Research On Behaviors Of Compression-creep And Undrained Shear Of Saturated Clay Based On A Thermodynamic Constitutive Model

Deep understanding of the basic mechanicproperties of saturated clay is the key toimprove the level of geotechnical design in the soft soil areas. Rational analyses ofcomplex geotechnical engineering problems encourtered in these fields should be ableto predict the consolidation compression-creep and undrained shear response ofsaturated clay accurately. But with constantly expansion in the scope and the scale ofgeotechnical engineering practise, there are still many to be done. The set of constitutiverelationship used to model soil behavior therefore must incorporate these basicmechanical properties that are exhibited by saturated clays.TsinghuaThermodynamicSoil Model, which is based on non-equilibrium thermodynamics,makes attempt to describe various complicated behaviors of saturated soil in a morerigorous and unified theoretical framework. The involving issues mainly includecontraction/dilation, strain-softening, non-isothermal consolidation and cyclic behavior,etc.Based on the model and by Matlab code, consolidation compression-creep andundrained shear behaviors of saturated clay, especially the stress-induced anisotropyresulted from anisotropic consolidation and principal stress rotation, have been mainlystudied in the paper.The process of consolidation compression and creep for saturated clayiscomplicated and may continue over a relatively long time, and a variety of factors canattribute to it.The results show that the consolidation compression response of saturatedclay is rate-dependent, its preconsolidation pressure will enhance as the controlled rateat which soil is loaded or consolidated increases. The highly sensitive to strain rate alsomakes the process path-dependent, for the strain rate usually varies in differentstress/strain paths. A detailed consideration of deformation and energy dissipationmechanisms of soil under deformed is carried out on the particle level, and thus,Tsinghua ThermodynamicSoil Model is able to capture the complex hysteresisfeaturesand stiffness changes exihibited by saturated clay in thecompression-rebounding-recompression procedure. Creep is usually consideredto be another important evidence of rate dependence for saturated clay, theunfinished and successive adjustment of contact state among particles at the end of loadings referred as “elastic relaxation”, as well as viscous effect, partlyexplains the soil’s creep phenomenon. Meanwhile,“quasi-overconsolidation”caused by creep is believed to bea kind of hardening behavior as a result ofincrease in soil’s density.In practice, soil has often experienced anisotropic consolidation history andinvolved significant rotation of the principal stress directions under fieldconditions. According to laboratory tests and the proposed model, these are themost two important causes for undrained shear strength and deformationanisotropy of saturated clay. And the strength anisotropy increase with thedifference of consolidated stress that is applied in the anisotropic consolidationprocedure. The undrained shear strength tends to decrease, while the peak strainto increase gradually as the principal stress direction of soils rotates from0°to90°. Under the wave and traffic loadings, the magnitude of soil’s principal stresswill hardly change, but the direction will rotate periodically. However, the pureprincipal stress rotation can also cause the disturbance of microstructure ofintact soil, and thus result in strain and pore pressure accumulationas well asstiffness degradation. Meanwhile, as a result of anisotropic consolidation,non-coaxialityof saturated clay is another important manifestation of anisotropy.