China Safety Science Journal

Research on change rule of human physiological parameters under risk-taking behaviour

LI Xiangchun, WANG Huan, ZHANG Pei, LYU Jinbao, CHEN Zeyu, LI Qin

2019, 29(11): 1-7. doi:10.16265/j.cnki.issn1003-3033.2019.11.001

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In order to explore the workers' risk-taking behavior and reduce the occurrence of falling accidents, a high platform used for simulating working at height was built in the laboratory. Then the physiological indexes including skin temperature, EDA, respiration and pulse were collected by the software ErgoLAB. Finally, SPSS software was used for correlation analysis to find out changes of data before and after the risk-taking behavior and to clarify changed characteristics of these physiological parameters. The results show that when the risk-taking behavior occurs, subjects' skin conductivity level increases significantly, the change of heart rate rhythm accelerates observably with time, the dispersion degree of respiratory frequency decreases, and skin temperature rises slightly while its degree of deviation from the mean value decreases significantly, and that all the changes of physiological parameters are independent of gender.

Collision risk of parallel approach in yaw based on event model

WANG Lili, LU Shengnan

2019, 29(11): 8-13. doi:10.16265/j.cnki.issn1003-3033.2019.11.002

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In order to study influence of yaw angle on collision risks between two aircraft in parallel approach yaw, a collision risk model of parallel approach in yaw was established by using Event model and probability theory. Then by analyzing transformation of the model's collision box, variation law of extended collision box section with time t and yaw angle α was obtained. In the meantime, collision probability ratio R was introduced in order to deduce formula for risk calculation, and it was defined as the ratio of transformed collision box volume to that of original model. Finally, risk analysis was conducted with parallel approach yaw of runways outside Beijing Capital Airport as an example. The calculation results show that with given aircraft size and runway interval, collision risk will grow as yaw angle increases in the range of [0,90 °]. It can only meet safety target when yaw angle is smaller than 32 °.

Research on coal permeability model considering proppant embedding

LI Bobo, LI Jianhua, YANG Kang, REN Chonghong, XU Jiang

2019, 29(11): 14-19. doi:10.16265/j.cnki.issn1003-3033.2019.11.003

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In order to study permeability evolution mechanism under coupling effects of proppant and stress during coalbed methane extraction process, a coal adsorption deformation equation was established by using adsorption theory. Then, a permeability model considering proppant and stress was further constructed and verified through test data. The results show that coal adsorption and pore pressure is positively correlated and adsorption-induced deformation also has the same trend. Permeability of coal embedded in proppant is much greater than that in conventional reservoir, among which monolayer has the best anti-reflection effect. Coal permeability would decrease in form of an exponential function as effective stress increases, but will decrease first and then tend to change gently with the increase of pore pressure. Measured values are basically consistent with calculated values of an improved theoretical model as it is used to fit the curve.

Study on influence of indicator dimensionless on classification model of coal's bursting liability

WANG Chao, LI Yuefeng, ZHANG Chengliang, LIU Lei, HUANG Xuchao

2019, 29(11): 20-25. doi:10.16265/j.cnki.issn1003-3033.2019.11.004

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In order to evaluate the intensity level of the coal's bursting liability and to solve the difficult problem that fuzzy comprehensive evaluation method cannot distinguish the bursting liability of 8 kinds of coal samples, the Bayes discriminant analysis method was introduced for classification of coal's bursting liability. Firstly, the duration of dynamic fracture, elastic energy index, bursting energy index and uniaxial compressive strength were selected as classification indicators. Then the Bayes discriminant model was established by taking 110 groups of data of bursting liability as training samples. Finally, four dimensionless methods were used to process the original data of the evaluation index, and the corresponding discriminant model was established. The influence of dimensionless methods on the discriminant accuracy of Bayes model was also studied. The results show that the Bayes model based on normalized method has the highest accuracy, reaching 98.2%, that the classification results of 10 different engineering samples by Bayes model are in good agreement with actual situation, and that the proposed model can avoid the influence of indicator correlation on classification results of coal's bursting liability.

Prediction model of spontaneous combustion risk of extraction drilling based on improved CRITIC modified G2-TOPSIS method and its application

WANG Wei, JIA Baoshan, QI Yun

2019, 29(11): 26-31. doi:10.16265/j.cnki.issn1003-3033.2019.11.005

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Considering it is difficult to determine index weight in evaluation model of spontaneous combustion risk of gas extraction drilling, an improved G2 weighting method based on CRITIC was proposed. Firstly, Euclidean distance function was introduced to establish an optimal decision-making model and CRITIC's "differential-driven" type weighting method was used to modify "function-driven" G2 weighting method. Secondly, comprehensive weight of each index was obtained, and primary and secondary relationship of risk factors that influence drilling spontaneous combustion was evaluated. Then G2-TOPSIS extraction drilling self-ignition risk assessment model was constructed based on TOPSIS "driving function" G2 weighting method, degree of closeness was analyzed, and risk level was predicted. Finally, this model was applied to gas extraction drilling of 1303 working face in Jinniu Coal Mine. The results show that temperature difference of coal oxidation-reduction ignition point was the dominant factor for extraction drilling spontaneous combustion which is rated as Class III, and prediction results of this model are consistent with actual situation.

Thermal runaway characteristics and mechanism of nitric acid-styrene hybrid system

ZHU Yunfeng, QIAN Ya'nan, XU Wei, JIANG Juncheng, SHI Ning, WANG Zhirong

2019, 29(11): 32-38. doi:10.16265/j.cnki.issn1003-3033.2019.11.006

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Nitric acid oxidation is the key technology for the decolorization and refining of crude styrene. In order to investigate the thermal stability, adiabatic runaway characteristics, thermal runaway dynamics and runaway initiation mechanism of the reaction system, C600 thermal scanner, VSP2 adiabatic calorimeter, ReactIR in-situ FTIR spectrometer, combined with ReaxFF molecular dynamics simulation method were used to carry out experiments. The results show that θ₀ of styrene self-polymerization runaway is 132 ℃, the Δθ_ad is 209 ℃, the P_max is 1.2 MPa, the Ea is 131.3 kJ/mol, and the reaciton order is 3.6. The runaway process containing nitric acid is divided into two stages. The first stage is the styrene side chain oxidation reaction, and the θ₀ is 51 ℃, the Δθ_ad is 70 ℃, the Ea is 71.3 kJ/mol, and the reaciton order is 0.3. The second stage is styrene self-polymerization runaway, and the θ₀ is 131 ℃, Δθ_ad is 152 ℃, and P_maxis 2.1 MPa. In the industrial production process, it is necessary to strictly control the proportion of nitric acid in decolorization reaction, lower the reaction temperature, and prevent side reactions such as nitrification and oxidation.

Study on utilization efficiency and control of water mist in flame plume areas

HE Mingli, ZHANG Guang, HU Shaohua, LIU Yan

2019, 29(11): 39-44. doi:10.16265/j.cnki.issn1003-3033.2019.11.007

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In order to improve fire extinguishing efficiency of water mist, its cooling effect on flame is studied. Firstly, a motion, heat and mass transfer model of water mist in flame areas were established which was utilized to evaluate factors that affected its penetration distance and vaporization performance comprehensively. Then, a method to reasonably identify initial size and velocity of droplets and a co-flow jet water mist system which could improve utilization efficiency were proposed.The results show that those factors rank according to their influence degree from high to low is initial size of droplets, heat transfer temperature difference, initial velocity of droplets, flame plume velocity. Penetration distance and vaporization rate of water mist can be significantly improved by this system.

Numerical simulation study on influence of plank wall on fire spread in ancient building

LI Xianbin, PU Fan, ZOU Li, GAO Guoping, CONG Beihua

2019, 29(11): 45-50. doi:10.16265/j.cnki.issn1003-3033.2019.11.008

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Ancient timber buildings have special fire characteristics. In order to put forward feasible fire prevention and control measures, the influence law of the specific structure plank wall on the fire spread was researched. A specific fire in the main hall of Jing'an temple in Shanghai was simulated using Fire Dynamics Simulator(FDS) to obtain the influence of plank wall with different structures on the fire spreading. The results show that the plank wall acts as the main channel for longitudinal propagation of the flame, and the flame longitudinal propagation time increases and flashover delays with the increasing of upper opening size, that the upper opening can accelerate the fire smoke horizontal spreading speed, that different opening sizes have little influence on the settling velocity of smoke layer behind the main hall, and that the condition without opening increases the time that the smoke layer height falling to 4 m by 20 s.

Experimental study on inhibition of lithium ion battery combustion by inert gas combined with water mist

ZHUANG Weiqiang, ZHU Shunbing, LI Xun

2019, 29(11): 51-57. doi:10.16265/j.cnki.issn1003-3033.2019.11.009

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In order to study characteristics of lithium ion batteries during thermal runaway process, inert gas was added on the basis of water mist to carry out fire suppression test of lithium ion batteries. Lithium iron phosphate batteries with charge states of 0%, 50% and 100% were selected to conduct thermal runaway research in air, N₂ and CO₂ gas environments respectively. On the basis of the research on thermal runaway of lithium ion battery, the fire extinguishing test of lithium ion battery was carried out by using water spray device, and the thermal runaway process, temperature change, fire extinguishing time and other parameters were compared and analyzed. The results show that the thermal runaway of lithium ion battery goes through stages of burst valve, initial fire, stable combustion, flame attenuation, flame extinction and flame reignition, that both N₂ and CO₂ can reduce the combustion temperature and explosion intensity of lithium ion battery, and that CO₂ and pure water mist can inhibit the combustion of lithium ion battery better than N₂ and pure water mist, which proves the synergistic inhibition effect of inert gas and water mist on lithium ion battery fire.

Study on influence of fire extinguishing agents and pressure on performance of fire extinguishing pipe system

YANG Weikai, CONG Xiaomin, ZHAO Linshuang

2019, 29(11): 58-63. doi:10.16265/j.cnki.issn1003-3033.2019.11.010

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A temperature sensitive self-starting fire extinguishing pipe system with no power supply was designed for closed space fire accident of electric vehicle battery box. The fire source was simulated using n-heptane. The test was carried out in a test chamber using perfluorohexanone and hexafluoropropane as the extinguishing medium. The fire extinguishing process, pressure change in the pipe, use rate of fire extinguishing agent and fire extinguishing time were analyzed under the pressure of 0, 0.88 and 1.81 MPa. The results show that the fire extinguishing process of perfluorohexanone and hexafluoropropane fire pipe systems is similar, which can be divided into three stages: preheating-pipe rupture jet-flame extinguishing and continued jetting, that the actual use rate of extinguishing agent for hexafluoropropane fire extinguishing pipe system is 100%, that the actual use rate of perfluorohexanone fire extinguishing pipe system is between 50% and 95%, and the increase of pressure greatly increases the actual use rate of perfluorohexanone, that the hexafluoropropane fire extinguishing pipe system can extinguish the fire within 20 s, and that the fire extinguishing time of the perfluorohexanone fire extinguishing pipe system is longer than that of hexafluoropropane fire extinguishing pipe system.

Study on characteristics of multi-direction coupling flame spread and combustion after central ignition of inclined XPS sheets

DA Liangjun, XIE Qiyuan, LUO Shengfeng

2019, 29(11): 64-70. doi:10.16265/j.cnki.issn1003-3033.2019.11.011

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For the sake of studying development characteristics of thermoplastic sheets' flame spread after central ignition, a series of experiments were conducted on square XPS foam sheets at different inclination angles, and correlation between flame spread condition, velocity and the internal temperature was analyzed. The results show that the shrinkage after central ignition causes change of energy received in preheated zone, thus making upward flame spread more difficult along sheets with bigger inclination angle. In addition, when inclination angle is getting greater, velocities of upward flame spread increase, which is also greater than those of downward and horizontal flame spread. Besides, velocities of downward flame spread decrease firstly and then increase while horizontal flame spread velocities are less affected by inclination angle. It is also found that flame spread is sustainable if there is a violent temperature rise after heating. On the contrary, it is easy to extinguish if XPS foam shrinks significantly with a slow temperature rise.

Effects of ammonium polyphosphate on flame propagation characteristics of sugar dust

YUAN Yalong, CHEN Xianfeng, YUAN Bihe, TAN Hai, LIU Xuanya, HUANG Chuyuan

2019, 29(11): 71-76. doi:10.16265/j.cnki.issn1003-3033.2019.11.012

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In order to identify effects of APP on flame combustion characteristics of sugar dust, vertical open square experimental platform of pipe burning was used to study influence of APP with different mass fractions on characteristics, velocity and temperature of flame. Then analysis was made on pyrolysis of sugar dust and its mixture with APP by using thermal analyzer. The results show that flame brightness of sugar dust will gradually decrease as APP mass fraction increases. With an addition of APP of 6% mass fractions, the maximum propagation velocity of flame in pipelines will decrease from 17.3 m/s to 2.8 m/s, its maximum temperature decreases by 46.46% and residual amount of pyrolysis products increases from 0.71% to 16.06%. Flame inhibition effects of APP on powdered sugar include physical inhibition and chemical inhibition with its decomposition reaction absorbing heat from combustion reaction while decomposed products capturing free radicals from it, thus achieving the purpose of inhibiting flame propagation of powdered sugar.

Study on thermal characteristics of coal spontaneous combustion in gas atmosphere by TG-DSC coupling techniques

LOU Hezhuang, JIA Tinggui

2019, 29(11): 77-82. doi:10.16265/j.cnki.issn1003-3033.2019.11.013

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To characterize the thermal characteristics of coal spontaneous combustion in gas atmosphere, the thermal gravimetric analysis and differential scanning calorimetry (TG-DSC) were used to study the process of coal spontaneous combustion under different gas volume fractions. The change of parameters such as characteristic temperature, weight loss and heat release of coal spontaneous combustion under the influence of gas were analyzed. The dynamic parameters of weight gain and combustion stages of coal in gas atmosphere were obtained. The results show that with the increase of gas volume fraction, the weight loss and heat release decrease and the coal-oxygen recombination rate slowes, that the process of coal spontaneous combustion is divided into three stages: evaporation desorption, weight gain and combustion, that activation energy and activation factor increase with the increase of gas volume fraction in the low temperature oxidation stage of coal, but the whole change is not obvious, and that activation energy and activation factor decrease with the increase of gas volume fraction in the combustion stage of coal.

Study on combustion characteristics of lithium iron phosphate battery pack

DENG Kang, ZHANG Ying, XU Bole, MA Chuyuan, NIU Yi

2019, 29(11): 83-88. doi:10.16265/j.cnki.issn1003-3033.2019.11.014

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In order to clarify the fire hazard of lithium batteries, the combustion characteristics parameters of different quantities of lithium-ion batteries, such as cell surface temperature, flame shape, flame temperature, heat release rate, mass loss rate and flammable gas volume fraction, were studied by experiment. The results show that the thermal runaway temperature of lithium iron phosphate battery packis around 200-300 ℃, showing concentrated combustion, and the gas flame temperature can reach 1 100 ℃,that the fire environment of lithium iron phosphate battery pack has multiple spray flames with the increase of the number of batteries, and the peak of heat release rate is closely related to the spray flame, that the maximum mass loss rate of lithium iron phosphate battery pack changes in a power function with the increase of the number of batteries, and that the amount of heat released is proportional to the 1.28 power of the number of batteries.

Influence of new tunnel blasting on vibration characteristics of adjacent existing tunnel

WU Bo, LAN Yangbin, YANG Jianxin, HAN Yalong, PANG Xiaoyu

2019, 29(11): 89-95. doi:10.16265/j.cnki.issn1003-3033.2019.11.015

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In order to ensure safe operation of existing Hangzhou-Shenzhen railway while adjacent tunnels under blasting construction, by using field monitoring and numerical simulation, study was conducted on vibration characteristics and stress distribution law of existing tunnel lining under blasting dynamic load of adjacent new tunnel. Then FLAC^3D was adopted to simulate influence of blast on operating tunnels, safety of blasting scheme adopted in the field was briefly evaluated and corresponding explosion control measures were provided. The results show that during blasting construction of new tunnels, vibration velocity of arch waist of existing tunnel lining is larger than that of arch foot, and radial vibration velocity of arch waist is larger than that of other directions. Lining stress comes to maximum at arch waist of operating tunnels under blasting load and blasting will have an impact on running trains, so footage excavation shall be reduced or construction shall be carried out in periods when trains are not in operation.

Experimental study on minimum ignition temperature and explosion characteristics of micron-sized aluminum powder

CHEN Haiyan, YAO Qingguo, ZHANG Yansong, LIU Hao, ZHANG Xingxu

2019, 29(11): 96-102. doi:10.16265/j.cnki.issn1003-3033.2019.11.016

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In order to better prevent aluminum powder explosion, experimental study was conducted on influence sensitivity of different factors on minimum ignition temperature and explosion characteristics of micron-sized aluminum powder to reveal their influence degree. Minimum ignition temperature and explosion characteristics were tested through a dust cloud minimum ignition temperature test system and a 20L ball explosion device, respectively. The experimental results show that the smaller particles are, the larger specific surface areas will be, and the more likely aluminum powder is to be burned and exploded. The influence sensitivity of three factors on minimum ignition temperature of aluminum dust cloud ranks as particle size>dispersion pressure>concentration after they are analyzed one by one. And the rank of three factors which influence aluminum powder explosion parameters is concluded as particle size > ignition delay time > concentration after analysis on them one by one.

Experimental study on laminar flame speed of H₂/CH₄/air mixtures

SHANG Rongxue, YANG Yue, GAO Junhao, LI Gang

2019, 29(11): 103-108. doi:10.16265/j.cnki.issn1003-3033.2019.11.017

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To obtain the accurate measurement of laminar flame speed of H₂/CH₄/air mixtures, the laminar flame speeds were experimentally studied using Bunsen burner method incorporating two picture techniques of schlieren system and visible natural light system. According to the chemical dynamics mechanism, the laminar flame propagation characteristics of premixed fuel with different hydrogen fractions were simulated and calculated in order to investigate the influence of hydrogen fractions on the laminar premixed flame of H₂/CH₄/air mixtures. The results show that the method-independent laminar flame speeds of H₂/CH₄/air mixtures obtained by schlieren system are more equivalent to the laminar flame speed defined by the theory of combustion, that both the laminar flame speed and adiabatic flame temperature of H₂/CH₄/air mixtures increase with the growth of hydrogen fractions, that the equivalence ratio with the peak flame speed moves to the fuel-rich side by means of addition of hydrogen, and that with the continuous increase of hydrogen fractions, the mole fractions of vital radical H and the formation rate of OH radical rise significantly.

Experimental study on venting characteristics of large-diameter gas pipeline with explosion venting door

LI Ang, SI Junhong, ZHOU Xihua, LI Xuebing

2019, 29(11): 109-115. doi:10.16265/j.cnki.issn1003-3033.2019.11.018

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In order to study the effect of explosion venting door on gas explosion characteristics, explosion experimental system for large diameter gas pipeline was constructed, and the gas explosion tests were carried out under two conditions with and without explosion venting door. The gas explosion characteristic parameters were measured by high speed data acquisition system and industrial personal computer, and the change laws of characteristic parameters and explosion venting effects were analyzed. The results show that under the condition of gas concentration 9.5%, although the maximum pressure of explosion venting door condition is 1.65 times of that under the condition of empty pipe, the time of pressure reaching steady state is reduced, that when the explosion shock wave propagates from the measuring point 1 to point 3, explosion pressure decay rate of explosion venting door condition is 62.5%, while that is only 14.3% under the condition of empty pipe, that the venting door can significantly attenuate explosion pressure, that the attenuation of temperature has nothing to do with explosion venting door, and that the maximum average flame propagation velocity is 136.67 and 113.56 m/s under two conditions.

Impacts of foundation settlement and pseudo-dynamic load on buckling strength of storage tanks

SHI Lei, SHUAI Jian, XU Kui, YANG Wen

2019, 29(11): 116-121. doi:10.16265/j.cnki.issn1003-3033.2019.11.019

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The buckling of tank wall of large-scale oil tank is the elastoplastic instability phenomenon subjected to seismic loading. In order to explore the effect of foundation settlement on the buckling strength of unanchored storage tanks, the buckling behaviors of the tank were analyzed using the finite element computer by means of nonlinear stabilization algorithm. Various items of actual geometrical structure were presented thoroughly in the 3D finite element model(FEM), including concrete ringwall foundation of tank, unanchored bottom with slope, shell tapering from the base to the top, wind girders and supports, top angles, stiffening rings and support plates. Geometric nonlinearity, nonlinear boundary conditions and elastic plastic material of Ramberg-Osgood model were involved simultaneously in simulate course. The impacts of hydrodynamic pressure of liquid in the tank under horizontal seismic forces and the number and amplitude of foundation harmonic settlement on the buckling critical compressive stress were researched. The results show that the tank walls between stiffening rings will are prone to axial buckling by the action of foundation harmonic settlement and hydrodynamic pressure of the liquid, that the deformation of tank shells appears aperiodically, that the foundation harmonic settlement and hydrodynamic pressure of the liquid have a negative influence on tank shell buckling critical load, and that the resistance capacity reduces as the harmonic order number rises under the same settlement.

Wear recognition method for traction wheel groove of elevator based on image processing

XIE Xiaojuan, YANG Ningxiang, CHEN Jianxun, LIN Xiaoming

2019, 29(11): 122-128. doi:10.16265/j.cnki.issn1003-3033.2019.11.020

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In order to improve the inspection efficiency of the elevator traction wheel groove wear, a method based on image processing technology for identifying abnormal wear of elevator traction wheel groove was proposed. The relative discrete feature parameters of the traction wire ropes were extracted to characterize the cumulative abnormal wear of traction wheel groove, and the modified Canny operator was used to denoise and detect edges of the forward and lateral images of traction wire ropes. On this basis, the edges of ropes in the forward and lateral images were extracted by random Hough transform and least squares method. Finally, the abnormal wear degree of the traction wheel groove was calculated according to the number of pixels covered in images of tranction wire ropes. The results show that this proposed method can accurately evaluate the abnormal wear state of the traction wheel groove, and that compared with traditional measurement methods, this method can not only improve the inspection efficiency but also save the test cost.

Experimental study on vibration reduction performance of aerial assembly anti-vibration exoskeleton

WU Xiaodi, WANG Haibo, ZHANG Le, CHEN Yupeng, XUE Chaojun

2019, 29(11): 129-134. doi:10.16265/j.cnki.issn1003-3033.2019.11.021

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In order to evaluate anti-vibration exoskeleton's ability to reduce vibration of aerial assembly power tools, aviation assembly riveting process was simulated and riveting test of its vibration reduction performance was designed. Then a weighted average method was proposed to comprehensively evaluate its performance with mean value of pressure signals and weight coefficient of different postures during riveting period and riveting interval under conditions of wearing or not wearing exoskeleton. The results show that anti-vibration exoskeleton reduces 59.9% of riveting vibration and 50.4% of palm pressure when impacted by riveter for tester 1, and 49.5% and 36.9% respectively for tester 2. Its reduction performance is negatively related with pressure of riveting interval while wearing exoskeleton at 0.01, and it has no correlation with that in case of not wearing exoskeleton and riveting operating posture. It is also found that exoskeleton can reduce vibration of riveter by more than 50% and has an important protective effect on arms of assembly workers.

Corrosion prediction of gathering pipelines in condensate gas field

LUO Zhengshan, SONG Yingying, WANG Xiaowan, BI Aorui

2019, 29(11): 135-140. doi:10.16265/j.cnki.issn1003-3033.2019.11.022

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In order to improve the prediction accuracy of the corrosion rate of condensate gas field gathering pipelines, an internal corrosion prediction model based on GRA and RFR was constructed to analyze the causes of internal corrosion. The GRA was used to select characteristic variables as inputs of RFR, and the internal corrosion rate was used as target factor output. Taking the data of Yakela condensate gas field as an example, the PRF prediction model was verified by comparison with the Back Propagation(BP)neural network and Support Vecor Machine(SVM) prediction model. The results show that the main factors of corrosion in pipelines obtained by GRA are CO₂ volume fraction, Cl^-concentration, pressure, temperature and flow rate, that the root mean square error, average relative error of the RFR prediction model are lower than those of BP neural network and SVM prediction model, and that determination coefficient of RFR prediction model is 96.48%.

Study on constitutive model and influencing factors of plastic zone of rock burst roadway

ZHANG Shuguang, CHEN Lei

2019, 29(11): 141-148. doi:10.16265/j.cnki.issn1003-3033.2019.11.023

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In order to study the dynamic disaster caused by the rock burst to the deep tunnel, the constitutive model and the influencing factors of the plastic region of the rock burst were analyzed based on case study of Fuxin Evergrande Coal Mine. Considering the critical impact stress and the critical impact radius of the damage, the plastic region constitutive model of the rock burst roadway was established based on the elastic-plastic theory, and the model parameters were obtained through the three-axis test. The model was verified by field measured data. The influence of five factors on the critical impact stress and radius was analyzed, including elastic modulus, post-peak drop modulus, cohesion, internal friction angle and support stress. The results show that the critical impact stress is less than the self weight of the rock in the upper part of the tunnel, and the rock burst is easy to occur, which is in line with the actual situation, that the critical impact stress has a minimum value point with the increase of cohesion and internal friction angle, that the critical impact stress is gradually reduced with the increase of the cohesion, but increases with the increase of internal friction angle, that the greater the cohesion is, the greater the probability of rock burst will be, and that there is a monotonic relation between the elastic modulus, the peak-to-drop modulus and the supporting stress with the critical impact stress and the radius.

Inhibitory effect of SDBS and CaCl₂ compound solution on gas desorption of coal

LIN Haifei, TIAN Jiamin, LIU Dan, YAN Min, DING Yang

2019, 29(11): 149-155. doi:10.16265/j.cnki.issn1003-3033.2019.11.024

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In order to study the inhibitory effect of surfactant sodium dodecylbenzene sulfonate (SDBS) and CaCl₂ compound solution on the gas desorption of coal, coal samples from No. 4-5 coal seam in Xinjiang Sulfur Ditch were selected and HCA high pressure adsorption and desorption device was used to determine gas desorption parameters of dry coal sample, pure water, 2.5×10^-2g/mL SDBS, and coal samples soaked in SDBS and CaCl₂ mixed solution. The results show that SDBS and CaCl₂ compound solution can effectively reduce the surface tension of pure water and the contact angle of coal samples, that when the mass concentration of 2.5×10^-2 g/mL SDBS solution and the mass concentration of 2.5×10^-2 g/mL CaCl₂ solution are 1∶3, the surface tension of the solution is reduced to 24.22 mN/m, and the contact angle of coal samples is reduced to 15.175 °, that with the increase of desorption time, the gas desorption amount of coal body gradually increases in the Langmuir relationship and then stabilizes while the gas desorption rate decreases rapidly, and that when the mass concentration of CaCl₂ in mixed solution is 1.875×10^-2g/mL, the maximum gas desorption amount is 0.24 mL/g, the maximum desorption rate is 0.8×10^-2mL/(g·s), and the suppression efficiency is the highest.

Study on coal cracking under liquid nitrogen soaking based on nuclear magnetic resonance and stress analysis

WANG Chunxia, ZHANG Xuebo, LU Fangchao

2019, 29(11): 156-163. doi:10.16265/j.cnki.issn1003-3033.2019.11.025

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In order to study variation law of pore structure of coal under liquid nitrogen soaking, with dry coal as an experimental object, bituminous coal and anthracite were treated under different impacting time respectively. Then, pore variation characteristics of coal before and after liquid nitrogen soaking was analyzed through NMR experiment, and numerical simulation of soaking process was conducted by using COMSOL software before thermal stress was calculated and analyzed on the basis of distribution of coal temperature field. The results indicate that liquid nitrogen soaking has different degrees of damage to pores and fissures of various sizes of coal, and micropore volumes of bituminous coal and anthracite will increase by 86.43% and 20.28%, respectively when they are soaked for 30 minutes. Under liquid nitrogen soaking, low temperature gradually transfers from coal surface of to its inside while thermal stress generated at various points inside coal gradually increases with time until the maximum stress value reaches 9.84 MPa. Generation and change of thermal stress is the main mechanism for permeability increase of dry coal.

Study on causes of string hole in gas extraction cross seam under disturbance of hydraulic reaming

WANG Junming, LIU Qing, BAO Kun

2019, 29(11): 164-170. doi:10.16265/j.cnki.issn1003-3033.2019.11.026

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In order to improve gas drainage efficiency in coal mine by solving the problem of excessive pressure relief of hydraulic reaming and determining reasonable coal expansion amount, firstly, causes of string hole after reaming were revealed and clarified with Hoek-Brown principle. Secondly, fluid structure coupling mathematical model was constructed, and changes of stress and permeability of coal body under porous conditions after reaming and pressure relief were simulated and analyzed through COMSOL simulation software. Finally, occurrence of string-hole under different coal expanding amount was investigated based on field reaming tests. The results show that as coal-expanding quantity increases, radial displacement and deformation of coal near the hole will also increase. And probability of string-hole will grow sharply as permeability of coal around enlarged holes improves greatly when pressure relief is sufficient. It is found that field test results are basically consistent with that of theoretical analysis and simulation, which can provide some reference for implementation of hydraulic reaming technology in mines under similar geological conditions.

Study on control of mining influence by hydraulic fracturing in key strata

FENG Zhanjie, GUO Wenbing

2019, 29(11): 171-176. doi:10.16265/j.cnki.issn1003-3033.2019.11.027

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In order to reduce impact and damage of coal mining on surface structures, with 5304 working face of Sihe Coal Mine, Jincheng Coal Mining as a research object, theoretical analysis and numerical simulation were conducted to analyze control of working face's mining influence by hydraulic fracturing in key strata. Then collapse mode of overburden and surface subsidence laws of key strata before and after hydraulic fracturing were studied, and its control mechanism on surface subsidence was revealed. The results show that after hydraulic fracturing, the movement mode is transformed from bending subsidence to sliding shear drop along fracturing zone. As surface subsidence curve in the hydraulic fracturing zone becomes steep, subsidence value will increase while influence scope of surface mining on fracturing side decreases.

Societal risk analysis for vicinity of product oil pipelines

QI Xianzhi, WANG Xiaolin, XU Xuerui

2019, 29(11): 177-182. doi:10.16265/j.cnki.issn1003-3033.2019.11.028

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For the sake of reasonable planning and control of casualties risk within acceptable limit in vicinity of pipelines, a societal risk calculation model was established in which procedures to calculate potential loss of life and construct F-N curve were illustrated. Secondly, pipeline failure frequency was calculated by using modification of basic frequency. Then occurrence frequency of different types of accidents caused were calculated on the basis of pipeline failure frequency, hazardous consequence calculation and analysis and population statistics through a block -based demographic method. In the end, F-N curve was constructed and potential loss of life was calculated. The results show that risk of personal injuries was caused by medium and rupture leaks due to large release flow and high ignition probability. This model can be applied in societal risk calculation of product oil pipelines and population distribution planning for the vicinity of pipelines.

Effect of time factor on safety risk of chemical leakage in seismic NaTech events

ZHANG Dongni, MENG Yaobin, MA Haiguan, WU Ganlin, YE Wan

2019, 29(11): 183-188. doi:10.16265/j.cnki.issn1003-3033.2019.11.029

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This paper was aimed at making up for China' lack of research on the NaTech disasters caused by natural disasters, especially the lack of quantitative assessment of the safety and health risks to the public resulting from the release and wide spread of toxic and hazardous chemicals associated with such accidents. Taking the damage and leakage of PX storage tanks under earthquake in a coastal chemical industry park in China as the case study, the process of PX leakage and diffusion was simulated according to the disaster chain method, and the resulting public safety and health risks were evaluated quantitatively. The results show that the mass concentration of PX diffusion has certain spatial distribution characteristics and is dependent on the seasons and time when earthquakes often occur, and that TIBL should be considered in the risk assessment of Natech in coastal areas, in order not to underestimate the risk.

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