A strategy for rock/coal outburst prevention

The current practice of rock/coal outburst monitoring, prevention and control was reviewed. The uncertainty of major factors contributing to the occurrence of such hazards and the complexicity of mining conditions surrounding the occurrence were analyzed. A strategic concept for rock/coal outburst prevention was introduced. The objective is to identify the bursting potential in an area, rather than predicting the bursting, by introducing a multi- dimension index model： potential-of-bursting （POB）, taking into consideration major contributing factors. In application, once the index has passed certain critical level indicating high risk, actions must be taken to reduce the bursting potential and to effectively prevent the hazard from occurring. A conceptual 2D model involving stress and methane pressure was described to demonstrate the methodology for determining the POB. However in practice, a POB model has to be established through experiments, field monitoring and calibration against case studies. To achieve this objective, coordinated research and international collaboration will be needed.

Surrounding Rock Failure Mechanism and Control Technology of Gob-Side Entry with Triangle Coal Pillar at Island Longwall Panel in 15 m Extra-Thick Coal Seams

Taking the return air roadway of Tashan 8204 isolated island working face as the background, the evolution law of the stress field in the surrounding rock of the widened coal pillar area roadway during the mining period of the isolated island working face is obtained through numerical simulation. The hazardous area of strong mine pressure under different coal pillar widths is determined. Through simulation, it is known that when the width of the coal pillar is less than 20 m, there is large bearing capacity on the coal side of the roadway entity. The force on the side of the coal pillar is relatively small. When the width of the coal pillar ranges from 25 m to 45 m, the vertical stress on the roadway and surrounding areas is relatively high. Pressure relief measures need to be taken during mining to reduce surrounding rock stress. When the width of the coal pillar is greater than 45 m, the peak stress of the coal pillar is located in the deep part of the surrounding rock, but it still has a certain impact on the roadway. It is necessary to take pressure relief measures to transfer the stress to a deeper depth to ensure the stability of the triangular coal pillar during the safe mining period of the working face. This provides guidance for ensuring the stability of the triangular coal pillar during the safe mining period of the working face.

Failure behavior of a rock-coal-rock combined body with a weak coal interlayer

Using an MTS 815 testing machine,the deformation and failure behavior of a rock-coal-rock combined body containing a weak coal interlayer has been investigated and described in this paper.Uniaxial loading leads to the appearance of mixed cracks in the coal body which induce instability and lead to bursts in coal.If the mixed crack propagates at a sufficiently high speed to carry enough energy to damage the roof rock,then coal and rock bursts may occur-this is the main mechanism whereby coal bumps or coal and rock bursts occur after excavation unloading.With increasing confining pressure,the failure strength of a rock-coal-rock combined body gradually increases,and the failure mechanism of the coal interlayer also changes,from mixed crack damage under low confining pressures,to parallel crack damage under medium confining pressures,and finally to single shear crack damage or integral mixed section damage under high confining pressures.In general,it is shown that a weak coal interlayer changes the form of overall coal damage in a rock-coal-rock combined body and reduces the overall stability of a coal body.Therefore,the whole failure behavior of a rock-coal-rock combined body in large cutting height working faces is controlled by these mechanisms.

STUDY ON THE COAL-ROCK INTERFACE RECOGNITION METHOD BASED ON MULTI-SENSOR DATA FUSION TECHNIQUE

The coal-rock interface recognition method based on multi-sensor data fusiontechnique is put forward because of the localization of single type sensor recognition method. Themeasuring theory based on multi-sensor data fusion technique is analyzed, and hereby the testplatform of recognition system is manufactured. The advantage of data fusion with the fuzzy neuralnetwork (FNN) technique has been probed. The two-level FNN is constructed and data fusion is carriedout. The experiments show that in various conditions the method can always acquire a much higherrecognition rate than normal ones.

Effects of water intrusion and loading rate on mechanical properties of and crack propagation in coal–rock combinations

Tackling the problems of underground water storage in collieries in arid regions requires knowledge of the effect of water intrusion and loading rate on the mechanical properties of and crack development in coal–rock combinations. Fifty-four coal–rock combinations were prepared and split equally into groups containing different moisture contents(dry, natural moisture and saturated) to conduct acoustic emission testing under uniaxial compression with loading rates ranging from 0.1 mm/min to 0.6 mm/min. The results show that the peak stress and strength-softening modulus, elastic modulus, strain-softening modulus, and post-peak modulus partly decrease with increasing moisture content and loading rate. In contrast, peak strain increases with increasing moisture content and fluctuates with rising loading rate. More significantly, the relationship between stiffness and stress, combined with accumulated counts of acoustic emission, can be used to precisely predict all phases of crack propagation. This is helpful in studying the impact of moisture content and loading rate on crack propagation and accurately calculating mechanical properties. We also determined that the stress thresholds of crack closure, crack initiation, and crack damage do not vary with changes of moisture content and loading rate, constituting 15.22%, 32.20%, and 80.98% of peak stress, respectively. These outcomes assist in developing approaches to water storage in coal mines, determining the necessary width of waterproof coal–rock pillars, and methods of supporting water-enriched roadways, while also advances understanding the mechanical properties of coal–rock combinations and laws of crack propagation.

Deformation analysis of transversely isotropic coal-rock mass with porous and cracks

Coal-rock as a typical sedimentary rock has obvious stratification,namely it has transversely isotropic feature.Meanwhile,deformation leads to coal-rock mass having the characteristics of different porous and crack structures as well as local anisotropy.Equivalent axial and circumferential strain' formulas of the pure coal-rock mass specimen with a single crack were derived through the establishment of equivalent mechanical model of standard cylindrical coal-rock specimen,and have been widely used to a variety of media combined different structures containing multiple cracks.The complete stress strain curve of a real coal-rock specimen was obtained by the CTC test.Additionally,according to the comparison with the theoretical value,the theoretical mechanical model could well explain the deformation characteristics of coal-rock mass and verify its validity.Further,following features were analyzed:strain normalized coefficient and elastic modulus(Poisson's ratio) in vertical and parallel direction to the stratification,stratification angle,porosity,pore radius,normal and tangential stiffness of crack,and the relationship of different crack width with different tangential stiffness of crack.Through the analysis above,it substantiate this claim that the theoretical model with better reliability reflects the transversely isotropic nature of the coal-rock and the local anisotropy caused by the porous and cracks.

Coal–rock interface detection on the basis of image texture features

Based on the stability and inequality of texture features between coal and rock,this study used the digital image analysis technique to propose a coal–rock interface detection method.By using gray level co-occurrence matrix,twenty-two texture features were extracted from the images of coal and rock.Data dimension of the feature space reduced to four by feature selection,which was according to a separability criterion based on inter-class mean difference and within-class scatter.The experimental results show that the optimized features were effective in improving the separability of the samples and reducing the time complexity of the algorithm.In the optimized low-dimensional feature space,the coal–rock classifer was set up using the fsher discriminant method.Using the 10-fold cross-validation technique,the performance of the classifer was evaluated,and an average recognition rate of 94.12%was obtained.The results of comparative experiments show that the identifcation performance of the proposed method was superior to the texture description method based on gray histogram and gradient histogram.

Structure instability forecasting and analysis of giant rock pillars in steeply dipping thick coal seams

Structure stability analysis of rock masses is essential for forecasting catastrophic structure failure in coal seam mining. Steeply dipping thick coal seams （SDTCS） are common in the Urumqi coalfield, and some dynamical hazards such as roof collapse and mining-induced seismicity occur frequently in the coal mines. The cause of these events is mainly structure instability in giant rock pillars sand- wiched between SDTCS. Developing methods to predict these events is important for safe mining in such a complex environment. This study focuses on understanding the structural mechanics model of a giant rock pillar and presents a viewpoint of the stability of a trend sphenoid fractured beam （TSFB）. Some stability index parameters such as failure surface dips were measured, and most dips were observed to be between 46° and 51°. We used a digital panoramic borehole monitoring system to measure the TSFB＇s height （△H）, which varied from 56.37 to 60.50 m. Next, FLAC^3D was used to model the distribution and evolution of vertical displacement in the giant rock pillars; the results confirmed the existence of a TSFB structure. Finally, we investigated the acoustic emission （AE） energy accumulation rate and observed that the rate commonly ranged from 20 to 40 kJ/min. The AE energy accumulation rate could be used to anticipate impeding seismic events related to structure failure. The results presented provide a useful approach for forecasting catastrophic events related to structure instability and for developing hazard prevention technology for mining in SDTCS.

Similarity model tests of movement and deformation of coal-rock mass below stopes

For a study of the movement and deformation of coal-rock mass and low protected seams below a stope,as well as for fracture developments and rules of evolution of permeability,we designed a plane strain model test stand to carry out model tests of similar materials in order to improve the effect of gas drainage from low protected seams and to measure the movement and deformation of coal-rock mass using a method of non-contact close-range photogrammetry.Our results show that 1) using paraffin melting to take the place of coal seam mining can satisfy the mining conditions of a protective seam;2) coal-rock mass under goafs has an upward movement after the protective seam has been mined,causing floor heaving;3) low protected seams become swollen and deformed,providing a good pressure-relief effect and causing the coal-rock mass under both sides of coal pillars to become deformed by compression and 4) the evolution of permeability of low protected seams follows the way of initial values→a slight decrease→a great increase→stability→final decrease.Simultaneously,the coefficient of air permeability increased at a decreasing rate with an increase in interlayer spacing.

Leaching behavior of V,Pb,Cd,Cr,and As from stone coal waste rock with different particle sizes

This paper investigates the leaching behavior of heavy metals(V,Pb,Cd,Cr,and As) from stone coal waste rocks with various particle sizes using dynamic leaching experiments.The results show that the dissolved concentrations of V and As initially increased and then slightly decreased as time progressed and that the dissolved concentrations of Pb,Cd,and Cr were high in the early stage before decreasing.The particle size of the stone coal waste rocks strongly influenced the heavy metal concentration in the leaching solutions.The effects of the particle size of the stone coal waste rocks on the dissolved concentrations of V,Pb,and As decreased in the order fine fraction > medium fraction > coarse fraction,and the effects of particle size on the dissolved concentrations of Cr and Cd decreased in the order medium fraction > coarse fraction > fine fraction and coarse fraction > medium fraction > fine fraction,respectively.The quantities of heavy metals dissolved from the stone coal waste rock with fine particle sizes were observed to decrease in the order V(17104.36 μg/kg) > As(609.41 μg/kg) > Pb(469.24 μg/kg) > Cr(56.35 μg/kg) > Cd(27.52 μg/kg),and the dissolution rates decreased in the order As(2.96%) > Pb(0.93%) > V(0.35%) > Cd(0.25%) > Cr(0.01%).The specific surface area,pore size of the stone coal waste rocks,and chemical forms of heavy metals also influenced the release of heavy metals from the stone coal waste rocks.Kinetic analysis showed that the dissolution of heavy metals fundamentally agreed with the rate equation controlled by the shrinking core model.The results of this study are expected to serve as a reference for the evaluation of heavy metals contamination from stone coal waste rocks.

Carbon isotopic characteristics of hydrocarbon gases from coal-measure source rocks—A thermal simulation experiment

Gaseous hydrocarbon geochemistry research through a thermal simulation experiment in combination with the natural evolution process in which natural gases were formed from coal-measure source rocks revealed that the {δ{}+{13}C-1} values of methane vary from light to heavy along with the increase of thermal evolution degree of coal-measure source rocks, and the {δ{}+{13}C-2} values of ethane range from {-28.3‰} to {-20‰} (PDB). {δ{}+{13}C-2} value was {-28‰±} (R-O={0.45%}-{0.65%}) at the lower thermal evolution stage of coal-measure source rocks. After the rocks entered the main hydrocarbon-generating stage (R-O={0.65%}-{1.50%}), {δ{}+{13}C-2} values generally varied within the range of {-26‰}-{-23‰±}; with further thermal evolution of the rocks the carbon isotopes of ethane became heavier and heavier, but generally less than -20‰.; The partial carbon isotope sequence inversion of hydrogen gases is a characteristic feature of mixing of natural gases of different origins. Under the condition of specially designated type of organic matter, hydrogen source rocks may show this phenomenon via their own evolution.; In the lower evolution stages of the rocks, it is mainly determined by organic precursors that gaseous hydrocarbons display partial inversion of the carbon isotope sequence and the carbon isotopic values of ethane are relatively low. These characteristic features also are related to the geochemical composition of primary soluble organic matter.

Geochemical characteristics of Lower Permian coal-measure source rocks in Northeast Ordos Basin

General characteristics and biomarker distributions of Lower Permian coal-measure source rocks in northeastern Ordos Bsain have been analyzed in this paper. The results show that the source rocks are type Ⅲ kerogen, thermally mature, with high content of total organic carbon. The extracts of the source rock samples with different lithologies from Well Su 27 feature high Pr/Ph ratios, high C19 TT and C24 Te, high rearranged hopanes, a predominance of C29 sterane in regular steranes, and the absence of C30 4-methylsteranes. These data suggest that the source rocks were deposited in suboxic to oxic conditions with dominantly terrigenous higher plant input. In contrast, the source rocks from wells Shuang 1 and Yu 20, are characterized by low Pr/Ph ratios, low C19 TT and C24 Te, high C23 TT, similar content of C27 sterane and C29 sterane, and the presence of C30 4-methylsteranes, showing that the source rocks were deposited in reducing environment with algae and/or microorganisms and terrigenous higher plant input.

Study on the Theory and Method on Identification of the Mobile Block in the Face-Contacted Blocks Structure in Rocks Between Coal Seams to Mine the Left-over Coal Above the Gob

In mining the left-over coal above the gob,stope wall rock of mining area have hard limestone.through field observation,the face-contacted block structure was found in rocks between coal seams to mine the left-over coal above the gob.In order to probe into the movement law of rock strata and strata control measures,it is very important to identify the mobile block in face-contacted block structure of rocks between coal seams.This paper relies on the thought of block theory to establish appropriate parameter matrix and figure out its discrimination matrix in view of the fact that the block in face-contacted block structure has high intensity and stiffness,the

The contribution of bacteria to organic matter in coal-measure source rocks

On the basis of GC–MS analysis, a suite of nine coal-measure source rocks(Ro 0.51%–0.63%) from the southern margin of Junggar basin was found to contain many biomarkers for bacterially-generated hydrocarbons:hopane, sesquiterpene, C_(23)+ monomethyl alkanes(even carbon predominance), and C_(24)+ alkyl cyclohexane.Rock–eval and microscope analysis indicate that vitrinite(especially desmocollinite and homocollinite) plays a significant role in the generation of hydrocarbons in coalmeasure source rocks. Vitrinite performs this role by absorbing ultramicroscopic organic matter, generally in the form of resins or bacterial plastids. C_(23)+ monomethyl alkanes(even carbon predominance) and C_(24)+ alkyl cyclohexane series compounds are derived from bacterial metabolites of higher plants. The ultramicro organic matter adsorbed by vitrinite source rocks in the study area is probably ultramicro bacterial plastids. Because the organic matter of higher plants with low hydrogen content has been transformed into organic matter rich in hydrogen by bacteria, the hydrocarbon generation capacity of source rocks is greatly improved. In other words, in coal-measure source rocks, bacteria play an important role in hydrocarbon generation.

Dynamic Failure Model of Thin Coal and Rock Mass under Uniform Impact Load

During the excavation of deep coal and rock mass, the radial stress of the free face changes from three-dimensional compression state to two-dimensional stress, bearing the combined action of dynamic disturbance and static load at the same time. With that, many mines suffer from dynamic disasters, such as coal and gas outburst, rock burst and rock caving during deep mining excavation, which is often accompanied by plate crack, spalling and other disasters, seriously affecting the stability of stope and roadway. Taking thin rectangular coal and rock mass as the research object, the dual equation of the free vibration was derived and the exact solution model of the free vibration was established with the use of Hamilton dual system. Based on the action characteristics of the uniform impact load, the effective mode of the forced vibration was obtained by using the Duhamel integral principle and the orthogonality of the mode function. Based on the third strength theory and the numerical simulation results, the dynamic damage process and development trend of coal and rock mass were analyzed under uniform impact load. It was concluded that the starting position of dynamic damage can be judged by the first order main mode, and the development direction and trend of the damage can be judged by the fifth and sixth order main modes. It was concluded that the vibration mode functions of coal and rock mass with four side fixed (C-C-C-C), the two sides fixed and simply supported on the other (S-C-S-C) are mainly composed of three modes that are the first order (dominant frequency), the fifth order and the sixth order, from which the dynamic damage mechanism is preliminarily studied.

Platinum and Palladium in Coal Rock and Geochemical Anomaly in Eastern Yunnan Province,Southwest China

A series of geochemical anomalies of Pt and Pd were found in 1 358 recombined samples from a geochemical stream sediment survey in eastern Yunnan （云南） Province, China. Chemical optical emission spectroscopy, X-ray fluorescence analysis, and inductively coupled plasmas atomic emission spectrometry analyses of 22 elements and chemical compositions of 21 samples from coal-bearing strata from the Late Paleozoic, Mesozoic, and Cenozoic show Pt and Pd concentrated to some extent in coal rocks, with Pd/Pt〈1. As, Pt, B, Au, Pd, V, Sb, U, Pb, and W are enriched in the Lower Carboniferous coal-bearing strata of the Wanshoushan （万寿山） Formation; B, Mo, As, Pt, U, W, Pb, Pd, and V are enriched in the Lower Permian coal-bearing strata of the Liangshan （梁山） Formation; Pt, Cu, Mo, Pd, As, V, and Ag are enriched in the Upper Permian coal-bearing strata of the Xuanwei （宣威） Formation; As, B, Pb, Pt, Pd, U, W, Sb, Mo, Zn, and Ag are enriched in the Upper Triassic coal-bearing strata of the Xujiahe （须家河） Formation; and Pt, As, and Pb are enriched in the lignite of the Pliocene Ciying （茨营） Formation. Combining analyses of the sedimentary environment and local volcanic activity reveal that the coalbearing strata in the Xuanwei Formation are possibly related to the Permian Emeishan （峨眉山） basalt.

Resources of Kaolinite Rocks in China Coal Measures

The proved reserve of kaolinite rocks in China coal measures is about 1.673 billion tons. The types of kaolinite rocks contain tonstein, flintclay and soft kaolin. Their origin modes include alteration of volcanic ash, terrigenous clay deposit and weathering of coal and adjacent rocks. The organic matter and organic acid play an important role in the formation of kaolinite rocks of coal measures. The difference in properties between kaolinite rock and traditional kaolin requires different processing technologies.

Experimental investigation on behaviors of bolt-supported rock strata surrounding an entry in large dip coal seam

In order to investigate the behaviors and stability of rock strata surrounding an entry with bolt supporting in large dip coal seams (LDCSs) dipping from 25° to 45°, a self-developed rotatable experimental frame for similar material simulation test was used to build the model with the dip of 30°, based on analyses of geological and technological conditions in Huainan mine area, Anhui, China. The strata behaviors, such as extracting- and mining-induced stresses development, deformation and failure modes, were synthetically integrated during working face advancing. Results show that the development characteristics of mining-induced stress and deformation are asymmetrical in the roadway. The strata behaviors are totally different in different sections of the roadway. Because of asymmetrically geometrical structure influenced by increasing dip, strata dislocating, rock falling and breaking occur in roof. Then, squeezing, collapsing and caving of coal happen in upper- and lower-rib due to shearing action caused by asymmetrical roof bending and dislocating. Owing to the absence of supporting, floor heaving is very violent and usually the zone of floor heaving develops from the lower-rib to upper-rib. Engineering practices show that, due to the asymmetrical characteristics of rock pressure and roadway configuration, it is more difficult to implement bolt supporting system to control rock stability of roadways in LDCSs. The upper-rib and roof of entries are the key sections. Consequently, it is reliable to use asymmetrical bolt-mesh-cable supporting system to control rock stability of roadways based on the asymmetrical characteristics of roadway configuration and strata behaviors.

Controlling Effects of Surrounding Rock to Coal Seam Gas Occurrence

Surrounding rock of coal seam was one of the important factors to gas occurrence. The coal seam gas occurrence was studied by the index of roof strata thickness or sand content rate;we found that there were certain shortcomings. In order to reasonably evaluate the influence of coal seam surrounding rock on gas occurrence in Panji mining area, we quantitatively evaluated the effect of coal seam surrounding rock on gas occurrence by influence coefficient of roof strata thickness, and built six mathematical models of the variational gas content in the mining area which is divided into six gas geological units. The results shows that the coal seam gas content is mainly influenced by 20 mroof strata in each gas geological unit, the gas content presents the tendency of increase, and with the influence coefficient of strata thickness increases, they exist a significant linear relationship.

Stress distribution and surrounding rock control of mining near to the overlying coal pillar in the working face

The occurrence of overlying coal pillar(OCP)exerts a strong effect on the stress and strain distribution of the surrounding rock in the stope.In this paper,the stress distribution characteristics are analyzed via the numerical calculation with the account of OCP presence or absence.In addition,this study revealed the joint effect of side pressure relief area of the goaf and stress concentration in OCP on the final stress distribution.Furthermore,the rules of abutment stress distribution affected by three influencing factors,namely horizontal-vertical distances between OCP and working face and buried depth of OCP,are analyzed.The functional model linking the peak stress of surrounding rock with the above influencing factors is developed.The field application of the above results proved that the rib spalling and deformation of a 2.95 m-high and 5.66 m-wide roadway could be efficiently controlled by rationally adjusting working states of the support,and adopting the hydraulic prop coordinated with the p type metal beam and anchor cable to strengthen the surrounding rock of working face and roadway,respectively.The proposed measures are considered appropriate to satisfy the safe operation requirements.