| Based on the major demand of the country to improve the supply capacity of comprehensive transportation service in mountainous areas,China started to plan and build rack railway on a large scale.The maximum allowable slope of mountain rack railway line is480‰,which is much larger than conventional rail trains.Once fire occurs in the tunnel with large slope,the fire smoke will cause more harm and the evacuation of people will be more difficult.At present,the research on the slope on the tunnel fire smoke temperature rules is mainly limited to below 10%slope,and it is not clear whether the research conclusions can be applied to the mountain rack railway tunnel with large slope.Therefore,it is especially urgent to study the fires in large-slope tunnels with mountainous rack railway and to master the smoke spread rules of large-slope tunnel fires.In this paper,in order to investigate the effect of large slope on the smoke temperature distribution and spread of mountain rack railway tunnel,a1:20 scale tunnel fire experimental platform was designed and built,conducted 108 sets of scale tunnel fire experiments under different tunnel slope,heat release rate(HRR)and ventilation velocity conditions,recorded the temperature data under the ceiling,analyzed the influence of tunnel slope,HRR and ventilation velocity on the smoke temperature and The prediction models of maximum temperature rise under the ceiling of tunnel fire,downstream longitudinal temperature distribution and smoke back-layering length were established and validated for the accuracy of the models,with a view to providing technical support for the formulation of construction standards,design of fire safety and emergency plans for rack railway.The specific research work and results are as follows:(1)The rules of maximum temperature rise under the ceiling in the fire conditions of mountain rack railway large slope tunnel.The effect of tunnel slope,HRR and ventilation velocity on the maximum temperature rise under the ceiling of the tunnel fire was analyzed,and the results showed that:with the increase of tunnel slope,the maximum temperature rise decreases exponentially;the maximum temperature rise increases with the increase of HRR and decreases with the increase of ventilation wind speed,but with the increase of tunnel slope,the effect of HRR and ventilation velocity on the maximum temperature rise gradually becomes smaller.Based on the above analysis,a prediction model was established to predict the maximum temperature rise under the ceiling of the tunnel fire in the range of large slope,and the relative error of the model prediction was verified to be±19.6%.In addition,the position of maximum temperature rise deviation from the horizontal distance of the fire source was analyzed,and the results show that:when the tunnel is inclined,the position of maximum temperature rise is different from the horizontal tunnel,the greater the slope,the farther the deviation distance;deviation distance increases with the increase of the HRR,and increases with the increase of the ventilation velocity,the maximum position of temperature rise deviation from the fire source can be as far as 0.8m(corresponding to the full-size tunnel 16m).This may accelerate the spread of tunnel fires and adversely affect personnel evacuation and fire fighting and rescue.(2)Temperature distribution rules downstream under the ceiling of fire conditions in rack railway tunnels with large slopes.A dimensionless analysis of the downstream temperature distribution rule of the tunnel fire,combined with experimental data to study the influence of the variables on the downstream temperature distribution rule,the results show that:the downstream temperature along the tunnel longitudinal decay is a power function,the greater the slope of the tunnel,the lower the temperature inside the tunnel,the slower the temperature decays with distances,with the increase in tunnel slope,temperature decreases in inverse proportion instead of a linear decline;the temperature inside the tunnel increases with the increase of HRR and the temperature decay is accelerated;the larger the ventilation velocity,the lower the temperature inside the tunnel,the slower the temperature decay rate with distance.Based on the above analysis,on the basis of the previous studies,a prediction model for the downstream temperature distribution of the tunnel fire was found,and the relative error of the model prediction is±17.4%after verification.(3)The rule of smoke back-layering length under fire conditions in rack railway tunnels with large slope.Analysis of the effect of tunnel slope on the length of the tunnel fire smoke back-layering rule,the results show that:the smoke back-layering length decreases with increasing tunnel slope,there is a critical slopeα_c,when the tunnel slope is greater than the critical slopeα_c,there is no longer smoke back-layering phenomenon in the tunnel;in natural ventilation conditions,the critical slope is 15%≤α_c≤20%.The value of the smoke back-layering length increases with the increase of the HRR;the prediction model of smoke back-layering length under natural ventilation conditions proposed by the previous authors was modified to obtain a prediction model of the tunnel smoke back-layering length with a broader range of application.The effects of tunnel slope and HRR on the critical velocity were analyzed,and the results showed that the critical velocity decreased gradually with the increase of tunnel slope;the larger the HRR,the larger the critical velocity of the tunnel.On this basis,the critical velocity was determined based on the variation rule of the smoke back-layering length with ventilation velocity,and the horizontal critical velocity prediction model proposed by the previous authors was modified under the condition of no spraying,and the slope correction coefficient was determined by data fitting to establish a critical velocity prediction model that can be applied to inclined tunnels. |
