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Soil subgrade reaction in pile foundations is mostly based on theory of elasticity. Piles are subjected to vertical and lateral loads as well as moment loads. Therefore, the subgrade reaction incorporates two components, a vertical and a lateral, thus two discrete methods for deriving those components will be analyzed. It should be noted that the analyses presented deal with a single pile and not a group of piles. In the latter case, more complex models are required.

To derive the vertical subgrade reaction in pile foundations, a method that is based on theory of elasticity developed by Poulos and Davis (1980) will be utilized. The initial purpose of the method was to derive the settlements of a pile foundation; thus, the subgrade reaction is determined using the following formula:

where ** K_{V}** is the vertical coefficient of subgrade reaction,

where * E* stands for the modulus of elasticity of the soil (MPa),

The calculation of the correction factor is slightly different depending on the type of the pile. Piles are fundamentally divided into two categories:

*End-bearing piles*-
*Friction piles*

End-bearing piles distribute the largest portion of the vertical load to the toe of the pile. They operate in the same manner as a pillar of a structure. On the contrary, the bearing capacity of friction piles derives from shear stresses that develop at the sides of the pile.

Usually, end-bearing piles are used to transfer the load to a harder soil layer or rock whereas friction piles are utilized when this is not possible.

In their analysis to derive the subgrade coefficient (Poulos and Davis, 1980), a homogenous soil mass with a constant Poisson ratio ** ν**, and Young’s modulus

The correction factors for end-bearing and friction piles are calculated using Equations 3 and 4, respectively:

The aforementioned factors are thoroughly assessed in the following sections.

The settlement-influence factor depends on the ratio of the tip diameter ** d_{b}** to the top diameter of the pile

** I_{0}** can be derived via the diagram of

The compressibility correction factor, ** R_{k}**, depends on the

where * E_{P}* is the pile’s modulus of elasticity, and

An example showing the geometry that impacts the *R _{A}* factor is shown in

The base modulus correction factor, ** R_{b}**, is applicable in end-bearing piles.

The depth correction factor, * R_{h}*, is used in friction piles and also depends on the

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Deep Foundations

1 pages

Shallow Foundations

2 pages

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