Study On Mechanical Behavior And Constitutive Relations Of The Three Gorges Granite

As one of the most widespread geo-material in china, granite is generally applied in many industry of economic construction, especially in rock engineering. In the construction engineering which involves granite, such as mining activity, water conservancy and electric power engineering, civil engineering, tunnel and underground building, the mechanical behavior of granite under different loading is the base of design and construction, meanwhile, is used as important parameters for safety analysis, failure forecasting and safety protection. Based on the research of granite especially the Three Georges granite in the last 40 years, experimental study,theoretical study and numerical simulation have been finished as follows:(1) Through the mineral identification and electron microscope scanning, the mineral origin and microstructure of the Three Gorges granite are further described: the good cementation of the mineral of feldspar, quartz and mica brings on high density, and the average growth of the igneous brings on average stress and hard connection. This kind of mineral origin and microstructure result in high mechanical properties of granite, meanwhile, weathering can change the mineral origin and microstructure of rock and affect the mechanical properties of rock.(2) Based on the experimental research of uniaxial compression test, triaxial compression test, shear resistant test and fracture mechanical property test by others, the whole process stress strain test of the Three Georges granite have been carried out by the author to study the mechanical properties and get the conclusions: in uniaxial condition, the behavior of Three Georges granite is brittle failure; with the increasing of confining pressure, though it has the tendency from brittleness to ductility, it still belongs to elastic-brittle material in experimental meaning or engineering stress category. The real reason conduces to the failure of granite is tension but not shear.(3) Strength criterions of granite are studied. A large number of experimental data of worldwide granites are collected to draw the curves ofσ₁ ^σ₃ for fitting the different strength criterions. The results indicate that Mohr-Coulomb strength criterion is not applicable to the condition of tension and high confining pressure, while Yoshida, Balme and Hoek&Brown empirical strength criterions can properly describe the mechanical behavior under both tension and compression.(4) Based on the whole process stress-strain tests of the Three Gorges granite in RMT and MTS, the post-peak mechanical behavior of granite is studied. The relationship between strength parameters and post-peak strain softening parameters has been analyzed by fitting the post-peak yield function, and the strain softening constitutive model of the Three Gorges granite is established. In the strain softening process, it is found that the value of c decreases with the increasing of generalized plastic strain, while the value ofφkeeps constant.(5) The software FLAC3D which is frequently applied in geotechnical engineering is introduced. Based on the previous experimental data on MTS machine and the strain softening constitutive model, the whole process of granite stress-strain test is simulated by FLAC3D. By comparing the results of test and numerical simulation, it is found that: under low confining pressure, the granite post-peak stress decreases dramatically as brittle material; with the increasing of confining pressure, the ductile behavior gradually becomes obvious, the post-peak plastic deformation increases and also the peak strength and residual strength. In addition, some numerical cases with different mesh density and loading rate under various confining pressure (0, 5, 10 and 40MPa) have been carried out to study the effect of mesh density and loading rate.