Study On Deformation Properties Of Fractured Rock Mass

Deep research on the determination methods and influential factors for deformation parameters of the fractured rock mass has been carried out based on the rock mechanics tests, engineering geological investigation, probability statistics, intelligent inversion model and multiple linear regression method, etc. The major achievements are listed as follows:(1) The Em-BQ relationship is obtained by combining massive on-site test data, geological investigation records and indoor test logs of a number of large hydropower stations in China with Chinese Standard for engineering classification of rock masses. Then a BQ-based empirical method is put forward to estimate the deformation modulus of rock mass based on correlation analysis. By introducing a rock mass status factor M, a new empirical approach is further proposed to estimate the deformation modulus of rock mass by BQ index and rock elastic modulus. The new approach is used to calculate the rock mass deformation parameters of the Three Gorges Project, and the estimated results match well to the tested data. These methods provide a reliable way to estimate the deformation modulus of rock mass by BQ index.(2) The excavation-damage-considered LSSVM-PSO displacement back-analysis model is established by the orthogonal test, support vector machine and particle swarm optimization, etc. The underground cavern displacements of Dagangshan and Xiluodu hydropower stations are back analyzed, according to the on-site measurement on excavation damage zone and displacement, and then the scope and weaken degree of excavation damage zone are obtained. The excavation damage inversions for other projects are conducted, revealing the effect of geological structure on the excavation damage of rock mass. The results show that the more intact the rock mass is, the smaller the excavation damage zone, with larger weaken degree of rock mass mechanical parameters; the excavation damage zone will extend if there are faults and dikes across the underground caverns; the scope of the excavation damage zone is in inverse proportion to its weaken degree; the deformation parameters of rock mass within the excavation damage zone decreases as the caverns are excavated deeply.(3) Based on a theoretical formula for calculating the deformation modulus of rock mass containing a set of structural joint planes, a novel formula is derived to calculate the deformation modulus of fractured rock mass considering the effects of random joint planes. The hemispherical figures are applied to demonstrate fully the deformation modulus of random jointed rock mass in the 3D space. Furthermore, the proposed formula for deformation modulus of random jointed rock mass is used to study the structure effect of the deformation parameters of fractured rock mass of the Three Gorges Project. Comparing with the existing results, it shows that the new approach can not only be easily operated with satisfied accuracy, but also fully demonstrate the anisotropy property of rock mass.(4) The size effect of rock mass deformation parameters is studied by probability and multi-scale methods. A large number of on-site test data are used to determine the probability distribution type of rock mass deformation parameters by the random distribution function test. A multi-scale random analysis model is employed to estimate the REV of rock mass deformation modulus of the Dagangshan hydropower station and the REV-scale relationship. Then the deformation parameters of different scales are determined by multi-scale methods, including indoor and on-site tests, numerical simulation and back-analysis, etc. The macro-mechanical parameters and REV scale of Dagangshan hydropower station are obtained. Finally, the mechanism of size effect of rock mass deformation modulus is discussed and it shows the structural planes within rock mass are the intrinsic cause for this mechanism. The equivalent deformation modulus will decrease regularly with model size.