scholarly journals An Innovative Technology for Monitoring the Distribution of Abutment Stress in Longwall Mining

Energies ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 475
Author(s):  
Zhibiao Guo ◽  
Weitao Li ◽  
Songyang Yin ◽  
Dongshan Yang ◽  
Zhibo Ma
Keyword(s):  
Abutment Pressure ◽  
Longwall Mining ◽  
Innovative Technology ◽  
Mining Method ◽  
Pressure Monitoring ◽  
Motion State ◽  
Solid Coal ◽  
Detection Unit ◽  
Peak Value ◽  
Overlying Strata

Fracturing roofs to maintain entry (FRME) is a novel longwall mining method, which has been widely used in China, leading a new mining revolution. In order to research the change law of side abutment pressure and movement law of overlying strata when using the FRME, a new abutment pressure monitoring device, namely, the flexible detection unit (FDU), is developed and is applied in the field. The monitoring results show that compared with the head entry (also called the non-splitting entry), the peak value of the lateral abutment pressure in the tail entry (also termed the splitting entry) is reduced by 17.2% on average, and the fluctuation degree becomes smaller. Then, finite difference software FLAC3D is used to simulate the stress change of the solid coal on both sides of the panel. The simulation results show that the side abutment pressure of the tail entry decreases obviously, which is consistent with the measured results. Comprehensive analysis points out that after splitting and cutting the roof, the fissures can change the motion state of the overlying strata, causing the weight of the overburden borne by the solid coal to reduce; therefore, the side abutment pressure is mitigated.

Formation mechanism of stress arch during longwall mining based on key strata theory

2021 ◽  
pp. 014459872110427
Author(s):  
Feng Wang ◽  
Tong Chen ◽  
Bo Ma ◽  
Denghong Chen
Keyword(s):  
Formation Mechanism ◽  
Abutment Pressure ◽  
Longwall Mining ◽  
Measurement Data ◽  
Morphological Characteristics ◽  
Key Strata ◽  
Working Face ◽  
Major Principal Stress ◽  
Bearing Structure ◽  
Peak Value

The traditional stress arch hypothesis during longwall mining fails to elucidate the formation mechanism of stress arch, and the morphological characteristics and evolution of stress arch are indefinite. To solve these problems, a mechanical model was established for elucidating the formation mechanism of stress arch in overlaying strata. The influencing of key strata on the morphological characteristics of the stress arch was studied. Finally, the evolution of the stress arch during longwall mining was studied through numerical simulation. The results show that the bearing structure of the overlying strata served as the key strata, and the stress arch was formed when the key strata were subjected to deflection after playing a bearing structure role. This was the result of coordination and redistribution of major principal stress in the key strata. The morphological characteristics of the stress arch changed accordingly with the change in key strata. When the thickness of key strata and the distance between key strata and coal seam were gradually increased, the height and width of the stress arch increased accordingly; however, its height was always terminated at the top interface of key strata. At this time, the peak value of the abutment pressure of the working face gradually decreased while the influencing range gradually increased. During longwall mining, the stress arch developed upward by leaps and bounds with the bearing and fracture of key strata. When the overlying key strata were completely fractured, the stress arch disappeared. The results were verified using the field measurement data on the abutment pressure of the Y485 longwall face in Tangshan Mine.

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 Mechanism of Secondary Breakage in the Overlying Strata during Repetitious Mining of an Ultrathick Coal Seam in Design Stage

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
Hui Li ◽  
Dongsheng Zhang ◽  
Shuyin Jiang ◽  
Gangwei Fan ◽  
Mengtang Xu
Keyword(s):  
Coal Seam ◽  
Mining Area ◽  
Design Stage ◽  
Mining Method ◽  
Joint Stability ◽  
Mechanical Models ◽  
Physical Simulations ◽  
Research Findings ◽  
New Feature ◽  
Overlying Strata

When designing the mining of an ultrathick coal seam, the laws governing movement in the overlying strata during mining are a fundamental issue based on which several problems are addressed, including determining the mining method and the roadway arrangement, controlling the surrounding strata, and selecting the devices. The present paper considers possible problems related to strata overlying a large mining space subjected to repeated disturbances during the mining of an ultrathick coal seam, including repeatedly broken strata and the existence or inexistence of the structure. The BM coal seam in the No. 2 coal mine of the Dajing mining area in the East Junggar coalfield is studied. Physical simulations are performed on the movements of the overlying strata during slicing mining of the ultrathick coal seam, revealing the new feature of “break-joint stability-instability-secondary breakage” in the overlying strata. Mechanical models are constructed of the secondary breakage of the overlying strata blocks under both static and impact loading, and mechanical criteria are proposed for such breakage. Based on the research findings, methods for controlling the surrounding strata during slicing mining of an ultrathick coal seam are proposed, including increasing the mining rate and designing reasonable heights for the slicing mining.

scholarly journals Control Technology of Surface Movement Scope with Directional Hydraulic Fracturing Technology in Longwall Mining: A Case Study

Energies ◽  
2019 ◽  
Vol 12 (18) ◽  
pp. 3480 ◽  
Author(s):  
Zhanjie Feng ◽  
Wenbing Guo ◽  
Feiya Xu ◽  
Daming Yang ◽  
Weiqiang Yang
Keyword(s):  
Numerical Simulation ◽  
Hydraulic Fracturing ◽  
Longwall Mining ◽  
Numerical Models ◽  
Surface Subsidence ◽  
The Sustainable Development ◽  
Surface Movement ◽  
Directional Hydraulic Fracturing ◽  
Simulation Results ◽  
Overlying Strata

Mining-induced surface subsidence causes a series of environmental hazards and social problems, including farmland destruction, waterlogging and building damage in the subsidence area. To reduce mining damages, an innovative method of controlling the surface movement scope via artificial weak planes generated by hydraulic fracturing technology was proposed in this paper. Numerical models were built to analyze the influence of weak planes with different heights and dips on the overlying strata movement. The numerical simulation results showed that the weak planes structure cut off the development of the overlying strata displacement to the surface and affected the surface movement scope. When the weak planes’ dips were bigger than the angle of critical deformation, with the increase of the weak planes’ heights (0–120 m) the advance angle of influence changed from 53.61° to 59.15°, and the advance distance of influence changed from 173.31 m to 140.27 m which decreased by 30.04 m. In applications at Sihe coal mine in China, directional hydraulic fracturing technology was used in panel 5304 to form artificial weak planes in overlying strata. The measured surface subsidence and deformation value met the numerical simulation results and the mining-induced surface movement scope reduced. Moreover, no damage occurred to the surface buildings which were predicted to be in the affected area after extraction. This technology provided a new method to protect the surface structures from damages and had great benefits for the sustainable development of coal mines.

Assessment of rigid overlying strata failure in face mining

2010 ◽  
Vol 2 (4) ◽  
Author(s):  
Eva Jiránková
Keyword(s):  
Longwall Mining ◽  
Practical Importance ◽  
Assessment Method ◽  
Coal Seams ◽  
Deep Mine ◽  
Failure Assessment ◽  
Surface Measurements ◽  
Strata Failure ◽  
Simultaneous Assessment ◽  
Overlying Strata

AbstractThe method of overlying strata failure assessment of extracted seams is based upon the simultaneous assessment of surface subsidence and seismic activity, considering the spatiatemporal progress of mining, depending on the character of the rock mass. The rigid overlying strata failure assessment results in finding whether a failure of the firm overlying rocks occurred or whether a strutting arch was formed over the mined-out area. The practical importance of the overlying strata failure assessment consists in determining the size of the mined-out area at which the com-plete failure of the rigid overlying strata occurred and in the assessment of the current stress condition of the overlying strata failure. The assessment method is applicable in deep mine workings where thick coal seams are being mined by means of the method of longwall mining with controlled caving. The results of this method are used to amend contemporary known methods of rock-burst protection, namely (regarding the use of surface measurements for the evaluation) in overlying strata areas.

scholarly journals The Study of Key Stratum Location and Characteristics on the Mining of Extremely Thick Coal Seam under Goaf

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Gaochuan Guo ◽  
Yongkang Yang
Keyword(s):  
Coal Seam ◽  
Longwall Mining ◽  
Maximum Principal Stress ◽  
Engineering Practice ◽  
Coal Seams ◽  
Thick Coal Seam ◽  
Key Strata ◽  
Key Stratum ◽  
Arch Structure ◽  
Overlying Strata

The basis of traditional ground pressure and strata control techniques is the key strata theory, wherein the position of the key stratum can easily be determined for coal seams with regular thickness and without goaf. However, in the case of mining ultrathick coal seams underneath goaf, the traditional methods used for the calculation of key stratum position need to be improved in order to account for the additional coal seam thickness and the presence of an upper goaf. This study analyzed the failure height and collapse characteristics of overlying strata during excavation for determining the structure of the failed overlying strata. The results indicate that the intercalation and overlying strata gradually evolve into a large “arch structure” and a small “arch structure” during longwall mining, respectively. A mechanical model of the bearing characteristics of the interlayer key strata structure was established according to the structure of the intercalation rock layer, which is a hinged block structure. The results of the model indicate that the maximum principal stress occurs when the key strata portion of the arch structure bears the overlying load. Consequently, the movement and position of the interlayer key strata can be evaluated throughout the mining process of the ultrathick coal seams underneath goaf. This method was used to determine the position of interlayer key stratum of overlying strata in Xiegou coal mine. And the results agree with that of the engineering practice. The results are significant to determine the key strata position during ultrathick coal seam underneath goaf longwall mining.

scholarly journals Field and Numerical Modelling Investigations on the Stability of Underground Strata during Longwall Workings

2021 ◽  
Author(s):  
G Budi ◽  
Kolikipogu Nageswara Rao ◽  
Punit Mohanty
Keyword(s):  
Numerical Modelling ◽  
Longwall Mining ◽  
High Capacity ◽  
Field Monitoring ◽  
Longwall Face ◽  
Mining Method ◽  
Company Limited ◽  
Extensive Field ◽  
Powered Support ◽  
The Stability

Abstract Understanding the behaviour of underground workings is essential for the success of any mining method. The longwall mining method is one of the predominant underground methods to extract coal. Since 1978, in India, 22 underground coal mines of different collieries have been implemented the mechanized longwall method. SCCL is one of that colliery has mixed working experiences with longwall method in their mines. The longwall faces in GDK-10A, JK-5, and VK-7 of SCCL had produced good results, but the faces in GDK-7, GDK-9, GDK-11A, and PVK-5 had suffered due to the geological disturbances and unavailability of real-time information about the strata behaviour. By addressing the previous experiences of longwall workings, Singareni Collieries Company Limited (SCCL) has implemented a high capacity (1 × 1152T) powered support system in Adriyala Longwall Project (ALP) at a depth of 375m. In this study, extensive field monitoring with different strata monitoring instruments was conducted in ALP to analyze the gate roads convergence, stress variation on longwall and chain pillars at different stages of extraction (i.e., 8m, 25m, 35m, and 45m) and the pressure variation on the powered support systems. It was observed from the results that the convergence in the gate roads was increasing with the advance of the longwall face and the area of exposure. The pressure of the legs on the dip side was less than the pressure of the legs on the rise side, which implies a stable roof condition over the longwall face. To better understand the behaviour of ALP workings, a numerical modelling study with FLAC 7.0 has been conducted with actual physio-mechanical properties. The computed numerical modelling results have been remarkably well in consistent with the field monitoring results. The stability of chain pillars has been estimated at every stage of extraction by the Factor of Safety (FoS) criterion and it was found that the pillars could be ensured stability in longwall workings.

scholarly journals Fracture Mechanism in Overlying Strata during Longwall Mining

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Zhengyi Ti ◽  
Jiazhen Li ◽  
Meng Wang ◽  
Kang Wang ◽  
Zhupeng Jin ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Fracture Mechanism ◽  
Longwall Mining ◽  
Flexural Rigidity ◽  
Central Area ◽  
Short Side ◽  
Wall Area ◽  
Key Stratum ◽  
Coal Wall ◽  
Overlying Strata

We used the key stratum theory to establish a more realistic thin-plate mechanical model of elastic foundation clamped boundary and study the fracture mechanism of overlying strata during longwall mining. We analyzed the fracture characteristics and factors affecting fracture of the key stratum combined with the Mohr–Coulomb yield criterion. Besides, we used numerical simulation methods to verify the evolution pattern of the overlying strata fracture. The results show that the fracture mechanisms of the elastic foundation clamped structure’s key stratum varied depending on the position under longwall mining. The advanced coal wall area of the upper surface is a compressive-shear fracture. The center area of the lower surface is a tensile fracture. With the increase of the excavation length and the load of the key stratum, the central area and the advanced coal wall area of the long side are fractured before the advanced coal wall area of the short side. With the increase of flexural rigidity of the key stratum, the advanced coal wall area of the long side fractures before the central area and the advanced coal wall area of the short side. With the increase of the foundation modulus and the advanced load of the key stratum, the central area fractures before the surrounding advanced coal wall area. The advanced influence distance was positively correlated with the key stratum’s flexural rigidity and advanced load and negatively correlated with the foundation modulus and excavation length. The advanced influence distance was not affected by the load of the key stratum. The numerical simulation results show that, with the increase of the mining area, the fracture trace of overlying strata in goaf extended to the coal wall’s interior. The fracture range of overlying strata is larger than that of the miningd: area. This study has a practical value for water disasters, gas outbursts, and rock strata control.

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