Piles foundation is a slender structure member which have a very small area of cross-section as compared to its length. It is also known as Deep Foundation. It is used on those structures or at those places where the bearing capacity of the soil is lower than the required bearing capacity.
Generally, the Pile foundation is used when the structure is heavy such as the highrise buildings, bridges, and water tanks where a load of the structure is high and not equally distributed throughout the structure. Pile Foundations are capable to withstand and distribute a large amount of structural load to the ground level or soil surface.
It is necessary that the bearing capacity of soil should be sufficient that the structure should not face any type of settlement or distortion.
Different types of piles foundation
Different Types of Piles foundation is classified as:
- According to the function of Pile
- According to the material used in pile Foundation
- According to the installation method of Pile Foundation
1) According to the function of Pile Foundation
Based on the pile foundation function, they are grouped into three categories.
i) End bearing piles: In the end-bearing pile, the load of the structure is transferred to the bottom of the pile which rests on the hard soil or rock mass.The pile rest at the translation layer of a weak and strong stratum or base. The pile act like a column. The total capacity of a pile foundation depends on the bearing capacity of the bottom of the pile at which it rest or ends and the area of the tip of the pile.
ii) Friction Piles: In this friction pile, the structure load is transferred by the medium of friction along with the depth of the pile. The entire pile transfer load from the structure to the soil. By increasing the diameter, length, and roughness of the outer surface of the pile, the capacity of the friction pile can be increased.
2) According to the material used in pile Foundation
Based on material used to made or construct a pile foundation, it is classified as:
i) Timber pile: Timber is used as the main component of it. By its name, it was clear that these piles are made from a tree trunk or sawed timber section. Timber is cheaper as compared to other materials s,o timber pile are cheaper and east to construct timber pile foundation. It is also easy to handle because of its lightweight.
By joining two or three sawed timber together a required length of the pile is made up. But it has one defect that it can decay if comes in contact with water or moisture. So it is used below the water table only. Timber pile act as friction pile. It has the capacity to handle or bear a load of almost 60 tons. Normally it is driven up to 20 meters depth.
ii) Concrete pile: Concrete pile may be precast or cast-in-situ. Precast piles are manufactured first somewhere at the casting yard then transported to the site where pile foundation work is carried out. These piles are driven up to a depth of 27m depth. Normally, these piles withstand up to 100 tons loads without going any settlement.
iii) Steel piles: A steel pile is used where the hard-driving is required. The most common steel piles are screw pile and rolled H- section piles. They may be open-ended or closed-ended. After driven in the land, they are filled with concrete. The rolled H- Section steel pile is driven up to 36m deep into the land and can withstand 170 tons load. Whereas screw piles can be driven up to 24m depth but have the capacity to take loads up to 250 tons.
3) According to the installation or construction method of pile foundation
On the basis of construction, pile foundation is grouped into three main categories.
i) Large displacement piles
Precast Piles: They are manufactured at the casting site. They may be solid or hollow in nature. Timber pile and precast concrete are solid and steel piles and concrete tubes are hollow piles.At those places where underground water flows, precast piles are suggested.
Driven and cast-in-situ piles: These types of piles are made by boring soil up to the desired depth then concrete is poured inside it. During installation, careful supervision is required. According to the requirement, the depth of piles can vary which means additional piles can be provided if required.
ii) Small Displacement piles
Steel section piles and screw piles are small-displacement piles.
iii) Non-displacement piles
Bored and cast-in-situ piles are formed by boring and excavation. Then the void is filled with concrete.
Selection of pile Foundation
Generally, the design of the foundation is made on the preliminary estimated values before the actual construction begins. Before starting the work, the pile load test must be made to verify the design value. Design is revised according to the test result because of it the durability of the structure, the maintenance is maintained., And other things if any changes are required apart from design, then it should be suggested by the site engineer.
Factors affecting the selection of pile Foundation
- The selection of a pile foundation based on a load of the structure and condition of the soil.
- Location of the site.
- Type of structure.
- Cost of piles, life expectancy.
- Cost of maintenance and repair.
- The durability of a structure.
- Fund available for construction.
- Availability of construction materials.
- Position of the groundwater table.
All these above factors are largely analyzed and decided before selecting any particular pile foundations.
Also read: Electronic Distance Measurement (EDM)
Use of Pile Foundation
The followings are the uses of the Pile Foundation.
- To transfer the load to a stronger and less compressible stratum.
- Compact the loose granular soils.
- To carry uplift forces.
- Transfer loads in weak soil by friction between pile and soil.
- When the site is near the location of the river bed and chances of scouring are high to support structure at such sites.
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