New technological partition for “three zones” spontaneous coal combustion in goaf

On detailed analysis basis of spontaneous coal combustion for the three zones in mine goaf,we use O2 and CO concentrations to divide the three zones of the coal combustion.Through our experiment,we selected a typical working face and focused on the changes in gas concentrations.In order to overcome establishment limitations of actual layout location and underground conditions in a mine goaf,we based our observations on the three zones,combined them with numerical simulation,described the distribution and the changes in O2 and CO concentrations during the coal spontaneous combustion in the goaf,which provided us with an understanding of the distribution of coal spontaneous combustion in the three zones in the form of maps.Essentially,our study summarizes the changes of O2and CO concentrations in the entire goaf and shows them to be in agreement with our observations at the scene.The study shows that it is feasible to divide the three zones,given our comprehensive targets of O2,CO and our numerical simulation.This method avoids the limitation of dividing the three zones with a single target and the likely errors of observations at the scene.In addition,the method offers a basis for optimizing measures of fre-fghting with important and practical effects.

The numerical simulation and inversion fitting of radon concentration distribution in homogeneous overburden above active fault zones

Based on the convection and diffusion mechanisms of radon migration, in this paper we deduce the two-dimensional differential equation for radon transportation in the overburden above active fault zones with an unlimited extension along the strike. Making use of the finite difference method, the radon concentration distribution in the overburden above active faults is calculated and modeled. The active fault zone parameters, such as the depth and the width of the fault zone, and the value of radon concentration, can be inverted from the measured radon concentration curve. These realize quantitative interpretation for radon concentration anomalies. The inversion results are in good agreement with the actual fault zone parameters.

Numerical simulation to determine the gas explosion risk in longwall goaf areas:A case study of Xutuan Colliery

Underground gassy longwall mining goafs may suffer potential gas explosions during the mining process because of the irregularity of gas emissions in the goaf and poor ventilation of the working face,which are risks difficult to control.In this work,the 3235 working face of the Xutuan Colliery in Suzhou City,China,was researched as a case study.The effects of air quantity and gas emission on the three-dimensional distribution of oxygen and methane concentration in the longwall goaf were studied.Based on the revised Coward’s triangle and linear coupling region formula,the coupled methane-oxygen explosive hazard zones(CEHZs)were drawn.Furthermore,a simple practical index was proposed to quantitatively determine the gas explosion risk in the longwall goaf.The results showed that the CEHZs mainly focus on the intake side where the risk of gas explosion is greatest.The CEHZ is reduced with increasing air quantity.Moreover,the higher the gas emission,the larger the CEHZ,which moves towards the intake side at low goaf heights and shifts to the deeper parts of the goaf at high heights.In addition,the risk of gas explosion is reduced as air quantities increase,but when gas emissions increase to a higher level(greater than 50 m3/min),the volume of the CEHZ does not decrease with the increase of air quantity,and the risk of gas explosion no longer shows a linear downward trend.This study is of significance as it seeks to reduce gas explosion accidents and improve mine production safety.

Research of the electrical anisotropic characteristics of water-conducting fractured zones in coal seams

Water flooding disasters are one of the five natural coal-mining disasters that threaten the lives of coal miners. The main causes of this flooding are water-conducting fractured zones within coal seams. However, when resistivity methods are used to detect water-conducting fractured zones in coal seams, incorrect conclusions can be drawn because of electrical anisotropy within the water-conducting fractured zones. We present, in this paper, a new geo-electrical model based on the geology of water-conducting fractured zones in coal seams. Factors that influence electrical anisotropy were analyzed, including formation water resistivity, porosity, fracture density, and fracture surface roughness, pressure, and dip angle. Numerical simulation was used to evaluate the proposed electrical method. The results demonstrate a closed relationship between the shape of apparent resistivity and the strike and dip of a fracture. Hence, the findings of this paper provide a practical resistivity method for coal-mining production.

Spatial distribution,sources and ecological risk assessment of heavy metals in Shenjia River watershed of the Three Gorges Reservoir Area

Surface soil/sediment samples were collected from the Water-Level Fluctuation Zone(WLFZ), cultivated land and forest land at 50 different grid points from Shenjia watershed, the Three Gorges Reservoir area in August 2013. The spatial distribution, sources and ecological risk assessment for Arsenic(As), Cadmium(Cd),Chromium(Cr), Copper(Cu), Nickel(Ni), Lead(Pb)and Zinc(Zn) were analyzed in this study. The results showed all tested metals had similar distribution patterns except Ni and Cr, with areas of high concentrations distributed in the southwest(WLFZ and watershed outlet) of the study area. Ni and Cr,which were highly positively correlated and present in high concentrations, were primarily distributed in the south and middle zones of the study area. Lower concentration areas of all metals were uniformly distributed west of the high-elevation zones and forest land. Factor analysis(FA) and factor analysismultiple linear regression(FA-MLR) showed that the major sources of Cd were fertilizer and traffic sources,which together accounted for 87% of Cd. As, Zn and Cu levels were primarily supplied by industrial and domestic sources, accounting for 76% of As, 75% of Cu and 67% of Zn. Surface soils/sediments of the study watershed contaminated by Cd represent a high ecological risk, whereas other metals represent low ecological risks. The potential ecological risk index(PERI) analysis indicated that it had a low(widerange) ecological risk and a moderate(small-range)ecological risk primarily distributed in the outlet of the study watershed. Fertilizers and traffic are the primary sources of Cd pollution, which should be more closely controlled for the purposes of water quality and ecological conservation.

CFD simulation of spontaneous coal combustion in irregular patterns of goaf with multiple points of leaking air

Based on the non-linear air leakage seepage equation for an anisotropic porous medium, on the seepage diffusion equation of multicomponent gas and on the seepage synthetic heat transfer equation of a porous medium, the numerical model for field flow problems of irregular patterns of a goaf with multiple points of leaking air is established and simultaneously solved by the upwind mode finite element method (G3 computer program). According to the complexity of irregular patterns of a goaf with multiple points of leaking air, the flow pattern in a large area of such a goaf and the variation in gases of methane, oxygen and CO and in temperature are theoretically described. In the calculation, the goaf is regarded as a caving anisotropic medium and the coupling effect of methane effusion on spontaneous combustion is considered. The simulation results agree well with practical experience. In addition, the spontaneous combustion process is also simulated, indicating that 1) the spontaneous combustion often takes place near the area where fresh air leaks in and 2) the fire sources can be classified into static and dynamic zones. Therefore, in practical fire preventing and extinguishing, we should clearly distinguish the upstream air leaking points from the downstream ones in order to take proper measures for leakage stopping.

Study of 3-D Numerical Simulation for Gas Transfer in the Goaf of the Coal Mining

In order to simulate field distribution rules,mathematical models for 3-D air flows and gas transfer in the goaf of the coal mining are established,based on theories of permeability and dynamic dispersion through porous media. A gas dispersion equation in a 3-D field is calculated by use of numerical method on a weighted upstream multi-element balance. Based on data of an example with a U type ventilation mode,surface charts of air pressure distribution and gas concentration are drawn by Graphtool software. Finally,a comparison between actually measured results in the model test and the numerical simulation results is made to proves the numerical implementation feasible.

Soil nutrients in relation to vertical roots distribution in the riparian zone of Three Gorges Reservoir,China

Since the impoundment of the Three Gorges Reservoir(TGR), the riparian zone has been subjected to numerous environmental changes. This study was conducted to recognize the distribution of grass roots and its impacts on soil nutrients in the water level fluctuation zone of TGR. Roots of four predominant herbaceous plants in the study area, specifically, Cynodon dactylon, Hemarthria altissima, Hemarthria compressa, and Paspalum paspaloides, and their corresponding relation with soil nutrient contents were investigated. Root surface area density was determined with Win RHIZO, and the relationships of root distribution with soil depths and soil nutrient contents were studied. The results indicates that most roots are distributed in the top soil layer of 0-10 cm. Estimated root surface area density for the selected grass species ranges from 0.16 to 13.44 cm^2/cm^3, and decreases exponentially with an increase in soil depth. Soil organic matter and total nitrogen contents are significantly lower on bare control area than the corresponding values on the grasslands. Total nutrient contents on grasslands of C. dactylon and H. compressa are higher than those of other grass areas. Root length density and root surface area density are significantly correlated with soil organic matter and total nitrogen content for the four grasslands. The present results suggests that plant roots have significant effects on the distribution of soil nutrients in soil profiles in the riparian zone along the TGR. Nevertheless, additional investigations are needed to reveal the specific interactions between plant roots distribution, soil nutrients and water level fluctuations.

Effect of droplet characteristics on liquid-phase distribution in spray zone of internal mixing air-mist nozzle

In continuous casting production,droplet characteristics are important parameters for evaluating the nozzle atomization quality,and have a significant impact on the secondary cooling effect and the slab quality.In order to study the behavior of atomized droplets after reaching the slab surface and to optimize the spray cooling effect,the influence of droplet diameter and droplet velocity on the migration behavior of droplets in the secondary cooling zone was analyzed by FLUENT software.Results show that the droplets in the spray zone and on the slab surface are mainly concentrated in the center,thus,the liquid volume fraction in the center is higher than that of either side.As the droplet diameter increases,the region of high liquid volume fraction on the slab surface becomes wider,and the liquid phase distribution in the slab width direction becomes uneven.Although increasing the droplet velocity at the nozzle exit has little effect on droplet diffusion in the spray zone,the distribution becomes more uneven due to more liquid reaches the slab surface per unit time.A prediction formula of the maximum water flow rate on the slab surface for specific droplet characteristics was proposed based on dimensionless analysis and validated by simulated data.A nozzle spacing of 210 mm was recommended under the working conditions in this study,which ensures effective coverage of the spray water over the slab surface and enhances the distribution uniformity of water flow rate in the transverse direction.

Different environmental factors drive tree species diversity along elevation gradients in three climatic zones in Yunnan,southern China

Elevational patterns of tree diversity are well studied worldwide.However,few studies have examined how seedlings respond to elevational gradients and whether their responses vary across climatic zones.In this study,we established three elevational transects in tropical,subtropical and subalpine mountain forests in Yunnan Province,southern China,to examine the responses of tree species and their seedlings to elevational gradients.Within each transect,we calculated species diversity indices and composition of both adult trees and seedlings at different elevations.For both adult trees and seedlings,we found that species diversity decreased with increasing elevation in both tropical and subalpine transects.Species composition showed significant elevational separation within all three transects.Many species had specific elevational preferences,but abundant tree species that occurred at specific elevations tended to have very limited recruitment in the understory.Our results highlight that the major factors that determine elevational distributions of tree species vary across climatic zones.Specifically,we found that the contribution of air temperature to tree species composition increased from tropical to subalpine transects,whereas the contribution of soil moisture decreased across these transects.

Study on Integrated Recurrence Behaviors of Strong Earthquakes Along Entire Active Fault Zones in the Sichuan-Yunnan Region, China

Based on historical earthquake data, we use statistical methods to study integrated recurrence behaviors of strong earthquakes along 7 selected active fault zones in the Sichuan-Yunnan region. The results show that recurrences of strong earthquakes in the 7 fault zones display near-random, random and clustering behaviors. The recurrence processes are never quasi-periodic, and are neither strength-time nor time-strength dependent. The more independent segments for strong earthquake rupturing a fault zone has, the more complicated the corresponding recurrence process is. And relatively active periods and quiescent periods for earthquake activity occur alternatively. Within the active periods, the distribution of recurrence time intervals between earthquakes has relatively large discretion, and can be modelled well by a Weibull distribution. The time distribution of the quiescent periods has relatively small discretion, and can be approximately described by some distributions as the normal. Both the durations of the active periods and the numbers of strong earthquakes within the active periods vary obviously cycle by cycle, leading to the relatively active periods having never repeated quasi-periodically. Therefore, the probabilistic assessment for middle- and long-term seismic hazard for entireties of active fault zones based on data of historical strong earthquakes on the fault zones still faces difficulty.

Species Distribution, Diversity, and Abundance of Sea Cucumbers in Tropical Intertidal Zones of Aurora, Philippines

The distribution, diversity, and abundance of sea cucumbers in intertidal zones of Aurora were studied from February to June 2013 to obtain baseline data. A one-hour timed-search survey covering an approximate one kilometer over a ten-meter wide area was conducted in six coastal municipalities to obtain a comprehensive list of sea cucumber species found in the zones. Only four sampling stations (Baler, Dipaculao, Dilasag, and Dingalan) were selected for belt transect survey, 50 × 50 m, based on the availability of coralline, sandy, muddy sand, and rocky habitats which were laid perpendicular and parallel to each intertidal zone. Timed-search survey revealed a total of 15 species of sea cucumbers distributed among two Orders (Order Aspidochirotida and Order Apodida) and four Families (Family Holothuriidae, Family Stichopodidae, Family Synaptidae, and Family Chirotidae) were recorded. Synapta maculata is most common and has widespread distribution. Belt-tranect surveys showed Holothuria leucospilota is among the most frequently occurring species both during day time (58%) and night time (75%). The Dilasag sampling station had the most diverse species (0.71) while the Dipaculao sampling station had the densest species of Holothuria leucospilota (10,014 in∙ha−1) and abundant (95.91%) species.

Assessment of the Relationship between ESR Signal Intensity and Grain Size Distribution in Shear Zones within the Atotsugawa Fault System, Central Japan

For the first time, a relationship between ESR signal intensity and grain size distribution (sieve technique) in shear zones within the Atotsugawa fault system have been investigated using fault core rocks. The grain size distributions were estimated using the sieve technique and microscopic observations. Stacks of sieves with openings that decrease consecutively in the order of 4.75 mm, 1.18 mm, 600 μm, 300 μm, 150 μm and 75 μm were chosen for this study. Grain size distributions analysis revealed that samples further from the slip plane have larger d50 (average gain size) (0.45 mm at a distance of 30 - 50 mm from the slip plane) while those close to the slip plane have smaller d50 values (0.19 mm at a distance of 0 - 10 mm from the slip plane). This is due to intensive crushing that is always associated with large displacement during fault activities. However, this pattern was not respected in all shear zones in that, larger d50 values were instead observed in samples close to the slip plane due to admixture of fault rocks from different fault activities. Results from ESR analysis revealed that the relatively finer samples close to the slip plane have low ESR signals intensity while those further away (coarser) have relatively higher signal intensity. This tendency however, is not consistence in some of the shear zones due to a complex network of anatomizing faults. The variation in grain size distribution within some of the shear zones implies that, a series of fault events have taken place in the past thus underscoring the need for further investigation of the possibility of reoccurrence of faults.

Distribution pattern of rare plants along riparian zone in Shennongjia Area

Due to the importance of riparian zone in maintaining and protecting regional biodiversity, increasingly more ecologists paid their attentions to riparian zone and had been aware of the important effects of riparian zone in basic study and practical management. In this study, 42 sampling belts (10 m?00 m) parallel to the bank of Xiangxi River at different elevations in Shennongjia Area were selected to investigate the riparian vegetation and rare plants. 14 species of rare plants were found distributing in riparian zone, accounting for 42.4% of the total rare plant species in Shennongjia Area. The main distribution range of the 14 rare plant species was the evergreen and deciduous mixed broadleaved forest at elevation of 1200-1800 m, where, species diversity of plant community was the maximum at the moderate elevation. The analysis of TWINSPAN divided the 14 rare species into 3 groups against the elevation, namely low elevation species group, moderate elevation species group, and high elevation species group. The analysis of DCA ordination showed similar results to that of TWINSPAN. In the paper, the authors discussed the reasons forming the distribution pattern of rare plant species, and pointed out that the important function of riparian zone on rare plant species protection.

Quantitative Analysis and Affecting Factors of the Overlapping Degree of Interfacial Transition Zone between Neighboring Aggregates in Concrete

Based on the nearest surface function formula, a quantitative formula to measure the overlapping degree between the interfacial transition zone （ITZ） of neighboring aggregate particles was put forward. The formula was further deduced to quantitatively analyze the influence of the volume fraction of aggregate, ITZ thickness and the maximum aggregate diameter on the overlapping degree between neighboring ITZ. The volume of ITZ was quantitatively calculated in actual concrete by comparing the nearest surface function formula with an approximate method, that is the surface area of the aggregates multiplied by the uniform thickness of the ITZ layers. The results showed that the influencing order of these three factors on the overlapping degree between neighboring ITZ in turn was the interface thickness, aggregate volume fraction and the maximum aggregate diameter; As long as the interface thickness 50 μm and the aggregate volume fraction 50%, the calculated error between two methods mentioned above is about 10 %.

Assessment and analysis of strata movement with special reference to rock burst mechanism in island longwall panel

This study presents a novel approach using theoretical analysis to assess the risk of rock burst of an island longwall panel that accounts for the coupled behavior of stress distribution and overlying strata movement. The height of destressed zone(HDZ) above the mined panel was first determined based on the strain energy balance in an underground coal mining area. HDZ plays a vital role in accurately determining the amount of different loads being transferred towards the front abutment and panel sides. Subsequently, based on the load transfer mechanisms, a series of formulae were derived for the average static and dynamic stresses in the island pillar through theoretical analysis. Finally, the model was applied to determining the side abutment stress distribution of LW 3112 in the Chaoyang Coal Mine and the results of ground subsidence monitoring were used to verify the predicted model. It can be concluded that the proposed computational model can be successfully applied to determining the safety of mining in island longwall panels.

Plastic zone distribution laws and its types of surrounding rock in large-span roadway

In order to study the distribution laws and types of plastic zone of surrounding rock in large-span roadway, we analyzed the distribution laws with different spans and lateral pressures using FLAC3D numerical calcu- lation software. Based on the roadway support difficulty and distribution laws of the plastic zone of sur- rounding rock, we defined the large-span roadway and classified the types of large-span rectangular roadways. As a result, the distribution laws of the plastic zone on surrounding rock in a rectangular roadway with different spans and lateral pressures were obtained. The results show that the area of the plastic zone on surrounding rock increased with the increase of the spans and lateral pressures, and the plastic zone was symmetrical to the center line of roadway. At λ=0.5, 1.0, 1.5, and 2.0, the plastic zone presented ＂addle- shape＂ distribution, ＂ellipse＂ distribution, ＂thin and high＂ distribution and ＂inverse trapezium＂ distribu- tion, respectively. In addition, we classified the roadways into four types according to the different lateral pressures and spans, including small-span, moderate-span, large-span and extreme-large-span roadways.

2022年门源M_(S)6.9地震的同震滑动分布:联合InSAR、GPS和地表位错的贝叶斯建模

2022年1月8日青海省门源M_(S)6.9地震发生于托莱山断裂东段和冷龙岭断裂西段的交汇部位,其运动学特征关系到青藏高原北缘的动力学行为,同时也是区域地震危险性评估中的基础数据.本研究针对该地震,综合InSAR和GPS观测的同震位移场,以及野外地质调查的同震位错数据,采用贝叶斯反演方法,构建同震滑动分布,断层模型采用三角网格更好地刻画断层的不规则几何形态.结果显示,本次左旋走滑型地震的主要滑动发生在冷龙岭断裂西段,深度范围约2~6 km,计算的地震矩为0.95×10^(19)N·m,对应矩震级M_(W)6.65.利用多数据的联合反演解析出,沿走向存在两个滑动集中区,东侧的最大滑动达约4.8 m.震间亏损能量和库仑应力分析表明,托莱山断裂和冷龙岭断裂仍存在未来发震潜能;该地震造成的应力变化,对长期地震空区金强河—毛毛山段落有加载作用,因此,该段未来地震危险性值得关注.

Water quality and eutrophication in the Guangzhou Sea Zone of the Pearl River estuary

To gain a better understanding of water quality and eutrophication, we investigated the seasonal and spatial distribution of water quality at 17 stations in the Guangzhou Sea Zone （GZSZ）. Nutrients, chlorophyll-a （Chl-a）, salinity, chemical parameters were determined in February, May, oxygen demand, and other physical and chemical August and October from 2005 to 2007. The concentrations showed ranges of 93.2-530.4 μmol/L for dissolved inorganic nitrogen （DIN）, 0.62-3.16 μmol/L for phosphate （PO4-P） and 50-127 μmol/L for silicate （SiO3-Si）, The results indicated that DIN was strongly influenced by domestic sewage coming from Guangzhou City and NO3-N was the main form of DIN in most areas, while concentrations of phosphate and silicate were generally controlled by Pearl River runoff, land-based sources along the land or islands, and algae assimilation. N/P ratios were very high in both dry season and wet season, and varied from 57 to 667, suggesting that P was potentially the most limiting nutrient in the GZSZ. The concentrations of Chl-a were 3-96 μg/L, and were highly correlated with the distribution characteristics of COD, The concentrations of nutrients have increased over the past two decades （1982-2007）. This means it is necessary to control the input of nutrients to the GZSZ, especially that of phosphate.

Landslide distribution and sliding mode control along the Anninghe fault zone at the eastern edge of the Tibetan Plateau

Tibetan Plateau is known as the roof of the world.Due to the continuous uplift of the Tibetan Plateau,many active fault zones are present.These active fault zones such as the Anninghe fault zone have a significant influence on the formation of special geomorphology and the distribution of geological hazards at the eastern edge of the Tibetan Plateau.The Anninghe fault zone is a key part of the Y-shaped fault pattern in the Sichuan-Yunnan block of China.In this paper,high-resolution topographic data,multitemporal remote sensing images,numerical calculations,seismic records,and comprehensive field investigations were employed to study the landslide distribution along the active part of the Anninghe.The influence of active faults on the lithology,rock mass structures and slope stress fields were also studied.The results show that the faults within the Anninghe fault zone have damaged the structure and integrity of the slope rock mass,reduced the mechanical strength of the rock mass and controlled the slope failure modes.The faults have also controlled the stress field,the distribution of the plastic strain zone and the maximum shear strain zone of the slope,thus have promoted the formation and evolution of landslides.We find that the studied landslides are linearly distributed along the Anninghe fault zone,and more than 80%of these landslides are within 2–3 km of the fault rupture zone.Moreover,the Anninghe fault zone provides abundant substance for landslides or debris flows.This paper presents four types of sliding mode control of the Anninghe fault zone,e.g.,constituting the whole landslide body,controlling the lateral boundary of the landslide,controlling the crown of the landslide,and constituting the toe of the landslide.The results presented merit close attention as a valuable reference source for local infrastructure planning and engineering projects.