Study On The Cables Fire Spread Behavior And Smoke Flow Characteristics Of Urban Underground Utility Tunnel

With the rapid development of economy,the urban underground space has been vigorously developed.As a new type of underground space,the urban underground comprehensive pipe corridor has become an important infrastructure and "lifeline" for the construction of major cities.There are a variety of voltage cables in the power cabin of the urban underground comprehensive pipe corridor,a variety of coupling factors such as the concentration of combustible cables,aging and inflammability of the outer protective sleeve of the cable,etc.,which increase the possibility and danger of cable fire in the urban underground comprehensive pipe corridor.Due to the special structure of the cable,its fire spread is different from that of combustible solid surface.The smoke in the urban underground comprehensive pipe corridor is popular,also different from other underground space;The smoke spreading behavior is also different in different urban underground complex pipe corridors.Therefore,it is of great significance to study the fire spreading behavior and smoke flow characteristics of underground comprehensive pipe corridor cables.In this paper,rubber insulated copper core cable with insulation layer thickness of 3 mm is selected to carry out fire experiments in the "type 1" pipe corridor experimental platform.By changing several factors such as cable core number,root number,cable layer spacing and cable transverse clearance,the paper compares and analyzes the changes of flame height,flame width and fire spreading speed of cables,and reveals the fire spreading behavior of urban underground comprehensive pipe corridor cables.The experimental results show that with the increase of the number of cable cores,the flame height and flame width of the cable both increases,and the fire spreading speed decreases linearly.With the increase of the number of cable roots,the flame height,flame width and fire spreading speed of the cable all increase.Multi-layer cable fire experiment,when the cable layer spacing is less than 10 cm,with the increase of spacing,approximate linear increase flame height,flame width approximate linear decreases,and when the cable layer spacing fixed cable flame width decreases with increasing lateral clearance of the cable,flame height along with the increase of the cable lateral clearance first increases then decreases,cable lateral clearance flame height of 1.0 cm is the largest.In terms of the fire spreading speed of multi-layer cables,when the cable layer spacing is 4.5 cm or 7.0 cm,the fire spreading speed of each layer increases from the bottom layer to the top layer,and decreases from the bottom layer to the top layer when the cable layer spacing is 9.5 cm or 10.0 cm.When the transverse clearance of cable is 1.0 cm ~ 2.5 cm,the fire spreading speed of middle layer cable is the smallest,and when the transverse clearance of cable is 3.0 cm ~ 4.0 cm,the fire spreading speed of each layer cable decreases from the bottom layer to the top layer successively.Through the research and analysis of the smoke temperature distribution in the fire of "type 1" multi-layer cable,it is found that the temperature in the vertical area decreases with the decrease of the height,and the vertical area temperature in the near combustion area increases again due to the flame radiation heat transfer under the influence of the movement of the burning area of the cable.In the period of rapid development of cable fire,the temperature of the transverse ceiling and wall surface gradually increases,but when the overall horizontal spread of the cable flame,the influence range of flame radiation and hot flue gas changes with the movement of the burning area of the cable,and the temperature change of the near burning area is larger than that of the far burning area.Through the urban comprehensive "T" type structure pipe gallery cable fire spread and smoke flow characteristics of the numerical simulation research,determine the different typical position size of the cable fire risk,fire tube is analyzed in the vertical and lateral area of the gallery of temperature distribution,found the intersection point is easy to form the "smoke" storage phenomenon,analyzes and studies focusing on the intersection area,the ceiling is obtained temperature linearly increased with the increase of fire power,smoke layer height and decreased with the increase of the vertical wind speed.Based on the engineering background of urban underground pipe rack,by conducting "type 1" pipe gallery cable fire experiment and the "T" type pipe gallery cable fire numerical simulation research,reveals the city underground pipe gallery cable fire behavior and change mechanism of the smoke flow characteristics,the results of the study of urban underground pipe gallery provides some references for the performance-based fire protection design.There are 63 figures,12 tables and 85 references in the dissertation.