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22 pages, 12876 KiB

Open AccessArticle

Development Law of Water-Conducting Fracture Zones in Overburden above Fully Mechanized Top-Coal Caving Face: A Comprehensive Study

by Tao Hu, Kaiqiang Han, Chunhua Song, Jiancheng Che, Bo Li, Taihu Huo and Tongxu Hu

Processes 2024, 12(10), 2076; https://doi.org/10.3390/pr12102076 - 25 Sep 2024

Cited by 1 | Viewed by 774

Abstract

Although it is of great significance to master the height of the water-conducting fracture zone (WCFZ) to prevent coal mine disasters and ensure safe production, the most important thing is to predict the height and range of the WCFZ ahead of the working [...] Read more.

Although it is of great significance to master the height of the water-conducting fracture zone (WCFZ) to prevent coal mine disasters and ensure safe production, the most important thing is to predict the height and range of the WCFZ ahead of the working face design before coal mining. Therefore, the 150313 fully mechanized top-coal caving working face of the Yinying coal mine was taken as the engineering background. The development laws of WCFZ were studied using comprehensive research methods, including similar simulation experiments, key strata theory, the experience formula, the numerical simulation, etc. The results show that the WCFZ evolution stage is “goaf–caving zone–fracture zone” and the developing pattern is in a non-isosceles trapezoid gradually developing upward and forward. The height of the WCFZ in the 150313 working face is 89.36 m, and the fracture/mining ratio is 12.46, which is consistent with the actual production. Apparently, the set of indoor research methods in this paper is feasible to predict the height and scope of the WCFZ. The research results can provide a scientific reference for safe mining of the 15^# coal seam in Shanxi Province and the prevention and control of roof water hazards. Full article

(This article belongs to the Special Issue Process Safety and Monitoring of Intelligent and Green Mining Technology)

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23 pages, 15633 KiB

Open AccessArticle

Control Study on Surrounding Rock of Gob-Side Entry Retaining below near Distance Goaf

by Shengrong Xie, Zaisheng Jiang, Dongdong Chen, Liwei Zhai and Zhiqiang Yan

Processes 2024, 12(9), 1966; https://doi.org/10.3390/pr12091966 - 12 Sep 2024

Cited by 1 | Viewed by 726

Abstract

To explore the control technology on surrounding rock of gob-side entry retaining (GSER) below a goaf in a near distance coal seam (NDCS), research was conducted on the floor ruin range, the floor stress distribution features, the layout of the GSER below near [...] Read more.

To explore the control technology on surrounding rock of gob-side entry retaining (GSER) below a goaf in a near distance coal seam (NDCS), research was conducted on the floor ruin range, the floor stress distribution features, the layout of the GSER below near distance goaf, the width of the roadside filling wall (RFW), and the control technology of the GSER surrounding rock below the near distance goaf after upper coal seam (UCS) mining. The results show that (1) the stress of the goaf floor has obvious regional features, being divided into stress high value zone (Zone A), stress extremely low zone (Zone B), stress rebound zone (Zone C), stress transition zone (Zone D), and stress recovery zone (Zone E) according to different stress states. The stress distribution features at different depths below the goaf floor in each zone also have differences. (2) Arranging the roadway in Zone A below a coal pillar, the roadway is at high stress levels, which is not conducive to the stability of the surrounding rock. Arranging the roadway in Zone B below the goaf floor, the bearing capacity of the surrounding rock itself is weak, making it difficult to control the surrounding rock. Arranging the roadway in Zone C, the mechanical properties of the surrounding rock are good, and the difficulty of controlling the surrounding rock is relatively low. Arranging the roadway in Zone D and Zone E, there is a relatively small degree of stress concentration in the roadway rib. (3) When the RFW width is 0.5–1.5 m, stress concentration is more pronounced on the solid coal rib, and the overlying rock pressure is mainly borne by the solid coal rib, with less stress on the RFW. When the RFW width is 2~3 m, the stress on the RFW is enhanced, and the bearing capacity is significantly increased compared to RFW of 0.5–1.5 m width. The RFW contributes to supporting the overlying rock layers. (4) A comprehensive control technology for GSER surrounding rock in lower coal seam (LCS) has been proposed, which includes the grouting modification of coal and rock mass on the GSER roof, establishing a composite anchoring structure formed by utilizing bolts (cables); the strong support roof and control floor by one beam + three columns, reinforcing the RFW utilizing tie rods pre-tightening; and the hydraulic prop protection RFW and bolts (cables) protection roof at roadside. This technology has been successfully applied in field practice. Full article

(This article belongs to the Special Issue Process Safety and Monitoring of Intelligent and Green Mining Technology)

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35 pages, 4987 KiB

Open AccessArticle

Study on the Damage Evolution and Failure Mechanism of Floor Strata under Coupled Static-Dynamic Loading Disturbance

by Hailong Li, Haibo Bai, Wenjie Xu, Bing Li, Peitao Qiu and Ruixue Liu

Processes 2024, 12(7), 1513; https://doi.org/10.3390/pr12071513 - 18 Jul 2024

Viewed by 960

Abstract

In the field test, we found that the failure depth of the goaf floor strata tends to be further because the periodic breaking and caving of the immediate roof, upper roof, and roof key stratum has dynamic stress disturbance effects on the floor. [...] Read more.

In the field test, we found that the failure depth of the goaf floor strata tends to be further because the periodic breaking and caving of the immediate roof, upper roof, and roof key stratum has dynamic stress disturbance effects on the floor. To further analyze its formation mechanism, this paper studies the damage evolution and fracture mechanism of goaf floor rock under the coupled static-dynamic loading disturbance caused by roof caving, based on the stress distribution state, the damage evolution equation of coal measure rock, the damage constitutive model, and the fracture criterion of floor rock. The main conclusions are listed as follows: 1. Based on the mining floor stress distribution, the floor beam model establishes the response mechanism of floor rock stress distribution. Also, the equation of stress distribution at any position in floor strata under mining dynamic load is given. 2. Combining the advantages of Bingham and the Generalized-Boydin model, the B-G damage constitutive model is established, which can describe the constitutive characteristics of coal measure rock under the coupled static-dynamic loading disturbance well. Furthermore, the variation law of parameters changing with strain rate is analyzed. 3. According to the twin-shear unified strength yield theory and the B-G damage constitutive model, coal measure rock’s twin-shear unified strength damage fracture criterion is established. Finally, the stress distribution expression of floor strata under concentrated and uniform dynamic loads is introduced, and the fracture criterion of goaf floor strata under a coupled static-dynamic loading disturbance is proposed. Full article

(This article belongs to the Special Issue Process Safety and Monitoring of Intelligent and Green Mining Technology)

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25 pages, 11804 KiB

Open AccessArticle

The Fracture Evolution Mechanism of Tunnels with Different Cross-Sections under Biaxial Loading

by Lexin Jia, Shili Qiu, Yu Cong and Xiaoshan Wang

Processes 2024, 12(5), 891; https://doi.org/10.3390/pr12050891 - 28 Apr 2024

Viewed by 1007

Abstract

Biaxial compression tests based on an elliptical tunnel were conducted to study the failure characteristics and the meso-crack evolution mechanism of tunnels with different cross-sections constructed in sandstone. The progressive crack propagation process around the elliptical tunnel was investigated using a real-time digital [...] Read more.

Biaxial compression tests based on an elliptical tunnel were conducted to study the failure characteristics and the meso-crack evolution mechanism of tunnels with different cross-sections constructed in sandstone. The progressive crack propagation process around the elliptical tunnel was investigated using a real-time digital image correlation (DIC) system. Numerical simulations were performed on egg-shaped, U-shaped, and straight-walled arched tunnels based on the mesoscopic parameters of the elliptical tunnel and following the principle of an equal cross-sectional area. The meso-crack evolution and stress conditions of the four types of tunnels were compared. The results show that (1) fractures around an elliptical tunnel were mainly distributed at the end of the long axis and mainly induce slabbing failure, and the failure mode is similar to a V-shaped notch; (2) strain localization is an important characteristic of rock fracturing, which forebodes the initiation, propagation, and coalescence paths of macro-cracks; and (3) the peak loads of tunnels with egg-shaped, U-shaped, and straight-walled arched cross-sections are 98.76%, 97.56%, and 90.57% that of an elliptical cross-section. The elliptical cross-section shows the optimal bearing capacity. Full article

(This article belongs to the Special Issue Process Safety and Monitoring of Intelligent and Green Mining Technology)

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17 pages, 9319 KiB

Open AccessArticle

Critical Failure Characteristics of a Straight-Walled Arched Tunnel Constructed in Sandstone under Biaxial Loading

by Jian Gao, Xiaoshan Wang, Yu Cong, Qiqi Li, Yequan Pan and Xianglin Ding

Processes 2024, 12(4), 841; https://doi.org/10.3390/pr12040841 - 22 Apr 2024

Viewed by 1279

Abstract

To characterize the failure of rock mass surrounding underground tunnels, biaxial compression tests were conducted on a real sandstone model with a straight-walled arched hole. The acoustic emission (AE) system and digital image correlation (DIC) optical inspection equipment were used to investigate the [...] Read more.

To characterize the failure of rock mass surrounding underground tunnels, biaxial compression tests were conducted on a real sandstone model with a straight-walled arched hole. The acoustic emission (AE) system and digital image correlation (DIC) optical inspection equipment were used to investigate the crack evolution process and failure precursors of the tunnel. A two-dimensional particle flow code (PFC2D) was used to conduct numerical simulations on the sample, so as to investigate the mesoscopic failure mechanism of rock mass. The results show that the failure of the single tunnel constructed in sandstone occurs mainly in the walls on both sides (between the spandrels and arch feet), showing slabbing failure characteristics and a certain abruptness. The crack initiation in sandstone in early stage is not obvious, and the crack propagation in rock mass is rapid when acoustic emissions are enhanced. The small increments in the AE count and amplitude and the continuous reduction in the b-value can be used as precursors for the failure of rock mass. When the height–span ratio is 0.8 and 1.0, the stress distribution around the chamber is more uniform, and when the height–span ratio is greater than 1.0, the stress is mainly concentrated in the vault and arch bottom. In the PFC simulations, tensile fractures firstly initiate in the middle of walls and at the arch feet, arcuate fracture concentration zones are then formed, in which shear fractures appear and a few particles spall from the surfaces. When approaching the ultimate bearing capacity, rock masses on both sides of the tunnel are fractured over large areas, and the slender coalesced fractured zone develops to the deep part of rock mass, causing failure of the sample. Full article

(This article belongs to the Special Issue Process Safety and Monitoring of Intelligent and Green Mining Technology)

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21 pages, 8012 KiB

Open AccessArticle

A Method for Predicting Ground Pressure in Meihuajing Coal Mine Based on Improved BP Neural Network by Immune Algorithm-Particle Swarm Optimization

by Xingping Lai, Yuhang Tu, Baoxu Yan, Longquan Wu and Xiaoming Liu

Processes 2024, 12(1), 147; https://doi.org/10.3390/pr12010147 - 7 Jan 2024

Cited by 7 | Viewed by 1745

Abstract

Based on the background of dynamic mining pressure monitoring and pressure prediction research on the No. 232205 working face of the Meihuajing coal mine, this study systematically investigates the predictive model of mining pressure manifestation on the working face of the Meihuajing coal [...] Read more.

Based on the background of dynamic mining pressure monitoring and pressure prediction research on the No. 232205 working face of the Meihuajing coal mine, this study systematically investigates the predictive model of mining pressure manifestation on the working face of the Meihuajing coal mine by integrating methods such as engineering investigation, theoretical analysis, and mathematical modeling. A mining pressure manifestation prediction method based on IA-PSO-BP is proposed. The IA-PSO optimization algorithm is applied to optimize the hyperparameters of the BP neural network, and the working face mining pressure prediction model based on IA-PSO-BP is established. The mean absolute error (MAE), mean square error (MSE), and coefficient of determination (R²) are selected as evaluation indicators to compare the prediction performance of the BP model, PSO-BP model, and IA-PSO-BP model. The experimental results of the model show that the convergence speed of the IA-PSO-BP model is about eight times faster than that of the BP model and two times faster than that of the PSO-BP model. Compared with the BP and PSO-BP models, the IA-PSO-BP model has the smallest MAE and MSE and the largest R² on the three different data sets of the test set, indicating significantly improved prediction accuracy. The predicted results conform to the periodic variation pattern of mining pressure data and are consistent with the actual situation in the coal mine. Full article

(This article belongs to the Special Issue Process Safety and Monitoring of Intelligent and Green Mining Technology)

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13 pages, 5129 KiB

Open AccessArticle

Microseismic Monitoring of the Fracture Nucleation Mechanism and Early Warning for Cavern Rock Masses

by Jin-Shuai Zhao, Yue-Mao Zhao, Peng-Xiang Li, Chong-Feng Chen, Jian-Cong Zhang and Jiang-Hao Chen

Processes 2023, 11(9), 2800; https://doi.org/10.3390/pr11092800 - 20 Sep 2023

Cited by 2 | Viewed by 1407

Abstract

The rock mass is susceptible to instability and damage during cavern construction. The blast-induced cracking process of the rock mass contains a wealth of information about the precursors of instability, and the identification of fracture nucleation signals is a prerequisite for effective hazard [...] Read more.

The rock mass is susceptible to instability and damage during cavern construction. The blast-induced cracking process of the rock mass contains a wealth of information about the precursors of instability, and the identification of fracture nucleation signals is a prerequisite for effective hazard warning. A laboratory mechanical test and microseismic (MS) monitoring were carried out in the Baihetan Cavern to investigate the fracture nucleation process in the rock mass. MS monitoring shows that pre-existing microcracks were closed or new cracks were generated under the action of high stress, which caused the migration of microcracks. As the crack density increases, the fracture interaction gradually increases. The study of the rock fracture nucleation mechanism helps to reveal the MS sequences during the rock fracture process, and the fore-main shock was found in the MS sequence during access tunnel excavation. This study can effectively provide guidance for the early warning of rock mass failure and the stability analysis of underground caverns under blasting excavation disturbance. Full article

(This article belongs to the Special Issue Process Safety and Monitoring of Intelligent and Green Mining Technology)

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14 pages, 4150 KiB

Open AccessArticle

Experimental Investigation of the Relationship of Failure Mode and Energy Dissipation in Grouted Rockbolt Systems under Pullout Load

by Shuisheng Yu, Yawei Wang, Honghao Yang and Shucan Lu

Processes 2023, 11(9), 2601; https://doi.org/10.3390/pr11092601 - 31 Aug 2023

Viewed by 1100

Abstract

In underground engineering, the deformation of surrounding rock caused by “three heights and one disturbance” leads to the failure of grouted rockbolt systems, which causes huge economic losses to the mining industry. The research shows that the failure process of grouted rockbolt systems [...] Read more.

In underground engineering, the deformation of surrounding rock caused by “three heights and one disturbance” leads to the failure of grouted rockbolt systems, which causes huge economic losses to the mining industry. The research shows that the failure process of grouted rockbolt systems is the result of energy accumulation and release, but the relationship between failure mode and energy dissipation is rarely studied. Based on this, the load transfer behavior, energy dissipation, failure mode and failure mechanism of the grouted rockbolt systems are investigated from the perspective of energy in this study using the indoor pullout test. Test results show that the load decreases rapidly, and the absorbed energy decreases due to the whole-body splitting crack. The absorbed energy of the specimen in the splitting crack mode is lower than that in the pullout failure mode. When the pullout load reaches its peak, the pullout load of the specimen with split failure mode decreases sharply. Meanwhile, the load of the specimen with pullout failure mode is relatively slow, and the energy absorption rate decreases gradually due to the occurrence of cracks. However, the reduction in the energy absorption rate under pullout failure is lower than that under split failure. The radial pressure in the grouted rockbolt systems increases due to the wedge action. When the radial pressure exceeds the tensile strength of concrete, the specimen will experience split failure, otherwise pullout failure will occur. Full article

(This article belongs to the Special Issue Process Safety and Monitoring of Intelligent and Green Mining Technology)

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