Impact Of Chemistry-Temperature-Stress Coupling On Mechanical Properties Of Rocks

The rocks are usually under very complicated geological conditions. Among a diversity of factors that influence the degradation of rocks, chemistry, temperature and stress are very important. This dissertation presents a research on the experimental properties of granite subjected to the combined effect of chemistry, temperature, and stress, and an analysis of the mechanical properties and damage mechanism of granite influenced by multiple factors. The research begins with a single factor and then a combined effect of multiple factors on mechanical properties of rocks is studied. The following four aspects are covered in this dissertation:(1) Uniaxial compression tests were conducted on granite subjected to high temperature ranging from 20 ℃ to 800 ℃ and then different cooling ways(natural cooling in furnace and rapid cooling in water), and different failure modes obtained from the tests were analysed. The effects of temperature and cooling ways on mechanical properties of granite were investigated from longitudinal wave speed, stress-strain curve, peak stress, axial peak strain, radial peak strain, Young’s modulus and microstructure. The results indicate that the longitudinal wave speed, peak stress and Young’s modulus of granite decrease with the increase of heating temperature and a greater decrement is found by rapid cooling than by natural cooling. The higher the heating temperature, the more severe the degradation of mechanical properties is. The thermal shock generated by rapid cooling might exacerbates the deterioration of mechanical property of granite. The axial peak strain of granite subjected to rapid cooling is less than that subjected to natural cooling, implying that the brittleness of granite is more obvious through rapid cooling in water than through natural cooling in furnace.(2) The variation of mechanical properties of granite under uniaxial compression after soaking in different chemical solution(water, Na OH solution and HNO3 solution) and being subjected to different freeze-thaw cycles were studied by laboratory tests. The results show that for all the chemical solutions(water, Na OH solution and HNO3 solution), with the increase of freeze-thaw cycles, longitudinal wave speed, Young’s modulus, relative Young’s modulus and peak stress decrease by exponential function, rate of longitudinal wave loss and rate of peak stress loss increase by power function, and axial peak strain changes by Guass function. With the increase of freeze-thaw cycles, the damage and deterioration of granite in HNO3 solution is larger at a smaller number of freezethaw cycles than that at a larger number of freeze-thaw cycles, while an opposite phenomenon is found for granite soaking in Na OH solution.(3) Though experimental investigation of granite behavior under a combined effect of chemistry, temperature and stress(i.e., soaking in water, Na OH solution, HNO3 solution and being subjected to freezing-thawing cycles being heated to high temperature and being subjected to uniaxial compression), the variation of mechanical properties of granite was analysed. The results illustrate that the temperature has some influence on the failure modes of granite under the combined effect of chemistry, temperature and stress, in the way that the failure mode of granite under uniaxial compression changes from column cleave shearing slip. With the increase of heating temperature, the longitudinal wave speed, the peak stress, Young’s modulus and the relative Young’s modulus of granite decrease by exponential function, the rate of longitudinal wave loss increases by power function, the peak stress,the relative peak stress,the axial peak strain and the relative axial peak strain increase by logistic function, which is consistent with the trend of how mechanical properties change for natural granite as the temperature changes. HNO3 solution aggravates the deterioration of granite, while Na OH solution has certain inhibitory effect on the deterioration of granite, however, with the increase of temperature, this inhibitory effect weakens gradually and even disappeares, instead, promoting the deterioration of granite.(4) The damage mechanism of granite subjected to high temperature, chemical soaking, freeze-thaw cycles and combined effect of them was analysed according to micro mechanical and chemical mechanism. It can be concluded that the internal structure and mineral composition of granite changes due to temperature stress and chemical reaction, which in macroscopic view can be presented as the damage and deterioration of mechanical property. By defining damage variable, the damage degree of granite under the combined effect of chemistry, temperature and stress can be analysed quantitatively.By analysing the results of experimental tests, the influence of high temperature, chemical soaking, freeze-thaw cycles and the combined effect of them on the damage, deformation and failure of rocks were summarized. The research results are valuable in solving many practical problems of rock engineering.