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Table of Content

    28 June 2020, Volume 30 Issue 6
    Safety science theory and safety system science
    Multi-objective optimization design for safety system based on isolation-inoperability competing failure mechanism
    ZHAO Jianqiang, XIONG Yanming, ZHANG Youjian
    2020, 30(6):  1-7.  doi:10.16265/j.cnki.issn1003-3033.2020.06.001
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    In order to avoid single indicator-based design flaw, a multi-objective optimization design method of safety system based on isolation-inoperability competing failure mechanism was proposed. Considering that the core of this method was thresholds setting of isolation component and inoperability component, three performance indices, including PLOAS, reliability loss, mass cost, were utilized to express influence of thresholds setting on system safety, reliability, and mass respectively. On this basis, a relevant multi-objective optimization function was established, and linear weighted method was applied to converse multi-objective optimization problem to a single one. The results show that the proposed method is suitable for solving multi-objective optimization problem based on isolation-inoperability competing failure mechanism, and Pareto solution sets can be obtained not only for three objectives optimization problem, but also for two objectives optimization problem under strong restriction of safety.
    Safety social science and safety management
    Study on causes of accidents in construction of natural gas pipelines
    SUN Shimei, GAO Xiaodi, SUN He, FU Gui
    2020, 30(6):  8-13.  doi:10.16265/j.cnki.issn1003-3033.2020.06.002
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    In order to prevent natural gas pipeline construction accidents, causes of 32 natural accidents of such were analyzed by using "2-4" model causal factor coding system.16 causal factors involved in the accident were obtained through statistical analysis of 29 factors at 4 levels, and 5 most frequent ones were analyzed in detail. The results show that for all investigated accidents, the major reasons for them are personnel's faulty operation from the category of illegal and unsafe operation, inconformity of external conditions before construction with requirements from unsafe states, insufficient mastery of equipment and material characteristics from safety knowledge, failure to realize importance of construction procedures from safety awareness, unreasonable deployment of on-site safety supervision personnel from safety management structure defect, and continuous rain from natural factors.
    Analysis on chain intermediary mechanism of mindfulness's influence on safety performance
    NIU Lixia, LIU Yong, LI Naiwen
    2020, 30(6):  14-22.  doi:10.16265/j.cnki.issn1003-3033.2020.06.003
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    In order to prevent unsafe behaviors of miners and improve safety performance of coal mining enterprises, mechanism and boundary conditions of mindfulness on safety performance were actively explored. A questionnaire survey and data analysis were conducted for 1 125 miners in Liaoning, Inner Mongolia and Shaanxi by using follow-up survey method, and a hypothetical model was verified. The results show that mindfulness is significantly positively correlated with safety performance and self-control while it is significantly negatively correlated with mind wandering. Self-control is significantly positively correlated with safety performance,but significantly negatively correlated with mind wandering, and there is a significant negative correlation between mind wandering and safety performance. Self-control plays an intermediary role between mindfulness and safety performance, mind wandering plays an intermediary role between mindfulness and safety performance, and they together play a chain-mediated role between mindfulness and safety performance. That is, miners with a high level of mindfulness can improve self-control ability, thereby reducing frequency of mental wandering and ultimately improving their safety performance.
    Safety engineering technology
    Robust geotechnical design of soil-pile foundation system considering multiple failure modes
    DU Xiuli, CAO Xiuxiu, ZHONG Zilan, HOU Benwei, WANG Wei
    2020, 30(6):  23-30.  doi:10.16265/j.cnki.issn1003-3033.2020.06.004
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    In order to address uncertainties of geotechnical parameters and loads in pile foundation design, firstly, a RGD method considering multiple failure modes was proposed. Four typical failure modes, vertical ultimate limit state (ULS), vertical serviceability limit state (SLS), horizontal strength failure and horizontal deformation failure were analyzed. Then, Monte Carlo simulation (MCS) and point estimate method (PEM) nesting were adopted to compute mean value and standard deviation of failure probability for soil-pile foundation system, and the latter was used as an indicator to measure robustness. Finally, optimal design of soil-pile foundation system was finalized with robustness and cost as objectives. The results show that piles with different geometries have different dominant failure modes. With the increase of geometries, key failure mode changes from horizontal strength failure to vertical SLS, which has significant influence on gradient of of system' failure probability.
    Study on combustion properties of magnesium oxysulfate cement/polystyrene composites
    YU Shuijun, XIE Gaochao, REN Mo, YANG Dailin
    2020, 30(6):  31-36.  doi:10.16265/j.cnki.issn1003-3033.2020.06.005
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    In order to solve problem that polystyrene is inflammable and easy to produce poisonous gas, magnesium oxysulfate cement and polystyrene particles were used to make magnesium oxysulfate cement/polystyrene composite material. Then, effects of different ratios of lightly-burned magnesium oxide and heptahydrate magnesium oxysulfate on combustion performance of polystyrene particles were studied by LOI test, UL-94 vertical combustion test, smoke density test, and TGA. The results show that when content of magnesium sulfate maintains unchanged, weightlessness range and rate of polystyrene composites decreases with the increase of lightly-burned magnesium oxide, and so does the maximum mass loss rate while residual carbon rate increases with it at 700 ℃ with its maximum rate able to reach 80.73%. LOI of polystyrene coated with magnesium oxysulfate cement can reach up to 37.2%, and it increases along with that of magnesium oxysulfate when lightly-burned magnesium oxide stays fixed. It shows the same trend of LOI increasing along lightly-burned magnesium oxide when the other is unchanged. UL-94 level of composite materials can all reach V-0, and their smoke density is about 30 times lower than that of pure polystyrene particles. Flame retardation and smoke suppression of polystyrene are significantly improved by magnesium oxysulfate cement.
    Application research of light scattering principle in dust measurement system
    FU Shigen, LI Quanming, HU Jiaguo, DONG Hewei
    2020, 30(6):  37-42.  doi:10.16265/j.cnki.issn1003-3033.2020.06.006
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    In order to prevent harm caused by respiratory dust and to monitor mass concentration of individual exhalation dust, a portable personal concentration monitoring test prototype was developed by using infrared light emitting photodiode as a light source according to principle of light scattering, and its pneumatic control circuit and optical control and detection circuit were designed.Then, prototype and comparison instrument were put in a self-made dust test device together with dust gas which featured a flow rate of 2 L/min and a particle size of 5 μm. The results show that when mass concentration of dust is between 0-150 mg/m3, measured voltage of prototype increases along with increase of dust concentration, and they maintain a good linear relationship. The relative error between measured concentration value of prototype by using regression equation and that of comparison instrument is within ±4%, indicating that the device meets requirements of relevant dust verification regulations.
    Influencing factors on explosion and toxicity of high-sulfur natural gas
    XIAO Junfeng, CHEN Jian, DAI Chengcheng, LU Ping
    2020, 30(6):  43-49.  doi:10.16265/j.cnki.issn1003-3033.2020.06.007
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    In order to study interrelation between influencing factors in high-sulfur natural gas leakage accidents, single-factor analysis and uniform design method were used to study influence of CH4 and H2S content ratio, ventilation rate and pipeline pressure on explosion and toxicity risk of high-sulfur natural gas based on numerical simulation by FLACS software. The results show that factors influencing explosion limit of natural gas is ventilation rate > pipe pressure > CH4 and H2S content ratio, among which the first factor is negatively correlated with limit range while the other two are positively correlated with it, and ventilation rate has the most significant effect. It is the opposite for factors that affect gas leakage toxicity which is negatively correlated with ventilation rate and content ratio but positively correlated with pipeline pressure, and content ratio exerts the most significant effect on gas toxicity.
    Reinforcement effect and stability analysis of high speed railway roadbed
    JIA Jianqing, JIA Chao, LAI Yuanming, ZHAO Yangyang, WANG Hongtu
    2020, 30(6):  50-56.  doi:10.16265/j.cnki.issn1003-3033.2020.06.008
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    In order to determine reinforcement effects and technical parameters of dynamic compaction on roadbed, with silt and silty clay roadbed of a high speed railway as research object, bearing capacity and deformation law and features of reinforced roadbed by dynamic compaction at 15 and 20 m falling distances were studied through site experiment and numerical simulation. The results show that as tamping times increase, compaction settlement for each tamping decreases and gradually stabilizes, and settlements of last two tamping of each falling distance can meet termination condition of engineering design. When dynamic compaction is applied, water content, dry density and specific penetration resistance of surface soil are all significantly improved with obvious reinforcement effect achieved in efficient reinforcement area. And bearing capacity characteristic values of roadbeds in three test points are greater than 150 kPa, which meets designing requirements. In early stage of dynamic compaction, numerical simulation results are slightly smaller than those of field test, but they agree well with each other as tamping times increase.
    Structural equation model between safety accidents and network capability of construction enterprises
    ZHANG Jianshe, ZHANG Wenyu, CHENG Ruiya, LUO Chunyang, WANG Tianxing
    2020, 30(6):  57-63.  doi:10.16265/j.cnki.issn1003-3033.2020.06.009
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    In order to investigate how safety accidents affect network capability of construction enterprises, connotation of network capability was defined and it was divided into five dimensions, network vision, network construction, network management, network learning and emotional embedding. Then, hypothesis of relationship between safety accidents and network capability was put forward, data were collected through questionnaire survey and empirical analysis was made using SEM. The results show that safety incidents have a significant and direct impact on network vision, network construction, network management and emotional embedding, among which influence on network vision and emotional embedding is greater than that on network construction and network management. And they exert a significant and indirect impact on network learning through intermediary role of network vision and emotional embedding, among which that role of emotional embedding is greater than that of network vision. Therefore, construction enterprises can reduce impacts of safety accidents on network capacity through strategic planning of network in time, strengthening coordination between organizations and emotional ties.
    Risk assessment of instrument transition flight training
    CHEN Huaqun, LIU Junjie
    2020, 30(6):  64-70.  doi:10.16265/j.cnki.issn1003-3033.2020.06.010
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    In order to improve safety of instrument flight training for student pilots, training procedure and a risk assessment method based on instrument flight rules and aviation operation control theory were proposed, and a model algorithm based on airspace collision risk and route safety obstacle clearance was built. Then, a complete assessment process of instrument flight release was established, risk evaluation process and index system for procedure implementation were determined, and instrument flight training was carried out according to route transportation flight mode. Finally, the algorithm was verified with classic training test of Red Deer Base in Canada as an example. The results show that this model algorithm based on collision risk and obstacle clearance can systematically analyze relative elements and realize quantitative risk assessment of training content in all sessions
    Comprehensive governance technology for fully-mechanized mining face across abandoned roadways in thick coal seam
    ZHANG Yaohui, LI Xifan, XIONG Zuqiang, WANG Cheng
    2020, 30(6):  71-77.  doi:10.16265/j.cnki.issn1003-3033.2020.06.011
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    In order to address impacts of various types of abandoned roadways on normal mining of working face in thick coal seam, field surveys, theoretical analysis and other methods were used to summarize occurrence characteristics and hazards of abandoned roadways which were divided into complete types along bottom, complete types along top, and fallen ones, and different treatment methods for them were proposed. Meanwhile, in order to meet needs of various construction schemes, sulfoaluminate-based multifunctional grouting materials were developed, and comprehensive governance technology for fully-mechanized mining face passing abandoned roadways in thick coal seam was proposed. Finally, with Sihe coal mine, Chengzhuang coal mine and Guozhuang coal mine taken as engineering backgrounds, filling pillar support, high water filling and deep-hole grouting methods were applied respectively to treat abandoned roadways, and their governance effectiveness was investigated. The results show that after specific treatment of empty roadways, there will be no sloughing and roof accidents, and roof pressure becomes normal, thus ensuring safe mining of working faces.
    Residual strength analysis of internally corroded submarine pipeline based on FOA-GRNN model
    BI Aorui, LUO Zhengshan, SONG Yingying, ZHANG Xinsheng
    2020, 30(6):  78-83.  doi:10.16265/j.cnki.issn1003-3033.2020.06.012
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    In order to explore residual strength of submarine pipelines with internal corrosion, and provide reference for maintenance so as to ensure safe operation, a FOA-GRNN calculation method of residual strength was proposed and a prediction model was constructed by using GRNN based on influencing factors like wall thickness, diameter, corrosion depth, length, width and ultimate tensile strength. Then, FOA was used to optimize the model, and negative influence of smooth factors were set artificially. Influencing factors and residual strength database were simulated and generated by finite element method, and trained and predicted through FOA-GRNN model. Finally, with experimental data of pipeline ultimate strength blasting from PETROBRAS Research Institute as an example, the prediction model was verified. The results show that average relative error of FOA-GRNN model is 16.53% for residual strength prediction of finite element simulation data, and 7.81% for experimental data prediction, which are reasonable and accurate.
    A prediction method for bounced landing of aircraft based on DBN
    JIA Bo, SUN Yanjin, ZHANG Guiming
    2020, 30(6):  84-91.  doi:10.16265/j.cnki.issn1003-3033.2020.06.013
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    In order to grasp causes of bounced landing of aircraft which is a frequently occurring issue during flight operation, and effectively prevent such incidents, a prediction method for bounced landing based on DBN was proposed. Secondly, correlation between incidents and landing airports' environment was evaluated by using aviation data, and with an actual incident of China Eastern Airlines as an example, changing trend of bounced landing along with throttle stick position at touchdown was explored. Then, impacts of pilot control, aircraft status and unstable approach on incidents were discussed. Finally, different combinations of information were used as inputs to train the model, and their prediction accuracy was compared to find optimal one. The results show that DBN-based method is suitable for predicting bounced landing by utilizing flight data. When network input includes direct influencing factors such as airports' environment, throttle lever position, as well as indirect ones like unstable approach, this model can accurately predict accidents with a prediction accuracy as high as 94.78%.
    Experimental study on rapid sealing and venting characteristics of explosion venting door under different conditions
    LI Ang, SI Junhong, ZHAO Xidong, ZHOU Xihua
    2020, 30(6):  92-97.  doi:10.16265/j.cnki.issn1003-3033.2020.06.014
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    In order to study influence of explosion venting door on characteristic parameters of gas explosion, and verify its venting effect and fast sealing performance, gas explosion tests were carried out by using self-made large explosion pipeline system for conditions of 5.5%, 7.5%, 9.5% and 11.5% gas concentration. Then, explosion parameters were measured by data acquisition system, and their change laws and flameproof effect were analyzed. The results show that pressure peak are attenuated by 42.25%, 50.54%, 53.27% and 52.88% respectively under four working conditions. Along with increase of gas concentration, explosion pressure peak decays as a quadratic function, and average enclosed fire zone is 14 h, indicating that explosion venting door has significant venting characteristics and can close fire zone rapidly. Temperature change law is basically same, and in spite of gas concentration changes, explosion venting door does not inhibit gas explosion flame. Under four operating conditions, the maximum average value of flame propagation speed are 103.56, 105.73, 136.67 and 138.34 m/s separately.
    Experimental investigation on phase transition and heat transfer characteristics for liquid carbon dioxide in loose coal
    YU Zhijin, YANG Song, GU Yu, DENG Jun
    2020, 30(6):  98-105.  doi:10.16265/j.cnki.issn1003-3033.2020.06.015
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    In order to investigate heat transfer characteristics of LCO2 injected in loose coal and study influence of injection parameters on temperature field of coal, experiments on LCO2 injection process were carried out by using self-made test platform. Then, temperature changes of coal and influence of injection parameters on refrigeration range were analyzed. The results show that when LCO2 is injected into loose coal, phase transition occurs immediately, and an intensive heat transfer process starts and forms a phase-change cooling area (<-56.6 ℃) which sees a logarithm increase over injection time in direction of CO2 jet. Meanwhile, the cooling area increases in a form of exponential, logarithm and linear function respectively along with increase of injection flow, caliber and pressure
    Impacts of methane content on compound flame propagation characteristics of methane-coal dust
    LIU Jing, CHEN Xianfeng, ZHANG Bo, GAO Wenao, ZHAO Qi, SUN Weikang
    2020, 30(6):  106-112.  doi:10.16265/j.cnki.issn1003-3033.2020.06.016
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    In order to explore impacts of methane content on coal explosion process and to master flame propagation law of coal-methane explosion, particle size and pyrolysis process of two kinds of coal powder samples were studied by a particle size analyzer and a synchronous thermal analyzer. Then, a 1 500 mm× 80 mm× 80 mm semi-open vertical combustion pipe was used to analyze impacts of coal powder at median particle size of 65 and 25 μm for different methane volume fractions on structure, temperature and velocity of methane-coal dust compound flame. The results show that coal flame for 25 μm is brighter than that for 65 μm, and increase in methane volume fraction has a stronger promotion effect on 65 μm coal dust flame. When volume fraction approaches the equivalence ratio, the more regular flame front is, the greater flame velocity is. And as it increases, both flame temperature and velocity show a trend of increasing first and then decreasing. Flame temperature reaches the maximum value at the content of 9%, and the maximum flame velocity of 65 and 25 μm pulverized coal are 26.53 and 39.28 m/s when it is 8% and 10% respectively.
    Public safety
    Risk assessment in construction of small-diameter deep drainage tunnel
    WANG Junwu, HU Die, WU Han, WANG Mengyu, LIU Denghui
    2020, 30(6):  113-120.  doi:10.16265/j.cnki.issn1003-3033.2020.06.017
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    In order to identify construction risk of small-diameter deep drainage tunnel shields and accurately evaluate risk level, a HAZOP-based risk identification method and an evaluation method based on rough sets and cloud models were proposed. Firstly, construction risks were identified comprehensively by using HAZOP and an evaluation index system was established according to attribute reduction theory of rough sets. Then, a risk assessment model for small-diameter tunnel shield construction was established by combining rough sets and cloud model. Finally, the model was verified with deep tunnel project of East Lake as an example. The results show that evaluations of the model are basically consistent with actual situation, and major factors causing high- level construction risks include delayed adjustment of tunneling parameters, deficient training and evaluation, clogged grouting pipes, falling down of hoisting equipment, and unspecific engineering geological and hydrogeological surveys, and they should be checked and avoided.
    Research on characteristics of expressway truck accidents in different regions
    LI Zhenming, NIU Yi, FAN Yunxiao, WANG Rui
    2020, 30(6):  121-127.  doi:10.16265/j.cnki.issn1003-3033.2020.06.018
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    In order to fully explore differences of truck accident characteristics in different regions and prevent high occurrence of truck accidents, methods such as taxonomy and social network analysis were applied to study data of major accidents in Zhejiang from South and Jilin Province from North respectively. Then, based on preliminary classification analysis of data, a network diagram of influencing factors and a ranking table of centrality were constructed, and two sets of data were compared. The results show that there are great differences in number, severity, cause and complexity of truck accidents between two provinces. Weather condition, vehicle type and fatigue driving are important factors that affect accident severity while region difference, weather and driving experience exert comparatively significant influence on unsafe driving behaviors.
    Research on non-motorized vehicle users' violating riding intention and accident proneness
    TANG Tianpei, ZHOU Xizhao, SHENG Dian, CAO Yang
    2020, 30(6):  128-134.  doi:10.16265/j.cnki.issn1003-3033.2020.06.019
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    In order to reduce safety issues caused by non-motorized vehicle users' VRI, based on Ex-TPB, a SEM of these users' AP was developed with VRI as a mediator by introducing six extended latent variables. Then, data were obtained through a survey, and psychological factors which influenced VRI and AP were studied from a perspective of social psychology. The results show that the proposed model could explain 82.6% of variance for VRI, and 75.8% of that for AP. Moral norm has obviously negative impacts on VRI, while descriptive norm, perceived behavior control, conformity tendency, attitude exert significantly positive impacts on it, but their extent of influence abate successively. Moral norm, descriptive norm, perceived behavior control, attitude not only have direct impacts on AP, but also indirect ones on AP via a mediator of VRI, and their mediating effects are significant. Conformity tendency has no significant direct effects on AP, but mainly exerts indirect effects on AP by promoting VRI.
    Flow field characteristics of fire plume in different restricted forms based on PIV
    ZHANG Wei, ZHANG Ying, LI Changwei, YUAN Dachao
    2020, 30(6):  135-141.  doi:10.16265/j.cnki.issn1003-3033.2020.06.020
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    In order to explore effects of different restricted forms on flow field of fire plume, fine thermocouple and PIV technologies were used to monitor fire plume's height, temperature and flow field of diffusion burner in free space, side wall space and corner space, and then flow field characteristics in different restricted forms were studied. The experimental results show that when dimensionless source power Q* is less than 1.5, dimensionless flame height Lf/D increases linearly which will become steady approximately when Q* exceeds 1.5. Lateral velocity in different restricted spaces all conform to approximate Gaussian distributions, and sidewall space and corner space cause a certain deviation of flame center. Vortex diameter is between 3.5 and 8 cm at Q* is 1.982, and its size gradually increase along with increase of side wall surface because vortex will fall off, which will release a lot of heat in a short time and exerts a stretching impact on fire plume. As a result, combustion reaction of fire is promoted, and then a larger vortex is generated.
    Simulation study on personnel evacuation considering impacts of fire products
    YE Chenghao, LIU Yuechan, SUN Chao, JIANG Yongqing, WANG Bo
    2020, 30(6):  142-151.  doi:10.16265/j.cnki.issn1003-3033.2020.06.021
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    In order to explore impacts of fire products on personnel evacuation in the event of a fire in buildings, relevant parameters of fire products were extracted through full-scale numerical simulation of building model, concept of personnel evacuation speed coefficient was introduced, and an evacuation speed model based on effects of fire products was established. Secondly, a new method to determine safe evacuation was put forward before numerical simulation was carried out for such evacuation considering impacts of fire products. Meanwhile influence of spray intensity and smoke exhaust rate on speed coefficient was analyzed. The results show that the proposed evacuation model can better reflect evacuation effects in the real fire site than traditional research methods. And addition of spraying and smoke extraction can effectively reduce impacts of fire products on evacuation speed.
    Technology and engineering of disaster prevention and mitigation
    Assessment on seismic resilience of water supply network based on projection pursuit cluster
    LI Yanfeng, YIN Jiaxiao, LIU Chaofeng, WANG Wei, YU Xiaochen, LI Zipeng
    2020, 30(6):  152-157.  doi:10.16265/j.cnki.issn1003-3033.2020.06.022
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    In order to ensure safe operation of urban water supply network at different levels, based on resilience analysis and seismic damage mechanism of network, a seismic safety resilience evaluation index system of the network was established which considered pipelines' physical properties, external environment and hydraulic function in pipes. Then, projection pursuit method was introduced to project evaluation index linearly, and a projection pursuit cluster model for assessment was established to analyze seismic safety resilience level and to obtain resilience grade and order of each pipes. Finally, this model was applied to evaluate a water supply network, and its assessment results were compared with those obtained by dynamic classification method and pedigree clustering method. The results show that the proposed evaluation model based on projection pursuit cluster can successfully grade and rank seismic safety resilience of water supply network and comprehensively reflect influence of different elements including pipes' material and connection type.
    Sequential probabilistic back analysis on hydraulic conductivity of tailings materials
    JIANG Shuihua, ZENG Shaohui, HUANG Jinsong, YAO Chi
    2020, 30(6):  158-165.  doi:10.16265/j.cnki.issn1003-3033.2020.06.023
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    In order to ensure seepage analysis accuracy of tailings dam, deduce hydraulic conductivity probability distribution of tailings material and to reduce its uncertainty, sequential probabilistic back analysis method of material parameters based on Bayesian updating was proposed. Then, a surrogate model of water table and likelihood function were constructed. Finally, with Daheishan tailings dam taken as an example, sequential probabilistic back analysis of hydraulic conductivity of multi-layered tailings materials was conducted based on monitoring data of water tables. The results show that the proposed approach can effectively infer hydraulic conductivity and probability distributions as well as reduce their variation coefficients which is reduced by 18.25% for soil layer closer to monitoring points. Realistic uncertainties of hydraulic conductivity and representation cannot be well deduced only from monitoring information of water levels, and it is necessary to further collect field information of multiple sources and incorporate it into probabilistic back analysis
    Flame characteristics of ceiling jet flow driven by strong plume in bifurcation tunnels
    LI Zhisheng, GAO Yunji, LI Xiaosong, ZHANG Yuchun, MAO Pengfei
    2020, 30(6):  166-171.  doi:10.16265/j.cnki.issn1003-3033.2020.06.024
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    In order to explore transverse and longitudinal length and flame area distribution features of ceiling jet flow driven by strong plume in a bifurcation tunnel, 5 groups of fire locations (0.1, 0.3, 0.5, 0.7 and 0.9 m) and 4 HRR (47.9, 63.8, 77.7 and 95.7 kW) were selected. Transverse lengths of intermittent flame and transverse continuous flame for typical working conditions were calculated and corresponding critical temperature values were determined, which were 325 and 620 ℃ respectively. Based on critical values of continuous flame, its transverse and longitudinal flame length as well as flame area were obtained. The results show that there is a non-monotonic trend for transverse flame length as distance from fire source to sidewall increases from 0.1 m to 0.7 m, and it will reach maximum value at 0.3 m. Nevertheless, longitudinal length continuously decreases as distance rises from 0.1 m to 0.9 m, and it is always larger than transverse length under same conditions. Flame area increases first with spacing grows from 0.1 m to 0.3 m and then decreases as it continuously increases to 0.7 m.
    Emergency technology and management
    Evaluation method for plateau airports' emergency support capacity
    DENG Wei, XIA Zhenghong
    2020, 30(6):  172-177.  doi:10.16265/j.cnki.issn1003-3033.2020.06.025
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    In order to address lack of a scientific quantitative evaluation method for plateau airports' emergency support capacity, firstly, content and features of these capabilities were studied, and operation characteristics of plateau airports and current situation of their emergency support were analyzed. Then, an evaluation index system was proposed which took into consideration emergency preparedness, emergency monitoring and warning, emergency response and rescue, recovery and construction afterwards. And a comprehensive evaluation model based on AHP and multilevel matter element extension was established. Finally, by using this model, emergency rescue support capacity of one plateau airport in southwest China was evaluated based on its actual operation data. The results show that this airport has "high" emergency support capability, and among all secondary indicators, only "recovery and construction afterwards" is rated as "general". Such evaluation results are basically consistent with conclusions of its annual work report on emergency management, which verifies rationality of the proposed evaluation index system and model.
    Occupational health
    Stress and fatigue characteristics of neck muscles in lateral flexion posture in confined space
    ZHANG Yihong, JIN Longzhe, XU Mingwei, WEI Yixuan
    2020, 30(6):  178-184.  doi:10.16265/j.cnki.issn1003-3033.2020.06.026
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    In order to reduce incidence of occupational muscular disorders since musculoskeletal injury has become one of the key problems in prevention and control of occupational diseases in China, firstly, a neck musculoskeletal model was established by AnyBody platform, and stress of muscles in lateral flexion position of neck was obtained through reverse dynamics simulation analysis. Then, 8 healthy subjects were selected, electromyographic signals of their sternocleidomastoid and trapezius muscles were collected with sEMG technology, and median frequency (MF) was used as an indicator to assess muscle fatigue based on MF decline rate. Finally, by setting up different temperature and humidity, effects of high temperature and humidity environment in confined space on neck muscle fatigue were investigated. The results show that with the increase of lateral flexion angle, load of neck muscles is increasing gradually, and fatigue rate becomes faster. At the same time, high temperature and humidity working environment will also accelerate fatigue of neck muscles under lateral flexion posture.