Abstract: The soil samples are subjected to different load rates, stress durations, stress paths and stress courses in continuous load rate unconfined compression tests. If the lateral pressure of uniaxial unconfined compression tests is defined as the adaptive shear stress of soils, the difference between the axial and lateral pressures of the uniaxial unconfined compression tests is defined as the adaptive shear stress of soils. The experimental studies show that the adaptive shear stress is not affected by the pore water pressure. More importantly, the experiment and analysis have proved that the uniaxial unconfined strain of reconstituted saturated clay samples has the unique relationship with the adaptive shear stress.