Soil conditioning is increasingly used to improve the performance of tunneling in many types of soil. Addition of suitable agents leads to enhanced properties of the soil at various points of the tunneling process. In this paper a new vane shear device is introduced, which allows to measure shear strength of clay mixtures under pressure and with different vane velocities. The new testing apparatus and the corresponding procedure are evaluated on kaolinite clay conditioned with foam and polymer additives. A strong pressure and rate dependency of the shear strength and a large effect of polymer type could be observed.