Lateral load pile design theory

Hi, I have some question about the pile under lateral loads.

1.- I was tried to review the design theory for lateral loaded piles, but the documentation contain a web link which it is not active.

2.- I tried to search the document at the web, but the information it is deprecated, so I am not sure if the software design basic are still valid, please could you give some information about de design basic and what  the software are designing.

3.- Other topic it is about the nature of the load "ciclic", the help it does not give any information about this kind of load.

4.- Respect to how the software determine the p-y curve, the help indicate it is a nonlinear approach, but does not give any information about the theory of behaviour assume.

Best Regards,