Research On Ventilation Method Of Shield Tunneling

With the vigorous development of municipal construction in major cities,the construction of shield tunnels has become more and more widely used in the construction of various types of underground foundation projects such as urban rail transit and municipal public roads due to its safety,rapidity,and high efficiency.Most of the subway tunnels in the construction process are long single-headed tunnels and needed to be dug deeply,therefore,their ventilation and environmental conditions are very bad and certain ventilation methods must be adopted to improve the air quality of the working face.during construction process.The concept of turbulence model is introduced and mathematical model of ventilation airflow and related assumptions is put forward and the numerical simulation model is rationally simplified,finally,the numerical simulation method and route is proposed in this thesis.Taking the section of Chengdu Metro Line 7 from South Building Materials Station to Chengdu Dongjia Station as the prototype of the tunnel,according to the existing subway construction ventilation standards,the parameters of the draw-out ventilation scheme of the shield tunnel are calculated to provide the parameter conditions for the numerical simulation.Based on the calculated parameters,a simulation model is created and the grid is divided.Turbulence model parameters are calculated and boundary conditions are set.The heat source and the wet source of the construction area are calculated,and a reasonable source area is divided in the FLUENT software,and the calculated heat source value and water vapor value are set for the source item.Selecting the solution method under the same kind of conditions,the simulation of push-in ventilation and draw-out ventilation is carried out,and the simulation results are compared and analyzed.After analyzing the simulation results of the draw-out scheme and understanding its shortcomings,two improvements are proposed.One is to add the secondary air blower and the air duct at a reasonable position,and the second is to increase the ventilation of the secondary air duct vent and carry on the simulation of these two programs,and analyze its air flow conditions and improve extraction ventilation program for the tunnel environment temperature and humidity improvement.At the end of the thesis,the four kinds of ventilation schemes to the improvement of the temperature and humidity in the tunnel environment are compared,the superiority of the improved draw-out ventilation scheme is verified.The analysis and results of the four types of ventilation schemes provides a strong theoretical support for the physical design of exhaust ventilation and the selection of ventilation schemes in practical projects.