In-situ Stress Measurement And Stability Analysis Based On The Unified Strength Theory In Large Scale Underground Caverns Zone

In underground engineering, the construction of underground powerhouse in a hydropower station is often related to the safe operation of the whole station and enormous benefits because of its large scale, complicated space composing and effects between caverns. The theories in stability analyses and the methods of design are urgent heated issues.The effects of irregular surface, in-situ stress field's distribution and different constitutive relations on stability have been studied in this paper. The stability of large caverns during the excavation and supported was analyzed in the case of the construction of Huanren powerhouse The relationships between the in-situ stresses and geological structures have been established by the data acquired from in-situ measurements and laboratory tests; the algorithms to establish the model under complex geologic conditions and to judge the relationships between faces and zones are proposed, and the pre-processing and post-processing functions of complex model's assembling and interfaces'inserting were realized; the factors effecting on the value of in-situ stresses, and the model of the stress field's distribution in powerhouse zone by multiple linear regression were analyzed, the distribution of the whole stress field effected by many factors was obtained; since the unified strength theory has seldom been used in rock mechanics, there's not corresponding constitutive models in FLAC3D, the special unified double shear modules with a non-associated flow rule for the FLAC3D was developed, base on the unified strength theory the stability of the underground caverns with large scale was analyzed. The main achievements are shown as below:(1) The values and directions of the in-situ stresses in powerhouse area were measured with the method of CSIRO cells, the relationships between the stress and the new cathaysian structures were established. The direction of the max principal stress is about 280o, and the corresponding range of the value is about from 5 to 7MPa.(2) According to the difficult of FLAC3D software in building models with irregular surfaces, the algorithms of quasi-three dimension models'stretching after zones'sub-divided and tetrahedron shaped sub-zones'dividing to establish the models with irregular surfaces and to insert the interfaces to the assembled zones were proposed. (3) According to the data acquired from the measurements and the geological conditions, distribution of the in-situ stress field was obtained by multiple linear regression, which can be served as the basis of boundary conditions.(4) Based on the principles of united strength theory and fast lagrangian analysis of continua in 3D, finite-difference forms of the unified strength theory was deduced, and non-associated flow rule for the calculation was established. The special module is developed for numerical simulation.(5) Under the conditions of united strength theory as the plastic rule and boundary conditions obtained by boundary-loading-extracting, the stability of the powerhouse caverns during its'excavation and supporting was analyzed.The development and distribution of plastic zones were similuated, acquire the change process of displacement was obtained.