Research On Key Parameters Of Air Duct Press-in Ventilation For High-altitude Tunnel Construction By Drill-and-blast Method

China plans to expand road network coverage,improve access to Tibet and Xinjiang,and gradually increase the construction of high-altitude railroad tunnels,and measures to solve the tunnel ventilation need to be constantly improved.High altitude construction tunnels due to low air pressure,air density is small,to provide a good air conditions for the construction personnel near the tunnel palm face is particularly critical.The air leakage rate of air ducts is directly related to the ventilation effect and equipment selection,which is more important for the ventilation of high altitude tunnels.Based on a high-altitude tunnel,this paper analyzes the air leakage of air ducts,ventilation parameters and the velocity field and temperature field of air flow in the tunnel through model tests,theoretical calculations and numerical simulations.Specific research contents and results include:(1)A study of duct press-in ventilation was conducted through model tests to analyze the effects of joint location,number of joints,joint width,and temperature difference between inside and outside of the duct on the air leakage rate of the duct.The results show that the closer the joint is to the inlet end,the greater the air leakage rate,and the air leakage rate increases as a function of three times with the number of joints and changes as a function of two times with the width of the joints.(2)Research on thermal factors of tunnel construction environment,calculation and analysis of different kinds of heat sources affecting the tunnel environment,and research on ventilation parameters of high altitude tunnel construction,analysis of ventilation time,ventilation length,and the amount of air required in different cases,air leakage and fan power,etc.,to design the ventilation scheme of construction tunnel,and apply the theory to a high altitude tunnel project in practice.(3)Taking the average temperature within the ventilation length as the characterization factor,the three influencing factors of duct location,duct outlet distance from the palm surface and duct diameter were simulated by orthogonal test design,and the order of influence of each factor on the temperature field in the tunnel was analyzed by the polar difference method to determine the best duct arrangement scheme.(4)Fluent software was used to test the effect of ventilation in a high altitude tunnel,and the effect of air leakage on the tunnel cooling pairs.The results show that the duct leakage has an important impact on the effect of tunnel construction ventilation,the shorter the ventilation time,the greater the impact of air leakage on the flow field in the tunnel,the ventilation time can’t be less than 15 min.the center of the tunnel temperature is the lowest,the temperature gradually increases to both sides of the tunnel,the ventilation plan can reduce the ambient temperature in the tunnel at the specified time,to ensure the safe and orderly construction.Through the study of each parameter in the press-in ventilation of high-altitude tunnel construction by drilling and blasting method,it ensures the safe and orderly construction,provides technical support for the construction of a high-altitude tunnel,and the airflow organization distribution and temperature field distribution law of the construction tunnel provides a reference for other tunnel construction ventilation.