Stability of roof structure and its control in steeply inclined coal seams

To improve the effectiveness of control of surrounding rock and the stability of supports on longwall topcoal caving faces in steeply inclined coal seams, the stability of the roof structure and hydraulic supports was studied with physical simulation and theoretical analysis. The results show that roof strata in the vicinity of the tail gate subside extensively with small cutting height, while roof subsidence near the main gate is relatively assuasive. With increase of the mining space, the caving angle of the roof strata above the main gate increases. The characteristics of the vertical and horizontal displacement of the roof strata demonstrate that caved blocks rotate around the lower hinged point of the roof structure, which may lead to sliding instability. Large dip angle of the coal seam makes sliding instability of the roof structure easier.A three-hinged arch can be easily formed above both the tail and main gates in steeply inclined coal seams. With the growth in the dip angle, subsidence of the arch foot formed above the main gate decreases significantly, which reduces the probability of the roof structure becoming unstable as a result of large deformation, while the potential of the roof structure's sliding instability above the tail gate increases dramatically.

Probability and reliability analysis of pillar stability in South Africa

A deterministic approach is frequently used in engineering design. In this quantitative design methodology, a safety factor, which is typically a strength-to-stress ratio, is derived as an index for the stability assessment of the engineering design. In underground coal mining applications such as pillar design,however, the inputs of pillar design are variables. This is widely overlooked in the deterministic approach. A probabilistic approach assessing the probability of failure or reliability of a system might be an alternative to the conventional quantitative methodology. This approach can incorporate the degree of uncertainty and deviations of variables and provide more versatile and reliable results. In this research, the reliability of case histories from stable and failed pillars of South Africa presented by Merwe and Mathey is examed. The updated Salamon and Munro strength formula(S-M formula) and Merwe and Mathey strength formula(M-M formula) are evaluated through a probabilistic approach. It is concluded that stable pillar cases have a reliability value greater than 0.83 while the reliability value of failed pillar cases are slightly larger than 0.50. There seems to be a positive relation between safety factor and reliability. The reliability of a pillar increases with pillar width but decreases with depth of cover, pillar height and entry width. The reliability analysis also confirms that M-M strength formula has a better distinction between the stable and failed pillar cases.

Empirical equations between characteristic impedance and mechanical properties of rocks

Based on a great number of experimental data on various mechanical properties of rock in the literature,six empirical equations between the characteristic impedance(product of density and P-wave velocity)and mechanical properties of rock are proposed.These properties include uniaxial compressive strength,tensile strength,shear strength,mode I fracture toughness,Young’s modulus,and Poisson’s ratio.These empirical equations show that the values of the aforementioned properties increase with increase in characteristic impedance.It also implies that the characteristic impedance of rock may be considered as an index to represent the main properties of rock.In this sense,it is possible to consider using characteristic impedance to classify rock masses for studies in the future.

Distributed Cooperative Mechanism and Application for Monitoring of Urban Subway Construction

In this paper, combining the technologies of Computer Supported Cooperative Work (CSCW), Workflow and Network, the authors aim to organize virtual distributed cooperative work environment (VDCWE) and expound the running mechanism of cooperative workflow and design its algorithm for monitoring of urban subway construction. And then a prototype system was built based on the above, capable of supporting user analyzing, dealing with and managing data of monitoring, and real-timely releasing corresponding information, providing interactive virtual and distributed coordination meet-environment, dynami-cally and transparently, in favor of clients' interoperability and solving practicing problems, and so on.

Ground stability of underground gateroad with 1 km burial depth： A case study from Xingdong coal mine, China

本文采用数值模拟、案例分析、现场试验相结合的综合研究方法分析千米埋深煤矿巷道围岩稳定性。首先,在试验巷道进行了地应力监测与煤岩体力学性能测试;然后,通过FLAC^(3D)数值模拟软件分析了试验巷道围岩位移场、应力场、塑性区与锚杆受力特征。研究结果表明,软岩特性与高地应力是深部巷道失稳的主要因素,高应力引起的剪切滑移破坏是深部巷道围岩的主要破坏模式;不合理的支护方式,特别是锚杆索长度短且预紧力低、缺少高强二次支护、底板无支护等亦是巷道失稳的原因。基于上述研究,提出了集长锚杆索、可缩性环形支架、注浆加固于一体的联合加固措施,并通过现场监测验证了支护方案的合理性。本文研究成果为深入理解千米深井巷道破坏机制提供了借鉴。

Abutment pressure distribution for longwall face mining through abandoned roadways

Abutment pressure distribution is different when a longwall panel is passing through the abandoned gate roads in a damaged coal seam. According to the geological condition of panel E13103 in Cuijiazhai Coal Mine in China, theoretical analysis and finite element numerical simulation were used to determine the front pressure distribution characteristics when the longwall face is 70, 50, 30, 20, 10, and 5 m from the abandoned roadways. The research results show that the influence range of abutment pressure is 40 to 45 m outby the face, and the peak value of front abutment pressure is related to the distance between the face and abandoned roadways. When the distance between the longwall face and abandoned roadways is reduced from 50 to 10 m, the front abutment pressure peak value kept increasing. When the distance is 10 m, it has reached the maximum. The peak value is located in 5 to 6 m outby the faceline. When the distance between the longwall face and abandoned roadways is reduced from 10 to 5 m, the front abutment pressure sharply decreases, the intact coal yields and is even in plastic state. The peak value transfers to the other side of the abandoned roadways. The research results provide a theoretical basis for determining the advance support distance of two roadways in the panel and the reinforcement for face stability when the longwall face is passing through the abandoned roadways.

Flotation Separation on Rare Earth Minerals and Gangues

The flotation process of native rare earth minerals such as bastnasite, monazite, mixed minerals of bastnasite and monazite, using the new effective collector Dh was studied, respectively, and the flotation properties were described. The good qualities of the new collector Dh were revealed through comparing with other collector of rare earth minerals. The test results of different ore samples showed that at moderate pulp pH (8.5～9.5), rare earth minerals could be effectively separated from barium, calcium and silicon bearing intergrowth minerals (barite, calcite and silicate minerals) and high quality rare earth concentrates could be obtained successfully by the new collector Dh, acid silica gel, turpentine and reagents fitting together rationally. In order to determine optimum technical conditions, the effect of pulp pH, pulp temperature, pulp density and the effect of dosage of reagents (Dh and acid silica gel) on the flotation were investigated in the test. Simultaneously, the mechanism of the flotation of rare earth minerals from intergrowth minerals was explored. The infrared spectra for Dh and rare earth cation by analysis in theory showed that Dh formed chelate complex with rare earth cation and were adsorbed on the surfaces of rare earth minerals. The mechanism of the intergrowth minerals depressed by acid silica gel can be explained as gummy colloid hydrolyzed from acid silica gel which were selectively absorbed on the gangue minerals, making them hydrophilic and depressed, with pulp pH value of alkalescent.

Three-dimensional experimental study of loose top-coal drawing law for longwall top-coal caving mining technology

Based on the loose medium flow field theory, the loose top-coal drawing law of longwall top-coal caving（LTCC） mining technology is studied by using self-developed three-dimensional（3D） test device. The loose top-coal drawing test with shields and the controlled test without shields are performed in the condition without any boundary effect. Test results show that shields will cause reduction in drawing volume of coal in the LTCC mining. The deflection phenomenon of drawing body is also observed in the controlled test, which is verified that the deflection of drawing body is caused by shield. It is found that the deflection angle decreases with increasing caving height, with the maximum value of atailand the minimum value of 0. In addition, the formula to calculate the drawing volume is proposed subsequently.The deflection of drawing body is numerically simulated using particle flow code PFC3 Dand the proposed formula to calculate drawing volume in LTCC is also verified.

Application of hot spring gases to the study of active volcanoes in the Changbaishan Mountain region, Northeast China

The authors reviewed the history of geochemistry involved in active volcano monitoring and analyzed the relationship between variations in volcanic gas composition observed at the Changbaishan Volcano Observatory and volcanic activities. It is concluded that both geochemical method and routine gas analysis can provide the information about volcanic activity and earthquake activity, and both of them can play an important role in predicting volcano eruption.

Impact of longwall mining on groundwater above the longwall panel in shallow coal seams

Since longwall mining causes subsidence through the overlying strata to the ground surface, the surface water and groundwater above the longwall panels may be affected and drained into the lower levels.Therefore, loss or interruption of streams and overburden aquifers is a common concern in coal industry.This paper analyzed the potential effects of longwall mining on subsurface water system in shallow coal seam. In order to monitor different water level fluctuations throughout the mining period, three water wells were drilled down to the proposed deformation zone above the longwall panel. A GGU-SS-FLOW3 D model was used to predict water table contours for the periods of pre- and post-mining conditions. The field data from the three water wells were utilized to calibrate the model. The field test and numerical model can help to better understand the dewatering of shallow aquifers and surface waters related to ground subsidence from longwall mining in shallow coal seam.

Pressure-relief effect of coal rock body of long distance lower protective seam mined based on FLAC^(3D)

According to the specific geological condition, analyzed the stress distribution ofthe overlying strata, the displacement of pressure released seam, thickness variation andthe distribution of plastic zones by FLAC^(3D) software to simulate mining of the long-distancelower protective seam.The research results show that the distribution of verticalstress appears as a 'Double-hump' within the pressure-relief range of the protected coalseam and the swelling deformation curve of coal bodies takes an 'M' shape.The swellingis divided into initial swelling, swelling increase and swelling compression stability.Themaximum swelling ratio of the pressure released seam is 1.84%, protection angle of thelower protective coal seam along the strike direction is about 55°, protection angle belowthe dip direction is about 50°, protection angle above the dip direction is about 55°, andthe coal seam compression zone resembles a 'U' shape.

Argillization mechanics of rock from the Xing’anling Group in the Beier depression of the Hailar basin

The reservoir of the Xing'anling Group in the Beier depression of the Hailar basin is loosely cemented with many tuffaceous grains.This causes argillization and collapse of the grain framework of the reservoir sandstones.A detailed study on the characteristics of rocks and minerals was carried out through polarized microscope,X-ray diffraction,X-ray fluorescence,SEM and energy spectrum analysis.The results indicate that the reason for argillization is the abundant pyroclastic,and especially tuffaceous,grains in the reservoir.The alkaline component is relatively high in some strata.These are easily altered to montmorillonite in diagenesis.Na+montmorillonite swells strongly when exposed to water.This is the fundamental reason for the reservoir's argillization and plugging.

高温和酸性环境作用下砂岩的能量演化规律与破坏特征研究

砂岩广泛分布于中国山岭地区,隧道经常修建于山岭砂岩地层中,在隧道施工和运营过程中,隧道围岩容易受到高温和酸性溶液的共同影响。本文通过开展单轴压缩试验和计算机断层扫描试验,研究了高温和酸性溶液作用下砂岩的能量演化规律和破坏特征,分析了不同条件下砂岩的抗压强度、弹性应变能密度、耗散能密度、破坏模式及裂隙分布特征。结果表明,高温和酸性溶液对砂岩的能量分布和破坏模式有显著影响,且在不同阶段对砂岩的破坏模式和裂隙分布特征的影响各有差异,高温对砂岩能量分布和破坏模式的影响比酸性溶液对其影响更为明显;此外,砂岩的弹性应变能及耗散能与破坏特征呈明显的线性关系。本研究可以为复杂高温条件下隧道设计及施工和相关隧道工程的稳定性提供理论依据。

Role of the rhizosphere of a flooding-tolerant herb in promoting mercury methylation in water-level fluctuation zones

The water-level fluctuation zone(WLFZ) has been considered as a hotspot for mercury(Hg) methylation. Flooding-tolerant herbs are gradually acclimated to this water-land ecotone, tending to form substantial root systems for improving erosion resistance. Accompanying rhizosphere microzone plays crucial but unclear roles in methylmercury(Me Hg) formation in the WLFZ. Thus, we conducted this study in the WLFZ of the Three Gorges Reservoir, to explore effects of the rhizosphere of a dominant flooding-tolerant herb(bermudagrass) on Me Hg production. The elevated Hg and Me Hg in rhizosphere soils suggest that the rhizosphere environment provides favorable conditions for Hg accumulation and methylation. The increased bioavailable Hg and microbial activity in the rhizosphere probably serve as important factors driving Me Hg formation in the presence of bermudagrass. Simultaneously, the rhizosphere environments changed the richness, diversity, and distribution of hgc A-containing microorganisms. Here, a typical ironreducing bacterium( Geobacteraceae) has been screened, however, the majority of hgc A genes detected in rhizosphere, near-, and non-rhizosphere soils of the WLFZ were unclassified. Collectively, these results provide new insights into the elevated Me Hg production as related to microbial processes in the rhizosphere of perennial herbs in the WLFZ, with general implications for Hg cycling in other ecosystems with water-level fluctuations.

The Simulation Optimization of Miners’ Unsafe Behavior Control Method

Making optimal safety investment decisions are important for improving worker’s safety level and reducing accident frequency. To study the complex relationship between safety investment and miners’ behavior-based safety, we proposed the index system of the influential factors on miners’ unsafe behaviors and utilized system dynamics(SD) method to construct the analysis model. Based on the empirical research on a mining company in Hunan, miners’ behavior-based safety level under different investment conditions were simulated, then 12 kinds of schemes’ simulation were obtained. Finally,the optimal scheme was achieved. The scheme is: Safety cost per ton of coal is 3.8 dollars, investment proportion is: Organizational management(0.44), safety climate(0.16), working environment(0.08),technological equipment(0.32). This scheme reached the target value of 90 in the 28th month, which was 9 months shorter than that of the original one. The optimized results show that increasing the behavior-based safety investment and adjusting the proportion appropriately, can improve miners’ behavior-based safety level effectively.

Comprehensive analysis on China's National Climate Change Assessment Reports: Action and emphasis

Climate change assessment is central for lowcarbon management practice. This paper investigates China's National Climate Change Assessment Reports of 2007, 2011, and 2015. These three reports are compared with other climate change assessment reports by data mining. The necessity of national climate change assessment is analyzed with the requirements at home and abroad. The latest progress surrounding climate change impacts, adaptation, and mitigation is outlined with the increasing temperature rise in China and the urgency of climate change commitments. The achievements in climate change assessment indicate the increasing climate change vulnerability on sectors and regions in China and the strategies and priorities for low-carbon actions. Distinct gaps and differences are identified in the coverage of industry, regions, and vulnerability assessment between our assessments and other evaluation reports. These gaps and differences demonstrate the importance and future improvements of China's national climate change assessment in international climate governance. The outlook for China's fourth assessment report is proposed.