Study On Rheological Mechanical Properties Of Rock And Its Engineering Applications

Rheological mechanical experiment of rock is not only the most important means to know about the rheological mechanical properties of rock, but also an important base to construct the rheological constitutive model of rock. Many high dam bases in hydraulic and hydropower engineering are constructed on the batholiths of hard rock. Moreover the construction of high dam accompanies often with some rock engineering problems of high sleep slope and huge underground caves. Therefore study on the rheological mechanical properties of rock, especially triaxial rheology experiments of rock, must be carried out in order to predict the long-term stability of rock engineering. Construction of rock rheology model is an important part of theoretical research on rock rhelogy. In recently several years, many important developments on rock rheology model have been impressive, especially in conversing rheological parameters according to field experimental data, and then developing the identification for unknown models. However, rheological model theory of rock material has not been very mature up to now. Many great rock engineering are being or will be designed or built in recent decade, which will bring severe challenge for theoretical research on rock rheology model. Research results that can reflect the accelerative rheological model of rock material are not very ideal. Nowadays, study on rheological properties of rock and constitutive model theory is still the difficult and hot problem. Therefore, the comprehensive method of experimental investigation, theoretical analysis and numerical simulation is adopted in this thesis. Based on the triaxial rheological experimental results of rock, rheological mechanical properties of rock are made a detailed discussion by non-linear and damage mechanics theory, which investigates mainly the rheological mechanical properties of hard rock with different confining pressures under saturated state. And then non-linear rheology constitutive model of rock is proposed. In the end, the investigation results on rheological mechanical properties of rock are applied to the practice of great hydropower rock project, which solves the practical problems.In this dissertation, the main investigation work focuses on the following.(1) With the servo-controlled testing machine, uniaxial compressive experiment is performed on the marble specimens with different length-to-diameter ratios. Onbasis of experimental results of marble specimens with different sizes, the relation between mechanical parameters of rock material and size is analyzed. A damage statistical constitutive model with considering size effect of rock, which considers the non-linear relation of unit volume failure or elastic modulus and the size, is established by adopting the damage constitutive theory of continuous medium. Triaxial compressive experiments of rock are carried out on the servo-controlling testing system. The effect law of confining pressure on the transient mechanical properties of rock under triaxial compression is investigated from the strength, deformation and energy view. At the same time, the transient failure mechanism of rock under triaxial compression is made a detailed analysis.(2) In order to know about the rheological properties of rock specimen in Jinping First Stage Hydropower Project, triaxial compression rheological experiments with rock specimens were carried out on the rock servo-controlling RHEOLOGY testing machine. Based on the triaxial rheological experimental results, the variance law of axial and lateral strains of greenschist specimens with the time under different confining pressures is investigated. The variance tendency of axial and lateral rheological rates under different deviatoric stresses is discussed in detail. The deformation property of rock during the course of triaxial rheology is also analyzed. At the same time, volume rheology and rheological rate law is made a discussion. The triaxial rheological law of hard rock specimen is mastered, which brings important reference for the identification of parameters when carrying out the rheological numerical finite element analysis. In order to have a more clear knowledge for the mechanical property of rock rheology from the mechanism and essence, the SEM experiments are carried out for fracture shaping of rock specimens under the action of short-term and long-term loading. Through investigating the effect of microscopic structure variance in rock specimen on triaxial rheological mechanical properties, macroscopic rheological mechanical properties of rock are explained from the microscopic viewpoint, which illustrates the rheological fracture mechanism of rock under complex stress states.(3) Based on the triaxial rheology curves on rock servo-controlling rheology equipment, a new non-linear viscous component is put forward. When non-linear viscous component is parallel connected with the plastic component, a new non-linear visco-plastic body (NVPB) can be gotten, which may reflect the accelerative rheological properties of rock. At the same time, by connecting NVPB model andfive-component visco-elastic model in series, a new seven-component non-linear visco-elasto-plastic rheology model of rock(Hohai Rheology Model) can be proposed, which can describe better the three-stage creep deformation of rock, especially non-linear accelerative creep deformation of rock. Then using complete compressive and shear rheological curve gained on rock servo-controlling RHEOLOGY testing machine, the proposed seven-component non-linear visco- elasto-plastic rheology model of rock (Hohai Rheology model) is carried out the identification successfully. On basis of proposed Hohai Rheology Model, the rheological equations of rock at the constant stress and stress rate, constant strain and strain rate are deduced. The non-linear creep property and relaxation property of rock are carried out the analysis and investigation on the theory. At the same time, three-dimension creep equations of rock are deduced by adopting non-linear visco-elasto-plastic model theory. What's more, based on the Hohai Rheology Model, a new generalized non-linear visco-elasto-plastic rheology model of rock with considering the stress threshold by introducing a plastic component.(4) Shear rheology experiments were carried out for the shale in Longtan Hydropower Project by using a servo-controlled shear rheology testing machine. The variance law of shear displacement of shale with the time is analyzed. The variance tendency of shear rheological rates under different stress states is discussed. At the same time, the variance of shear strength of rock with the time is made a discussion. When the proposed nonlinear rheological component (NRC model) by the author is parallel connected with Kormanura model, a new nonlinear rheology model can be gained, which can describe the accelerating rheological properties. Using the shear rheological curves of shale, the proposed nonlinear viscoelastoplastic shear rheology model of rock is carried out the identification, which gets the viscoelastoplastic rheological parameters of the shale.(5) The cohesion and internal friction coefficient are important material parameters that decide the strength and deformation property of rock. By taking into account the variance law of cohesion and internal friction coefficient of rock with time, a new non-linear visco-plastic body of rock with considering the cohesion and internal friction coefficient (CF-NVPB model) is put forward. And then by connecting CF-NVPB model and generalized Kelvin visco-elastic model in series, a new non-linear visco-elasto-plastic rheology model of rock with taking into account the cohesion and internal friction coefficient is proposed, which can reflect fully theaccelerative rheological property of rock. Based on proposed non-linear visco-elasto-plastic rheology model of rock with considering cohesion and internal friction coefficient, non-linear creep and relaxation property of rock are made a detailed analysis.(6) Based on the analysis of non-linear rheology damage mechanism, a non-linear creep damage model of rock, which can reflect the accelerative rheological property, is put forward by adopting time damage and energy damage theory. At the same time, proposed creep damage model is carried out to validate fully in accordance with complete experimental curves of rock rheology. On basis of proposed non-linear visco-elasto-plastic rheology model of rock, after damage variable is introduced in the proposed non-linear visco-elasto-plastic rheology model by adopting damage mechanics theory, a non-linear visco-elasto-plastic rheology damage constitutive model is constructed. Moreover, non-linear creep damage and relaxation damage equations of rock are deduced, and non-linear rheology damage properties are analyzed.(7) Experimental and theoretical investigation results on rheological mechanical properties of rock are applied to the engineering practice of rock mass engineering in the high dam base of Jinping First Stage Hydropower Project and high slope rock engineering in the right bank of Goupitan Hydropower Project. The long-term stability of rock engineering under complex stress state is predicted, which brings forward reasonable evaluation and suggestion for long-term stability and safety of rock engineering.