The Argillite Transverse Isotropic Elastic-plastic Coupling Deformation And Strength Criterion Of The Pilot Study

Anisotropy of rocks can occur at the micro, meso and macro scales in all. The crystals of minerals have some degree effects on the anisotropy of rocks. The effects mainly depend on the arrangement of mineral aggregates which were formed by the collection of the mineral crystals. At the mesoscopic level, the combining form of components and mineral aggregates of rocks have great effects on the anisotropy of rock mechanics behaviorAnalysis of mineral micro-components and meso structure, experiments of macroscopic mechanical properties of argillite with a clear stratification structure were launched in this paper.(1) At the micro scale, the components of argillite:quartz, kaolinite, muscovite and clinochlore were analyzed by XRD. Arrangements of the crystals of these minerals have effects on the anisotropy of mineral aggregates was pointed out.(2) At the mesoscopic scale, by scanning electron microscopy experiment, the micrographs of microscopic structure of the argillite were photographed. Analysis showed that the main type of structure in argillite was crystalloblastic texture, which contains granular mineral aggregates made of quartz crystal, and schistose mineral aggregates made of the crystals of kaolinite, muscovite and clinochlore. But the main component was schistose mineral aggregates. Under gravity, these mineral aggregates arranged to the dominant horizontal direction, and this kind of arrangement determined the argillite with transversely isotropic mechanical properties.(3) At the macro scale, experiments of uniaxial compression and triaxial cyclic loading tests of argillite rock samples with different angles were launched. Studied the deformation and strength properties of argillite, and found the obvious existence of elastoplastic coupling deformation. Under different loading angles, the apparent elastic moduli decayed exponentially with the increase of plastic strain. Obtained the relation of experience function between apparent elastic moduli and plastic strain by fitting method. Through the analysis of cyclic loading and unloading stress-strain curve, plastic strain, elastic strain and elastoplastic coupling strain were separated from the total strain. At the beginning of loading, the main deformation was plastic. With the increasing of load and total strain, the proportion of plastic strain in total strain gradually decreased, while the proportions of elastic strain and elastoplastic coupling strain increased. The compressive strength of argillite varied with the difference of confining pressures and loading directions. Strength anisotropy of argillite significantly affected by the confining pressures, and with the gradual increasing of confining pressures, the degree of strength anisotropy reduced. Proposed anisotropic empirical Mohr-Coulomb strength criterion with cohesion and the friction coefficient changing with loading directions. Through the data fitting method, obtained the values of relevant parameters, and graphed the strength surface of this criterion in three-dimensional space composed ofσ1,βandσ3.