矿业科学学报

Progress of lithology identification technology while drilling

Yue Zhongwen, Yue Xiaolei, Yang Renshu, Wang Xu, Li Wei, Dai Shiqing, Li Yang

2022, 7(4): 389-402. doi: 10.19606/j.cnki.jmst.2022.04.001

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Abstract:
Lithology identification while in drilling is a convenient and efficient technology to obtain information about formation. It has the advantages of instant, accurate, environmental protection and energy saving. It can be applied to field of engineering such as rock bound aries determination, support parameter design, blast parameter design, and regional formation strength parameter identification. And it has always been the focus of research by scholars in domestic and foreign. This paper systematically analyzes the research status and development trend of lithology identification while in drilling technology, combined with the application of lithology identification while drilling technology in recent years, discusses the technology of lithology identification while drilling as a new method and new theory of intelligent detection. First, the development history of key technologies for lithology identification while drilling in domestic and foreign is summarized. Secondly, it focuses on the research status, including the technical principle and system composition, and compares and evaluates some typical lithology identification systemsin domestic and foreign. Thirdly, the response relationship between the drilling parameters and the rock during the drilling process is summarized, and the established drilling index and evaluation system, and the factors affecting the lithology identification while drilling is discussed according to the two drilling methods of rotary cutting and rotary cutting-impact. Finally, according to the development trend of the research field of lithology identification while drilling technology, the problems existing in the engineering application at this stage are summarized, and the future research of lithology identification while drilling technology is prospected.

Technology path and assumptions of intelligent surrounding rock control at longwall working face

Yang Shengli, Wang Jiachen, Li Ming

2022, 7(4): 403-416. doi: 10.19606/j.cnki.jmst.2022.04.002

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Abstract:
The intelligent surrounding rock control at longwall working face is the necessary condition to realize the intelligent mining of working face. This paper redefined the connotation of the surrounding rock system at longwall working face and clarified the scope of surrounding rock control and clarified the scope of surrounding rock control, which includes small structure of support surrounding rock within its basic topic range in the vertical direction, and the far field rock layer that will have an effect on surrounding rock control at longwall working face. The factors of surrounding rock system at longwall working face are classified, there are "controllable factors" and "uncontrollable factors" according to the mode of action. The points and basic principles of intelligent surrounding rock control are determined. Multi-parameter intelligent detection, precise analysis of pattern discriminations, self-determination, quick implementation and dynamic evaluation of control effects which is technological framework for intelligent control is established. Furthermore, scientific issues and critical technical problems of intelligent surrounding rock control at longwall working face are elaborated. The four key technology assumptions based on this are "intelligent mining system at working face", "adaptive intelligent control technology of equipment-surrounding rock", "intelligent control of complex conditions surrounding rock", and "stability analysis of surrounding rock system at longwall working face under unified coordinate system". The extractability of the information on the working conditions of support is analyzed with the actual case, and the intelligent prediction of mine pressure at longwall working face is realized by the stacked LSTM algorithm.

Generalized Δlog R model with spontaneous potential and its application in predicting total organ carbon content

Miao Huan, Wang Yanbin, Ma Zhentao, Guo Jianying, Zhang Yujian

2022, 7(4): 417-426. doi: 10.19606/j.cnki.jmst.2022.04.003

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Abstract:
In order to accurately predict the total organic carbon content of Middle Permian taodonggou group source rocks in Turpan Hami basin, based on the analysis of the relationship between logging parameters of multiple wells and organic matter abundance in the study area, the generalized Δlog R model is extended, that is, a generalized Δlog R model with spontaneous potential is proposed. It is found that the source rock in the study area has a weak positive correlation with resistivity density, a weak negative correlation with spontaneous potential, spontaneous gamma and density, and little correlation with neutrons. Compared with other methods, the correlation coefficient (R²) of the generalized Δlog R model with spontaneous potential is 0.804 2 and the average error rate is 15.58 %, which is the best method to predict the total organic carbon content of the source rocks of the Middle Permian Taodonggou group in the area. The results provide a basis for logging evaluation of source rocks in the study area.

Research and application of inversion parameters based on geological statistics inversion in transparent mines rock major modeling

Chen Baiping, Cui Fan, Liu Bo, Du Yunfei, Wang Zichang

2022, 7(4): 427-436. doi: 10.19606/j.cnki.jmst.2022.04.004

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Abstract:
In order to provide the basic data of lithology modeling with high resolution in the early stage of coal precise mining geological guarantee, this paper established the p-wave impedance model of wedge-shaped coal seam according to the thickness and storage conditions of coal measure strata based on geostatistical inversion theory. The influence of different probability density functions and transverse range parameters on thickness inversion of coal seam are analyzed through multiple inversion experiments. The effect of inversion under different amount and location constraints is further discussed. Experimental results show that geostatistical inversion parameters have a great influence on the inversion results. Reasonable probability density function, lateral range and constrained well selection can improve the accuracy of inversion. Results shows that geostatistical inversion can predict about 1 m thin coal seam, and the error range between the inversion coal seam thickness and the logging data is 1.82 % ~12.24 %. It is therefore feasible to predict the thickness of thin coal seam, and can provide valuable modeling data for the early lithologic geological modeling of "transparent mine".

First-break picking technology based on level set method and U-Net

Li Yang, He Dengke

2022, 7(4): 437-445. doi: 10.19606/j.cnki.jmst.2022.04.005

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Abstract:
In order to solve the discontinuous problems in the seismic first-break breaking using the U-Net network, a variantone based on level set method is proposed. Firstly, the feature map of seismic image is extracted based on U-Net network, and the loss is calculated pixel by pixel. Then the level set loss is calculated by using the level set method. Finally, the weighted sum of the two is taken as the final loss function. The improved network uses the level set method to ensure the continuity of first breaks between the adjacent seismic channels, and retains its ability of "end-to-end" fine classification. The Focal Loss function is used to alleviate the imbalance of sample categories of the training set. The mixed training set combined with the synthetic data and the actual field data is used to overcome the training set insufficiency problem. The results tested by the theoretical data and actual seismic data show that the improved U-Net network can improve the picking accuracy and robustness in low signal-to-noise ratio seismic data.

The comparison of quality control standards for land reclamation between China and the USA: A case study of grassland surface coal mines

Li Jing, Ma Tianyue, Yan Xiaoxiao, Anna Waitkus

2022, 7(4): 446-455. doi: 10.19606/j.cnki.jmst.2022.04.006

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Abstract:
Mineral resource extraction causes serious damage to land ecology and environment, therefore a perfect reclamation quality standard is crucial to the construction of ecological civilization in mined area. It is important to optimize the land reclamation quality control standards by revealing the differences in their methods and contents between China and the USA. This study systematically compared the quality control standards for land reclamation in the northern grassland region of China and Wyoming, in terms of reconstruction of landform, soil, vegetation, and hydrology. The result shows that the geomorphological reconstruction does not focus enough on the restoration of pre-mining landscape and landscape coordination, the soil reconstruction index system is comparatively weak, the control of vegetation reconstruction is limited to quantitative values of measurable indicators and does not considering the pre-mining plant growth, and there is a lack of control standards for hydrological restoration quality. The study proposes the following improvement through a point-by-point approach: (1) adjusting the parameter range of terrain indicators to control the terrain restoration to approximate the pre-mining landscape; (2) enriching the soil quality control index system according to the mining species and reclamation direction; (3) improving the control standards of vegetation type and reconstruction time frame, setting the pre-mining reference area and using mathematical statistics to verify the reclamation quality; (4) increasing the control standards of water resources restoration according to the pre-mining information; (5) promoting the standards to the national level. The results of the study can provide a theoretical basis for scientific guidance on quality control of land reclamation and improvement of indicating reclamation success.

Study of the nonlinear mechanical behavior of rock materials using the FFT numerical method based on the actual mesostructure

Li Mingyao, Peng Lei, Zuo Jianping, Wang Zhimin, Li Shaojin, Xue Xiren

2022, 7(4): 456-466. doi: 10.19606/j.cnki.jmst.2022.04.007

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Abstract:
Rock heterogeneity (such as mineral inclusions, micro-cracks, micro-voids and other microstructures) significantly affects its nonlinear mechanical behavior and failure process. This paper utilizes the Fast Fourier transform-based(FFT) numerical method which does not require meshing of complex microstructure but directly obtains the microstructure of heterogeneous materials through the pixels of the image. In addition, the method can be naturally combined with digital image processing (DIP). An actual-microstructure-based FFT method is thereby developed to simulate the elastoplastic behavior of the heterogeneous rocks under external load. The influence of microstructure on the nonlinear behavior is discussed as well as the internal relationship between the microstructure and the macroscopic mechanical properties. The results show that the real-microstructure-based FFT method can well predict the nonlinear behavior before and after the peak strength of the rocks under different depths and confining pressures. The shape, size and distribution of microstructure directly determine the distribution of stress field in clay rock. The actual-microstructure-based FFT method proposed in this paper can reasonably consider the rock heterogeneity, and provides an important tool for studying the influence of the rock microstructure characteristics on the nonlinear mechanical behavior.

Study on calculation method of bending moment and deflection of underlying layer under soil pressure

Wang Xueqing, Wang Zhuangzhuang, Wang Jianhua

2022, 7(4): 467-473. doi: 10.19606/j.cnki.jmst.2022.04.008

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Abstract:
Surface layer is an important part of foundation pit supporting system. For the purpose of designing the surface layer reasonably, this paper established a forced model of the surface layer by using the small deflection bending theory of thin plate, and the forced analysis was carried out on the surface layer of shotcrete foundation pit support type. In order to simplify the calculation, the concrete surface layer is assumed to be an elastic body, and the surface layer is simplified as a rectangular thin plate with four sides simply supported on the foundation pit slope, which derives in the general expressions of the deflection and bending moment of the bottom layer under active earth pressure. And the bending moment and deflection of the bottom layer after the foundation pit excavation are simulated by the finite difference software FLAC^3D. The results show that the theoretical values of the deflection and bending moment are in agreement with those of numerical simulation, the margin of error between the calculation value and the simulation value of the maximum deflection and maximum bending moment are 6 % and 13 % respectively, the distribution laws which simulation cloud pictures of the deflection and bending moment show are consistent with those calculated by the formulas. The deflection and bending moment both reduce gradually from the surface center to boundary, which verifies the effectiveness of the proposed method. The formulas can provide reference for the design of surface layer.

A study on relationships between measured crustal stresses and depth based on spherical shell model

Liu Bingquan, Li Liyun, Wei Mengxi, Wang Bonan, Wang Zhidong

2022, 7(4): 474-480. doi: 10.19606/j.cnki.jmst.2022.04.009

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Abstract:
Due to the exploitation of mineral resources in the deep underground space, it is more and more important to study the variation trend of deep in-situ stress field. In recent years the researches have updated many in-situ stress data. It is necessary to improve the existing estimation methods on this account. Based on the basic theory of elasticity and spherical shell model, this paper studied the effect of gravitational body force varying with depth and internal pressure, and obtained the theoretical formula of macro in-situ stress distribution; Employing the latest and widely distributed measured data, this paper fitted the crustal physical parameters in the theoretical formula, and obtained the fitting formula of vertical in-situ stress and average horizontal in-situ stress varying with depth. The results show that: the distribution of crustal stresses with depth is no longer linear on the macroscopic scale of the Earth; however, within the current depth range of human activities, basically the average in-situ stresses vary linearly with depth, which is closest to the results of the Dinnick hypothesis at γ=22 kN/m³ and λ=0.9; with the increase of depth, the average lateral pressure coefficient gradually approaches 1, which is closer to the measured data than the envelope proposed by Brown and Hoek; the high pressure in the crust will cause horizontal tensile stress, but the compressive stress generated by gravity is higher and therefore the vertical and horizontal in-situ stress in the whole crust are compressive stress. The research results provide a theoretical prediction model for the estimation of crustal stress distribution trend, especially in deep underground space.

Modified Hoek-Brown criterion model for laminated rock based on fracture mechanics

Li Yingjie, Wang Bingqian, Zuo Jianping, Xue Dongjie, Liu Dejun

2022, 7(4): 481-489. doi: 10.19606/j.cnki.jmst.2022.04.010

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Abstract:
Based on the fracture mechanics theory of the isotropic Hoek-Brown strength criterion, this paper established the initiation conditions of the bifurcated microcrack along bedding which begins with the meso-fracture mechanism of laminated rocks. Then the author substituted the critical angle which indicates that the initial crack most likely causes the fracture of the rock into above established conditions and derived the anisotropy expression of the parameter m₁ for the weak plane of bedding leading to the crack deflection. Through introducing the correction coefficient for the mixed fracture of the rock along the bedding and the matrix, this paper obtained the anisotropic modified model of Hoek-Brown strength criterion. Compared with the established anisotropic Hoek-Brown model and shale triaxial test results, the validity of the model was proved. The modified model inherits the fracture mechanics analysis of the isotropic Hoek-Brown strength criterion for the selection of rock failure characteristic quantity, and reflects the microscopic failure mechanism of the rock, also considers the effect of bedding anisotropy. The parameters in the modified criterion have a clear physical meaning. The parameter m in the model is related to the angle of the bedding plane, the tensile strength, compressive strength and friction coefficient of bedding and matrix. The change in the friction coefficient of the bedding plane will cause the position of the minimum value of m and the rock strength characteristics changed.

A study on collision warning of gas wells in coal-gas cross mining area

Wang Wen, Yang Kun, He Yun, Wang Bin, Gao Fei, Pan Yexin

2022, 7(4): 490-497. doi: 10.19606/j.cnki.jmst.2022.04.011

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Abstract:
Along with the gradual normalization of coordinated cross-mining of multiple mineral resources, the safety situation of natural gas wells has become increasingly serious. Taking coal-gas cross-mining in the Ordos Basin as the research object, this paper proposed an anti-collision early warning method based on vibration wave monitoring prevent the occurrence of collision accidents between roadheader and gas well. Through the steel pipe percussion vibration test and coal mine excavation vibration test, the attenuation law of vibration waves in the steel pipe and coal rock is studied, and the formula for calculating the distance from the roadheader to the natural gas well is deduced according to the vibration attenuation law. The results show that the attenuation coefficients of vibration waves in steel pipes and coal rocks are different, but the attenuation laws are basically the same, both conforming to the exponential attenuation law, with the vibration waves first decaying rapidly and then slowly. It provides a reference for the realization of surface monitoring of the distance from the roadheader to the natural gas well, preventing collision and predicting early warning.

Characteristics and evolution law of low-temperature oxidation of oxidized coal at recrudescence stage

Chen Rongfang, Guo Zhiguo, Zhang Jun, Zhao Yu

2022, 7(4): 498-504. doi: 10.19606/j.cnki.jmst.2022.04.012

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Abstract:
In order to explore the low-temperature oxidation characteristics and evolution law of oxidized coal, this paper adopted a temperature-programmed experiment system. Firstly, the low-temperature oxidation temperature-programmed experiment was carried out on the oxidized coal formed by N₂ anaerobic cooling after the coal samples were pre-oxidized to 60 ℃, 90 ℃, 120 ℃, 150 ℃, 180 ℃ and 210 ℃ respectively. At the same time, in order to further reveal the characteristics of low-temperature oxidation behavior of oxidized coal formed under different fire extinguishing conditions, the low-temperature oxidation temperature programmed test was carried out on the oxidized coal formed after fire extinguishing with three different volume fractions of N₂ when the coal sample was pre-oxidized to 120 ℃. This reveals the changes of oxygen consumption rate, production rate of signature gases (CO, CO₂) and heat release intensity of these two kinds of oxidized coals during low temperature oxidation process. The results show that the oxygen consumption rate, signature gas generation rate and heat release intensity of oxidized coal are all lower than those of raw coal. Furthermore, the spontaneous combustion characteristic parameters of coal samples pre-oxidized to 90 ℃ are closer to that of raw coal, indicating that coals pre-oxidized to critical temperature are more likely to reignite. When pre-oxidized to 120 ℃, the higher the volume fraction of N₂, the closer the spontaneous combustion characteristic parameters of this oxidized coal are to the original coal, indicating that the coal with higher volume fraction of N₂ has stronger recrudescence ability. Therefore, it is necessary to prevent the recurrence of coal when mining the coal body in the near coal seam group, the recrudescence working face and the unsealing fire area.

Determining reasonable position of roadway for close coal seam

He Fulian, Yang Yang, Li Liang, Ouyang Feng, Zhang Xiao, Fu Lihong

2022, 7(4): 505-512. doi: 10.19606/j.cnki.jmst.2022.04.013

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Abstract:
To study the layout of the short-distance thick underlying coal seam stopping roadway in Yanzishan Mine, a mechanical model of the remaining coal pillars in 4216 and 4218 of No. 4 sides of the overlying coal seam through theoretical calculation, and clarified the transfer law of the principal stress difference of the remaining coal pillars in the floor. The author simulated the distribution characteristics of vertical stress, horizontal stress and difference between principal stresses at different depths of floor by using FLAC^3D numerical software, and analyzeds the principal stress difference and the stress reducing area roadway within the reasonable factors that influence of the reasonable inner distance. The results show that the roadway layout should avoid the peakand be in the environment of principal stress difference. When the horizontal distance of the lower coal seam is more than 30 m from the edge of the overlying coal pillar, the vertical stress is close to the original rock stress, the average principal stress difference is less than 1.24 MPa, and the principal stress difference change rate is low. Finally, the mining roadway of the working face of the lower coal seam is arranged with an inner stagger distance of 30 m. The field practice shows that the deformation of the surrounding rock is small under the misspacing, which can ensure the safety and efficient production of the mine.

2022 Vol. 7, No. 4