Rheological Strength Aging Model Of Hard Brittle Fracture Rock In High Dam Zone And Its Engineering Application

With the increasing development of China's economic construction and water conservancy and hydropower resources development, not only the number of rock projects are rising, but also the excavation scope are extending, which leads to highlight problems associated with the stability of rock mass. The key factor with respect to rock engineering stability evaluation is to acquire comprehensive and deep perception of rheological and mechanical characteristics and the corresponding determination of mechanical parameters in rock engineering. Moreover, in-depth analysis of long-term operational stability of engineering rock is required. Therefore, discovering the functional relationship of weakened material parameters affected by stress and time variation, especially proposing rheological strength damage model concerned with the time effect, plays a crucial role in these topics. In this thesis, based on precious literatures, large-scale in situ shear creep test results in Dagangshan Hydropower Station Dam, and triaxial laboratory tests on rheological properties of fragile diabase, variation principles of mechanical parameters of diabase under different time and stress conditions, were determined. Then, a rheological strength damage model was proposed, and its verification was proved by situ engineering. The main contents of this thesis were listed as following:1. With the help of automatic triaxial rock rheology servo instrument, triaxial laboratory tests on rheological properties of fragile diabase in Dagangshan Hydropower Station Dam were carried out. The variation mechanism of brittle rock over time under different confining pressure and stress levels was discussed, regarding axial, lateral and volumetric deformation respectively. Meanwhile, deformation characteristics of diabase under triaxial rheology, stress-strain curves characteristics, strain rate characteristics, and influence of creep on the deformation and strength of brittle rock, were studied. The creep damage threshold of diabase was analysed as well. This thesis demonstrates the creep process curve of diabase from both micro-mechanics and macro-mechanics views. Initially basic principle of the diabase rheological properties was acquired, and rheological fracture mechanism of brittle rock was indicated.2. Based on the shear creep test results in Dagangshan Hydropower Station Dam, the thesis discussed shear creep deformation laws concerning load history, distinguished the shear creep models of diabase, and obtained the shear creep parameters of the diabase in the dam site by inversion. By utilizing the isochronous stress-strain curves method, non-steady creep discriminance, steady creep velocity method respectively, and long-term shear rheological strength of the diabase were obtained. After that, the different results were compared, ensued with the determination of long-term shear rheological strength of the diabase. Through comparisons of long-term shear strength and transient shear strength, attenuation percentage of the strength parameters of rock mass under long-term constant loads was obtained.3. The thesis determined the mechanical parameters of diabase in creep process, analyzed the weakening law of the mechanical parameters of rock mass, and established the damage evolution equations (i.e. the formula of elastic modulus, cohesion and friction angle, in accordance with stress and time of rock mass). The process of creep damage evolution of diabase was described from a quantitative view, and the functional relation was certificated by the strength variation of rock creep damage.4. Based on the results of uniaxial compression tests, triaxial compression tests, and load-unload tests, systematic analysis on the diabase deformation characteristics, strength characteristics and energy dissipation characteristics under different stress states was made from the different views regarding deformation, strength, energy, and damage, and the instantaneous mechanical properties and deformation damage law of the diabase were gained. With the help of fracture strain model, the internal propagation principle of rock and intensity failure mechanism was identified.5. The mechanical parameter variations of diabase were introduced to the strength formula, and the model that could reflect the aging rheological damage intensity of diabase was established.6. Secondary development of the finite difference software Flac3D was processed through programming of C++and FISH language, which achieved programming of rheological aging evolution model, and then it was applied to the study of long-term stability of the Dagangshan Hydropower Station Dam slopes. Displacement vector fields, stress vector fields and distributions of yield areas were analyzed comprehensively and systematically. Eventually space-time evolution principle and characteristics of mechanical response of rock mass were summarized, while sensible engineering suggestions on the excavation and long-term stability of rock mass in the dam regions were given. In conclusion, the research on these issues will certainly make contribution to the further seepage influence study of rock mass, providing basic information and theoretical foundation.