scholarly journals The corresponding relationship between the change of goaf pressure and the key stratum breaking

2019 ◽  
Vol 16 (5) ◽  
pp. 913-925
Author(s):  
Jianlin Xie ◽  
Jialin Xu
Keyword(s):  
Rock Mass ◽  
Internal Pressure ◽  
Load Transfer ◽  
Physical Simulation ◽  
Field Measurements ◽  
Monitoring Methods ◽  
Key Stratum ◽  
Working Face ◽  
Actual Rock ◽  
Overlying Strata

Abstract Existing studies mostly focus on the stress change of coal in front of a goaf, but rarely conduct field monitoring on the internal pressure of a goaf, primarily due to the complex environment and other restrictive conditions of goafs. This paper first used physical simulation to monitor and analyze the internal pressure of goaf and found that goaf pressure presented a stepwise growth with the key stratum breaking. In addition, field measurements were conducted to monitor the goaf pressures of two different working faces. Goaf pressures both presented linear growth with the advance of the working face. According to comparative analysis, there were some differences between the two monitoring methods in terms of the corresponding relationship. This reflects that in the actual rock mass, after the breaking of a key stratum, the loads of the strata under its control are not transferred to the goaf instantaneously and load transfer characteristics are probably related to roof separation distribution characteristics of overlying strata, the bulking characteristics of caved rock mass, lateral stress limitation and other factors. The results of this study will offer some guidance for studies on the movement laws of overlying strata and the load transfer of overlying strata above goafs.

scholarly journals Strong Ground Pressure Mechanism and Control at the Longwall Top Coal Caving with a Single Key Stratum in Goaf

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Ke Yang ◽  
Xiaolou Chi ◽  
Wenjie Liu ◽  
Litong Dou ◽  
Zhen Wei
Keyword(s):  
Structural Model ◽  
Field Measurements ◽  
Directional Hydraulic Fracturing ◽  
Key Stratum ◽  
Ground Pressure ◽  
Working Face ◽  
Support Resistance ◽  
Roadway Deformation ◽  
Longwall Top Coal Caving ◽  
Strong Ground

A strong ground pressure in the multiseam environment manifested by rib spalling and roadway deformation at the fully mechanized working face was assessed by a comprehensive combination of field measurements, physical simulations, and theoretical analysis for two coal seams in the Buertai Coal Mine in China. A structural model of overlying stratum collapse at the working face with the key stratum breaking instability was proposed, the mechanism of strong ground pressure at the longwall top coal caving working face with a single key stratum in goaf was identified, and respective control countermeasures were developed. The latter implied the directional hydraulic fracturing for supporting the key stratum-surrounding rocks, which effectively reduced the cyclic weighting intensity and weighting interval in the working face with a single key stratum in the goaf. The working face cyclic breaking interval was assessed at 30 m. After the key stratum collapse, soft rocks underwent synergistic deformation and a cutting-type failure. The goaf effect on the hydraulic support resistance in the fully mechanized working face was assessed, and cutting blocks from the overlying stratum collapse were identified as the main sources of strong ground pressure.

scholarly journals Study on Rules of Fault Stress Variation Based on Microseismic Monitoring and Numerical Simulation at the Working Face in the Dongjiahe Coal Mine

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Ke Ma ◽  
Fuzhen Yuan ◽  
Duanyang Zhuang ◽  
Quansheng Li ◽  
Zhenwei Wang
Keyword(s):  
Numerical Simulation ◽  
Rock Mass ◽  
Coal Mine ◽  
Maximum Principal Stress ◽  
Microseismic Monitoring ◽  
Stress Variation ◽  
Fault Activation ◽  
Working Face ◽  
Damage Theory ◽  
Overlying Strata

Microseismic monitoring technology was used to study the real-time evolution of rock mass damage generated by a working face as it approached a fault in Dongjiahe Coal Mine. The influence of vertical zoning of overlying strata on damage at the fault was analyzed. Numerical simulation using finite element method based on meso-statistical damage theory was used to investigate the nonlinear and nonuniform failure behaviour of the rock mass near the fault. The response of the fault stress to excavation activity and the rule of fault activation were examined. The results show that the fault damage has segmental characteristics. Microcracks are first generated at the fractured zone that is divided into lower, middle, and upper sections, located 30∼70 m, 120∼180 m, and 230∼280 m above the coal seam, respectively. There was also a segmentation phenomenon in the stress response of fault. The risk of fault activation was evaluated by using the ratio of shear stress to the maximum principal stress. When the working face was 260 m and 140 m away from the fault, the activation risk at the upper-middle and lower sections began to increase, respectively. When the fault was within 60 m, the risk of fault activation was highest.

scholarly journals Mechanism of Overlying Strata Structure Instability during Mining below Unconsolidated Confined Aquifer and Disaster Prevention

2021 ◽  
Vol 11 (4) ◽  
pp. 1778
Author(s):  
Xiaozhen Wang ◽  
Weibing Zhu ◽  
Jialin Xu ◽  
Hongkai Han ◽  
Xiang Fu
Keyword(s):  
Load Transfer ◽  
Water Inrush ◽  
Prediction Method ◽  
Mine Safety ◽  
Economic Losses ◽  
Confined Aquifer ◽  
Cemented Sand ◽  
Key Stratum ◽  
Working Face ◽  
Fundamental Reason

There is a layer of the unconsolidated confined aquifer (UCA) made of non-cemented sand and grit on the bed of Quaternary thick topsoil in many coal mines in east and north China. Existing on the bedrock of coal measures, it poses a serious threat to coal mine safety. Worse, it caused many supports crushing and water inrush disasters (SCWIDs) and resulted in significant economic losses. Aiming at the above problems, this paper adopts a simulation experiment, field measurement, engineering detection, and theoretical analysis to conduct the research. The research reveals the overburden’s destructive rules during mining under UCA. The results indicate that UCA plays an important role in the process of load transfer due to its mobility and replenishment in time. When mining close to the aquifer, the load transfer of aquifer leads to overburden breaking entirely and sliding instability of the bond-beam structure, then, the water flowing fractured zone develops rapidly and connects the aquifer, which is the fundamental reason for SCWID under the UCA. Based on the mechanism of SCWID, a prediction method of support crushing and water inrush hazard zones was put forward. Artificial pre-split blasting based on the location of a key stratum was applied to prevent SCWID. The proposed methods have been used in 7131 working face and safe mining was achieved.

scholarly journals Numerical Study on the Movement Laws of Overlying Strata in Shallow-Buried Stope Based on the Goaf Compaction Effect

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Guangchao Zhang ◽  
Guangzhe Tao ◽  
Miao Chen ◽  
You Li ◽  
Pan Li ◽  
...  
Keyword(s):  
Rock Mass ◽  
Fracture Zone ◽  
Evaluation Method ◽  
Numerical Study ◽  
Integrated Approach ◽  
Yield Model ◽  
Working Face ◽  
Measurement Results ◽  
Caving Zone ◽  
Overlying Strata

This study presents an integrated approach including the theoretical analysis and numerical modelling to investigate the failure characteristics of the overlying strata in the shallow-buried stope. The mechanical characteristics of the caving zone are first revealed and then calibrated by using the double-yield model. The theoretical results show that the mechanical properties of the collapsed rock mass are closely related to its crushing expansion coefficient and uniaxial compressive strength. The vertical stress of the collapsed rock mass increases slowly with the strain and then increases exponentially after a certain critical strain. The simulation indicates that the fracture zone volume is 1.7-1.8 times that of the caving zone in the 31108 working face, and the failure volume of the overlying strata is 9-10 times that of the stope. The simulated height of the caving zone and fracture zone is 9 m and 20 m, respectively. The comparison between the numerical and field measurement results demonstrates that the new evaluation method using shear-tensile strain behaviors can accurately predicate the height of the two zones. The proposed numerical method could be a viable alternative approach to two zones height calculation.

scholarly journals Experimental Study on the Application of BOTDA in the Overlying Strata Deformation Monitoring Induced by Coal Mining

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Jing Chai ◽  
Wengang Du
Keyword(s):  
Stress Concentration ◽  
Frequency Shift ◽  
Measurement Data ◽  
Deformation Monitoring ◽  
Physical Model Test ◽  
Abscission Layer ◽  
Key Stratum ◽  
Concentration Phenomena ◽  
Working Face ◽  
Overlying Strata

The coal mine working face overlying strata is often disturbed by multiple mining, leading to adverse effects on the working face’s safe production and ground surface movement. In the three-dimensional physical model test with the size of 3000×2000×2000 mm, after the overburden gets stable when the first working face had been extracted, by using three vertical distributed optical fibers based on the BOTDA principle, the deformation law of the overburden caused by the contiguous coal face mining is studied. Results show that, before the working face advanced to 840 mm (near the fiber), the stress law of the overburden was as follows: the middle of the model was under pressure state and the remaining part was under tension state, and the key stratum produced stress concentration phenomena caused by the secondary mining; when the face advanced to 840 mm (through the fiber), the frequency shift curve of the key stratum and the strata on it combined, and the stress concentration in the key stratum disappeared, indicating that the bearing structure of the key stratum gets unstable; compared with the previous monitoring data, when the working face far away from the fiber, the information reflected by the frequency shift data gradually gets single when the working face is far away from the fiber compared with the previous measurement data. The overburden deformation increased dramatically after the key stratum gets unstable. The surrounding rock and fiber will detach when the stratum goes though large deformation such as abscission layer, fracture, and collapse, and the frequency shift monitored by BOTDA cannot characterize the rock deformation in this situation. The experimental method and the results of this paper serve as useful reference for the application of BOTDA technology in geotechnical engineering.

scholarly journals Breaking and mining-induced stress evolution of overlying strata in the working face of a steeply dipping coal seam

2021 ◽  
Author(s):  
Xiaolou Chi ◽  
Ke Yang ◽  
Zhen Wei
Keyword(s):  
Shear Stress ◽  
Coal Seam ◽  
Acoustic Emissions ◽  
Field Measurements ◽  
Vertical Stress ◽  
Mine Pressure ◽  
Shear Stresses ◽  
Working Face ◽  
Damaged Zone ◽  
Overlying Strata

AbstractThe breaking features and stress distribution of overlying strata in a steeply dipping coal seam (SDCS) differ significantly from those in a near-horizontal one. In this study, the laws governing the evolution of vertical stress release and shear stress concentration in the overlying strata of coal seams with different dip angles are derived via numerical simulation, rock mechanics tests, acoustic emissions, and field measurements. Thus, the stress-driven dynamic evolution of the overlying strata structure, in which a shear stress arch forms, is determined. Upon breaking the lower part of the overlying strata, the shear stress transfers rapidly to the upper part of the working face. The damaged zone of the overlying strata migrates upward along the dip direction of the working face. The gangue in the lower part of the working face is compacted, leading to an increase in vertical stress. As the dip angle of the coal seam increases, the overlying strata fail suddenly under the action of shear stresses. Finally, the behavioral response of the overlying strata driven by shear stresses in the longwall working face of an SDCS is identified and analyzed in detail. The present research findings reveal the laws governing the behavior of mine pressure in the working face of an SDCS, which in turn can be used to establish the respective on-site guidance.

scholarly journals Stress and deformation analysis of gob-side pre-backfill driving procedure of longwall mining: a case study

2021 ◽  
Author(s):  
Rui Wu ◽  
Penghui Zhang ◽  
Pinnaduwa H. S. W. Kulatilake ◽  
Hao Luo ◽  
Qingyuan He
Keyword(s):  
Rock Mass ◽  
Stress Distribution ◽  
Coal Seam ◽  
Abutment Pressure ◽  
Longwall Mining ◽  
Vertical Stress ◽  
Floor Level ◽  
Working Face ◽  
Floor Heave ◽  
Stress And Deformation

AbstractAt present, non-pillar entry protection in longwall mining is mainly achieved through either the gob-side entry retaining (GER) procedure or the gob-side entry driving (GED) procedure. The GER procedure leads to difficulties in maintaining the roadway in mining both the previous and current panels. A narrow coal pillar about 5–7 m must be left in the GED procedure; therefore, it causes permanent loss of some coal. The gob-side pre-backfill driving (GPD) procedure effectively removes the wasting of coal resources that exists in the GED procedure and finds an alternative way to handle the roadway maintenance problem that exists in the GER procedure. The FLAC3D software was used to numerically investigate the stress and deformation distributions and failure of the rock mass surrounding the previous and current panel roadways during each stage of the GPD procedure which requires "twice excavation and mining". The results show that the stress distribution is slightly asymmetric around the previous panel roadway after the “primary excavation”. The stronger and stiffer backfill compared to the coal turned out to be the main bearing body of the previous panel roadway during the "primary mining". The highest vertical stresses of 32.6 and 23.1 MPa, compared to the in-situ stress of 10.5 MPa, appeared in the backfill wall and coal seam, respectively. After the "primary mining", the peak vertical stress under the coal seam at the floor level was slightly higher (18.1 MPa) than that under the backfill (17.8 MPa). After the "secondary excavation", the peak vertical stress under the coal seam at the floor level was slightly lower (18.7 MPa) than that under the backfill (19.8 MPa); the maximum floor heave and maximum roof sag of the current panel roadway were 252.9 and 322.1 mm, respectively. During the "secondary mining", the stress distribution in the rock mass surrounding the current panel roadway was mainly affected by the superposition of the front abutment pressure from the current panel and the side abutment pressure from the previous panel. The floor heave of the current panel roadway reached a maximum of 321.8 mm at 5 m ahead of the working face; the roof sag increased to 828.4 mm at the working face. The peak abutment pressure appeared alternately in the backfill and the coal seam during the whole procedure of "twice excavation and mining" of the GPD procedure. The backfill provided strong bearing capacity during all stages of the GPD procedure and exhibited reliable support for the roadway. The results provide scientific insight for engineering practice of the GPD procedure.

scholarly journals Research on Deformation Mechanisms of a High Geostress Soft Rock Roadway and Double-Shell Grouting Technology

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Fengnian Wang ◽  
Shizhuang Chen ◽  
Pan Gao ◽  
Zhibiao Guo ◽  
Zhigang Tao
Keyword(s):  
Mechanical Properties ◽  
Rock Mass ◽  
Large Deformation ◽  
Coal Mine ◽  
Soft Rock ◽  
In Situ Stress ◽  
Deformation Monitoring ◽  
Deformation And Failure ◽  
Working Face ◽  
High Geostress

In this study, the deformation characteristics and mechanical properties of coal and rock mass in the S2N5 working face of the Xiaokang coal mine are analyzed to address the problem of large deformation of soft rocks with high in situ stress surrounding roadways. Through a newly developed grouting pipe, a double-shell grouting technology, consisting of low-pressure grouting and high-pressure split grouting, is proposed for the Xiaokang coal mine. In addition, the effect of grouting is evaluated by borehole peeping and deformation monitoring. The results show that the double-shell grouting technology can effectively improve the overall mechanical properties of the surrounding coal and rock mass, preventing the large deformation and failure of the roadway. This technology can be useful when analyzing and preventing large deformation of soft rock roadways.

scholarly journals Movement Laws of Overlying Strata above a Fully Mechanized Coal Mining Face Backfilled with Gangue: A Case Study in Jiulishan Coal Mine in Henan Province, China

2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Zhengkai Yang ◽  
Zhiheng Cheng ◽  
Zhenhua Li ◽  
Chunyuan Li ◽  
Lei Wang ◽  
...  
Keyword(s):  
Coal Mining ◽  
Main Roof ◽  
Surrounding Rock ◽  
Surface Subsidence ◽  
Key Strata ◽  
Key Stratum ◽  
Mining Face ◽  
Failure Depth ◽  
Gangue Backfilling ◽  
Overlying Strata

The aim of this study is to obtain movement laws of overlying strata above a fully mechanized coal mining face backfilled with gangue and solve the problem of surface subsidence during coal mining. This study was carried out based on gangue backfilling mining of Jiulishan Coal Mine (Jiaozuo City, Henan Province, China) from the perspectives of deformation of backfilled gangue under compaction, surrounding rock of a stope, and activities of key strata. The method combining with rock mechanics, viscoelastic mechanics, control theory of rock mass under mining, and numerical simulation was used based on physical and mechanical characteristics of backfilled gangue. On this basis, the research analyzed the temporal-spatial relationships of activities of surrounding rock of the stope, compressive deformation of backfilling body, failure depth of the floor, deformation characteristics of the main roof with laws of surface subsidence. The movement characteristics of overlying strata above the fully mechanized coal mining face backfilled with gangue and the traditional fully mechanized mining face were compared. It is found that, under the same conditions of overlying strata, movement laws of overlying strata are mainly determined by the mining height of coal seams and the heights of a caving zone and a fracture zone are nearly linearly correlated with the mining height. Through analysis based on thin-plate theory and key stratum theory, the location of the main roof of the fully mechanized coal mining face backfilled with gangue in coal seams first bending and sinking due to load of overlying strata was ascertained. Then, it was determined that there are two key strata and the main roof belongs to the inferior key stratum. By using the established mechanical model for the main roof of the fully mechanized coal mining face backfilled with gangue and the calculation formula for the maximum deflection of the main roof, this research presented the conditions for breaking of the main roof. In addition, based on the theoretical analysis, it is concluded that the main roof of the fully mechanized coal mining face backfilled with gangue does not break, but bends. The numerical simulation results demonstrate that, with the continuous increase of strength of backfilled gangue, the stress concentration degree of surrounding rock reduces constantly, so does its decrease amplitude. Moreover, the compressive deformation of backfilling, failure depth of the floor, and bending and subsidence of the main roof continuously decrease and tend to be stable. The mechanical properties of backfilling materials determine effects of gangue backfilling in controlling surface subsidence. Gangue backfilling can effectively control movement of overlying strata and surface subsidence tends to be stable with the increase of elastic modulus of gangue.

scholarly journals A Mechanical Model of the Overlying Rock Masses in Undersea Coal Mining and a Stress-Seepage Coupling Numerical Simulation

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Jie Fang ◽  
Lei Tian ◽  
Yanyan Cai ◽  
Zhiguo Cao ◽  
Jinhao Wen ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Coal Seam ◽  
Coal Mining ◽  
Water Inrush ◽  
Mining Area ◽  
Analysis Model ◽  
Fractured Zones ◽  
Working Face ◽  
Seam Mining ◽  
Overlying Strata

The water inrush of a working face is the main hidden danger to the safe mining of underwater coal seams. It is known that the development of water-flowing fractured zones in overlying strata is the basic path which causes water inrushes in working faces. In the engineering background of the underwater mining in the Longkou Mining Area, the analysis model and judgment method of crack propagation were created on the basis of the Mohr–Coulomb criterion. Fish language was used to couple the extension model into the FLAC3d software, in order to simulate the mining process of the underwater coal seam, as well as to analyze the initiation evolutionary characteristics and seepage laws of the fractured zones in the overlying strata during the advancing processes of the working face. The results showed that, during the coal seam mining process, the mining fractured zones which had been caused by the compression-shear and tension-shear were mainly concentrated in the overlying strata of the working face. Also, the open-off cut and mining working face were the key sections of the water inrush in the rock mass. The condition of the water disaster was the formation of a water inrush channel. The possible water inrush channels in underwater coal mining are mainly composed of water-flowing fractured zones which are formed during the excavation processes. The numerical simulation results were validated through the practical engineering of field observations on the height of water-flowing fractured zone, which displayed a favorable adaptability.

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