Coal Roadway Excavation Research Articles

Wave Field Characteristics of Small Faults around the Loose Circle of Rock Surrounding a Coal Roadway

The geological conditions of coal roadway excavation are complicated. Seismic advanced detection is strongly influenced by the loose circle of fractured rock surrounding the competent coal seam. However, the three-dimensional wave field characteristics of small fault advanced detection in the condition of the loose circle of coal roadway have not examined. In this paper, numerical modeling and field tests were conducted to address this knowledge gap. The results indicate that when a seismic source near the tunnel face is excited, the body waves and a Love channel wave propagate in the tunneling direction toward the small fault, then produces reflected body waves whose amplitude is relatively weak, and a reflected Love channel wave whose amplitude is relatively strong. When reflected body waves and the reflected Love channel wave enter the loose circle of surrounding rock, the former's signal is unrecognizable in seismic record; but the latter converts to a Love wave whose amplitude is strong in the loose circle of coal seam. The Love wave which has a large interval from other wave trains in the time domain is easily recognizable in seismic record, which makes it suitable for advanced detection of small fault. The signal-to-noise ratio of seismic record of X component is higher than those of Y component and Z component.

Model of stress distribution during coal roadway excavation and its numerical validation

This paper establishes a mechanical model of the stress distribution in front of the driving face during coal roadway excavation. Theoretical research shows that the stress state in the plastic zone of the driving face is consistent with the limit equilibrium equation, and the elastic zone is in accordance with the equilibrium equation based on elasticity mechanics. Based on this improved mechanical state solution model, different coal material constitutive hypotheses are used for the analysis. The width of the plastic zone calculated under the brittle-perfectly elastic model can reach 2–5 times the height of the roadway, and the stress concentration coefficient can reach two or more times. 3DEC numerical simulation software was used to simulate the stress distribution of the heading face. The results of the simulation are similar to those of the theoretical analysis. Compared with the elastic-perfectly plastic model, the calculated results of the brittle-perfectly elastic model are more consistent with the numerical simulation results. The heading face coal during roadway excavation shows obvious damage, and the strength characteristics of the coal decrease.

A new cross‐borehole hydraulic caving technique in the coal seam with a soft layer for preventing coal and gas outbursts during coal roadway excavation

AbstractPredrainage of gas by cross‐boreholes is an important method to prevent coal and gas outbursts in the process of a coal roadway excavation. Limitations of technologies and poor effects of preventing coal and gas outbursts occur in the coal seam with a soft layer. In this study, a new hydraulic caving technology for cross‐boreholes has been proposed to solve this problem. A CT equipment was used to observe the development of coal fissures around cross‐boreholes in the coal seam with a soft layer. The plastic zone range and permeability distribution of ordinary hydraulic slotting technologies and the new hydraulic caving technology also were compared by numerical simulation. The field test of hydraulic caving was taken in the Xuehu Mine (China). The results show that the fracture development degree of soft coal is greater than that of hard coal at the same distance from cross‐boreholes. The fracture development degree in the plastic zone is greater than that in the elastic zone. The hydraulic caving technique can achieve the same effect as the ordinary hydraulic slotting with less workload. The mass of coal discharged from a cross‐borehole was 1.15 t/m and the average methane concentration of single drainage borehole increased by 1.09‐4.1 times, and the average methane extraction amount of single drainage borehole increased by 6.06 times. Elimination of coal and gas outburst had been completed after 110 days of extraction in the area of hydraulic caving, and Q and S values are lower than the critical value during roadway excavation. It is conclusion that hydraulic caving technique can effectively improve the permeability and rapidly eliminate coal and gas outburst in the coal seam with a soft layer.

A new method for determining coal seam permeability redistribution induced by roadway excavation and its applications

Changes in coal seam permeability induced by roadway excavation may lead to many engineering problems, such as low gas extraction concentration in in-seam boreholes, coal and gas outburst disasters, and gas emissions in the process of coal roadway excavation. To solve these problems, this paper proposed a new method to directly determine the distribution of coal seam permeability around roadways. For this purpose, method principle was analyzed, equipment was developed, and field experiments were carried out in Baiyangling coal mine. Finally, the engineering applications of the method were analyzed, and a field application effect experiment was conducted to verify the new method. The results showed that the coal seam permeability around roadways was divided into four stages. In stages I and II, permeability increased, in stage III, permeability decreased, and stage IV maintained the initial permeability of the coal seam. These test results will aid in increasing the gas extraction concentration of in-seam boreholes and will guide the design of gas control areas. Using the verification experiment, it was concluded that the new method is able to accurately determine the redistribution of coal seam permeability caused by roadway excavation and provide theoretical guidance in solving engineering problems.

Effects of coal seam dip angle on the outburst in coal roadway excavation

The prevention and forecast of coal and gas outburst has always been one of the key issues in coal mining safety. By simulating the process of tunneling in coal seam with different dip angle through FLAC3D software, the dangerous zone in which outburst may occur and the probability of outburst near the working face were predicted through the distribution of stress, displacement and plastic zone. Then we discussed the size of unstable area in the surrounding rock through the distribution of stress and the variation curve of the displacement on the roadway wall. The results show that, with an increase of the coal seam dip angle, the risk of outburst in the working face rises gradually. And the dangerous areas in which may outburst occur moves to the upper part of coal seam. The size of unstable area in the surrounding rock increases with the increase of coal seam dip angle.

A Novel Hydraulic Mode to Promote Gas Extraction: Pressure Relief Technologies for Tectonic Regions and Fracturing Technologies for Nontectonic Regions

Extraction of gas (coalbed methane) produces clean energy and can ensure that coal mines maintain high-efficiency production. The currently available coal seam permeability enhancing technologies and modes have certain application restrictions. Therefore, a novel mode is proposed to promote gas extraction. This mode divides complex coal seams into tectonic regions and nontectonic regions based on geological structures. Then, the characteristics of different regions are matched with the advantages of different hydraulic technologies; thus, pressure relief technologies are proposed for tectonic regions, and fracturing technologies are proposed for nontectonic regions. The permeability of coal seams will be sharply increased without leaving unfractured areas. This mode will promote the effectiveness of gas extraction, shorten the extraction time, and ensure safe and efficient production in coal mines. A field application shows that this mode has a better effect than slotted directional hydraulic fracturing technology (SDHFT). The gas concentration and pure gas flow were increased by 47.1% (up to 24.94%) and 44.6% (up to 6.13 m3/min), respectively, compared to SDHFT over 9 months. The extraction time was reduced by 4 months. This mode reduced the number of times that gas concentration exceeded government standards during coal roadway excavation, and the coal roadway excavation speed was increased by 16% (up to 158 m/month).

Development of Double-arm Rock Drilling Car for Full Face Tunnelling

Blasting excavation is widely used in coal mine roadway excavation, its construction method is flexible, convenient, low cost and adaptable. It can excavate mine tunnels of any shape and length under any environmental conditions. However, the main rock drilling equipment used in the mine is pneumatic rock drilling equipment generally. Although these equipment are simple and reliable, their drilling efficiency is low, the degree of automation is poor, and the working conditions are bad, especially the ability to drill deep holes and large holes is poor, which can not meet the needs of large structural parameters mining method. The newly developed double-arm rock drilling rig for full-face roadway excavation is suitable for the current common construction method of roadway blasting driving. It can replace the traditional pneumatic rock drilling equipment, and drill large holes and small holes simultaneously. It fully meets the requirements of blasting technology. It can not only drill and excavate holes, but also drill roof, side wall and floor bolts holes, to achieve high and low position of drilling operations, for improving the efficiency of roadway excavation, promoting the level of coal mine machinery and equipment in China, these have important practical significance.

Mechanical and Coal Burst Breeding Mechanism of Coal Samples under True Triaxial Loading and Unloading

A true triaxial loading and unloading experiment entailing “y‐direction stress loading, z‐direction stress unloading, and x‐direction displacement fixing” of coal samples was conducted. Through analysis of the stress characteristics, fracture characteristics, and energy evolution in coal samples, the mechanical and coal burst breeding mechanisms of coal samples under true triaxial loading and unloading were revealed. The experiment found that the yield stress and peak stress of coal samples were not only affected by the initial loading and unloading of lateral stress but also had a negative exponential relationship with the ratio of the unloading rate and the loading rate (RURLR), thereby establishing the stress equation of coal samples under a true triaxial loading and unloading. There was a yield turning point in the stress‐time curve of coal samples, and the difference in triaxial stress and acoustic emission before, and after, yield was significant. It was found that a high unloading rate and high initial stress are precursors to coal sample bursting. During loading and unloading, the high‐energy area expanded, but its location was always fixed to within a certain area. The energy in this area was rapidly released to form a burst source when the sample was subjected to high‐speed unloading. The nonbursting coal samples and the burst coal samples showed characteristic slabbing and bursting behaviours, respectively: the former corresponding to the acoustic emission energy value being two orders of magnitude lower than the latter. The research results can provide a reference for the study of mechanical behaviours and coal burst criteria in the rock surrounding a coal roadway excavation.

Application of Pre-extraction Drilling in Anti-burst of Low Permeability Coal Seam

In order to eliminate the outburst danger of coal seam with low gas permeability and consider the economic cost of anti-burst measures, the gas pre-extraction coal seam gas prevention technology in the coal roadway excavation process is studied to relieve the coal seam pressure and gas content. The pressure is reduced, and the gas content of the coal body is reduced to 8m3/t within the allowable excavation range. The maximum gas cuttings Smax of the gas is reduced to less than 6kg/m after the anti-burst effect test, which effectively eliminates the prominent danger of the coal seam. During the implementation of the regional anti-burst measures, it can assist the gas release from the gas release, reduce the gas content of the coal seam, release the gas potential of the coal body, and strictly implement the regional defense according to the requirements of the two “four-in-one” anti-burst measures. The comprehensive anti-burst measures supplemented by the sudden measures and the local anti-burst measures eliminate the prominent danger of the coal seam and ensure the safe excavation of the coal roadway.

Cross-borehole hydraulic slotting technique for preventing and controlling coal and gas outbursts during coal roadway excavation

Coal and gas outbursts comprise the predominant hazards in Chinese coal mines. A large number of accidents have occurred during coal roadway excavation. In this study, we propose the application of a cross-borehole hydraulic slotting technique for preventing and controlling coal and gas outburst disasters during coal roadway excavations. In this technique, a high-pressure water jet is applied in a coal body to cut a slot. This helps to increase the permeability of the coal seam, improve the gas-extraction efficiency of the borehole, and prevent and control coal and gas outburst disasters during excavations. In the field test in which hydraulic slotting was employed, the average mass of coal that was discharged from a slotted borehole is 8.2 t; the weight of the largest discharged mass is 16 t. The diameter of the slotted borehole is 12.87 times the diameter of a conventional borehole, which effectively improves the borehole's influence range. After half a month of gas extraction, the average gas-extraction concentration for the slotted borehole is 26%, whereas the average gas-extraction concentration of the conventional borehole is 7%, that is, the gas-extraction concentration for the slotted borehole is approximately 3.7 times the gas-extraction concentration of the conventional borehole. After four months of gas extraction, the residual gas content and gas pressure for the 11091 transportation roadway satisfy the requirement of the State Administration of Work Safety. A conventional borehole requires a minimum period of six months to prevent and control outbursts, whereas a slotted borehole requires a minimum period of four months. These results suggest that the technology can improve the efficiency of gas drainage, reduce the gas drainage time, and is a potential application for preventing and controlling future gas disasters.

Stress distribution of mine roof with the boundary element method

Mine roof, is a stiff rock strata, located on the top of coal seam, which can prevent the deformation and control the stability of coal roadway after the coal roadway is tunneled, so mine roof is one of the most important structures in coal mining engineering. In this paper, mine roof is treated as elastic plate, which is studied thoroughly at the theoretical level. Based on the mechanical models of plane and stress analysis for elastic roof, using the boundary integral equation which is obtained by the natural boundary reduction, this paper obtains stress functions of elastic half roof, as well as the analytical and numerical solutions to the each stress field functions. We also analyze the rules of different stress distributions for roof under a concentrated force and a uniform distribution load, the results of calculation show uniformity of the stress distribution. In order to research the mine roof deformation law, Mohr–Coulomb model is established to describe the deformation behavior of roof surrounding rock, FLAC3D is also used to simulate the deformation of roof after the coal roadway is tunneled under different length of coal roadway excavation. The comparison result between BEM solution and FLAC3D simulation shows advantages to solve the problem by boundary element method, and numerical simulation proves the deformation behavior of roof is influenced by the length of coal roadway excavation.

Technology Research on Rapid Excavation of Large Section Super-Long Coal Roadway

The design construction length of conveyance roadway of the mine working face is nearly 5000m and the section area of driving is 18m2, belongs to large section super-long coal roadway. Through advanced mechanized supporting facilities tunneling construction and using reasonable support pattern and labor organization, it ensured the safety of workers, reduced the labor intensity, and realized the safety and rapid excavation with 440m/month. The economic and social benefit is obviously. It could provide reference meaning for other large section coal roadway rapid excavation at home and abroad.

The Optimization Research of Outburst Prevention Measures of Coal Roadway Excavation Area in South Second Underground Mine of Liziya

In order to comprehensively control south second underground mine of Liziya and accident-prone gas outburst, low coal seam permeability coefficient, disaster caused by outburst and following prevention with and high cost and so on, the targeted outburst prevention optimization measures in coal roadway excavation area is puts forward, by applying independently developed " drilling and slotting integration " hydraulic slotting equipment in the process of drilling construction, making coal seam of pre-drainage area carry on antireflection, exposure area of drilling in coal is increased, achieve the purpose of increasing coal seam permeability and drilling extraction radius, improve extraction effect and shorten reaching standard time of gas extraction, provide a more complete solution for outburst prevention measures of underground area in mine.

The Abrasive Resistance Study about the Cutting Picker 40Cr of Coal Cutter

The cutting pick is primarily used in footing excavation such as coal mining and roadway excavation, so the performance of cutting tooth directly affect the mining capacity, the driving efficiency, and the service life of the tool. The quality of domestic mining pick is lower than that abroad, especially the tooth body wear of the whole shearer picks accounts for half of its overall failure. Thus tooth body 40Cr was treated by various heat treatment processes in this experiment, so as to improve the hardness and wear resistance of cutting tooth, analysis the surface wear scar of morphology, research the wear mechanism, that made for reducing the consumption of cutting tooth, improving work efficiency, and easing the labor intensity of workers undergound.

Optimization for Prediction Indexes of Coal and Gas Outburst in Coal Roadway Excavation Working Face Based on Grey Synthetically Relational Degree

Coal and gas outburst is a strong dynamic phenomenon in the process of coal mining, which the fierce degree and destroy effect is beyond imagination, also can cause the occurrence of secondary disasters, such as fire, gas explosion. Especially in coal roadway excavation face, it is frequent. Therefore, the reasonable prediction and evaluation for associated factors of coal and gas outburst in coal roadway excavation working face is important and guiding significant for coal production, sustained and healthy development. With the mathematical model of grey synthetically relational degree analysis, we gain quantitative analysis of six prediction indexes of coal and gas outburst, and determine the best predictors, provide quantitative basis for the selection of coal and gas outburst prediction indexes.

Research of Ventilation and Dust Removal Technology for Whole Rock Fully-Mechanized Excavation Face

The whole rock fully-mechanized excavation with big cross section, high rock hardness and strong cutting intensity of fully-mechanized coal winning machine has a higher dust concentration than coal roadway excavation, so ventilation dust removal technology is in need in whole rock face. Based on the dust migration and distribution numerical simulation in whole rock tunnel excavation, optimization design of long pressing and short pumping hybrid ventilation and dust removal system were carried out. Eventually, the comprehensive dust prevention measures with air curtain closing dust source, dust electromotor exhausting dust and retaining curtain capturing dust were realized in this paper, which achieved a good removal efficiency of dust.

Study on gas monitoring technology based on information fusion

In view of the deficiency of current gas monitoring systems in coal mine roadway excavation, a two-level information fusion technology, which adopted the adaptive weighted algorithm and the BP neural network technology, was applied to gas monitoring. The results show that the adaptive weighted algorithm can realize self-regulation by decreasing the weight value of the failed sensor automatically, so as to eliminate the effect of the failed sensor and ensure the effectiveness and accuracy of the gas monitoring system. The BP neural network can not only effectively predict the gas gush quantity of the excavation roadway, but also accurately calculate the gas concentration in the region where one or more sensors have failed, so as to provide the basis for judging the safety status of the roadway excavation. The experiments prove the superiority and feasibility of the application of information fusion in gas monitoring.