| Consideration of the time-dependent deformation behavior of cohesive soils may be important in the design and analysis of embankments and their foundations, braced and unbraced excavations, submarine slopes, building foundations, tunnel headings, and open pit mines. At present, most methods for the analysis of time-dependent behavior are limited to certain special problems such as one dimensional consolidation and undrained creep. There exist no generally available constitutive relationships capable of accounting for the general time-dependent drained, partially drained, and fully undrained behavior of cohesive soils. The objective of this dissertation, therefore, is the development of a general constitutive model for use in numerical analyses of time-dependent geotechnical problems.; The constitutive relationships developed in this dissertation are structurally similar to those developed by Kavazanjian (1977). Soil deformations and pore pressure changes are attributed to separate, but interdependent, drained and undrained contributions. Both the drained and undrained constitutive models have time-dependent and time-dependent components. Partially drained behavior is modeled by superimposing drained and undrained behavior.; The components of the constitutive relationship are based largely on the work of Kavazanjian (1977). His equations have been generalized herein to account for anisotropic consolidation, the intermediate principal stress, and stress reorientation. A new technique is introduced for determining the pore pressures that develop during undrained creep.; Drained soil behavior is modeled using components of the isotropic work-hardening perfect plasticity theory developed at Cambridge University (Cam-Clay theory). The Cam-Clay theory is combined with Taylor's (1942) secondary compression theory to model the time-dependent volumetric and shear strains that develop during secondary compression.; As part of this research program, a series of 47 triaxial and plane strain laboratory tests were performed on undisturbed San Francisco Bay Mud over a wide variety of total stress-time paths. The stress-strain-time behavior of Bay Mud observed during these tests was compared with the stress-strain-time behavior predicted using the new constitutive equations. The resulting comparisons showed good agreement. Based on this good agreement, it was judged that the new model holds significant promise for future use in predicting the time-dependent field behavior of geotechnical structures. |
