Study On Fire Smoke Flow Characteristics And Influence Of Gas Leakage And Diffusion In Underground Utility Tunnel

As a "lifeline project" for urban operation,the underground comprehensive pipe gallery is an infrastructure that consolidates various pipelines,including electricity,communication,gas,and water supply and drainage,to achieve unified planning,construction,design,and management of pipelines.However,with the growing demand for resources,more and more municipal pipelines are being incorporated into the underground comprehensive pipe gallery,resulting in a complex internal environment and significant safety hazards.Cable fires caused by circuit overload,short circuits,and gas leaks caused by corrosion and punctures are two typical accidents with a high risk and impact in the comprehensive pipe gallery.Therefore,this article focuses on cable fires and gas leaks in the underground comprehensive pipe gallery,and studies the influence of fire source characteristics and cross-sectional shapes on smoke flow characteristics during the burning stage through theoretical analysis and numerical simulation.Additionally,the post-disaster smoke flow characteristics under different ventilation and smoke exhaust conditions are compared and analyzed.Finally,a field measurement of temperature and humidity in a typical comprehensive pipe gallery is conducted,and based on the measured data,the influence of ventilation conditions,leakage sources,temperature,and humidity on gas leak diffusion is studied through numerical simulation methods.The main work and research results of this article are as follows:(1)Based on the characteristics of closed underground comprehensive pipe gallery fires,an FDS fire numerical model is established.By designing different fire power sources,a combustion self-extinguishing model is proposed for the interior of the pipe gallery,and the changes in the content of different combustion products during the combustion stage are analyzed.On this basis,based on the vertical temperature distribution theory,the N-percentile method,buoyancy frequency method,and integral ratio method are used to compare and analyze the smoke layer height under different fire power sources with FDS calculation results.Considering the relationship between smoke layer thickness,smoke mass flow rate,and the longitudinal and transverse ratio of the pipe gallery,a one-dimensional horizontal spread prediction model for smoke layer thickness during the smoke spreading stage in the underground comprehensive pipe gallery is proposed.The smoke layer heights of rectangular and horseshoe-shaped crosssections are compared and analyzed to provide a theoretical basis for predicting smoke spreading in underground comprehensive pipe gallery fires.(2)A longitudinal airflow velocity model and longitudinal and transverse temperature prediction model for a rectangular cross-section comprehensive pipe gallery are established by varying the power and location of the heat source.The impact of crosssectional shape on longitudinal airflow velocity and longitudinal and transverse temperature distribution is compared and analyzed.Based on relevant regulations,the study explores the effect of different ventilation and smoke exhaust conditions on postdisaster smoke flow characteristics and proposes corresponding recommendations for post-disaster ventilation and smoke exhaust processes in underground comprehensive pipe galleries.(3)Based on the small hole leakage theory,a detailed CFD gas leakage model is established to study the effect of ventilation conditions and leakage sources(leakage orifice size,pipeline operating pressure)on the diffusion of gas leakage in underground comprehensive pipe galleries through parameters such as alarm time,methane diffusion distance,and backflow length.A prediction model for alarm time,methane diffusion distance,and backflow length is proposed,providing a reference for the timely detection of pipeline leakage accidents and prediction of hazardous areas.(4)A study was conducted to measure and analyze the temperature and humidity of the internal environment of typical underground comprehensive pipe galleries.Key parameters were analyzed based on the measured data to investigate the effects of different temperature and humidity levels on gas leak diffusion.The adverse effects of gas leaks during the winter and summer seasons were compared.Ventilation recommendations were proposed for the normal operational phase based on the actual measurement results and numerical simulations to provide guidance for the safe operation of underground comprehensive pipe galleries.