报告人：台湾大学 葛宇宁 副教授
Triaxial Testing of Railroad Ballast within the Parallel Gradation Scaling Framework
The parallel gradation modeling technique was originally developed by John Lowe in 1964, to allow assessment of large grain-size geomaterial properties in smaller, more typical testing facilities. The parallel gradation model states that a model smaller grain-size distribution granular material, of the same composition as the prototype material, can be used in triaxial testing at a scaled down grain-size, if the model material grain-size is exactly parallel to the prototype material. Therefore, a model granular material composed of smaller, but parallel, grain-size distribution can be used to predict shear and compressive properties of a larger granular material, such as rock fill. Emphasis has focused on monotonic loading, where the material is progressively loaded to failure. Cyclical testing of this model has been absent.
This presentation presents an investigation of the possibility of using the parallel gradation modeling technique in a cyclical triaxial testing framework. Three separate gradations of ballast material were used in this research. The largest gradation contains a top particle size of63.5 mm(2.5-inches) and is marketed as #3 modified railroad ballast. The second two gradations contained a top size of38 mm(1.5-inches) and19 mm(¾-inches) respectively.
These gradations were manufactured to have a grain-size distribution curve, parallel to the63.5 mmprototype gradation. Triaxial samples weighing over190 kgwere loaded cyclically 10,000 times. Particle shape comparisons between the gradations were assessed for both fresh ballast as well as the ballast used in the triaxial testing. Conclusions are drawn from this testing program regarding the validity of the parallel gradation modeling technique within the cyclical triaxial testing framework.
Cyclic Plasticity Model for Geo-Materials Based on Fuzzy Set Plasticity
This presentation discusses the developments and enhancements of a fuzzy set cyclic plasticity model, which is based on classical plastic flow-theory and mixed hardening concepts, but which employs expressions and algorithmic tools, that are far simpler to visualize, integrate and implement than many other constitutive models based on conventional mixed kinematic-isotropic concepts. The present formulation accurately simulates stress-strain, strength, dilatancy, pressure dependence, and non-proportional loading features for geomaterials subjected to both low and high-cycle loading, including fatigue and elastic-shakedown phenomena. Applications of damage evolutions, long-term effects, non-proportional loading, and principal stress rotation are also presented.