Values of small-strain shear modulus Gmax, for a Champlain Sea clay deposit were obtained both under an embankment built 18 years ago, and outside of the area influenced by this embankment. The small-strain shear moduli Gmax were measured in the laboratory by using resonant column tests and in the field by spectral analysis of surface waves. In addition to verifying the two methods, comparison of the in situ and laboratory values allowed evaluation of the influence of the sampling and the need to correct the laboratory values to account for the age of the deposit. The test program also made it possible to verify the influence of the deposit's consolidation and the existing models predicting small-strain shear moduli in clay deposits. Key words : shear modulus, shear-wave velocity, resonant column, in situ test, surface waves, soft clay.