Study On The Criterion Of Yield And Failure For Geomaterials

The yield and failure of geomaterials are the most fundamental but most important problems in the geotechnical engineering, then vast research has been carried out and abundant achievements have been acquired. However, because of the complexity of geomaterials'mechanical characteristics, some problems still haven't been solved now. How to reflect geomaterials'special mechanical characteristics which are different from those of metals? How to establish the energy yield criterion and how to describe failure of geomaterials? In order to solve the problems put forward above, the characteristics, the energy yield criterion and the failure of geomaterials are researched in this paper. The main study works and results are listed as follows:1. After comparing the difference of materials properties and the induced difference of mechanical characteristics between metals and geomaterials, it′s concluded that geomaterials are frictional materials with multiphase and has frictional characteristics. The shear strength mechanism of geomaterials especially the frictional strength is analyzed, and then the calculation methods of elastic strain energy for different types of materials are presented.2. Based on the analysis of geomaterials'failure characteristics, the yield of geomaterials is researched on the energy point of view, then the triple shear energy yield criterion and the corresponding Drucker-Prager criterion are established. The Mohr-Coulomb criterion and the triple shear energy criterion are used to validate the true triaxial test data, and the errors show that the results of the triple shear energy criterion are more close to the test data than those of the Mohr-Coulomb criterion. It's proved that the energy criterion is correct. At last the materials'yield criteria are systematically researched by the means of stress, strain and energy.3. Based on the triple shear energy yield criterion, the perfect-plastic triple shear energy constitutive model of geomaterials is established and numerically realized. The triple shear energy constitutive model is used in slope stability, cavern excavation, bearing capacity of foundation engineering and so on. The results indicate that the Mohr-Coulomb model is conservative than the energy model.4. Based on the analysis of yield and failure of materials, it's concluded that the two conceptions are different, and the real failure occurs only when both stress and train reach limit values. The different description methods of yield and failure are compared, and the strain criterion for ductile shear failure based on the largest principal shear strain for geomaterials is established. Some tentatively discussions are carried out by researching the failure process from first yield to the connection of plastic zone and then failure at last.