Causality Mechanism of Coal Bump Occurred in Longwall Roadways

Coal bump occurring in longwall roadways accounts for more than 87% of total coal bump events. However, there is no practical mechanical model that can explain the causality and process of coal bump, resulting in that the prediction and prevention of rockburst heavily depend on engineering experience or lessons. Considering the mechanical characteristics of surrounding rock, the suspended roof behind working face and stress state of the rib coal, a seesaw structure model related to incentive of the coal bump and a mechanical model related to instability of rib coal block are established in this paper based on theoretical analysis and numerical calculation, which is capable to clarify the causality mechanism, process, key factors and critical state of coal bump. The hard suspended roof behind the working face produces periodic abutment pressure on the coal around the working face. The result of numerical calculation shows that, under the condition of high compressive stiffness of hard coal around the working face, the roof in front of the working face rebounds upward. The phenomena of roof rebound suggests that the overlying strata of the working face form a seesaw structure. In the area of roof rebound, the normal stress on the roof-coal interface is reduced. Stress analysis of a rib coal block has been conducted. Result shows that, the tectonic stress perpendicular to the rib can overcome the fractional resistance pushing the rib coal into the roadway once the normal stress on the roof-coal interface de-stresses to a certain level. Accordingly, a critical state equation of coal bump has been established. It can be concluded that, de-stressing of the roof-seam interface caused by roof rebound triggers coal bump. The tectonic stress is its force source, and the tensile strength of coal and the shear strength of the coal seam with roof and floor are bump resistances. This study clarifies the causality mechanism and process of coal bump occurred in longwall roadway that provides a theoretical basis for prediction and prevention technology.

Palaeoclimatic significance of non - striate disaccate pollen in Yellandu coalfield of Godavari graben, Telangana State

The present palaeopalynological study deals with the significance of non - striate disaccate pollen from bore hole Q - 563 of Yellandu coalfield (Jawahar Khani - 5 coal block), Kothagudem sub-basin and to determine the age and palaeoclimatic interpretations of the study area based on the pollen morphological characters. For the palynological investigation, sixty samples were thoroughly analyzed in which fairly diversified palynofloral assemblages of Gondwanic affinity were recorded. About 30 genera and 50 species of palynomorphs, belong to Glossopteridales, Coniferales, Cordaitales of gymnospermous pollen, pteridophytic spores. In the present communication, the palynoflora belongs to Glossopteridales viz. Scheuringipollentites barakarensis, S. maximus, S. tentulus, Ibisporites diplosaccus, Primuspollenites levis, P. densus and Sahnites thomasii etc. Frequency distribution pattern of the palynotaxa reveals that the assemblage is dominated by the non - striate disaccates followed by striate disaccates, monosaccates (gymnosperms) and pteridophytic spores. The diversified palynoassemblage of both non striate and striate disaccates pollen strongly signifies that the Yellandu coal belt of Godavari graben belongs to Barakar Formation of Early Permian age (Late Sakmarian – Early Artinskian). Predominance of non - striate disaccate pollen recorded from the Yellandu sediments indicates a warm and high humid climatic condition with fluvial environment of deposition.

Palaeobotanical and biomarker evidence for Early Permian (Artinskian) wildfire in the Rajmahal Basin, India

This study provides a combined analysis on the palynology, fossil charcoal and biomarkers of the subsurface coal deposits from a borehole RMB #2 drilled at the Dhulia Coal Block, Rajmahal Basin, India, in attempts to establish the chronology of sedimentation and to propose palaeobotanical as well as geochemical evidence for the occurrence of wildfires in these sediments. The palynological investigation suggests a Scheuringipollenites barakarensis palynoassemblage from the lower Barakar Formation, dated as Artinskian (Early Permian) in age. This assemblage reveals the dominance of Glossopteridales and sub-dominance of taxa belonging to Cordaitales and Coniferales. Fossil charcoal in sediments is usually recognized as a direct indicator for the occurrence of palaeo-wildfires. More data involving the anatomical features of fossil charcoal analyzed by Field Emission Scanning Electronic Microscope broaden our knowledge on Early Permian wildfires from the peninsula of India. The studied macroscopic charcoal fragments exhibit anatomical details such as homogenized cell walls, uniseriate simple and biseriate alternate pitting on tracheid walls and rays of varying heights pointing to a gymnospermous wood affinitity. The excellent preservation of charcoal fragments, shown by their large sizes and almost unabraded edges, suggests a parautochthonous origin. The embedded biomarker study performed for charcoal sediments and its characterization demonstrate the presence of n-alkanes, isoprenoids, terpenoids and aromatic compounds. A bimodal distribution pattern of n-alkanes with a Cmax at n-C25 is identified. Diterpenoids and pentacyclic terpenoids are identified, indicating the input of an early conifer vegetation and bacterial activity, respectively. The identified polyaromatic hydrocarbon (PAH) compounds, together with the charcoal fragments, clearly suggest that repeated wildfire events occurred during the deposition of these Artinskian sediments in the Rajmahal Basin.

Simulation of Cavity Extension Formation in the Early Ignition Stage Based on a Coal Block Gasification Experiment

Underground coal gasification (UCG) is a highly efficient new type of coal mining technology with broad future prospects. In order to study the cavity extension formation in the early ignition stage of UCG, a block coal scale UCG simulation experiment was carried out. The results show that after the ignition, the temperature above ignition point rose fastest, and the coal combustion interface and high temperature area moved toward to the above of ignition point, while the temperature of the left and right sides of ignition point rose a little slowly. According to the results of dissected block coal, it is indicated that the extension scale in the vertical direction was significantly larger than other directions; the combustion cavity form was an irregular rectangle like a pear. The results of this experiment revealed the cavity extension process from ignition of UCG channels to the formation of cavity, which provided a foundation for the study of extension characteristics of UCG channel in the entire UCG process.

Experimental Study on Properties of Methane Diffusion of Coal Block under Triaxial Compressive Stress

Taking the standard size coal block samples defined by ISRM as research objects, both properties of methane diffusion of coal block under triaxial compressive stress and characteristic influences caused by methane pressure were systematically studied with thermo-fluid-solid coupling with triaxial servocontrolled seepage equipment of methane-containing coal. The result shows the methane diffusion property of coal block under triaxial compressive stress was shown in four-stage as follow, first is sharply reduce stage, second is hyperbolic reduce stage, third is close to a fixed value stage, fourth stage is 0. There is a special point making the reduced rate of characteristic curve of methane diffusion speed become sharply small; the influences of shape of methane diffusion speed characteristic curve caused by methane pressure are not obvious, which only is shown in numerical size of methane diffusion speed. Test time was extended required by appear of the special point makes the reduce rate of methane diffusion speed become sharply small. The fitting four-phase relation of methane diffusion of coal block under triaxial compressive stress was obtained, and the idea is proposed that influences of the fitting four-phase relation caused by methane pressure were only shown in value of fitting parameters.

VALUATION OF ROCK GEOLOGICAL FEATURES OF COAL BLOCK OF SOUTHWESTERN COAL-BEARING REGION OF LVIV-VOLYN BASIN WHEN IMPLEMENTING INTEGRATED METHANE EXTRACTION PROJECTS

Article shows prospects in Southwestern coalfield for production of high-quality coking coal for the development of the Lviv-Volyn basin, and the prospects of methane extraction in coal-gas fields. The article also describes the features of geological conditions of the area and compares those with the productive area of the basin. 1-Tyahlivska well field is a developed object to the investment project for methane preliminary drainage and industrial production with short payback.

Analysis of Energy Dissipation with Stress Wave during Impact Coal Cutting

Impact coal cutting is a new kind of coal cutting method, totally different from conventional coal cutting in mechanism. To increase the blocky coal in long-wall coal face with low energy consumption, impact coal cutting is a good way to go. In this paper, an analysis of energy dissipation in impact coal cutting using stress wave is carried out. Firstly, the production, transmission and dissipation of energy are analyzed during the process of coal impact cutting, and the energy distribution area is also obtained. Secondly, the transmission rule of stress and energy are studied by the method of stress wave; through measuring the amplitude attenuation quantity of the first and any other cycle in oscillograph, the attenuation radio can be worked out. Lastly, the propagation process of energy was analyzed based on the impacting rule and propagation rule of energy; the relation between impacting consumption of energy and minimal irreversibly lost energy is expounded. It is pointed out that if the coal block is destroyed, the impacting consumption of energy must be more than the minimal irreversibly lost energy.