Numerical Simulation Study On Diffusion Regularity And Control Measures Of Harmful Gases In Manual Digging Piles Construction

In the construction of construction projects,a variety of harmful gases will be generated.Due to the lack of ventilation during construction,the concentration of harmful gases in the construction environment will increase continuously,which may eventually damage the health of construction workers and cause safety accidents.This paper analyzes and summarizes the characteristics,influencing factors,impact range and hazards of harmful gases in the construction process.And we used questionnaire survey to research on pollution indicators,pollution sources and pollution prevention measures of harmful gases.According to the investigation,the sources of harmful gas pollution are classified by dividing the construction stage and the construction area.In this paper,the construction activities of manual digging piles in construction process are selected to analysis the wind field,diffusion law of harmful gases and the influence of different control measures on the diffusion of harmful gases by using ANSYS FLUENT.Hydrogen sulfide and ammonia were selected as the harmful gas analysis factors.The main conclusions are as follows:(1)Select the hole of the artificial digging pile,the hole depth and the ventilation wind speed as the influencing factors.For the wind field analysis of the artificial digging pile,it is found that the vortex effect is formed due to the obstruction and reflection of the inner wall of the pile,and the strength is different.The wind vortex with different positions will also change the diffusion efficiency of harmful gases in the pile.With the increase of the hole diameter,the diffusion efficiency of harmful gas in the artificial digging pile will decrease.With the increase of the hole depth,the diffusion efficiency of harmful gas in the artificial digging pile will decrease first and then increase;as the ventilation speed increases,it is harmful.The efficiency of gas discharge will gradually increase.(2)Taking the mass concentration of harmful gas as the index,the diffusion law of harmful gas in the artificial digging pile is analyzed:As the aperture increases,the concentration of harmful gases in the internal depth gradient will gradually increase.The maximum concentration of harmful gas at the analysis interface z=1.5m increases with the increase of the aperture;With the increase of the hole depth,the concentration of harmful gas in the depth gradient will experience rapid decline,rise and fall,and finally stabilize.The maximum concentration of harmful gas at the plane of the analysis interface z=1.5m is nonlinear;With the increase of ventilation speed,the concentration of harmful gases changes almost the same when the three ventilation speeds are below 3 m in height.In the follow-up stage,the concentration of harmful gases is the lowest under the condition of high ventilation wind speed.The maximum concentration of harmful gas at the interface z=1.5m increases slightly,but the area of high concentration tends to decrease,and the area of low concentration tends to appear on the opposite side of the ventilation pipe.Therefore,it can be considered that the diffusion efficiency of harmful gas increases with the increase of ventilation wind speed.(3)By changing the ventilation mode,the distance between the ventilation pipe and the pile bottom,the diameter of the ventilation pipe and the ventilation angle of the ventilation pipe are selected for numerical simulation.The simulation results show that:The distance from the bottom of the ventilation pipe to the maximum mass concentration of harmful gas is the most important factor.The ventilation angle of the ventilation pipe and the diameter of the ventilation pipe have little influence on the maximum concentration of harmful gas,which are secondary factors.For hydrogen sulfide,the ventilation effect decreases first,then increases and then decreases with the distance from the bottom of the ventilation pipe increases.The ventilation effect first increases and then decreases with the diameter of the ventilation pipe increases.With the decrease of the ventilation angle between the ventilation duct and the horizontal direction,the ventilation effect first decreases and then increases.For ammonia,the ventilation effect decreases first,then increases and then decreases with the distance from the bottom of the ventilation pipe increases.The ventilation effect first increases and then decreases with the diameter of the ventilation pipe increases.With the decrease of the ventilation angle between the ventilation duct and the horizontal direction,and the ventilation effect is first decreased and then increased.