Pressuremeter tests are an efficient tool to derive shear modulus of grounds, and its decay with shear strain. Non-linear behaviour of grounds during cavity expansion, and its consequence on shear modulus and stress with the distance to the pressuremeter cavity, have to be taken into account. For tests in fine soils, for which constant volume can be assumed during the test, retrofitting of unload-reload loops based on closed form solutions integrating the non-linear elastic behaviour can be implemented. In a first phase, this paper presents a practical straightforward method to derive shear modulus decay with shear strain based on the cylindric cavity expansion theory including non-linear elasticity under undrained conditions. In a second phase, the method is applied step by step to a pressuremeter test in clay with unload-reload loops. Finally, on a third and last phase, this paper compares the previous results from to i) other interpretation methods of pressuremeter tests, including numerical modelling and approaches integrating prior strains transformations, but also to ii) other investigation tests providing the initial shear modulus G0 associated with very small strain levels or the shear modulus decay with strain level.