Coal Mining Engineering Research Articles

Research on 3D geological modeling based on boosting integration strategy

Accurate geology modeling is critical in coal mining engineering for increasing mining efficiency and safety. Traditional 3D modeling approaches rely on drill hole data to fill in unknown geographical characteristics using interpolation or machine learning methods. However, the cost of individual borehole projects is high, and borehole distribution is sparse; the filling of sparse boreholes by interpolation smoothes the geologic data to some extent, and some abnormal geologic conditions cannot be shown in the interpolated geologic data; and the classification of subsurface space by machine learning is hampered by sparse training samples and model overfitting or underfitting. As a result, this paper proposes a method to reduce the complexity and uncertainty in the process of 3D geological modeling by integrating the classification results of multiple classifiers based on the machine learning classification model and constructing a 3D geological model based on gas extraction borehole data using the Boosting integration strategy. The results reveal that the Boosting integration model outperforms a single machine learning model in geological modeling, with improved classification accuracy and resilience. A comparative investigation of different classifiers demonstrates that the Boosting integrated model outperforms a single classifier in geological modeling. The geologic profile analysis confirms the dependability and stability of the Boosting integrated model, which can provide an effective solution for 3D geologic modeling of coal mine workings and is critical for increasing mining productivity and lowering accident risks.

Dynamic mechanical response and crack evolution law of raw coal loaded by dynamic-static coupling under three-dimensional constraints

This paper presents the investigation of the dynamic mechanical properties of coal rock under complex stress conditions at depth, based on the improved Separate Hopkinson Pressure Bar Test System. A total of 15 groups of coal samples were used to perform dynamic impact tests under different conditions. The changing rules of dynamic strength, crushing, fractal dimension and damage modes of coal under different stress conditions were analyzed. A total of nine groups of coal samples were selected for numerical simulation using ANSYS/LS-DYNA. The results show that: (1) The stress–strain curves of coal specimens under different strain rates, different confining pressures and axial pressures have basically the same trend and the curves show a certain jump forward. (2) The peak dynamic stress of the coal specimens increased linearly with the increase of strain rate and confining pressure, and the ambient pressure limited the expansion of internal cracks of the coal specimens under impact loading. Based on the experimental and simulated data, the maximum relative errors between the experimental and simulated data were determined to be 2.9578% for Group A, 6.177% for Group B, and 6.382% for Group C, respectively. (3) The damage modes of the coal samples under the three-dimensional dynamic-static combined loading were mainly “X” type and “conical” shear damage. The fractal dimension increases with the increase of strain rate, decreases with the increase of confining pressure, and first decreases and then increases with the increase of axial pressure. This research achievement can provide theoretical support for the prevention of dynamic disasters in deep coal mine engineering.

The influence of pulse frequency on the energy evolution law and rock-breaking effect of pulsed abrasive water jet

Compared to continuous abrasive jet and high-pressure water jet, pulsed abrasive water jet can intermittently generate high water hammer pressure and is commonly used in applications such as coal mining and petroleum engineering for rock-breaking purposes. Pulse frequency is one of the key factors affecting the evolution of abrasive acceleration and jet impact energy, thereby influencing the system's energy transfer efficiency and cutting ability. The equation of motion for abrasive acceleration is established based on the two-phase flow theory, and the variation law of abrasive velocity with pulse frequency is solved. Fluent-EDEM (Extended Discrete Element Method) was used to simulate the abrasive water jet flow field structure and abrasive acceleration process under different pulse frequency conditions, and the intrinsic influence mechanism of pulse frequency on impact energy was clarified. Combined with rock-breaking experiments using pulsed abrasive water jets, the following conclusions are drawn: as the pulse frequency increases, the inertia of the abrasive makes it unable to respond in a timely manner to the high pulsation frequency of water, resulting in a reduction in the exchange rate of intermittent energy and a gradual decrease in the maximum velocity of the abrasive. This trend is more pronounced at a higher pulse frequency. Within the same time period, the cumulative impact energy of the pulsed abrasive water jet decreases first and then increases with the increase in pulse frequency, indicating the existence of an optimal impact frequency that maximizes the cumulative impact energy of the pulsed abrasive water jet. Under fixed jet pressure conditions and the same erosion time, the pulsed abrasive water jet with a frequency of 30 Hz exhibits the best rock-breaking capability.

Methodology and performance of annular fluid enhanced self-excited oscillation in pulsed submerged waterjet for coal mine engineering

Submerged waterjets often yield low coal-breaking efficiency and have limited permeability. This study introduced a novel approach to enhance submerged waterjets by harnessing the annular fluid hydraulic energy of a borehole. A new waterjet modulator was developed using large eddy simulation (LES) combined with the response surface method (RSM). The reliability of the method was verified by submerged waterjet high-frequency pulsation pressure test experiments. The results indicated that the pulsation amplitude of the annular fluid enhanced self-excited oscillation pulsed waterjet (AFESOPW) was 330.05%, 45.17%, and 32.56% higher than those of the continuous waterjet, self-excited oscillation pulsed waterjet (SOPW), and pre-optimized waterjet, respectively. Additionally, the pulsating pressure peak increased by 42.84%, 19.60%, and 25.81%, respectively. Under the submerged condition, the outlet pulsating pressure peak of the AFESOPW was 1.32–1.58 times the inlet pressure. The self-priming annular fluid weakened the hinderance of the submerged environmental pressure and enhanced the waterjet pulsation effect.

Study on Mechanism of Static Blasting-Induced Hard Rock Fracture Expansion

How to deal with hard rock cheaply and safely is a pressing issue in today’s coal mining. Weakening fractures of hard rock have always been a significant concern in China’s coal mine engineering. In this study, mechanical derivation, laboratory experiments, and numerical simulation research methodologies are used to evaluate the fracturing process of the static crushing agent (SCA). From a mechanical standpoint, the mechanism of fracturing hard rock by a crushing agent is investigated. It is assumed that single-hole fracturing is separated into three stages: the microfracture stage, the fissure development stage, and the breaking stage. The swelling and fracturing properties of SCA were quantitatively analyzed. It was found that the swelling pressure of SCA increased with the increase in pore diameter, and the range of the swelling pressure was 43.5 MPa to 75.1 MPa. SCA exhibited a delayed fracture initiation, but the rate of breakage was relatively high. The cracking effect of a single-hole specimen under no peripheral pressure was simulated using PFC2D, and the results were consistent with experimental observations. The internal dynamic effect, crack extension, distribution characteristics, and the development law of double-hole expansion pressure were analyzed for double-hole specimens with different hole diameters, hole spacings, and circumferential pressures. It was observed that the cracking effect was positively correlated with the pore diameter, while the pore spacing and surrounding pressure were negatively correlated. The size of the expansion pressure was negatively correlated with the pore diameter, while the pore spacing and surrounding pressure were positively correlated.

The impact of depositing waste from coal mining and power engineering on soils on the example of a central mining waste dump

The impact of depositing waste from coal mining and power engineering on soils on the example of a central mining waste dump

The role of porosity in the dynamic disturbance resistance of water-saturated coal

Porosity significantly affects the dynamic response of water-saturated coal and the safety of coal mine engineering in water-rich areas. For mastering the dynamic response of water-saturated coal to the porosity, this study used the coal with four levels of the porosity for dynamic tests. In this process, the dynamic compressive tests were operated on these coal specimen in both of water saturation and dry states, and the reduction factor of dynamic mechanical parameters of the coal in water-saturated state to these in dry state were focused to eliminate the effect of self dynamic properties of the coal. The results indicate that the dynamic mechanical properties non-linear positively correlate with the porosity, and its sensitivity to porosity gradually weakens as with the increase of the porosity. This effect is intuitively expressed in the dominant fracture propagation features recorded by a high-speed camera, and microscopically attributed by the size and number of microfractures around the dominant fracture. The dynamic stress intensity factor model of the dominant fracture was further established with consideration of total cohesive force for the equivalent particle on the fracture surface. It well reveals the effect mechanism of porosity on the meso-deterioration and macroscopic mechanical properties of the coal around the roadway. On this basis, the applicable conditions and suggested methods were put forward to improve the dynamic stability of water-saturated coal with various porosity.

Effects of mineralogical composition on uniaxial compressive strengths of sedimentary rocks

Figuring out rock strength plays essential roles in the sub ground mining activities, such as oil and gas well drilling and hydraulic fracturing, coal mining, tunneling, and other civil engineering scenarios. To help understand the effects of the mineralogical composition on evaluating the rock strength, this research tries to establish indirect prediction models of rock strength by specific input mineral contents for common sedimentary rocks. Using rock samples collected from the outcrops in the Sichuan Basin, uniaxial compression tests have been conducted to sandstone, carbonate, and shale cores. Combining with statistical analysis, the experimental data prove it true that the mineralogical composition can be utilized to predict the rock strength under specific conditions but the effects of mineralogical composition on the rock strength highly depend on the rock lithologies. According to the statistical analysis results, the predicted values of rock strengths by the mineral contents can get high accuracies in sandstone and carbonate rocks while no evidences can be found in shale rocks. The best indicator for predicting rock strength should be the quartz content for the sandstone rocks and the dolomite content for the carbonate rocks. Especially, to improve the evaluation accuracy, the rock strengths of sandstones can be obtained by substituting the mineral contents of quartz and clays, and those of carbonates can be calculated by the mineral contents of dolomite and calcite. Noticeably, the research data point out a significant contrast of quartz content in evaluating the rock strength of the sandstone rocks and the carbonate rocks. Increasing quartz content helps increase the sandstone strength but decrease the carbonate strength. As for shale rocks, no relationship exists between the rock strength and the mineralogical composition (e.g., the clay fractions). To provide more evidences, detailed discussion also provides the readers more glances into the framework of the rock matrix, which can be further studied in the future. These findings can help understand the effects of mineralogical composition on the rock strengths, explain the contrasts in the rock strength of the responses to the same mineral content (e.g., the quartz content), and provide another indirect method for evaluating the rock strength of common sedimentary rocks.

Study on the Mining Technology and Construction Safety Management Measures of Coal Mine Engineering

Study on the Mining Technology and Construction Safety Management Measures of Coal Mine Engineering

An Innovative Directional Blasting Technique for Coal Mine Exploration and Engineering Testing

Blasting is a key method of controlling large-area hanging roofs and strong mine pressure in coal mine. The crack propagation direction after blasting has a decisive influence on control effect, and the existing blasting techniques have poor directionality, making it difficult to form a continuous, precise crack. A compound blasting technique (CBT) was proposed; this could achieve a precision, directional crack by using the combination of perforating bullet and explosives, with perforating bullet detonation first and then explosive blasting. The principle of directional crack formation by CBT was studied and a complete set of equipment was introduced, and the effect of continuous directional crack forming was studied experimentally. A CBT test was conducted in Tashan coal mine (Datong mining area): the results showed that a single crack surface was formed in the borehole after the compound blasting, which indicated the desired blasting effect. The CBT improves the accuracy and controllability of fractures and realizes precise directional control of rock strata.

Effects of Accumulated Damage on the Dynamic Properties of Coal Measures Sandstone

The coupling effect of accumulated damage and impact load substantially affects the integrity of the surrounding rock structure in deep coal mining engineering, which has inhibited safe and effective coal mining. Therefore, dynamic compression tests were performed on coal measures sandstone specimens with accumulated damage using the SHPB device. The effects of a high strain rate and accumulated damage on the sandstone’s mechanical behavior and damage evolution were investigated. The results reveal that accumulated damage has a considerable impact on specimen stress–strain curves and lowers dynamic compressive strength and deformation modulus substantially. The sandstone failure mode looks to be shear failure from a macroscopic perspective, while it appears to be intergranular fracture between the mineral particles from a microscopic perspective. The macroscopic and microscopic failure mechanisms of the sandstone specimens likewise conformed to the energy absorption law. The accumulated damage factor and the accumulated damage correction coefficient were presented in order to construct a statistical damage constitutive model of rocks based on the Weibull distribution. This model provides a decent description of the effects of accumulated damage and the strain rate on sandstone’s mechanical behavior, with parameters that are all of evident physical significance.

Optimization of Numerical Simulation Algorithm for Spontaneous Combustion in Goaf via a Compression Storage and Solution Method of Coefficient Matrix

In coal mine engineering, numerical software is used to analyze the behavior of coal rock damage and fluid migration. The order of the coefficient matrix used in numerical calculations is increasing, and this increases the computation steps in obtaining the coefficient matrix solution. The storage and solution of the coefficient matrix are key factors influencing the efficiency of the numerical software. Therefore, to save storage space and reduce the computation steps, the coefficient matrix must be effectively compressed and stored. In this work, the structural characteristics of different coefficient matrices are analyzed in detail, and we find that for different computational regions, as long as the nodes are numbered according to certain rules, the corresponding coefficient matrices will have similar structural characteristics. The nonzero elements are symmetrically distributed in the diagonal band, and all the elements on both sides outside the band are zero. Based on this, the coefficient matrix is compressed by a pivoting scheme, and the compressed matrix is directly eliminated by dislocation Gaussian elimination. Thus, a compressed storage method that integrates the compression and solution of the coefficient matrix is established. The compressed storage and calculation module is incorporated into our self-developed simulation software COMBUSS-3D to simulate the evolution of the temperature field in the goaf of Luling Coal Mine. Compared with the conventional method, the compressed storage module can significantly improve the computing rate of the simulation, by approximately 80%.

Research and Application of Integrated Presplitting Blasting in Nonpillar Mining Technology

This article introduces a technology of integrated presplitting blasting, which can be applied to a new nonpillar coal mining method (i.e., Gob-side Entry Retaining by Roof Cutting (GERRC)) under the condition of thick and hard roofs. First, the new nonpillar coal mining method emerging in China is explained. Then, the concept of integrated presplitting blasting was put forward, and the mechanism of the technology was explained by the method of numerical simulation. Through a mining case with a thick hard limestone roof, the relevant design of nonpillar mining and the design parameters of integrated presplitting blasting are explained in detail. After field practice verification, from the construction process and test results, as well as combined with underground pressure observation and analysis, it shows that technology and design are reasonable. This research supplements the mining technology system of coal mining engineering and the proposed technologies and methods have strong applicability, especially for related coal mines nonpillar mining and safe and efficient mining.

Evaluation of Water Inrush Risk in Deep Mines Based on Variable Weight and Unascertained Measure Theories and GIS

Water inrush is a serious geological disaster in deep coal mining and rock engineering in China. The occurrence of water inrush is affected by the interaction of many controlling factors in underground reservoir areas. In order to improve the accuracy of water inrush risk evaluation, the changes in index weights due to the change in influencing factors and the uncertain factors should be both considered. In this study, an evaluation model that integrates variable weight and unascertained measure (VWUM) theories was established. First, a modified credible degree recognition was established to make the evaluation results represent both the evaluation grade and the difference in the degree to which the indexes belong to the same grade. Then, the VWUM model was established by coupling the variable weight, unascertained measure, modified credible degree recognition, and geographic information system (GIS). Last, the VWUM model is applied to a case study to evaluate water inrush risk. Results indicates that more detailed risk grades and their spatial distribution zones can be obtained by the VWUM model compared with those obtained by the water inrush coefficient. The VWUM model can provide a more accurate evaluation result.

Research and Analysis on Mining Technology and Construction Safety Management of Coal Mine Engineering

Research and Analysis on Mining Technology and Construction Safety Management of Coal Mine Engineering

Study on Dynamic Mechanical Properties and Failure Mechanism of Sandstones under Real-Time High Temperature

The research on dynamic mechanical properties of rocks under high temperature is the basis for safe and efficient implementation of deep coal mining and underground coal gasification engineering. In this paper, the split Hopkinson bar (SHPB) with real-time high-temperature function was adopted to systematically study dynamic mechanical properties of sandstones. The research showed that under the condition of a fixed temperature, with the increase of strain rate, the dynamic compressive strength and dynamic peak strain of sandstone increased gradually, and the variation of dynamic elastic modulus with strain rate was not obvious. With the increase of temperature, the dynamic compressive strength of sandstone increased first and then decreased, the dynamic peak strain increased gradually, and the dynamic elastic modulus decreased overall. The variation law of macroscopic failure mode and energy dissipation density with temperature was revealed, and the change mechanism was explained considering the influence of high temperature on the internal structure of sandstone. Based on the principle of component combination and the theory of micro-element strength distribution, the dynamic statistical damage constitutive model was established, and its parameters had certain physical significance. Compared with the experimental results, the established model can well describe the dynamic stress-strain relationship of sandstone under real-time high temperature.

Research on Mining Process and Technology in Coal Mining Engineering

Research on Mining Process and Technology in Coal Mining Engineering

Application Analysis of Roadway Driving and Support Technology in Coal Mining Engineering

Application Analysis of Roadway Driving and Support Technology in Coal Mining Engineering

Prediction and Evaluation of Coal Mine Coal Bump Based on Improved Deep Neural Network

Coal bump prediction is one of the key problems in deep coal mining engineering. To predict coal bump disaster accurately and reliably, we propose a depth neural network (DNN) prediction model based on the dropout method and improved Adam algorithm. The coal bump accident examples were counted in order to analyze the influencing factors, characteristics, and causes of this type of accidents. Finally, four indexes of maximum tangential stress of surrounding rock, uniaxial compressive strength of rock, uniaxial tensile strength of rock, and elastic energy of rock are selected to form the prediction index system of coal bump. Based on the research results of rock burst, 305 groups of rock burst engineering case data are collected as the sample data of coal bump prediction, and then, the prediction model based on a dropout and improved Adam-based deep neural network (DA-DNN) is established by using deep learning technology. The DA-DNN model avoids the problem of determining the index weight, is completely data-driven, reduces the influence of human factors, and can realize the learning of complex and subtle deep relationships in incomplete, imprecise, and noisy limited data sets. A coal mine in Shanxi Province is used to predict coal bump with the improved depth learning method. The prediction results verify the effectiveness and correctness of the DA-DNN coal bump prediction model. Finally, it is proved that the model can effectively provide a scientific basis for coal bump prediction of similar projects.

Application Practice of Safety Management in Coal Mining Engineering

Application Practice of Safety Management in Coal Mining Engineering