The aim of determining the P-y reaction curves. The instrumented pile allows the bending moment profiles to be obtained. The uncertainty on the moment measurement is first quantified. The displacements are determined from a polynomial function fitted on the moment data and calculated by double-integrating the moment. An analytical integration type is used. The soil reaction is obtained through double derivation : the moment data are interpolated using quintic Splines, which are derived twice. The Spline functions are selected by studying the static equilibrium of the pile in force and moment. An analysis of the pile response through the obtained P-y curves is discussed including uncertainty of measurements. The principle of the analysis is to introduce an uncertainty on the experimental bending moment data, and to quantify its effect on the P-y curve.