T–z curves for piles from pressuremeter test results

Abstract

Pile design is not only based on the assessment of bearing capacity, but can involve settlement calculations when the structures supported by piles need high service requirements. In this context, the load transfer approach with t–z curve models is one of the calculation methods used. The main issue for this method is the choice and implementation of the t–z curve modelling the behaviour of the soil around the pile and accounting for the progressive shaft friction mobilisation. In this paper, three types of t–z curve models from pressuremeter test results are compared: one proposed previously by R. Frank and S. R. Zhao in 1982 and two others presented here. The stiffness of each model is studied and a comparison is performed by considering 90 full-scale static load tests extracted from the IFSTTAR pile database. Measured and calculated values of the pile head displacement are compared for several loading levels considering different soil and pile types. For the three t–z curve models, the ratio of the measured pile head settlement value to the calculated one is analysed and the scatter of each t–z curve model is studied. Some considerations regarding the safety of the pile settlement calculations are proposed.