Behavior of undrained shear strength of saturated soft clay under consolidation

By integrating the functions of large-diameter consolidometer and miniature vane shear devices, a systematic apparatus is devised and developed to be capable of performing shear tests at any point in time during the consolidation process of saturated soft clay. Considering the non-uniformity change of the excess pore-water pressure in space and time, each miniature vane shear device is equipped with a miniature pore-water pressure transducer at the bottom of its hollow axial shaft mounting blades. The large-diameter consolidometer is equipped with miniature earth pressure cells. Thus the apparatus has a function of automatic real-time monitoring of changes of the effective stresses at the positions of vane shear tests. By using this systematic apparatus, the vane shear tests are carried out at different points in time during the consolidation process of saturated soft clay subjected to different consolidation pressures. The changes of real-time deformation and pore-water pressure are monitored during the consolidation process, and the effective stresses and the undrained shear strengths at the positions of vane shear tests are derived. The correlation between the shear strength and the effective stress is analyzed. It is shown that the traditional linear relationship exists between the undrained shear strengths at the end of consolidation under different pressures and effective stresses. However, under a certain consolidation pressure, the shear strength increases non-linearly with the increase in the effective stress during the consolidation process. Moreover, under different consolidation pressures, the larger the consolidation pressure, the higher the shear strength at the same effective stress generated during the consolidation process. The undrained shear strength gained during consolidation is dependent on the effective stress and the void ratio before shearing. The fact that the rate of dissipation of pore-water pressure is less than the rate of deformation is the main reason for the rapid increase in the undrained shear strength at the early stage of consolidation when the effective stress before shearing is relatively low.