Study On A Model Of Blocks For Cracked Rock Mass Of Deep Roadway And Its Applications In Engineering

At present, as the rapid development of national economy, the scale and depth of underground engineering tends to increase in various industries mainly including water conservancy, transportation, metallurgy, coal and so on, especially in the coal industry, mining depth of the coal is increasing year by year. Comparing with the shallow rock, the deep rock mass located in complicated geology environment, the high stress, high temperature, high seepage pressure and strong time-dependent effect cause essential changes in mechanics structure, basic behavior characteristic and response to project of deep rock. Influenced by these factors, the deep rock mass exhibits marked characteristics of soft rock, though it is hard and steady in shallow. For the existence of sharp contradictory between the high ground stress and low strength of surrounding rock mass, the stress concentration and stress redistribution made by the excavation of the deep underground project result in a wide range of rock mass entering the fracturing condition after peak, and during the process, it is often accompany the nonlinear large deformation of the cracked rock mass.Aim at the broken status and the characters of strong nonlinear mechanical phenomenon of surrounding rocks in deep coal mine, a model of blocks for cracked rock mass of deep roadway is proposed. Then combining the experiment research, theoretical analysis and numerical simulation, this paper systematically studies the mechanics feature of rock blocks, block bonding interface and the structural characteristic of cracked rock mass around the roadway. Lastly, the fruits of the above studies are applied to analyze the stability control of the return airway at the -648 m level of Gubei colliery in Huainan mining area.Generally, the main research works included in the dissertation are as following:1) Based on the multi-angle experimental results of sandstone in Gubei colliery, such as conventional triaxial compression tests and pre-peak unloading confining pressure tests, a more systematic analysis on the deformation and strength characteristics of the soft rocks under different circumstances in different states of stress is carried out from the deformation, strength, and failure view, which has access to the basic mechanical properties and the dilatation-bulking deformation and failure mechanism of the rock. It is clear that post-peak bulking deformation is the main reason of the nonlinear large deformation of cracked rock mass.2) Based on the results of experimental test, the evolution characteristics of the typical stress values(including crack closure stressσcc,initial dilatancy stressσci,damage dilatancy stressσcd and peak stressσf) with the confining pressure are researched. And the experimental critical condition criterion of sandstone entering pre-peak damage dilatancy and post-peak bulking deformation is proposed. Then considering the pre-peak inelasticity characteristic of rock, and the damage and degradation process of mechanics parameters (cohesion, angle of internal friction, dilation angle) during unloading, a progressive failure constitutive model, which can reflect pre-peak damage dilatancy and post-peak bulking deformation of the deep rock mass is established. The incremental iterative scheme of the constitutive model is derived, its numerical implementation and model verification are proceeded by using the UDEC (universal distinct element code) and the validity of the model is proved. 3) Based on the classical elastoplasticity theory, a block bonding interface elasto-plastic constitutive model is established by using tensile and shear function of the block contact interface as yield criterion and considering the progressive soften of the cohesion and tensile strength after the block bonding interface yield failure. The incremental iterative scheme of the above constitutive model is then derived, and the program about the constitutive model is compiled by VC++ Programming Language, and embedded it in the distinct element code UDEC. At last, by the numerical direct shear test, the advantage of the numerical constitutive model embedded is proved comparing the simulation results with the UDEC built-in Coulomb slip model with residual strength.4) Aim at the structural characteristics and the dynamic mechanical behavior of cracked rock mass of deep roadway among the underground cavernunderground cavern, a Voronoi discrete block model is proposed combining with the variety of the Voronoi figures. Then the characteristic of the model is pointed out and the calibration technique of micromechanics parameters is studied by referring the PFC2D's method to obtain the micromechanics parameters. At the same time, the sensitivity analysis about the variation of the micromechanics parameters impacted on the macro-deformation characteristics of materials (mainly the young's modulus and compressive strength) is carried out, and the adoption principle of the micromechanics parameters value is obtained further more.5) Using the return airway at the -648 m level of Gubei colliery in Huainan mining area as an engineering example, the researches about failure evolutionary process of surrounding rock in deep roadway and the plan of excavation support are carried out on the basis of the deformation and failure mechanism of rock mass, the dilatancy-bulking progressive constitutive model, the block bonding interface constitutive model and Voronoi discrete block model. Firstly, According to the geological conditions of the return airway, a corresponding computational model is proposed, following the laboratory experimental results, the corresponding micromechanics parameters are determined by means of numerical biaxial compression test. And then failure evolutionary law and characteristic of surrounding rock mass are systematically analyzed and summarized from the views of displacement vector field, the primary stress vector field, as well as size and depth of the plastic yielded zone and broken bulking zone. On this basis the stepped combined support method is put forward and lastly by the numerical simulation and field monitoring, the availability of the support method is verified both from theory and practice, so as to provide important basis for scientific designing and safe construction of engineering in deep roadway cracked rock mass.