Types Of Pile Foundations

A Pile Foundation is one type of slender structural member made of steel, concrete, wood, or composite material. A Pile may be cast in situ excavating a hole and filling it with a concrete or precast concrete member which is driven into the soil. There are different types of Pile foundations used in construction.

In case, the strata of good bearing capacity are not available near the ground, the foundation of the structure has to be taken deep to attain a bearing stratum that is suitable in all respects.

The most common forms of deep foundations are :

Pile foundations
Cassions or Well foundations
Cofferdams

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Types of Pile Foundation

Types of Pile Foundation Based on function piles are classified as,

End Bearing Pile
Friction Pile
Composite Pile
Tension Pile
Anchor Pile
Fender Pile
Better Pile
Sheet Pile

1. End Bearing Pile

These pile foundations penetrate through the soft soil and their bottom or tips rest on the hard stratum. These piles act as columns. The soft material surrounding the pile provides some support. For end-bearing pile Qu = Qp

2. Friction Pile

When the foundation of the structure has loose soil, then the friction piles are extended to a depth that frictional resistance developed at the sides of the piles equals the load coming on the piles. A friction pile is generally utilized where hard foundation strata are available at greater depth.

3. Compaction Pile

When piles are driven in loose granular soil with the aim of increasing the bearing capacity of the soil, the pile’s arc is termed a compaction pile.

4. Tension Pile

These pile foundation anchor down the structures subjected to uplift due to hydrostatic pressure or due to the overturning moment. It is also called an uplift pile.

5. Anchor Pile

Anchor piles are used to resist the horizontal pull from sheet piling or other pulling forces.

6. Fender Pile

Fender piles are mainly used to protect the seashore structures against impact from ships or other floating objects.

7. Better Pile

They are used to resist large horizontal forces or inclined forces.

8. Sheet Piles

They are used as bulkheads or as an impervious cutoff to reduce seepage and uplift under hydraulic structures.

Sheet Piles are used for the following purposes,

To isolate the foundation from adjacent soil.
To prevent the underground movement of water.
To prevent the transfer of machine vibration to adjacent structures.
To construct a retaining wall in docks, wharves, and other marine structures.
To protect river banks.
To retain sides of foundation trenches.

B. Types of Pile Foundation Based on Materials and Composition

Types of Pile Foundations — Types of Pile Foundation Based on Materials and Composition

1. Precast Concrete Piles

Precast concrete piles arc those which are manufactured in a factory in a place away from the construction site, and then driven into the ground at the place required. Naturally, these pile foundations require heavy pile-driving machinery.

Precast Piles may be square, octagonal, or circular in cross-section and may be tapered or Parallel sided longitudinally. Because of driving stresses and handling stresses (i.e. transportation and lifting) the precast concrete piles are usually reinforced.

The size of the pile may vary from 30 cm to 50 cm in a cross-sectional dimension, and up to 20 m or more in length. The reinforcement may consist of longitudinal steel bars of 20 mm to 40 mm in diameter, 4 to 8 nos. with lateral ties of 6 to 10 mm in diameter at 100 mm c/c spacing for top and bottom lm length and 300 mm c/c spacing for the middle length.

A concrete cover of at least 50 mm is provided. The grade of concrete should be M20

2. Cast -in-Situ Concrete Piles

In the cast-in-situ concrete pile, a bore is dug into the soil by inserting a casing. This bore is then poured with concrete after placing steel reinforcement if any.

The casing may be kept in Position or it may be withdrawn. The piles with casing areas are known as eased cast-in-situ concrete Piles and those without casing are known as uncased cast-in-situ concrete piles.

1. Raymond Piles Foundation

The Raymond piles are mainly a type of friction pile. It is provided with a uniform taper of I in 30 resulting in shorter piles.

The lengths of Reymond standard piles vary from 6 to 12 m. The diameter of piles varies from 40 to 60 cm at the top and 20 to 30 cm at the bottom.

The Pile consists of a thin corrugated shell (casing) closed at the bottom. The steel shell is reinforced with spirally wound hard-drawn wire on an 8 cm pitch.

The shell is driven into the ground with a collapsible steel mandrel or core it having the same taper. When the Pile is driven to the desired depth mandrel is mechanically collapsed and withdrawn, leaving the shell inside the ground.

The shell is inspected internally by using the light from a mirror or flashlight or drop light. This empty shell is gradually poured with concrete up to the top.

2. Mac Arthur Piles

Mac Arthur is made of a corrugated steel shell of a uniform diameter which remains in place, as in Raymond Piles.

A heavy steel casing with a core is driven into the ground as shown in fig. These pile foundations are used when the desired depth is reached, the core is withdrawn and a corrugated steel shell is placed in the casing:

Finally, concrete is placed in the shell, by gradually compacting it, and withdrawing the steel casing:

3. BSP-base driven Piles

These pile foundations consist of a helically welded shell of the steel plate and the plug of concrete is placed at the bottom of the piles.

Pile driving is done by dropping the hammer on the concrete plug. The casing is driven to the desired depth and then it is filled with concrete.

4. Swage Piles

Swage Piles are used with an advantage in some soils where the driving is very hard or where it is designed to leave the watertight shell, for some time before filling the concrete.

Firstly, a steel shell is placed on a precast concrete plug and a steel core that is not long enough to reach the plug is inserted in the plug.

In the second stage, as the pipe is over the plug until the core reaches the plug, the pipe is swaged out by the taper of the plug thus forming a watertight joint.

In the third step, the pipe is driven up to a specific depth. The driving force is practically exerted by the core on the plug and the pipe is pulled down rather than driven.

In the fourth stage, when the pile is placed at the desired depth, the core is removed and poured with concrete.

5. Button bottom Piles

These pile foundations are being used where the end-bearing area needs to increase. The pile uses a concrete plug, in the shape of a button. This button forms an enlarged hole in the soil during driving.

These piles can be used up to lengths of about 23 m and for loads up to 50 tonnes.

In the first stage, a steel pipe with 12 mm thick walls is set on the concrete button. The concrete button diameter is 25mm larger than the pile diameter.

In the second stage, the pipe and button are driven to a specified depth. In the third stage, resting on the button corrugated steel shell is inserted in the pipes

In the fourth stage, the casing is withdrawn leaving the button in place, and the shell is filled with concrete. Reinforcement may be used if necessary.

Uncased cast-in-situ concrete Piles

These pile foundation piles do not use casing and hence are cheaper. However, great skills are required in their construction.

These piles are used only where it is certain that neither soil nor water will fall into the hole, or squeeze into and reduce the size of the hole, and also where adjacent piles will not damage the green concrete.

It is essential to have a close installation inspection since no inspection is possible after they are installed.

Following are the cast-in-situ concrete pile foundations:

Simplex Piles
Franki Piles
Vibro Piles
Pedestal Piles
Pressure Piles

1. Simple Piles

Simplex piles can be driven through soft or hard sois. In this type of pile, a steel tube fitting with a cast iron shoe is driven into the ground up to the desired depth. Reinforcement, if necessary is put inside the tube, concrete is then poured into the tube, and the tube is slowly withdrawn, without concrete being tamped, leaving behind the cast iron shoe.

In these pile foundations, if the tamping of concrete is done at regular intervals as the tube is withdrawn, we get the simplex tamped pile.

2. Franki Piles

In these piles, a plug of dry concrete gravel is formed on the ground surface by a heavy removable pipe shell.

A Drop hammer having weight of about 20 to 35 KN is free-dropped on the plug. This results in the formation of a dense plug that penetrates the ground and drags the tube with it on account of friction developed between the tube concrete plug.

When the tube has reduced the desired depth, the tube is held in the position by cables and the hammer is applied to the concrete plug, forcing it down and outward. This results in the enlargement of the base into a mushroom shape.

If required a fresh charge of semi-dry concrete is not to enlarge the bulb.

After that the shaft is manufactured by introducing successive charges of concrete, ramming each in turn, and withdrawing the casing gradually about 300 mm at a time. Corrugations will be formed on the surface of a completed pile.

The pile diameter in Frank piles varies from 50 cm to 60 cm, while the enlarged base may have a diameter of about 90 cm. The pile has a load-carrying capacity of 60 tonnes (660 kN) to 90 tonnes (900 kN).

In the next stage, the shaft is manufactured by inducing successive charges of concrete. ramming each in turn, and withdrawing the casing gradually about 300 mm at a time. Corrugations will be formed on the surface of a completed pile.

3. Vibro Piles

These pile foundations are used where the ground is soft, thus offering little frictional resistance to the flow of concrete. The standard and expandable pile can be driven by the Vibro process.

These piles are formed by driving a steel tube and shoe, filling it with concrete, and withdrawing the steel tube.

Standard Vibro piles are made in the size of 45 and 50 cm diameter for loads of 60 to 70 tonnes. They can be formed in lengths of 25 m and over.

A Steel tube having a cast-iron shoe fitted at the bottom is driven by a 2 to 2.5 tonnes hammer operated by steam or compressed air delivering up to 40 blows per minute, with a stroke of about 1.4 m.

4. Pedestal Piles

These piles are used where a thin bearing stratum is reached with reasonable depth. The pedestal pile gives the effect of spread footing on this comparatively thin bearing.

The core and casing are driven together into the ground, till they reach the desired level.

The core is taken out and a charge of concrete is placed into the tube. The core is again placed in the casing to rest on the top of poured concrete; pressure is applied on the concrete through the core, and at the same time the casing is withdrawn. The process is repeated until the casing is completely removed.

Steel Piles

H – piles
Box piles
Tube piles

1. H – Piles

These pile foundations are usually of wide flange sections. They are suitable for trestle-type structures in which the piles extend above ground level and also act as columns.

Since they have small cross-sectional areas, therefore, they can be easily driven in soils in which it will be difficult to drive ordinary displacement piles. They are used as long piles with high bearing capacity.

2. Box piles

They are rectangular or octagonal in form and filled with concrete. These pile foundations are used when it is not possible to drive He-piles into hard strata.

3. Tube piles

In this type, tubes or pipes of steel are driven into the ground. Concrete is filled inside the tube piles. Because their circular piles are easy to handle and easy to drive in. cross-section, these pile foundations are easy to handle and easy to drive in.

Timber Piles

These piles are prepared from trunks of trees. They may be circular or square. These types of timber piles have a diameter of 30 to 50 cm with a length not exceeding 20 times its top width.

The Cast iron shoe is provided at the bottom and at the top, a steel plate is fixed. If a group of timber piles is driven, the top of each pile is brought at the same level and then a concrete cap is provided to have a common platform.

Composite Piles

The hole is then filled with sand and it is well-rammed. The sand to be used should be moist at the time of placing. The top of the sandpile mostly covers with concrete for restricting the ejecting upwards due to lateral pressure.

Sand piles are spaced at 2 to 3 m, usually under the columns of the structure. A load test should be carried out to determine the bearing capacity of a sand pile. A properly constructed sand pile resting on firm strata can take up a load of 100 tonnes/m2 or more.

The length of sandpiles is kept about 12 times its diameter. The diameter of the sand pile is dependent upon the load acting on the pile.

C. Classification of Pile Based on Installation Method:

Based on the method of installation Piles may be classified as follows

1. Driven Piles

These Piles are generally forced insertion into the soil with a heavy hammer on their tops. Mainly, the precast concrete, timber, and steel piles are driven by driving, which may be driven into position either vertically or at an inclination.

2. Driven and Casts-in—Situ Piles

These pile foundations are castes by driving a casing with a closed bottom end into the soil. The casing is later filled with concrete. The casing may or may not be withdrawn.

If the casing of the pile is not removed, it is called an uncased Pile, and if the casing is not withdrawn, it is called a cased Pile.

3. Bored and Cast-in-Situ Piles

These pile foundations are formed by excavating a hole into the ground and filling it with concrete.

4. Screw Piles

These pile foundations are screwed into the soil.

5. Jacked Piles

These pile foundations are jacked into the ground by applying a downward force with the help of a hydraulic jack.

6. Under Reamed Piles

These pile foundations are researched and developed by C.B.R.I. to be used as the foundation for black cotton soil, filled-up ground, and other types of soils having poor bearing capacity.

The under-reamed pile is a bored cast-in-situ concrete pile having one or more bulbs or under-reams in its lower portion. The bulbs or under-reams are formed by the under-reaming tools.

The under-reamed piles generally have a diameter of 20 cm to 50 cm and that of the bulb varies from 2 to 3 times the diameter of the pile. The length of under-reamed piles is about 3 m to 8 m.

The spacing of piles may vary from 2 m to 4 m. The under-reamed piles can also be used for sandy soils with a high water table.

The load-carrying capacity of under-reamed piles can be increased by adopting piles or larger diameters or extending the length of piles or making more bulbs at the base.

Generally, a single under-ream pile may have one or more bulbs. When two or more bulbs are provided at the base, it is known as a multi-bulb under-reamed pile. The vertical spacing between two bulbs varies from 1.25 to 1.50 times the diameter of the bulb.

Uses of Pile Foundations

Pile foundations are preferred in the following situations

The load of the superstructure is heavy and its distribution is uneven
The topsoil has poor bearing capacity.
The subsoil water is high so .pumping of water from the open trenches for the shallow foundations is difficult and uneconomical.
There are large fluctuations in the subsoil water level.
Where timbering to the trenches is difficult and costly.
The structure is situated on the seashore or river bed, where there is a danger of scouring the action of water.
Canal or deep drainage lines exit near the foundation.
The topsoil is of expansive nature.
Piles are used for the foundation of transmission towers, an off-shore platform that is subjected to uplift forces.

Factors Affecting the Selection of Pile Foundations

The following factors should be considered while selecting pile foundations:

Nature of Structure
Loading Condition
Availability of funds
Availability of materials and equipment
Types of soil and its properties
Groundwater table
Self-weight of Pile
Durability of Pile
Cost of Pile
Maintenance of Pile
Length of Pile required
Numbers of Pile required
Case study of an adjacent building
Facilities available for pile driving
Difficulties in pile driving

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