Research On Rock Mass Mechanical Characteristics And Stability Of High Slope Of Baihetan Hydropower Station

Relying on the project of Jinsha River Baihetan hydropower station, scientific researches were as the topic of the dissertation about rock mass mechanical characteristics and long term stability of the high slope. Based on the field investigation, engineering geological environmental conditions and rock mass structure characteristics were surveyed and described in detail, and controlling discontinuities were graded and classified. Tiaxial mechanical experiments of basalt structures were conducted under loading and unloading. According to the tiaxial mechanical experiments, mechanics parameters of basalt structures were obtained, deformation and failure rules of basalt structures were researched under different stress conditions, and then constitutive models of basalt structures were advised. Rheological behaviors of controlling shear zones were experimented under compressive shear conditions. Based on rheological experiments, Rheological mechanical parameters of shear zones were acquired, deformation rules of shear zones were researched under compressive shear conditions, and then rheological model was analyzed and rheological model parameters were identified. Geostress of the high slope was simulated numerically by Flac3D. Stress field distribution rules were analyzed widely. By Flac3D, deformation and long term stability of the high slope were researched under natural conditions and reservoir operation conditions.After systematic research, the dissertation has made the following achievements.(1) Results of indoor and in-situ test have shown that the research area’s geostress is more complicated. The vertical stress is more than the gravity stress. The maximum horizontal stress is generally greater than vertical stress. Geostress is controlled by the gravitational stress and the tectonic stress, and the tectonic stress is dominated. (2) The research area’s geologic evidences was analyzed systematically in terms of original construction, tectonic reworking supergene modification. Discontinuities’ grading and classification criteria were established. On the basis of the grading and classification criteria, shear zones and faults and joint fissures and deep fractures were graded and classified. Then controlling discontinuities of high slope were identified.(3) Tiaxial mechanical experiments of basalt mass structures were carried out. Based on tiaxial mechanical experiments, mechanics parameters of basalt structures were obtained, which consist of strength parameters and elastic modulus and Poisson’s ratio. The stress-strain full curves of basalt mass structures were analyzed under loading and unloading. Effects on mechanical properties and failure modes were analyzed from unloading lateral stress rate and stress path. Energy characteristics of basalt mass structures were analyzed under loading and unloading. Results have shown that basalts show more obvious brittleness under unloading.(4) Basalt mass structures were assessed by Mohr-Coulomb strength criterion and Hoek-Brown strength criterion. Under low lateral stress, the above strength criterions are suitable for basalt mass structures in terms of failure stress state and failure mechanism. On the basis of the stress-strain full curves, constitutive models of basalt mass structures were advised. Basalt mass structures show elastic-brittle-plastic characteristics under loading. Basalt mass structures show elastic-yield-brittle-plastic characteristics under unloading.(5) Compressive shear rheological experiments of shear zones were implemented, which aimed at the types of rock with debris and debris with clay. Then residual shear experiments of shear zones were carried out as well. According to the rheological experiments, rheological mechanics parameters of shear zones were procured, which consists of long term strength and residual strength and shear modulus and viscosity coefficient. Characteristics and rules of rheological mechanics parameters were researched. Then suggested rheological parameters of shear zones were obtained.(6) Based on strain rules of shear zones, a logarithmically experience constitutive model was set up, and then model parameters’ rules were analyzed. By model identification, shear zones show viscoelastic characteristics under compressive shear stress conditions. Under high stress condition, shear zones could be described by Cvisc model. Under low stress condition, shear zones could be described by Burgers model. Most rheological experiments were carried out under low stress condition, and then shear zones were regression analyzed by Burgers model. After model parameters were obtained, their evolutional rules were analyzed. On the basis of the regression analysis results, rheological parameters of Baihetan hydropower station were obtained. (7) Based on generalized geological model, the three-dimensional numerical simulation model of high slope was set up by Ansys. Using Mohr-Coulomb model, Geostress was simulated by Flac3D. After model validation, geostress boundary conditions were obtained and geostress distribution rules were analyzed. Horizontal stress of research area is divided into upper and lower segments bounded by700meters elevation. The upper slope’s geostress come from gravitational stress, and the lower slope’s geostress is comprised of the gravitational stress and the tectonic stress.(8) Under natural conditions, the high slope of Baihetan hydropower station was simulated in rheology by Flac3D. Distributive rules of stress and plastic zone and deformation referring to rock mass and shear zones of the high slope were analyzed. Rock mass and shear zones’stresses would be in stable gradually in3months, and their deformation would be in low speed creep stage in6months. Rock mass’s maximum deformation of the left bank slope would develop gradually in superficial slope. Maximum deformation of the right bank slope would develop gradually along the shear zones C3and C3-1from outside to inside. Faults F14have obviously restraint effects on deformation of rock mass and shear zones.(9) Under reservoir operation conditions, the high slope of Baihetan hydropower station was simulated in rheology by Flac3D. Distributive rules of stress and plastic zone and deformation referring to rock mass and shear zones of the high slope were analyzed. Rock mass and shear zones’stresses would be in stable gradually in3months, and their deformation would be in low speed creep stage in6months. Rock mass’s maximum deformation of the left bank slope would develop gradually in superficial slope, which located at prospecting line IX to X2and downstream faults F14. Faults F14have obviously restraint effects on deformation of rock mass and shear zones. Deformation of the right bank slope would develop gradually along the shear zones C3and C3-1from outside to inside. Maximum deformation of the right bank slope would locate at exposed shear zones C3and C3-1upstream faults F20. Under reservoir operation conditions, stress and deformation of the spandrel groove slope would adjust gradually, and would be in stable gradually in6months. Maximum deformation of the left spandrel groove slope would locate at the arch dam top,834meters elevation. Maximum deformation of the right spandrel groove slope would locate at680meters elevation.