The Study On The Rheological Properties Of Saturated Soft Clay Around The Tunnel Under Subway Loading

Aiming at solving the engineering geological problems induced by the subway operation, such as the axial settlement of soft clay embankment of the railway tunnel, the paper studies the Theological properties of saturated muddy soft clay around the tunnel under subway loading in Shanghai areas, though a series of experiments conducted on the undisturbed soil samples, including the field monitoring test, the indoor cyclic triaxial test, the Cu shearing test and the electronic microscope scanning test. The results are as following:1. There are two main dynamic response frequencies of the saturated soft clay around the tunnel when the subway operating. The high frequency is between 2.4 Hz and 2.6 Hz, while the low frequency is between 0.4 Hz and 0.6 Hz.2. In the direction of horizontally deviating from the subway tunnel axis, the vibration loading and the soil dynamic response induced by subway operation regularly fade down with the deviating distance increasing.3. Three typical characteristic curves exist in the cyclic creep curves of saturated soft clay under cyclic loading. They are the peak creep curve, the base creep curve and the valley creep curve.4. The cyclic creep of the saturated soft clay is composed of recoverable elastic strain and accumulated plastic strain, and there is a linear relation between recoverable elastic strain and CSR (Cyclic Stress Ratio) when stress level is under the destructive CSR.5. Two critical CSRs exist under stepped cyclic loading, which are the stable CSR and the destructive CSR, dividing the soil's accumulated plastic strain development into the gradual stability stage, the quick increase stage and the instantaneous destruction stages.6. The accumulated plastic strain and the residual pore water pressure of the saturated soft clay both experience the development of quick increasing-uniform increasing-weakening stabilizing, while the load level is below the destructive CSR. 7. With the only linear relationship to the logarithmic cyclic loading duration, most of the accumulated plastic strain and the residual pore water pressure are generated in the initial stage of the long term subway loading, and influenced by the loading frequency and the drain condition in the cyclic triaxial tests.8. After the cyclic triaxial test, the sample's re-consolidated Cu shear strength is bigger than that of the undisturbed soil sample.9. Under the long-term cyclic loading, the microstructure of the saturated soft clay experiences a certain degree of "adjustment" and "reorganization", which is related to the soil's macro-rheological properties.10. There is a bigger degree of "adjustment" and "reorganization" of the microstructure of the saturated soft clay under a higher loading level, a longer cyclic loading duration and a lower loading frequency.