A pile foundation is a deep foundation that is relatively stronger and has a lesser settlement. Types of piles- driven pile, bored pile, end-bearing pile, friction pile, tension pile, sheet pile, displacement pile, non-displacement pile etc. Static & Dynamic methods for pile foundation load-carrying capacity. Pile load test method and sample report format.

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Civilverse Admin 4 September 2020
Pile Foundation- Advantages, Classification & Load
Capacity
civilverse.org/pile-foundation
Table of Content for Pile Foundation-
Introduction
Advantages of Pile Foundation
Classification of Piles
Load Carrying Capacity- Static Method, Dynamic Method, In-situ Penetration Test
and Pile Load Test.
Negative Skin Friction
The load of the structure is transferred to the earth by foundations. The foundations are
stable until the soil beneath the footing has enough strength to accommodate the stresses
arising due to the load of the structure.
The strength of the soil depends upon the type of soil, gradation of soil, depth of strata,
degree of compaction, depth of water table etc. It is a general trend that the strength of
the soil increases with depth.
When the soil near the earth surface does not have enough strength, deep foundations are
made to transfer the load to deeper strata. Pile foundation, piers, well foundation and
caisson foundation are examples of the deep foundation.

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Deep foundation having diameter lesser than 0.6m is called pile. Pier has a diameter of
more than 0.6m and is often referred to as ‘Drilled-Pier’.
Advantage of Pile Foundation-
1. Pile foundation have a lesser differential settlement.
2. Pile Foundation can transfer the load to strong strata through deep water.
3. It helps in sustaining structures which have horizontal loadings such as earth
pressure and wind load.
4. It is advantageous to use a pile foundation when it is estimated that earth can wash-
out, erode or scour from beneath the shallow foundation.
5. Pile foundation is advantageous for structures subjected to uplift pressure.
6. For expansive soils such as black cotton soil, pile foundation can be used to transfer
the load below the active zone.
7. Pile foundation can be used for collapsible soils that are subjected to the moisture
change.
Boring for Cast In-situ Concrete Pile

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Classification of Piles-
The piles can be classified in following manner-
Classification on the basis of Material-
1. Steel piles are thick steel pipes or rolled H-section provided with an epoxy coat
and a shoe at the bottom.
2. Timber piles are of straight, sound and defect-free timber. Timber piles are also
provided with steel shoes at both ends. Splicing is done by steel sleeves.
3. Concrete piles are made up of either pre-cast concrete or in-situ concrete. Pre-
cast piles can be prestressed. Cast in-situ piles are made by pouring concrete into
the borehole. The cast-in-situ concrete pile can be cased or uncased.
4. Composite piles are made up of two materials. They are rarely used as the two
materials don’t join properly.
Classification on the basis of Mode of Load Transfer-
1. End Bearing Piles transfer the load directly to the soil below it.
2. Friction pile transfer the load to the soil along its’ depth through friction. The
third type of pile is the combination of the above two.
Classification on the basis of Method of Installation–
1. Driven piles are driven into the earth by means of striking on their top. The
striking can be done by single acting hammer, double acting hammer, drop
hammer, diesel hammer or vibratory pile driver. Driven piles can be pre-casted or
cast in-situ.
2. Bored piles are the ones that are casted into the bore-hole. Bored piles can have
straight edges or bulbs. The bored piles with bulbs are called under-reamed
piles.
3. Screw Pile are screwed into the soil.
4. Jacked Pile are jacked into the soil by means of hydraulic jacks.
Classification on the basis of Use-
1. Load bearing pile transfer the load of the structure to the earth.
2. Compaction piles are used to densify the soil. These are driven piles. When a pile
is driven into the soil, the pile pushes the soil sideways. This process densifies the
soil in the nearby area of the pile.
3. Tension piles are used for structures subjected to the uplift pressure. These piles
hold the structure into its position and maintain the vertical stability of the
structure.
4. Sheet piles are used for retaining the earth/water. They are commonly used in
hydraulic structures to prevent seepage.
5. Fender piles are sheet piles used to protect the waterfront from the impact of
ships.

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6. Anchor piles are used as anchorage for sheet piles. It provides horizontal stability
to the sheet piles.
Classification on the basis of Displacement of Soil-
1. Displacement pile is the pile that displaces the soil around it from its original
position. All the driven piles are displacement piles because the earth around the
pile is densified due to lateral movement.
2. Non-displacement pile doesn’t displace the soil around it. All the bored piles are
non-displacement piles.
Load Carrying Capacity of the Pile Foundation-
Hydraulic Pile Driving Machine (Image Courtesy-
hydraulicpilingmachine.com)
The load-carrying capacity of the pile can be assessed theoretically as well as practically.
The methods are as follows-
1. Static Method for Pile Foundation-
The ultimate load-carrying capacity of the pile is equal to the sum of end bearing strength
of the soil and the friction developed along with the depth of the pile. This method gives a
more accurate result. The load-carrying capacity of the pile is calculated as-

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Load Carrying Capacity of Pile Foundation by Static Method
2. Dynamic Method for Pile Foundation-
The resistance offered to the pile when driving it through the soil can be correlated to the
strength of the soil and thus the load-carrying capacity of the pile. Since the load-carrying
capacity is correlated and hence it is not much reliable.
The empirical formulas used for this method are Engineering News Record Formula,
Modified Engineering News Record formula, Hiley formula, and Danish Formula.
3. In-situ Penetration Test for Pile Foundation-
The in-situ standard penetration test gives fairly reliable result. The penetration number
(N) can be used to calculate the strength of the soil. Cone penetration test can also be
used.

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Load Carrying Capacity of Pile Foundation by In-situ Penetration Method
4. Load Test for Pile Foundation-
It is the most reliable method. A test pile is subjected to the load and settlement is
observed. The bearing capacity is then calculated at the maximum permissible settlement.
Pile Load Test

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Load vs Settlement Curve of Pile Load Test
The load-carrying capacity of the pile is-
i. 2/3 of the load applied at 18mm settlement or 2% of pile diameter whichever is
lesser. And,
ii. 50% of the final load at which the total displacement equal 10% of the pile diameter
in case of uniform diameter piles and 7.5% of bulb diameter in case of under-reamed
piles.
Method of Pile Load Test-
The load is conducted on a test pile after the rest period of 3 days for sandy soil and 1
month for soft clay after casting. The test pile is subjected to loading through the reaction
girder. A gauge is installed and set at zero to check the settlement of the pile.
The load is applied in the increments of 20% to the allowable load and this rate is
maintained till the settlement is 0.1 mm per hour for sandy soil and 0.02mm for clayey
soil or a maximum of two hours (As per IS 2911-2010).
The gauge readings are recorded after a fixed time interval. The loading is gradually
decreased after reaching the allowable load and reverse readings are recorded. The final
rebound is recorded after 24 hours when final loading has been removed.
The net pile settlement is calculated
as-
Net Settlement of Pile Foundation in Pile Load Test

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A Pile Load Test Report Format has been attached here and also at the end of this
article.
Negative Skin Friction in Pile Foundation-
When the soil surrounding the pile settles more than the pile, it generates a downward
drag. This downward drag is called negative skin friction.
The negative skin friction imposes additional stresses on the pile. This additional stress
reduces the load-carrying capacity of the pile and may even cause the failure of the pile
foundation.
Hence, the net ultimate load-carrying capacity of the pile due to negative skin friction is-
A protective coating or sleeve can be provided to the pile to protect it from negative skin
friction.
Click Here for IS 2911-1979.
Click Here for PILE LOAD TEST REPORT FORMAT.
Happy Engineering!