The pressuremeter test is currently used by considering the soil as an elastic material. Nevertheless, depending on the permeability of the soil and its state of saturation, the soil response can be Drained or Undrained. Thus, from the theoretical point of view, it is sometimes difficult to estimate whether the modulus measured in the pressuremeter test is an actual or effective modulus. In the ARSCOP project, a first step has been taken and it is possible to calculate the effective modulus for a near-saturated fine soil. This calculation is valid for the moment for a thin soil whose skeleton has a linear response with a compressible fluid (water + air, [1], [2] ). It is thus possible to calculate an effective modulus and estimate the suction generated by the drilling (case where the radial stress is cancelled on the drilling wall). Nevertheless, this approach does not allow to find a pressure rise for an infinite mass and, for finite volume tests, the quantitative results are not satisfactory because the pressure increase is constant throughout the soil volume. To obtain more realistic results, it is necessary to take into account the non-linearity of the skeleton response (law of the type G / Gmax function of the distortion), the distortion being maximum near the probe and tending towards zero to infinity radius. The present study computes the horizontal elasto-plastic equilibrium by the summation of the equilibrium of each elementary part of radius, from the elastic state at the infinity radius, to the plastic state close to the borehole. It allows elasto-plastic interpretation of the pressuremeter test in Undrained clayey soil. It allows finding the difference between the Undrained and Drained shear modulus, and the relation between Effective Cohesion and Friction Angle. REFERENCES (maximum 2 references) 1 Boutonnier, L. 2007, October 23. Comportement hydromécanique des sols fins proches de la saturation. Cas des ouvrages en terre : coefficient B, déformations instantanées et différées, retrait / gonflement. Thèse INPG Grenoble. [2] [Monnet, J., Boutonnier, L., and Mahmutovic, D. 2021. Elastic interpretation of unsaturated ] Undrained pressuremeter tests in clays. In 6th International Conference on Geotechnical and Geophysical site characterisation. Budapest. p. p1.-7.