A literature review of formulas for stiffness are provided in Tables 5.3 and 5.4. As an example, the latest formulation (Shadlou and Bhattacharya 2016) of K_L is given in the Table E.1. Shadlou and Bhattacharya (2016) formulation considers the base shearing of the pile as well as the shaft resistance of the pile. This is in contrast to the conventional p‐y formulation where only compressional resistance (i.e. lateral pile‐soil interaction) is taken.

Ground profile/pile type	Rigid pile	Flexible pile
Homogeneous
Parabolic
Linear

L: Pile embedded length; D: Pile diameter; E_SO: Soil Young's modulus at 1 diameter depth; E_p: Equivalent Young's modulus of the pile; υ_s: Soil Poisson's ratio; .

Homogeneous soils are soils that have a constant stiffness with depth such as overconsolidated clays. On the other hand, a linear profile is typical for normally consolidated clays (or ‘Gibson Soil’) and parabolic behaviour can be used for sandy soils.

Eurocode 8 (Part 5) also provides stiffness of flexible piles. Expert judgement is required for choosing the formulas given in Table 5.3.

Conversely, one may carry out beam on nonlinear Winkler foundation model using state‐of‐the‐art p‐y curves to obtain the pile head stiffness values. The method to convert p‐y analysis to the pile head stiffness values is provided in Examples 6.2 and 6.3 of Chapter 6.