Experiment Studies And Theoretical Analysis Of Water-weakening Properties Of Slates

Some experiments and theoretical analysis were done to study the water-weakening properties of slates in different water absorption taken from the engineering of the western route of Water Transfer Project from Southern to Northern China. These researches includes the micro- structure and components measurement, mechanical properties in dry and wet conditions and the creep properties under long time effects. The main research work of this dissertation is as follows:1. The components and contents of clay and their distribution characters were analyzed by the measurement methods as OM, SEM, XRD and EDAX in dry conditions compared with those in water weakening to analyze the changes of grains;2. For the reason of the well-aligned clays, slates show the transversely isotropic properties and the mechanical parameters varied with the structural plane dip in mechanical experiments as shear tests, uniaxial and triaxial compression tests. The parameters are big when the angle varied near 0 or 90°and the samples may damage inside in press; while they varied greatly when the angle was in 30-60°and deformations may be slide from discontinuities.3. Slates can be divided into two kind bodies as one comprised many layer faces and another with little faces or no discontinuities from the layer faces inside the slates. Constitutive relations were set up with the Cosserat media theory and stratified rock theory and the predicted results of the theory were identical with the experimental results. The deformation forms were analyzed with the single discontinuities theory and Mohr-Coulomb strength criterion and the change law of the maximum strength varied with the angles was confirmed.4. Variation law of water absorption, dilation stress and dilation deformation with time were get from the water-absorption and dilation experiments. Water-weakening properties of slates can be confirmed by the uniaxial and triaxial compression tests in different absorption, and the change of strength and elastic modulus with the water absorption were also got. Through defining the change of elastic modulus as the damage variable, its variation law with the water-absorption was analyzed; when replacing the elastic modulus and other parameters in dry conditions with those in wet conditions, new constitutive relations with discontinuity inclinations and water-absorption were be achieved.5. From micro images and structures and theory analysis, water-weakening mechanism of slates can be explained as follows: when water entered into the inside, clay mineral grains attracts water molecules to its surfaces and formed the water layers which caused the grains expanded and produced the dilation stress; at the same time, the contact angles of slate surface declined which caused the surface tension decreased; with some other factors, the cohesive force inside slates decreased and showed the water-weakening properties in macro and the strength declined.6. The creep experiments showed that, the creep deformation was small and comprised transient creep and steady state creep stages. Axial stress and confining stress effect on the creep deformation were analyzed and the constitutive relations were obtained which can reflect the creep properties of slates and finally the water effect to creep were analyzed.The following innovative accomplishments can be obtained from the above research:1. According to the transversely isotropic properties of slates caused by the clay mineral alignments,...