Chapter 6: Numerical derivation of CPT-based p–y curves for piles in sand

The p–y method is the most commonly employed approach to analyse the behaviour of piles subjected to lateral loads. This method idealises the soil as a series of independent springs distributed along the pile length. The springs are assumed to be approximately independent as the width of a pile is generally much smaller than its length (Vesic, 1961). Each spring has its own load-transfer relationship known as the p–y curve, where p is the soil resistance force per unit pile length and y is the local pile deflection.

The most widely used design method for deriving p–y curves in sand is the API method (API, 2011). This method evolved from the seminal paper of Reese et al. (1974) who compiled results from lateral tests on relatively small piles. The most recent version of the recommendations is based on the interpretation of O’Neill & Murchison (1983). These recommendations adopt a hyperbolic tangent form for the p–y curve and the only input parameter required is the sand’s peak friction angle (ϕ′).The high sensitivity of the formulation to the selected ϕ′ value is, however, problematic given the difficulties faced by geotechnical practitioners who need to employ an in-situ test such as the standard penetration test (SPT) or cone penetration test (CPT) to assess the sand density and hence friction angle.