| The rock mass is a geologic body, which had been reconstructed by distortions and destructions, and it has petrographic components and specific structure. Having experienced many kinds of geological process, the integrated rock mass will be incised into the complex jointed rock mass by the discontinuities. As a result of existence of the discontinuities, the original homogeneous and isotropic properties of the rock mass are changed into new properties of non-homogeneous, nonlinear and aeolotropic. The strength of jointed rock mass depends on the strength of rock itself and discontinuity. At the same time, the strength weakness effects which are caused by the different combination forms of discontinuities must be considered. The research on strength characteristic of the rock mass is the precondition and foundation of the rock mass engineering stability estimation and designs.In recent years, along with the high speed development of Chinese economy, the demands for basic constructs expand unceasingly, therefore the domestic rock mass engineering constructs developed rapidly. Especially since the implementation of Development strategy of the West Regions in west China, in order to exploit and utilize the west resources fully, more and more energy, transportation, mine, water conservation projects are built in western area, more and more engineering activities relating with rock mass will occupy principal status, Correspondingly basic research correlated with the strength, deformation, penetrability, destruction disciplinarian of rock mass will be receive recognitions and attentions universally. In the former project practice, due to the lack of understanding on rock mass strength properties, project accidents and destructions also occurred. Therefore, for the security and the economy of project, the stability of engineering rock mass must be estimated. The key is the confirming of rock mass strength parameters reasonably.At present, in the engineering designs, there are many estimation methods on the strength parameters, such as in situ testing, analogism, RMR, back analysis of displacements, fuzzing mathematics, neural network technique and so on, which promoted the development of the rock mass mechanics greatly. They can obtain strength parameters of discontinuities or rock masses, but all have some problems at the same time.Therefore, this thesis studys the strength properties of jointed rock mass systematicly, and a set of methods calculating equivalent strength parameters and representative elementary volume (REV) of jointed rock mass by using the computer numerical test have been established, which are used in Triassic limestone rock mass project in west Hubei province. The relation between size effects of strength parameters and the REV of jointed rock mass which is a basic rock mass mechanics question has been discussed, and it has theory instruction significance and application value in selecting reasonable strength parameters in project.The research method adopt in this thesis is as follows:Firstly, to investigate and analysis the geology background, and classify the sorts and the groups of discontinuities developing in Triassic limestone rock mass. Having obtained the distributing rules of discontinuities, the stochastic discontinuities network model which is the foundation of research on the strength REV of jointed rock mass is estabilshed by using the Monte-Carlo stochastic simulation method. Secondly, the method ascertaining the size effects of strength characteristic of jointed rock mass and the corresponding strength REV has been studied by using the computer numerical test. In order to establish the computer numerical test analysis model, the jointed rock mass is changed into dual structure which is composed by rock and discontinuities. For a certain size rock mass region, exerting the loads on numerical test model to simulate rock mechanics tests, then the rock mass strength values are determined through the computer numerical test computation. To change the sizes of rock mass region unceasingly, and repeat the computer numerical test, the changes rule of strength parameters of the rock mass along with the rock mass volume changes will be obtained. When the rock mass volume achieves a certain magnitude, the strength parameters tend to invariable, then the volume is the size of the strength representative elementary volume (REV) of jointed rock mass, and the strength parameters obtained is the equivalent strength parameters of the jointed rock mass.Aiming at think itinerary discussed above, main issues and corresponding research contents involved are presented:(1) The research on the strength parameters and REV of jointed rock mass is a basic rock mechanics question, which should be paid more attention and need thorough research. The limitation of test method inside and outside the room to determine the strength parameters is analyzed. The definition of REV is introduced and its mechanics significance is also analyzed. The REV size is not only the quantitative standard for choosing the rock mass medium type, but also is the important basis for choosing mechanics parameters reasonably which is correlated to the equivalent continuous medium model. Moreover, the strength properties of rock masses which present size effects are connected with REV, If to discuss strength property without REV, there is not any significance. The research on the changes rule of rock mass strength parameters along with the variety of rock mass volume is the essential method to confirm the rock mass strength parameters and REV.(2) There are many rock mass projects building in west area of Hubei province such as Ma Shuihe bridge, Qingjiang bridge, Xiaohe bridge and so on, which are construct by Triassic limestone Rock Masses primarily. Because the discontinuities developing in rock masses present obvious directivity, the rock masses influenced by the discontinuities present remarkable aeolotropy. In order to establish reasonable rock mechanics model, the geologic structure shape, geological structure evolution history, landform and physiognomy conditions of Triassic limestone rock masses in the west area of Hubei province are analyzed in the light of engineering geology, then the groups and the stages of discontinuities developing in rock masses are classified, which is verified by typical discontinuities statistics.(3) The discontinuities in rock mass are the basic reason which causes the existence of rock mass REV, so we need to describe the stochastic discontinuities developing in rock mass fine, which is the foundation of research on REV and equivalent strength parameters. Using the Monte-Carlo stochastic simulation method, discontinuities network model (rock mass structure model) is established. Namely through the stochastic simulation, the implement course how to obtain the discontinuities network submitting to the geometry parameter probability model which is established according to the actual statistical is introduced.Then the questions such as how to estimate the length of surveying line and how to estimate the of trace lengths of discontinuities are discussed thoroughly.(4) During the course translating the discontinuities network model into the finite element mechanics computation model, the questions such as how to achieve the division of rock mass block body, structure system division and FEM elements mesh generation and so on are studied.(5) Based on the rock mechanics triaxial test principle, the theory confirming the rock mass strength REV and the strength parameters by the finite element numerical analysis method is presented in the thesis, and then is used in Triassic limestone Rock Masses of Xiaohe Bridge in the west of Hubei province. Exerting loads on six rock mass numerical models whose sizes are different to proceed computer numerical tests. The research indicated that the strength parameters of rock masses present obvious size effects. Along with the increasing of rock mass volume, the strength parameters present the tendency which decreases progressively. But when the rock mass volume achieved a certain value, the strength tends to invariable, and the strength REV size of jointed rock masses is suggested to be 5m×5m, in addition, the strength parameters (cohesion and fiiction angle) are 0.72 MPa and 28.9°separately.In summary, the characteristics of this thesis are as follows: (1) systemic research on the questions how to achieve the division of rock mass block body, structure system division and FEM elements mesh generation during the course translating the discontinuities network model into the FEM computation model; (2) Based on the rock mechanics triaxial test principle, the FEM numerical analysis method is adopted to confirm the rock mass strength REV size and the strength parameters; (3)The geological characters of discontinuities developing in Triassic limestone rock mass in the west area of Hubei province are induced in the light of engineering geology, which is the geological foundation to establish reasonable rock mechanics model.
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