Study On Property Of Low Frequency Vibration To Coupled Fields Seepage

During tunneling process, gas seepage is affected by mechanical vibration, low frequent drilling load. Therefore, it is of great importance of studying seepage property affected by low frequent vibration. It helps understand gas movement, gas outburst mechanism. To study the low-frequency disturbance loaded on coal gas seepage, this paper, from theoretical view, analyzes coal porosity, stress, gas capacity and permeability on condition of vibration. On basis of that, this paper establishes a mathematical model on basis of low frequency mechanical vibration, stress and seepage coupling. This test takes samples from No. 405 out-bursting mining site at a tunneling section in Shanxi Province. Then the mathematical model is written into every parameter range programmed in comsol.First of all, on theoretical analysis of sample skeleton deformation stress and low frequency actual mining vibration, coal skeleton deformation characteristics and volume compressibility factor, expressions are defined like vibrated coal skeleton deformation expressions, vibrating frequency, vibrating time and those associated with coal volumes. On basis of these, this also analyzes effective stress of inner skeleton, as to establish effective stress equation. Taking relation between stress and strain constitutive, this paper establishes volume strain equation as to verify its regularity by testing.Second, by vibrating various types of samples and testing their absorption capacity, this paper analyzes absorption property under vibration as well as analyzes the adsorption properties under vibration in those un-adsorbed coal samples. It finds that samples with external friction can, on one hand accelerate gas molecules, and on the other, form a negative charge layer, so that potential on samples increases. At the same time tearing out matrix film that surrounds coal matrix. Based on dynamic porosity equation, this paper analyzes free-state gas properties, establishing a equation of free-state gas content in dynamics of vibration and verifying saturated samples. By testifying porosity equation, volume strain equation and content equation, it finds that the calculated does not match to the measured ones, but calculated values can best reflect porosity, volume strain and regularity of gas content in process of low frequent vibration.In accordance with vibrated skeleton deformation strain, as well as strain change properties in geophysical field, this paper makes use of strain expressions and effective stress balance to establish a controlling equation on stress and coupled seepage field in low-frequency mechanical vibration. Based on Kozeny-Carman’s Seepage Expression, it also analyzes porosity compressibility, absorption inflation and vibration compressibility impacted on strain, as to set up permeability expression around gas content. By using permeability expression and gas content equation, it obtains seepage controlling equation from sample stress and coupled seepage fields. Therefore, this paper establishes a mathematical model on basis of low frequency mechanical vibration, stress and seepage coupling. By indirectly measuring on-site gas pressure in the out-burst tunneling process, it uses gas pressure values on coal seams and compares these values with those from mathematical models. It finds that calculated values can better demonstrate the regularity of impact in case of low-frequency vibration.Finally, by taking samples from in section area No. 405 out-bursting site at a tunneling section in Shanxi Province, this paper writes a mathematical model into every parameter range programmed in comsol, and studies all physical quantity regularities by calculation. By analyzing gas pressure and free-state gas content, this paper finds that when frequency increases, the free-state gas content increases. In case that gas pressure rises up, and peak pressure or when free-state gas expanded areas move more closer to tunneling sections, out-burst is more likely to take place. When vibrating frequency remains unchanged, free-state gas content inside sample increases as tunneling proceeds. The growth in gas pressure brings out more gasified areas. It also analyzes volume strain, porosity and permeability changes, and finds that as frequency increases, areas that are more closer to tunneling sites have more volume strain, porosity and permeability. The compressibility of sample expands, the more extensively porosity closes. In other words, when porosity decreases, permeability will also move down, forming more condensed gasified areas. When frequency remains and vibrating time continues, sample size shrinks, porosity decreases and seepage ability weakens. Thereby, areas that are closer to tunneling section will have a clear strain changes, porosity changes and permeability changes.By systematically analyzing coal strain and coupled seepage field conditions under low frequency mechanical vibration, it is obtained that low frequency vibration has an influence on regularity of porosity, volume strain, free-state gas content, gas pressure and permeability. The experiments results reveal the regularity of gas movement and the regularity of coal’s physical quantity during tunneling process. They are of great importance on preventing drilling spray, as well as prevent from accidental gas out-bursting. Furthermore, these experiments will have significant importance in understanding outburst mechanism, as to improve safety condition in highly condensed coal mining and in frequent out-bursting operations.