Microdeformation Mechanism Of Structural Clays And Elasto-viscoplastic Damage Model

Microdeformation Mechanism of Structural Clays and Elasto-viscoplastic Damage Model ABSTRACT On the basis of the investigation of the structure of natural sedimentation clays and the simulation of the deformation and rheology of soil particle skeleton under the internal molecule attractive force and electric charge repulsion and the exterior load, a elasto-viscOplastic damage model is constructed in which the soil structure is considered to be gradually damaged in the course of loading, and the effectiveness of the model is verified by the results of laboratory tests and field tests. The clays from natural sedimentation have always the structure (fabric and bond) and structure strength. Most sedimentation compression lines of natural clays are located above the intrinsic compression lines of reconstituted clays; theirs locations are dependent on the sedimentation condition and the action after sedimentation. The sedimentation compression lines, intrinsic compression lines can be normalized by a void index, then the difference of the structural clays and reconstituted clays are showed. The reconstituted clays represent the soil intrinsic properties independent of the natural state, and provide a reference frame being used to evaluating the properties of in-situ sedimentation clays. From the oedometer compression curves, the gradual damage course of soil structure is indicated apparently during loading. The large strain constitute equations are derived according to nonlinear continuum mechanics, the rate of Jaumann stress and the theory of Boit consolidation on account of the limitation of small strain theory in hydraulic fill, soft ground and large displacement projects. A large strain FEM program is compiled to compare the difference of large strain method and small strain method. The results show that the deformation and pore water pressure are almost the same to the total and updated Lagrange method and small strain method when the strain is less then 7%. The different is evidently increased when the strain is more than 10% and the final settlements of large strain method are smaller than that of small strain method. The pore pressures are not the same to large and small strain method, so the comparison of final settlement should be based on total stress method(complete drainage). Moreover, in order to achieve reasonable calculating precision and settlement values, the time step should be very small due to the linearization of the high non-linear equation of large strain. The point-surface contact element is put forward to solve the large strain simulation of contact, slide and rotation among multi-objects. Combining with updated Lagrange method, it can well simulate the cementation, slide, unhitch, the formation of new contact and turnaround of present contact. Then, the deformation of soil particle skeleton under the physical chemistry of electrical double ]ayer and exterior load are simulated, indicating the micro-mechanism of deformation, failure and creep for structural soil. Because conventional constitute models are constructed according to reconstituted clays, not considering the structure in natural clays and structure damage course during loading, a elasto-viscoplastic damage model and the parameter determining method are put forward. The calculating results of laboratory tests demonstrate that the model can simulate the yield pressure of structure soil, the...