Construction Ventilation And Outburst-proof For Highway Tunnel Through Coal Seam

Coal bed gas is the products of geological process. It is a multi-component gas thatis mainly composed of methane and mixed with other harmful gas. In the safetyaccidents of coal mines in China, gas accident is accounted for the highest proportion.With the development of technology and the national economy, the length ofunderground engineering, highway tunnel and railway tunnel is constantly extended.Sometime the coal bed can not be avoided for line section because of some reasons,though we intentionally bypass through the coal bed. Therefore the construction oftunnel through coal bed may be met.In the construction of tunnel through coal seam, in order to prevent coal and gasoutburst and other gas disaster, we should seek for an effective precaution against gasburst, and explore an effective construction ventilation scheme for the problem ofmethane accumulation. Coal seam in China mostly belongs to the low penetrability coalseam, and its structural characteristic is complex, so the permeability of coal seam isvery low. It is necessary to explore a useful and efficient excitation technique formethane extraction. The available techniques are vibration shot, methane drainage fromdrilling holes, hydraulic flushing and etc. Vibration is an enhanced technology ofpromoting coalmine gas drainage, and it also can combine with other extractiontechnologies. As early as1950s and1960s, America and Russia began to use ultrasonicto treat oil reservoir. But the migration mechanism of methane with vibration in coalbed is not clear and definite. Supported by the Program for New Century ExcellentTalents in University of Ministry of Education of China (Grant No. NCET-09-0844) andNational Natural Science Foundation (Grant No.50804060), through theoreticalderivation and numerical simulation, this paper studies the law of physical field andseepage field under vibration, analyzes the stability of surrounding rock and ventilationtechnology for the construction of gas tunnel.In the chapter one, this paper introduces the present research status of methanedesorption-adsorption, penetration mechanics of seam gas and the technology of gastunnel at home and abroad, and then proposes the research method and the mainresearch contents.In the chapter two, first, this paper discusses the characteristics ofdesorption-adsorption and the laws of desorption-diffusion of coal seam gas. Through the modified Langmuir methane isothermal adsorption equation, and the analysis of theeffect of temperature on methane desorption-diffusion, this paper develops the dynamicmodel of gas desorption-diffusion. Then, starting with structural characteristics of coalreservoir, coal seam is simplified as the geometric model of the two group fractures andthe three group fractures that can be describes with mathematical method. Finally, basedon internal swelling stress and fracture-matrix interaction, a permeability model and theporosity model are developed in this paper, and the law of gas permeability of the twogroup fracture and the three group fracture systems is analyzed. And the relationshipbetween gas pressure and coalbed stress and gas permeability is discussed.In the chapter three, from heating effect of vibration, based on the heat balanceequation with vibration, the permeability model and the porosity model, a new couplingmodel of effective stress field, gas pressure field, temperature field and seepage fieldunder vibration for low permeability coal seam is developed in this paper. The propertyof coal seam permeability with vibration is analyzed. The analysis results show thatvibration can raise gas desorption rate, increase fracture porosity, increase permeabilityof coalbed. Thus, the production of coalbed gas improves. Then the property of coalseam permeability with different frequency and different amplitude vibration isanalyzed. The results show that the permeability increases with the increasing ofvibration amplitude, increases with the increasing of vibration frequency at first, andthen decreases.In the chapter four, this paper studies the ventilation technology based on theconstruction of highway tunnel through coal seam. It researches the time-spaceevolution property of methane in tunnel with and without mechanical ventilation;determines the relationship of methane concentration with ventilation velocity andventilation time; establishes the formula between the quantity of methane extraction andthe maximum ventilation interval time, and the formula between the ventilation timeand the distance of tunnel exit to coal seam region, as well as ventilation velocity. Thispaper studies the stability of surrounding rock for the construction of gas tunnel, inorder to prevent coal and gas outburst, suggest the thickness of rock pillar.