundation subjected to medium and heavy loads.
Steel pile foundation are either a rolled steel section or a conical shape or it can be a sheet pile.
Classification based on supporting actions:
When the piles transfer the load of the building through the soft-soil layer to a suitable bearing stratum at greater depths, it is called a bearing pile
The pile remains on the stratum at greater depths.
When pile foundation moves the load only through the skin resistance without any end bearing then the pile are called friction piles.
Under-reamed pile foundation is commonly used in black cotton soils that swell or shrink when exposed to water or in large quantities upon drying.
It is a bored-in-situ stack that extends one or more or is provided with bulbs along its length known as under-rims.
Classification based on size:
Pile foundation with ems section at the bottom are called taped piles, these piles are used to increase the density of the subsoil by driving these piles into loose soil.
Tapped piles are also called as compiled piles.
Advantages of Pile Foundation:
- The piles can be pre-prepared according to its length.
- The precast process reduces completion time.
- It can be installed over a very large area & very long lengths.
- We can use piles in a place where drilling is not required.
- The piles are very neat and clean.
Disadvantages of Pile Foundation:
- A pile gets quickly damaged when driving through the stones and boulders.
- Piles can be attacked by marine borers in saltwater.
- A pile cannot be above ground level.
- It is very difficult to know the actual required length in advance.
- Vibrations are produced when the piles are driving which affects the neighbouring structures.
- Piles require heavy equipment to operate.
- Piles do not have low drainage.
Uses of Deep Foundation:
There are various types of deep foundation and pile foundation is among one of them.
The uses of pile foundation depends on:
- The type of pile used.
- the intended function for which the pile is used.
- The load which is to be applied on the pile
- the type of material which is used for the construction of the pile, the following are the uses of piles:
End bearing or compressive strength:
Sometimes we use the piles to achieve the required compressive strength in the soft soil.
We use the piles to transfer the load through soft soil to a suitable bearing stratum by using the end bearing or toe bearing property of the pile.
To build a structure within the water and on the water river or canal bed, we have to build the foundation through the river bed and within the scour depth.
In these types of situations if we go for shallow foundation then we may have to use cofferdam or some diversion which is very non-economic.
Tension or Uplift:
Pile foundation is usually used to carry the compressive nature of the load through the tip bearing or end bearing.
In the case of tall structures or towers, there may be tension that must be resisted by the piles.
For a tower carrying high power transmission lines,i.e, wind thrust can create stresses that must be resisted by a tension stack.
Also, include the use of deep foundations or a thick raft that is sometimes informal.
Turbines and silos for the foundation of buildings supporting vibration equipment where vibrations are important and can cause failures.
There are two options that you can go for large scale blocks to absorb vibration and mass block is very economical.
Sometimes piles are pushed into the weakened level of the soil to increase the bearing capacity of the soil.
Piles are called compile piles thus by using compile piles we can increase the bearing capacity of the soil.
To deal with any problem associated with soil or to lay a deep foundation, especially piles is a very good option when the time schedule is very tough.
They are fast in construction & not difficult to design.