The influences of temperature on the mechanical behavior of saturated clays are discussed first. Based on the concept of true strength and the revised calculation method of the potential failure stress ratio,the equat...The influences of temperature on the mechanical behavior of saturated clays are discussed first. Based on the concept of true strength and the revised calculation method of the potential failure stress ratio,the equation of the critical state stress ratio for saturated clays under different temperatures is deduced. Temperature is introduced as a variable into the UH model (3-dimensional elastoplastic model for overconsolidated clays adopting unified hardening parameter) proposed by Yao et al. and then the UH model considering temperature effects is proposed. By means of the transformed stress method proposed by Yao et al.,the proposed model can be applied conveniently to 3-dimensional stress states. The strain-hardening,softening and dilatancy behavior of overconsolidated clays at a given temperature can be described using the proposed model,and the volume change behavior caused by heating can also be predicted. Compared with the modified Cam-clay model,the proposed model requires only one additional parameter to consider the behavior of the decrease of preconsolidation pressure with an increase of temperature. At room temperature,the proposed model can be changed into the original UH model and the modified Cam-clay model for overconsolidated clays and normally consolidated clays,respectively. The considered temperature range here is from the melting point to the boiling point of the pore water (e.g. the experimental temperatures (20°C–95°C) mentioned in this paper are within this range). Comparison with existing test results shows that the model can reasonably describe the basic mechanical behavior of overconsolidated clays under various temperature paths.展开更多
A small strain unified hardening(SSUH) model is proposed in the present study to tackle the small strain behavior of clay. The model is an extension of the unified hardening(UH) model for overconsolidated(OC) clays ac...A small strain unified hardening(SSUH) model is proposed in the present study to tackle the small strain behavior of clay. The model is an extension of the unified hardening(UH) model for overconsolidated(OC) clays accounting for the small strain stiffness. The new features of the SSUH model over the UH model include:(a) a new elastic hysteretic stress-strain relationship to evaluate the stiffness degradation at small strains and to generate the hysteresis loop under cyclic loading condition;(b) a revised unified hardening parameter to enhance the plastic stiffness at small strains; and(c) a new overconsolidation parameter, which is crucial to make the UH model working with the elastic hysteretic stress-strain relationship effectively. With these enhancements, the SSUH model can describe a high initial stiffness and the highly nonlinear stress-strain relationship at small strains, in addition to the shear dilatancy and strain hardening/softening behaviors of OC clays at large strains. In comparison with the Modified Cam-clay(MCC) model, the proposed model needs two more small strain related parameters, which can be easily obtained from laboratory tests. Finally, some drained triaxial compression tests at large strains, drained triaxial compression/extension tests at small strains, an undrained compression test at small strains and a drained cyclic constant radial stress test are employed to validate the new model.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos.50879001,90815024,10872016,11072016)the National Basic Research Program of China ("973" Project) (Grant No.2007CB714103)
文摘The influences of temperature on the mechanical behavior of saturated clays are discussed first. Based on the concept of true strength and the revised calculation method of the potential failure stress ratio,the equation of the critical state stress ratio for saturated clays under different temperatures is deduced. Temperature is introduced as a variable into the UH model (3-dimensional elastoplastic model for overconsolidated clays adopting unified hardening parameter) proposed by Yao et al. and then the UH model considering temperature effects is proposed. By means of the transformed stress method proposed by Yao et al.,the proposed model can be applied conveniently to 3-dimensional stress states. The strain-hardening,softening and dilatancy behavior of overconsolidated clays at a given temperature can be described using the proposed model,and the volume change behavior caused by heating can also be predicted. Compared with the modified Cam-clay model,the proposed model requires only one additional parameter to consider the behavior of the decrease of preconsolidation pressure with an increase of temperature. At room temperature,the proposed model can be changed into the original UH model and the modified Cam-clay model for overconsolidated clays and normally consolidated clays,respectively. The considered temperature range here is from the melting point to the boiling point of the pore water (e.g. the experimental temperatures (20°C–95°C) mentioned in this paper are within this range). Comparison with existing test results shows that the model can reasonably describe the basic mechanical behavior of overconsolidated clays under various temperature paths.
基金supported by the National Program on Key Basic Research Project of China(973 ProgramGrant No.2014CB047001)+2 种基金the National Natural Science Foundation of China(Grant Nos.1127203151179003 and 41372285)Beijing Natural Science Foundation(Grant No.8132042)
文摘A small strain unified hardening(SSUH) model is proposed in the present study to tackle the small strain behavior of clay. The model is an extension of the unified hardening(UH) model for overconsolidated(OC) clays accounting for the small strain stiffness. The new features of the SSUH model over the UH model include:(a) a new elastic hysteretic stress-strain relationship to evaluate the stiffness degradation at small strains and to generate the hysteresis loop under cyclic loading condition;(b) a revised unified hardening parameter to enhance the plastic stiffness at small strains; and(c) a new overconsolidation parameter, which is crucial to make the UH model working with the elastic hysteretic stress-strain relationship effectively. With these enhancements, the SSUH model can describe a high initial stiffness and the highly nonlinear stress-strain relationship at small strains, in addition to the shear dilatancy and strain hardening/softening behaviors of OC clays at large strains. In comparison with the Modified Cam-clay(MCC) model, the proposed model needs two more small strain related parameters, which can be easily obtained from laboratory tests. Finally, some drained triaxial compression tests at large strains, drained triaxial compression/extension tests at small strains, an undrained compression test at small strains and a drained cyclic constant radial stress test are employed to validate the new model.
