Study On Mechanical Model Of Brittle Rock Under High Stress Condition And Its Engineering Applications

Strength characteristics of rock under the complex stress conditions and its fail behaviors have been one of the most important and very complex research topic in the area of civil and related projects for a long time ago. As the deep development has been into a trend in the rock projects around the world, where the geological and stress environment has become more complex, the study of rock mechanics under the condition of high stress in deep engineering has been put on the agenda, in particular, the establishment of rock strength criteria and its constitutive model, which has been one of th key issuses describing its strength characteristics and its rules of deformation and damage in underground rock engineering.In view of this, in order to meet the construction needs and the development demand of rock mechanics subject, based on the deep brittle rock multi-point mechanical and rheological experimental investigation, the strength criteria and its constitutive model which is applicable to the conditons of high stress have been systematically investigated and proposed using mechanical theory such as rock strength theory, elastoplastic mechanics, rheological mechanics and seepage mechanics. In the end, with intelligent inversion theory, the above investigation results are applied to the practice of great hydropower rock project, wich solves the practical problems encountered in the construction of the actual engineering. In sum, the main investigation works and results are listed as follows:1. Based on the multi-angle expertimental results of Jinping marble from the deep site, such as single and triaxial test, damage-control loading-unloading test, true triaxial test and acoustic emission test, a more systematic analysis on the deformation and strength characteristics,energy dissipation characteristics of the brittle rocks under different circumstances in different states of stress is carried out from the deformation, strength, energy and failure view,which has access to the brittle rock characteristics and the instantaneous basic mechanics of deformation and damage. And then using crack strain theory, the internal crack evolution and failure mechanism of the deep brittle rock are made in a detailed analysis.2. Based on the physical basis of two failure-control mechanism, a Generalized Polyaxial Strain Energy Strength Criterion(GPSE) is created using Griffith theory and Weibols's principle of effective strain energy. The GPSE strength criterrion for rock is verified by polyaxial test data of brittle rocks that have been published. And then the GPSE criteria expressed by Mohr's and Hoek's parameters respectively are derived on the basis of the criteria,which laid the foundation for application of actual projects.3. On the basis of GPSE criteria expressed by Mohr's parameters and laboratory test results, the damage evolution formulas on strength parameters and expansion parameters are proposed, and the strain hardening-softening constitutive model considered dilate effect (GPSEdshs )which is applied to the brittle rock under high stress condition is established. Then the finite difference format of the constitutive model is derivated in detail, and its numerical computing capabilities are achieved. Based on GPSE criteria, a safety evaluation named by dilate safty factor of wall rock of underground rock project is derived to make the security disturbance district of wall rock excavation from the perspective of theoretical and experimental.4. The results including fitting of triaxial compression test stress-strain curves of marble,simulation of EDZ of Canada Mineby test tunnel,comparison of analog results both dilate strain-softening constitutive and non-dilate constitutive,simulation of EDZ of testing tunnel in JinPing II diversion tunnel and so on prove that the model and the dilate safty factor are suitable for numerical calculation of underground brittle wall rockmass and suitable for space district characteristics of dilate damage of wall rockmass under high geo-stress condition. In addition, the analysis result shows that the Mohr-Coulomb model is conservative than the GPSEdshs model.5. In order to know about the rheological properties of marble of the deep site in Jinping II diversion tunnel, triaxial compression rheological experiments with water pressure coupled stress were carried out on the rock servo-controlling rheology testing machine. The aging deformation characteristics and evolution rule of the brittle rock under different confining pressure, stress level and whether water pressure or not are investigated from the axial deformation,lateral deformation and volumetric deformation, and the characteristics such as tautochrone,deformation rate, creep deformation,creep strength,creep failure and so on are discussed in detail which make us preliminary master the basic law of rheological behavior on Jinping marble under the complex environment,and illustrate aging failure mechanics of the brittle rocks.6. On the basis of previous studies and rheological experiments of brittle rock, non-stationary visco-elastop-plastic rheological model considering the effect of stress state is put forward.And then the corresponding creep equation and the relaxation equation are deduced, and the model of the creep and relaxation properties of the model are theoretically discussed. On this basis and the combination of seepage theory, the numeratical model of non-stationary visco-elastop-plastic rheological constitutive under the role of H-M is proposed, and its finite difference format is derived which is to achieve the numerical calculations in Flac3D. The numerical results show that the numerical procedure of rheological model is reasonable and correct. And then by the identification of the non-stationary visco-elastop-plastic rheological model, the creep test parameters of Jinping II marble under the water pressure coupled stress are successfully identified.7. Finally, with intelligent inversion theory, experimental and theoretical investigation results on mechanical properties of brittle rock are applied to .the study of wall rock stability in deep site of assisted tunnel of Jinping II diversion tunnel. Using numerical models of 2D and 3D, space-time evolutionary process and law of mechanical response of wall rockmass are systematically analysed and summaried from the views of the displacement vector field, the principal stress vector field, the principal stress path, as well as size and depth of plastic zone anddilate damage zone,and so is whether water pressure or not.The problems including the nature of deformation lag, the nature of failure lag and so on in the hard rockmass under high stress in the deep field are reasonably interpreted.Research on these issues provides the basis of information and theory for the smooth construction of Jinping II diversion tunnel.