Pile foundations can be divided into the following 6 types depending on the method of installation.
- Precast Driven Piles
- Inspired Cast-in-Situ Piles
- Bore Cast-in-Situ Piles
- bore precast piles
- Driven Steel Piles
- Inspired Timber Stacks
1. Precast Driven Piles
These are usually of RCC or pre-stressed concrete and are usually smaller in size for ease of handling. The main advantage of this type of pile is that in terms of its quality, dimensions, reinforcement and the use of concrete can be ensured as the pile is poured into a yard under controlled conditions. However care needs to be taken while handling, carrying and driving to avoid damage to the pile.
In addition, the limitation of length depending on the capability of the driving equipment is a disadvantage as these cannot be taken very deep apart from connecting. Typically, the depth at which these are used is limited to 36 metres.
2. Inspired Cast-in-Situ Piles
A steel casing pile with a shoe at the bottom is first driven to the required depth. The reinforcement cage for the pile is then lowered inside the casing and the pile is leveled. As the concreting of the pile progresses upwards, the casing is withdrawn keeping a suitable overlapping length. When such piles are driven into soft soil and the tube is withdrawn while concreting, it affects the resistance and alters the property of the soil and it also affects the capacity of individual piles. These are not suitable for use in soft soils, at greater depths or where keying with rock is required.
3. Bore Cast-in-Situ Piles
In the rugged cast-in-situ process, a larger diameter casing is used. A cover of 3 to 4 meters length is provided over the borehole which is driven with the help of baler. Further boring under this cover is carried out by chisels and the side walls are stabilized by circulating bentonite solution inside the borehole. Boring continues till the layer is decided for the installation of the structure. After the desired installer level is reached, the chisel is removed, the bore-hole is flushed, the reinforcement cage is lowered into the hole, and the support bars on top of the casing are held in position by welding.
Thereafter, concreting is done using a trellis, its end always being placed below the top level of the rising concrete. Concreting continues until a good quality concrete appears at the top of the bore hole. After this, the tremie is removed and when the concrete reaches the top, the casing pipe at the top is also removed. The bentonite mixture should be periodically checked for its specific gravity and changed, as due to continuous use, it may mix with clay and deteriorate in quality. This type of pile can also be used when the pile is locked into the rock because it can be more easily chiselled into the rock. These piles work as bearing-cum-friction piles. The diameter of such piles is usually more than 1.0 m and can go up to 3.6 m or more. They can be used singly or in groups and are good replacements for the good foundations needed for bridges across rivers with clay and mixed soils.
4. bore precast piles
In this, as the name suggests, a hole is bored using a casing and a pre-cast pile is inserted into it. After securing it in position, the cover is retracted. A special process used for bored pre-cast piles is the Benoto process in which a steel tube is pushed into the soil, twisted and reversed using compressed air. The tube is in the form of a cover and is driven to the full depth after the soil is progressively grasped by the tube. The process continues until the tube reaches the pre-determined level. The pre-cast pile is then lowered in and held in position. The tube is gradually raised after grouting fills the annular gap between the pre-cast pile and the soil.
5. Driven Steel Piles
Steel piles can be circular or in other structural shapes. Spheres are made either welded or as seamless piles. The steel or cast iron piles commonly used previously for bridge structures are of long diameter and screw type. These were used earlier when the loading was less. These piles are suitable to be driven through cohesive soils to reach hard soils and serve as bearing piles. They are not suitable where heavy scratching is expected and for bridge foundations when the foundations are widely located.
6. Inspired Timber Stacks
Wood piles have been used extensively in America. These have been used for temporary bridges on railways and highways in India. Wood piles are hardwoods, and are used in natural form with thin ends or suitable sizes. These are mostly used in bunches as end-bearing piles. They are typically used in lengths of 12 m and are expanded by splicing for use in deeper channels. The raised piles above the bed/low water level are suitably tied in the cluster.