| The relationships of physics, geometry and equilibrium are complex on the underground soft rock mass, and the rheological phenomenon is outstanding, which threats the processing and maintenance of underground minerals mining. It is of great significant for improving the theory of soft rock to establish the suitable loading standard of uniaxial compressive experiment and the energy loss and creep laws in the process of deformation and failure. The paper is consulted with the National Natural Science Foundation titled of “Research on the theory of changing between solid and liquid with multi-field coupling and energy consumption on deep soft rocks”(51374134)and “Study on the rheology softening theory of asphalt, rubber-plastic and soft rock material and their Simulation experimentation”(51074094). By studying the methods such as theoretical deduction, indoor experiments and numerical simulation, the mainly finished is demonstrated below :1. Researching on the damage fracture mechanism of soft rock. The four phases in soft rock deformation and failure are researched, and the four kinds of principle of equivalence hypothesis and the four basic equations of continuum mechanics are analyzed by conducting the uniaxial compressive experiment. The damage evolution equation based on the irreversible thermodynamics is established by thermodynamic potential. The three kinds of crack fracture modes are concluded, and the calculation principle of stress fields and stress intensity factor nearby the crack tip are analyzed, and the methods of solving compound fracture problems by equal strain energy density line is obtained, and the compound fracture criterion is summarized.2. Researching on thermal properties and preparation of similar soft rock. I come up with the concepts of similar soft rock which is based on the index and relative definition of soft rock and make up two kinds of similar soft rock specimen A and B with similar materials. After that I analyze the specific heat changing rules of similar soft rock under different curing time by testing the specimen A and siltstone. Under the same temperature, the longer the curing, the less specific heat. According to the results, water content is an important factor for the size of the specific heat. However, the specific heat of siltstone increases firstly and then decreases under the higher temperature, which is caused by the mineral composition and organic content of rock. So it is necessary to compound similar soft rock as the standard test specimen.3. Researching on the impacts of loading method and rate on the compressive strength of similar soft rock. First of all, the displacement loading method is adopted to soft rock specimens A, C, D for uniaxial compression test and the uniaxial compressive strength changes with loading rate on quasi static rate range is researched. Secondly, the load control is adopted to soft rock A for uniaxial compression experiment test, and obtain four order and three order polynomial by fitting the experimental curves of two kinds of loading method for soft rock A. The results show that the response for loading rate of the uniaxial compressive strength is related to sample strength grade and the selected loading rate intervals, and there will be different effects of loading rate on different strength grades of rock. The strength error caused by different loading methods account for about 20% of average intensity value. The conclusion “Uniaxial compressive strength is monotonic increasing with the increase of loading rate” is suitable for a certain strength of rock, which is not a general conclusion.4. Researching on the impacts of the aggregate size on thecompressive strength of similar soft rock. The similar soft rock B which contains different aggregate size is researched on the effect on compressive strength of similar soft rock. The uniaxial compressive strength firstly increases then decreases with the changing range of size between 20 mesh to 70 mesh. The third order polynomial can be better applied to the experimental data. The results show that when the aggregate size is 40 mesh, the uniaxial compressive strength reach the maximum value of 21.172 MPa. This research is a beneficial attempt to establish the relationship between material mesoscopic structure and macroscopic mechanical properties.5. Experimental researching on the law of damage energy dissipation of similar soft rock. At normal temperature, the impact of loading rate on damage energy dissipation is researched. The unloading elastic modulus and the second load secant modulus firstly increase then decrease with the increase of loading rate. However, the amplitude of damage variable and the energy dissipation are not obvious, and the change rule is consistent between them, and they are proportional to the relationship. According to the first law of thermodynamics, the energy equation that is established under heat transfer consideration. With the increase of temperature, the specimen absorbs more energy, and the strength and elastic modulus are reduced, and both of them have a linear relation with temperature factor. The energy dissipation and damage variable decrease with the rising of temperature, A is proportion to B, and the relation equations among the energy dissipation, temperature and damage variable are established. The cause includes: the heat-expansion and cold-contraction on rock mineral grains cause the changing of the contact between mineral grains, which decreases intensity, energy dissipation and reduces damage. However, the heat inputting to the rock reduces the increase of the internal energy, which can compress the storage space of releasable strain energy, and result in a decrease of releasable strain energy.6. Researching on the creep rule and numerical simulation of roadway of similar soft rock. Under normal temperature, the impacts of creep loading methods, pressure difference, axial pressure and confining pressure on steady-state creep rate are researched by the uniaxial and triaxial creep experiments of similar soft rock. Comparing with two loading methods, the loading history can result in different steady-state creep rate values. The relation between steady-state creep rate and pressure difference can be uniformly expressed by the exponential function, and the uniaxial creep rate is ten times the triaxial creep rate. It shows that the impact weights of two kinds of load increasing per unit strength on steady-state creep rate are different, by maintaining pressure difference constant, and increasing axial pressure and confining pressure at the same time, and the steady-state creep rate will be alternately varing with the effect of different combination relation of axial pressure and confining pressure. The power function creep model which reflects the transient creep deformation, attenuation and steady-state creep stage is established through data analysis. Combing with engineering examples, the distribution of stress and creep of the roadway are analyzed by ANSYS FEM software, and the changing relation of displacement and creep variables over time of key points are reseached. The simulation results conform to the theory and the actual situation in engineering, which have important meanings for guiding roadway of soft rock and other relevant engineering projects. |
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