Study On Fire Characteristics Of Nonaxisymmetric Double Fire Sources Of Urban Utility Tunnel

To relieve the pressure of ground land resources,improve and protect the urban landscape,the urban utility tunnel is getting more and more cities’favor.However,when the urban utility tunnel is vigorously promoted,it also brings huge security risks.Although urban utility tunnel fire will not cause casualties,but because its structure is long and narrow,in the event of fire,the high temperature smoke gathered below the urban utility tunnel ceiling is very difficult to discharge,which will make temperature dramatic increase inside the utility tunnel,bring huge security threat to the lining structure of utility tunnel,cause huge economic losses,and seriously affect people’s daily life.Therefore,it is of great practical significance to study the tunnel fire of the urban integrated tunnel,especially the non-axisymmetric double fire source,which can provide a theoretical basis for the development of the fire design standards and fire prevention measures of the urban utility tunnel.In this paper,a series of fire combustion experiments have been carried out on the self-designed 1/8 small-scaled urban utility tunnel test platform.The main research contents and results are as follows:First,a single rectangular fire combustion experiment is carried out in open space to study the flame shape and flame height of a single rectangular fire.The results show that the flame height L_fgenerated by a single rectangular fire increases with the increase of the dimensionless fire source power.The relationship between L_f/d and dimensionless fire source power is obtained,which verifies the reliability of the experiment.Then,the combustion experiment of non-axisymmetric double fire sources in open space are carried out.The flame merging probability based on the principle of statistics is used to quantify the flame merging degree of the double rectangular fire sources,and the piecewise prediction model of flame merging probability P_mand the critical criterion of flame merging are obtained.The relation between the dimensionless flame height L_f/D of double rectangular fire sources and the modified dimensionless fire source power is established.The change law of temperature rise on the vertical center line of double rectangular fire sources with height under different fire source spacing S/d is revealed.A series of non-axisymmetric double fire sources combustion experiments are carried out in horizontal urban utility tunnel to reveal the flame burning shape and the variation of temperature distribution under the horizontal utility tunnel ceiling with non-dimensional fire source power and fire source spacing.And The prediction formula of longitudinal temperature attenuation of the horizontal utility tunnel ceiling is established.A piecewise prediction model of double fire sources in the horizontal utility tunnel is established,and a critical criterion of flame merging is proposed.It is found that the P_mof double fire sources in the horizontal utility tunnel is higher than that of open space when the non-dimensional fire source power is larger.The relation expression between the dimensionless total flame length of ceiling jet and the dimensionless fire source power is obtained.A set of non-axisymmetric double fire sources combustion experiments are carried out under different tunnel slopes,and the influence of fire source power,fire source spacing and tunnel slope are considered.The longitudinal and transverse flame combustion shape and temperature distribution under the ceiling of double rectangular fire sources in utility tunnel are revealed under different slopes.And The prediction formula of longitudinal temperature attenuation of the horizontal utility tunnel ceiling is established under different slopes.The piecewise prediction models of double fire sources in utility tunnel under different slopes are established,and critical criterions of flame merging under different slopes are obtained.It can be found that the tunnel slope can promote the merging of double flames in the utility tunnel.Formulas for predicting the total flame length of the ceiling jet of utility tunnel under different slopes are established.