| The rapid development of the Chinese economy has resulted in an increased pace of infrastructures building all around the country.Direct implications include the fact that the design of modern highway tunnels has become more diverse and the construction level has constantly been improved.As the spiral tunnel' slope and curvature can be conveniently adjusted to bypass the geological structure according to the actual engineering needs,it has been frequently used to suit the complex topography.Unlike the general long straight tunnel,the diffusion of pollutants in the construction spiral tunnel is bound to be affected by factors such as slope and curvature.The research on the diffusion characteristics of pollutants during the construction of spiral tunnels is of great significance for creating a good construction environment and ensuring the physical and mental health as well as the safety of construction workers.The present work outlines the development history of tunnels in recent years,and introduces the pollutants and their hazards generated during tunnel construction.The status of domestic and foreign research on the diffusion characteristics of pollutants in tunnels is summarized.It has been observed that there are very few studies on the diffusion characteristics of pollutants in spiral tunnels.In the specific case on the construction process of Mi's village special spiral tunnel,an experimental research was carried out and a numerical simulation was conducted to study the pollutant diffusion characteristics in the tunnel.The following are the main research contents and conclusions:(1)Through the on-site inspection,sampling and testing,the dust concentration distribution and particle size dispersion along the path were obtained.The time-based diffusion characteristics of carbon monoxide after blasting are also obtained through on-site inspection,which provides calculation parameters and effective verification for numerical simulation.(2)The characteristics of the air field in the spiral tunnel were also analyzed.It was found that there are two eddy currents near the face of the palm,having a great influence on the air flow field.The reflow mainly occurs on the side away from the air duct and the wind is large.The change in the slope of the spiral tunnel has no significant effect on the migration law of the air flow field.When the radius of curvature increases,the return air velocity in the spiral tunnel increases as well.However,when the radius of curvature is small,the change has a significant effect on the air flow field migration law in the spiral tunnel.With the increase of the radius of curvature,the influence of the change on the air flow field migration law is reduced.(3)Due to the influence of eddy currents,the dust accumulates at a distance of 25 m from the surface.During the construction of the lower spiral,the dust concentration along the path increases with the increase of the slope,and therefore the difficulty of dust reduction in the spiral tunnel increases.The ventilation control system should be adjusted in time to strengthen the dust reduction measures.However,during the upper spiral construction phase,the dust concentration along the path decreases with the increase of the slope.At this time,the ventilation control system can be reasonably adjusted to reduce the ventilation cost.(4)The larger the radius of curvature of the spiral tunnel,the greater the return wind speed and the higher the dust concentration inside the construction.It is indicated that the concentration of dust should not be reduced randomly by increasing the amount of ventilation.Excessive wind speed may increase the level of dust pollution.Measures such as sprinkling water or optimizing ventilation layout should be considered to achieve dust reduction.(5)The diffusion of carbon monoxide is mainly the result of wind flow effects.Since the slope has no significant influence on the law of air flow movement in the tunnel,the diffusion law of carbon monoxide is not significant when the slope of the spiral tunnel changes within the range of 2%~10%.When the radius of curvature of the spiral tunnel increases,the velocity of the carbon monoxide gas mass' diffusion and concentration decreases gradually.However,when the radius of curvature is small,that is,R<400m,its change has a great influence on the migration law of carbon monoxide.When the radius of curvature is large,that is,R>400m,the influence of its change on the migration law of carbon monoxide is gradually smaller.For spiral tunnels with a small radius of curvature,the construction ventilation control system should be adjusted in time to increase the ventilation and improve the construction air environment. |
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