Study On The Safety Management And Early Warning Technology During Gas Tunnel Construction

China’s territory is vast and charming and around 75% of her land is a mountain or hill so that the gas tunnel is usually encountered when its traffic construction is carried. In the process of gas tunnel construction in addition to the disasters such as collapse, water bursting/mud bursting, rock burst occurring in the regular tunnel construction, there are the specific disasters which are gas explosion caused by gas, staff poisoning choke, coal and gas outburst. Therefore, the risk is great during gas tunnel construction so that some major gas accidents caused by poor tunnel construction management have repeatedly happened at home and abroad. Consequently, it is of important theoretical and realistic significance for preventing accidents and ensuring safety in production to deeply analyze the influence factors of gas emission in gas tunnel construction period, identify the various hazards existing in the process of its construction and explore the effective method of dynamic safety evaluation and early warning management during its construction. Hence by the literature and field research, theoretical analysis, numerical simulation and other methods the safety problems including the possible disaster forms, security key technology, dynamic security reliability evaluation and safety supervision organization design for highway gas tunnel construction were deeply probed into in the paper. Some significant results was obtained as below.1) By literature and field investigation a literature review and evaluation was performed about the current situation of gas tunnel construction and construction safety management and safety evaluation in nearly a decade both at home and abroad. And some new development points for gas tunnel construction safety assessment and management were put forward which were the practical assessment technology, dynamic and intelligent information management, the whole life cycle management for gas tunnel construction and multi-hazard comprehensive evaluation etc.2) The whole construction process of highway gas tunnel was deeply analyzed in which the forms and causes of the possible heavy disasters were also discussed. Based on the analysis on the gas generation causes and gas storing condition in coal seam and surrounding rock, a risk assessment multilayer index system for tunnel gas content was built which considered the coal micro-constitution, coalification degree, coal seam gas storage conditions, regional geological structure and engineering activities and other aspects. A deep analysis was also performed about the mechanism of the specific gas disaster caused by gas normal and specific emission and the general disasters that were not caused by gas including collapse, rock burst and water inrush in the process of gas tunnel construction.3) The geological forecast technology system for gas tunnel construction risk was studied which included five specific management and implementation steps that were in turns the macro analysis for geological conditions, geological survey and geological logging, comprehensive geophysical exploration methods, the implementation of advanced drilling and comprehensive analysis. During gas tunnel construction the manual gas monitoring and automatic monitoring should be performed all together in the same time. After the advantages and disadvantages of two monitoring methods were compared, a corresponding gas monitoring and management system was developed by the gas risk monitoring and early warning of the four-level gas concentration rank. Three important monitoring points of the starting point, abnormal gas concentration change turning point, peak point of gas concentration on the gas concentration monitoring curve were put forward to build an abnormal gas emission identification method during gas tunnel construction. And a qualitative identification method of the swing model method for the abnormal gas emission during construction was also built by using the swinging rate, deviation rate and change rate as the quantitative prediction and evaluation indexes.4) The management and disposal countermeasures for high gas concentration and coal-gas outburst were studied. By comparing the wind-tube type ventilation method with the tunnel type ventilation one, their corresponding ventilation management rules and ventilation quality management assessment criteria were built. The four-in-one comprehensive outburst prevention measures was put forward especially for the period of highway gas tunnel construction. The evaluation index system for coal-gas outburst was built which included tunnel buried depth, geological structure, drilling dynamic phenomenon, gas pressure, gas emission initial speed and the coal structure type. And then the outburst risk comprehensive prediction evaluation method for gas tunnel construction was gained with three level evaluation standard of no distinct danger, the highlight threats and the highlight danger. At last the practical verification was also carried for the comprehensive method.5) The risk identification techniques for highway gas tunnel construction was studied. The hazards during gas tunnel construction were divided into three types of inherent hazards, trigger and nature hazards. In order to check these hazards of the different type characteristics, the gas accident hazards was identified from three aspects of the gas accumulation, the ignition source and management defects. The results showed there were 17, 19 and 8 hazards respectively for the gas accumulation, the ignition source and management defect which would all possibly occur in the process of gas tunnel construction. In order to effectively manage them, a new comprehensive classification evaluation method for the major hazards identification of tunnel gas construction was put forward in the paper, which was called LFS method based on the combination of The LEC method, FTA method and supporting vector machine(SVM). By the method the unity of the three functions of the comprehensive risk degree evaluation of the hazards, key importance value calculation and classification of the hazards was realized.6) By using the GO method of the system reliability analysis and the SIMULINK package of MATLAB software for simulation modeling, the reliability evaluation for the gas monitoring system and ventilation system in gas tunnel construction was realized. The failure rate curve and the reliability analysis curve for the two safety critical systems of the gas monitoring system and ventilation system were also gained. And then based on the time-varying working course of the systems, three stages of the early failure period, the random failure period and the loss failure period for the two safety critical systems were quantificationally divided respectively. The cause and the corresponding safety management measures of the three failure stages were analyzed and built.7) The risk evaluation for the whole process of the gas tunnel construction was performed by establishing five kinds of evaluation indicators which were stratigraphic lithology, geological structure, coal seam thickness, buried depth of tunnel and hydrogeological conditions, as the key main factors impacting the construction risk of gas tunnel and dividing the gas tunnel construction risk into four levels. Then, FDA was used to establish the evaluation system of risk level evaluation of gas tunnel construction and its formal evaluation procedure. 23 gas tunnel prior-experienced risk sample were used for learning and judging of FDA so that the corresponding risk discrimination functions were obtained; Finally, the verification evaluation for 20 gas tunnels’ construction risk level was performed and evaluation conclusion was correspond to the actual situation. FDA risk evaluation method can also be applied for the risk assessment of the similar complex system engineering’s construction as gas tunnel.8) The possible safety accidents of the highway gas tunnel construction was overall analyzed by FTA method so that 75 kinds of accident minimum cut set ways and 33 kinds accident prevention minimum path set ways were gained. And then a matrix organization structure was put forward for dynamic safety implement for gas tunnel construction which owned 6 departments of the exploration and design department, electrical equipment department, technology department, guidance on-site inspection department, logistics department, rescue site inspection department, logistics department, rescue motor transport department. And the basic accident cause events were configured to their corresponding functional departments so that the safety management positions in different levels were set up and the corresponding job descriptions were made. Their safety responsibility of the corresponding position also were determined.The main innovation points of this thesis are as follows:1) By using the GO method of system reliability analysis and the platform of MATLAB software SIMULINK package for simulation modeling, the safety reliability evaluation for the gas monitoring system and ventilation system during gas tunnel construction was realized and the failure rate and reliability of safety critical systems analysis curve were gained. Then the cause and the corresponding safety management measures of the three stages including early failure period, random failure period and wear failure stage was analyzed.2) Five kinds of evaluation indicators were established which were stratigraphic lithology, geological structure, coal seam thickness, buried depth of tunnel and hydrogeological conditions, as the key main factors impacting the construction risk of gas tunnel and the gas tunnel construction risk was divided into four levels. Then, FDA was used to establish the evaluation system of risk level evaluation of gas tunnel construction and its formal evaluation procedure. And a lot of gas tunnel engineering samples were used to verified the risk evaluation method.3) The possible safety accidents of the highway gas tunnel construction was overall analyzed by FTA method of FTA so that 75 kinds of accident minimum cut set ways and 33 kinds accident prevention minimum path set ways were gained. And then a matrix organization structure was put forward for dynamic safety implement for gas tunnel construction. And the basic accident cause events were configured to their corresponding functional departments so that the safety management positions in different levels were set up and the corresponding job descriptions were made. Their safety responsibility of the corresponding position also were determined.In the thesis the research results has been verified to be effective in the real project and can be applied in the similar engineering.