Several computation methods for piles subjected to lateral loads have been so far proposed. Among these methods the most reliable one may probably be the P.H.R. I. method (Port and Harbour Research Institute method), which is based on a quntity of experimental results.
　A coefficient of deformation in this method that is called a soil constant is related to a standard penetration value N under consolideration of its only dependence on soil properties. In this report the history with respect to the coefficient of deformation for piles is outlined, and it is described that the soil constant may be estimated by soil test results. This proposed methods is agreeably confirmed by laboratory experiments in sandy soil, and by field tests in clayey soil.