Abstract: The viscosity coefficient is a key parameter which expresses the soil creep and flow characteristics. Electron microscope scanning, particle size analysis, X-ray diffraction and chemical analysis test of Huangshi, Zhangzhou and Qingdao areas soft clays are performed. The test results show that soft clay’s granulometric composition, mineral component, physicochemical properties and structure type influence the viscosity coefficient remarkably. In the soft clay creep process, the structure haploid had the directional arrangement or had the glide, its relative motion caused the bound water viscosity to reflect that then caused the viscosity coefficient change. The direct shear creep test is carried out and using Chen method to process creep test data. The test results show that because the microscopic structure increases along with the shearing stress damages gradually; the viscosity coefficient increased along with the shearing stress achieved the peak value, a consolidation pressure bigger peak value manifests is more obvious; the peak value correspondence's shearing stress is also bigger. A new seeking long-term strength method which the viscosity coefficient peak value correspondence's shearing stress replaced the critical shearing strength with the different consolidation pressure is proposed, and confirmed the accuracy of this method through the tentative data. The test results make contribution to understanding the creep mechanism and that the constitutive model can be set up according to the actual engineering.

Key words: structural soft clay, direct shear creep test, viscosity coefficient, bond water, long-term strength