An advanced t-z curves method using cyclic shaft friction degradation for the design of piles in sand

Abstract

A calculation model including an original cyclic t-z method is proposed for the analysis and the design of piles subjected to cyclic axial loads both in terms of displacements and resistance. This model allows the assessment of pile displacement and axial force distribution with depth for each load increment. The cyclic effects and especially the decrease of the shaft friction are accounted for by considering the current state of stress at the pile-soil interface. The approach is based on the ‘ABC’ method developed by the Imperial College. A procedure is developed to combine this method with t-z cyclic curves. Comparisons are made between the numerical results obtained from this cyclic t-z model and the experimental data of tests which were carried out during the project GOPAL (Grouted Offshore Piles For Alternating Loadings) and the French National Project SOLCYP (SOLlicitations CYlcliques sur Pieux): four cyclic loading sequences are considered for both driven and bored piles. The reliability of the proposed model is evaluated according to the loading level and the number of cycles. The use of this model also leads to the construction of cyclic stability diagrams.