| Rubber-soil (lightly cemented scrap rubber tire chips) is a promising solution for the global scrap tire problem. It is also a promising material for various geotechnical engineering applications because of its advantageous properties such as lightweight, high permeability, high ductility and ease to cast.; Intensive laboratory studies, mostly under triaxial testing, are conducted and a constitutive model is proposed. Firstly, the effective stress principle is proven applicable for Rubber-soil under normal engineering stress level although the inter-particle contact area is large. Secondly, because of the gravel-sized surface voids on the testing samples, membrane penetration is serious so an integrated remedy method is proposed, where the surface voids are patched up first and then a lubricated reinforced membrane is dressed on. It is found that the volumetric deformation of Rubber-soil is very recoverable even after 20% volume contraction but the over consolidation results illustrate a decreasing stiffness, which is believed due to volumetric damage. Shearing on the sample gives typical results as sands where clear phase transformation is observed, but the strains involved are higher and more recoverable. Besides, shear stiffness is observed decreasing with deformation, which is believed due to shear damage. There are other observations such as the difference in the curvatures of unloading and reloading curves in CD tests, which might be a frictional phenomenon.; Based on the laboratory observations and on the analogy of a continuum spring-block system, a constitutive model termed as Analogical Model is proposed. Fifteen model parameters are involved but most of them are typical soil parameters. The remaining ones have clear physical meanings and can be easily calibrated. It is found that the model can satisfactorily capture many features observed from the experiments, such as hardening, softening, apparent permanent deformations, stiffness decay due to damage, cyclic damage that leads to accumulation of strains and the frictional phenomenon of different curvatures between unloading and reloading curves. The model utilizes the hypothesis of the competition between bond mobilization, friction activation and bond degradation. It is believed that this model may be generalized to other bonded frictional materials although there are still many rooms for improvement. |
