Study On Optical Field Distribution And Evaluation System Of Pre-tunnel Pavement

Pre-tunnel belongs to the high brightness,semi-open space,light efficiency characteristics and driving field of view are different from the tunnel inside.On the one hand,the road surface is irradiated by natural light,and the distribution of the road surface light field has obvious time-varying characteristics.On the other hand,the contrast between the bright and dark areas of the road surface is obvious,and the uniformity of light field is low,which is easy to appear uncomfortable glare and stroboscope effect.However,the current tunnel lighting code lacks the specific design method of pre-tunnel structures,as well as the scientific evaluation system and technical index aiming at their working characteristics,which seriously restricts the popularization and application of this technology in practical engineering.Therefore,in this paper,the fluctuations of natural light in different time sequences and geographical locations were first considered,and a mathematical model of road surface light field distribution in pre-tunnel section was constructed based on the solar trajectory equation and the sky metammodel to provide a calculation method for road surface light field distribution.Then,the road illuminance distribution in the pre-tunnel section was simulated under the comprehensive influence of different time sequences,latitude and longitude,entrance orientation and structural parameters,so as to obtain the variation rule of the evaluation index of the light environment in the pre-tunnel section.Based on this,a pre-tunnel anti-glare and anti-stammering evaluation system was constructed for the light environment in the pre-tunnel section of the tunnel.Finally,according to the evaluation system,the design suggestions of pre-tunnel grid structure parameters are put forward,and verified by engineering application.The main achievements are as follows:(1)Based on the theory of solar radiation and the sky metamodel,a time-varying calculation model for road illumination in the tunnel dimming section is established by comprehensively considering the influence of direct sunlight and scattered sky light on the distribution of road light field.Increasing the number of sky elements can improve the calculation accuracy of the model in this paper,and has a greater impact on the calculated value of road dark area illumination.Considering both accuracy and computational efficiency,it is recommended that the sky be divided into 12 layers with a total of 247 sky elements when applying this model.(2)Based on the time-varying calculation model of road surface illumination in the tunnel dimming section,the time-varying characteristics of the distribution of road surface light field in the dimming section are obtained.Time,date,and latitude all affect the ratio K of scattering to direct illumination,thereby affecting the uniformity of the road surface in the dimming section.Within a day,K always reaches its minimum value at 12:00.Due to the coupling effect of date and latitude,the latitude at which K appears as the minimum value varies under different dates.At noon on the summer solstice,the sun directly shines on the Tropic of Cancer,the solar elevation angle is large,and K reaches the minimum at the Tropic of Cancer;At noon on the winter solstice,K reached the minimum at the Tropic of Capricorn;At noon on the spring and autumn equinoxes,K is the smallest at the equator.(3)Based on the variation characteristics of each technical index,its applicability to the glare evaluation of tunnel pre-tunnel section was analyzed.The occlusion rate Pc,unified glare value GR and stroboscopic frequency f were adopted as quantitative technical indexes,and the pavement pre-tunnel,anti-glare and anti-stroboscopic evaluation were carried out.With Lav≥k·L20(S),GR≤55,f≤6 or ≥11 Hz as the indicator thresholds,the light environment evaluation system of tunnel pre-tunnel section was established.Based on the indicator thresholds,optimization measures were proposed to limit the structural parameters of pre-tunnel grates.(4)After the application of optimization measures,the GR value decreased by more than5%.The light environment of the pre-tunnel section met the requirements of the pre-tunnel anti-glare and anti-staphylaxis evaluation system.The influence of discomfort glare and staphylaxis effect on drivers was greatly weakened,and the light environment of the pre-tunnel section was more suitable for drivers to pass through.Effectively improve the driving comfort.