Microstructure Features and the Macroscopic Acoustic Behavior of Gassy Silt in the Yellow River Delta

The morphological changes in isolated bubbles in gassy silt play a critical role in the microscopic structures between soil particles and bubbles and macroscopic physical properties.Based on X-ray CT scanning experiments under various vertical loads(four levels),self-designed acoustic macro experiments,and a series of formula revisions to the macro-air-bearing silt sound-velocity prediction model,this paper discusses the macro-and micro-scale features of gassy silts from the Yellow River Delta.The samples consisted of different proportions of silt from the Yellow River Delta and porous media,and they were used to form two types of aerosol silts with initial gas contents of 4.23%and 7.67%.The results show that the air bubble content and external load considerably affect the microstructural parameters and acoustic behavior of gassy silt in the Yellow River Delta.The macroscopic sound velocity showed a linear positive correlation with vertical load and relation to microstructural parameters in varying manners and degrees.Based on the traditional Biot-Stoll acoustic model,the gas-phase medium coefficient was introduced for the proper calculation and prediction of the sound velocity of air-bearing silt.The errors of the overall prediction varied between 5.6%and 9.6%.

Microstructure Characterization of Bubbles in Gassy Soil Based on the Fractal Theory

The microscopic characterization of isolated bubbles in gassy soil plays an important role in the macroscopic physical properties of sediments and is a key factor in the study of geological hazards in gas-bearing strata.Based on the box-counting method and the pore fractal features in porous media,a fractal model of bubble microstructure parameters in gassy soil under different gas con-tents and vertical load conditions is established by using an industrial X-ray CT scanning system.The results show that the fractal di-mension of bubbles in the sample is correlated with the volume fraction of bubbles,and it is also restricted by the vertical load.The three-dimensional fractal dimension of the sample is about 1 larger than the average two-dimensional fractal dimension of all the slices from the same sample.The uniform porous media fractal model is used to test the equivalent diameter,and the results show that the variation of the measured pore diameter ratio is jointly restricted by the volume fraction and the vertical load.In addition,the measured self-similarity interval of the bubble area distribution is tested by the porous media fractal capillary bundle model,and the fitting curve of measured pore area ratio in a small loading range is obtained in this paper.

Experimental and theoretical study on the dynamic effective stress of loaded gassy coal during gas release

In the process of mining coalbed methane(CBM),an unsteady state often arises due to the rapid extraction,release and pressure relief of CBM.In this case,the effective stress of coal changes dynamically,affecting the stability of the gassy coal seam.In this paper,gas release tests of gassy coal under conventional triaxial compression were performed,and the dynamic effective stress(DES)during gas release was obtained indirectly based on a constitutive equation and deformation of coal.The results show that the maximum increases in DES caused by the release of free gas and adsorbed gas under the stress of 1.1 MPa were 0.811 and 5.418 MPa,respectively,which seriously affected the stress state of the coal.During the gas release,the free gas pressure and the adsorbed gas volume were the parameters that directly affected the DES and showed a positive linear relationship with the DES with an intercept of zero.The DES of the coal sample increased exponentially with time,which was determined by the contents of free and adsorbed gas.Based on the experimental results and theoretical analysis,an effective stress model was obtained for loaded gassy coal during gas release.The results of verification indicated accuracy greater than 99%.

Study on Critical,Modern Technology for Mining in Gassy Deep Mines

To achieve safe and highly efficient mining in the gassy, deep mines of the Huainan collieries simultaneous coal and gas extraction, and the corresponding ventilation methods were developed. This includes a set of mining procedures and principles which help insure safe and efficient production. Furthermore, green mining, meaning the comprehensive use of emitted gas, proper treatment of the environment and appropriate mine temperature control, is now standard. The concepts of modem mining and the principles of pressure relief are described. Coal-gas simultaneous ex- traction and multi-pressure relief techniques were developed which require a combination of surface and underground gas extraction. The application of Y-ventilation systems, of roadways retained along goafs, of stress control techniques for highly fragile mine roofs and of powerful, automatic and reliable mining equipment contributes to safe operation of modem deep mines. Operating parameters for these techniques are described and the results of their use discussed.

Numerical simulation and experiment analysis of improving permeability by deep-hole presplitting explosion in high gassy and low permeability coal seam

Created a new damage model for explosive for LS-DYNA3D,taking advantageof the Taylor method aimed at the high gassy and low permeability coal seam,and numericallysimulated and analyzed the deep-hole presplitting explosion.The entire processof explosion was represented,including cracks caused by dynamic pressure,transmissionand vibration superposition of stress waves,as well as cracks growth driven by gas generatedby explosion.The influence of the cracks generated in the process of explosion andthe performance of improving permeability caused by the difference of interval between.explosive holes were analyzed.A reasonable interval between explosive holes of deepholepresplitting explosions in high gassy and low permeability coal seams was proposed,and the resolution of gas drainage in high gassy and low permeability coal seam was putforward.

Numerical simulation research on dynamical variation of permeability of coal around roadway based on gas-solid coupling model for gassy coal

Due to the change of initial stress state caused by roadway excavation, the permeability of the coal body may be changed during the excavation process. In this paper, according to the different stress states, the coal around the roadway was divided into the seepage open zone, seepage orientation zone, seepage decay zone and original seepage zone along the radial direction of the roadway. The loaded gassy coal was treated as a viscoelastic and plastic softened medium, and the mechanical behaviors of the viscoelastic zone, plastic softened zone and broken zone around the roadway were analyzed with the consideration of the loading creep, softening and expansion effect of the gassy coal. According to the law of conservation of mass and the Darcy law, the flow-solid coupled model for the gas transportation of the coal around the roadway was established considering the dynamic evolution of the adsorption characteristics, porosity and permeability of the coal, and the simulation software COMSOL was utilized to numerically simulate the stress state and gas flow regularity around the coal, which provided meaningful reference for investigating the stability of the coal and rock around the roadway.

Experimental study on creep mechanics characteristics of gassy under disturbance conditions

Creep mechanics characteristics of large scale tectonic coal was studied under gas draingae and disturbance conditions by using the new self-developed coal gas cou- pling three axial creep equipment.The results show that when σ_1 is smaller,σ_3 is larger, gas pressure and disturbance load are smaller,gassy coal has no disturbance to creep. When σ_3 is smaller,gas pressure and σ_1 are larger,disturbance load is constant,gassy coal has remarkable effects of disturbance to creep.The concepts of disturbance load sensitive domain and disturbance creep sensitive domain were put forward.Under same amplitude disturbance stress condition,blasting disturbance has a stronger influence on gassy coal deformation is related to frequency of disturbance load;gas drainage,blasting excavation and mining play an important role in coal-gas outbursting.The relationship of gassy coal creep and gas pressure gradient,the creep constitutive equation built with gas pressure gradient and disturbance load as independent variables within the framework of fluid-solid two phases coupling were established.

Evaluation of the Level of Pollution by Heavy Metals of Market Garden Soils along the Chari River in Ndjamena: Case of the 9th and 7th Districts

The main aim of this study was to characterize the metal content of soils used for market gardening along the Chari river: the 7th and 9th districts of NDjaména. To achieve this, two sites were selected: Gassi and Walia, and two control sites (Gassi and Walia). A total of fifty (50) soil samples were taken (24 from the Gassi site, 24 from the Walia site and 2 as control soils) and then analyzed to determine a number of physico-chemical parameters (pH, OM and electrical conductivity) and heavy metal concentrations in the various soils. The TME content (As, Cd, Cu, Cr, Ni, Pb, Hg and Zn) of the soils was determined by plasma-coupled Atomic Emission Spectrometry. In order to assess the level of contamination in Gassi and Walia soils, the geoaccumulation index (GeoIndex), contamination factor and degree of contamination were calculated. Results for physico-chemical parameters revealed that pH ranged from acidic (4.6) to moderately neutral (6.5), electrical conductivity was higher in cultivated soils (mean 292.14 μs/cm) than in control soils (mean 149.33 μs/cm), and soils were rich in organic matter. Overall, heavy metal concentrations in cultivated soils were higher than in control soils. The pollution estimate shows that soils in the area have no moderate contamination. The increase in TME concentrations in cultivated soils is thought to be due to the input of agricultural inputs to the soil. However, these levels are below the Average shale reference and Canadian guidelines for agricultural soil quality. Principal component analysis shows that metals are positively and significantly correlated with each other, and negatively and moderately significantly correlated with each other.

A proposal for mitigation of natural hazards by explosion of gassy lakes in Cameroon, West Africa

THE gas disasters at Lake Nyos in 1986 （1 746 casualties） and Lake Monoun in 1984 （37 casualties）,both in Cameroon, were caused by a sudden release of a large amount of CO2 stored in these lakes. TheCO2 is derived from a magmatic source, judging from the isotopic ratio of δ13C=-3.5±0.2‰ （PDB）and that of helium associated with the CO2, i.e. 3He/4He-8×10-6 or 5.7 Ra where Ra is the 3He/He ratio of the atmospheric helium. Follow-up surveys of Lake Nyos （209 m deep） revealed that thetemperature, concentration of dissolved ionic species （TDS） and free-CO2 generally co-vary and their profiles show a large decrease in the surface layer, limited change at mid depths and a significant increasetowards the lake bottom. This simultaneous increase in temperature, conductivity and free-CO2 in the bottom water supports the view that CO2 is being supplied to the lake in the form of warm, CO2-charged,mineralized water. Our recent observations （1993-1996） indicate that Lake Nyos still contains 12.4 gi-

Heat-fluid-solid coupling model for gas-bearing coal seam and numerical modeling on gas drainage promotion by heat injection

Improving the absorbed gas to active desorption and seepage and delaying gas drainage attenuation are considered as key methods for increasing drainage efficiency and gas output.According to the solid mechanics theory,the nonlinear Darcy seepage theory and thermodynamics,the heat-fluid-solid coupling model for gassy coal has been improved.The numerical model was founded from the improved multi-field coupling model by COMSOL Multiphysics and gas drainage by borehole down the coal seam enhanced by heat injection was modelled.The results show that the heatfluid-solid model with adsorption effects for gassy coal was well simulated by the improved multi-field model.The mechanism of coal seam gas desorption seepage under the combined action of temperature,stress and adsorption can be well described.Gas desorption and seepage can be enhanced by heat injection into coal seams.The gas drainage rate was directly proportional to the temperature of injected heat in the scope of 30-150 ℃ and increasing in the whole modelleddrainage process (0-1000 d).The increased level was maximum in the initial drainage time and decreasing gradually along with drainage time.The increasing ratio of drainage rate was maximum when the temperature raised from 30 to 60 ℃.Although the drainage rate would increase along with increasing temperature,when exceeding 60 ℃,the increasing ratio of drainage rate with rising temperature would decrease.Gas drainage promotion was more effective in coal seams with lower permeability than with higher permeability.The coal seam temperature in a 5 m distance surrounding the heat injection borehole would rise to around 60 ℃ in 3 months.That was much less than the time of gas drainage in the coal mines in sites with low permeability coal seams.Therefore,it is valuable and feasible to inject heat into coal seams to promote gas drainage,and this has strong feasibility for coal seams with low permeability which are widespread in China.

Gas-solid coupling laws for deep high-gas coal seams

A better understanding of gas-solid coupling laws for deep, gassy coal seams is vital for preventing the compound dynamic disasters such as rock burst and gas outburst. In this paper, a gas-solid coupling theoretical model under the influence of ground stress, gas pressure, and mining depth is established and simulated by using COMSOL Multiphysics software. Research results indicate that under the influence of factors such as high ground stress and gas pressure, the mutual coupling interaction between coal and gas is much more significant, which leads to the emergence of new characteristics of gas compound dynamic disasters. Reducing the ground stress concentration in front of the working face can not only minimize the possibility of rock burst accidents, which are mainly caused by ground stress, but also can weaken the role of ground stress as a barrier to gas, thereby decreasing the number of outburst accidents whose dominant factor is gas. The results have a great theoretical and practical significance in terms of accident prevention, enhanced mine safety, disaster prevention system design, and improved accident emergency plans.

煤气镇：时光交错100年

初来到煤气镇是十月份，秋季已至，它好像一个幽雅矜持的女子，安静地诉说着自己的忧愁。

Determination of a potential set of factors which influence the situation of methane emission into roadways being driven

The currently applied methodology of absolute gassiness forecasting in roadways being driven in Polish hard coal mines is based on the results of investigations frombefore more than twenty years. At present the roadways are being driven in majority ofcases in quite different conditions than those which had been the subject of the said investigations. The application of 'old' methods of forecasting of methane emission during driving of roadways often brings about great discrepancies between the results of the forecasts and actual situation. It is firstly necessary to determine a potential set of factorswhich exert an influence on situation regarding methane emission into roadways beingdriven in order to prepare a verified mathematical model of absolute gassiness forecastingOn the basis of available literature and the investigations conducted by the Central MiningInstitute an initial list of factors has been prepared which can have an impact upon methane emission into roadways being driven. The assumptions of heuristic method have beentaken advantage of for selection of parameters and indices describing the phenomenon ofmethane emission. It has been dictated by the fact that the available literature is lacking apretty unambiguous viewpoint on the subject under consideration and at the same time itis necessary to perform an a priori assessment of the information contained in a givenfeature (factor). A prepared initial set has been scrutinized to be verified on the basis of aconducted expert survey among seventy specialists in this field. After collecting of the results of the survey their statistical elaboration was prepared. The co-efficient of agreementof multiple ordering, the so called concordance co-efficient has been taken advantage of inorder to check the competency of experts. The investigations prove that the experts are inagreement in their opinions. The estimation of a collective assessment of all participants ofthe survey was conducted with the use of the rank sum's test by J. Gren, The results ofthe conducted analysis allowed determining a potential set of factors which influence thesituation of methane emission into roadways being driven. This set, after conductance offurther detailed investigations, can constitute a base for elaboration of a function describ-ing methane emission into roadways being driven in hard coal mines.

波尔多列级名庄——露仙歌CH．Rauzon Gassies晚宴

2007年7月13富隆酒业的波尔多列级名庄——露仙歌晚宴在中国大饭店的阿丽雅餐厅举行。当晚的五款不同年份的美酒和美食带给人不少惊喜:头盘的绿色沙拉,咸三文鱼沙拉搭配了2003和2001两个年份的露仙歌,口感顺滑优雅,不失活泼的结构与鲜嫩鱼肉邂逅,回味独特。