scholarly journals Mechanism of Support Optimization and Confined Blasting of Thick and Hard Rock with a Wedge-Structure Immediate Roof: A Case Study

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Tong Zhao ◽  
Peilin Gong ◽  
Kaan Yetilmezsoy ◽  
Majid Bahramian ◽  
Changyou Liu ◽  
...  
Keyword(s):  
Main Roof ◽  
Hard Roof ◽  
Working Face ◽  
Immediate Roof ◽  
Physical Simulations ◽  
Fracture Size ◽  
Wedge Structure ◽  
Confined Blasting ◽  
Support Optimization ◽  
Strata Behavior

Based on the occurrence conditions of a thick and hard main roof and wedge-structure immediate roof in the Zhuxianzhuang Coal Mine, the fracture characteristics and instability migration law of a thick and hard roof (THR) were examined via physical simulations. Mining zones were divided with respect to the strata behaviors and roof control difficulty levels, and the principles and methods of zonal control under THR were put forward. This study proposed a coordinated control strategy of using confined blasting in water-filled deep holes, and reasonable support optimization, which could effectively reduce the roof fracture size, increases the supporting intensity and eliminate roof-control disasters. The length of confined blasting blocks and supporting intensity were calculated using a mechanical model for roof control in the strong strata behavior zone and less-strong strata behavior zone. These key parameters were determined as 20–25 m and 1.15–1.28 MPa, respectively, and the mining strategy was successfully applied in working face 880, performing high security and reasonable economical efficiency.

scholarly journals Numerical Investigation of Gob-Side Entry Retaining through Precut Overhanging Hard Roof to Control Rockburst

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Xiaoming Sun ◽  
Li Gan ◽  
Zhao Chengwei ◽  
Tang Jianquan ◽  
He Manchao ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Abutment Pressure ◽  
Feasibility Studies ◽  
Main Roof ◽  
Surrounding Rock ◽  
Distribution Characteristics ◽  
Hard Roof ◽  
Working Face ◽  
Stress Fluctuation ◽  
Peak Value

Gob-side entry retaining through precut overhanging hard roof (GERPOHR) method is one of the commonly used methods for nonpillar mining. However, feasibility studies of controlling rockburst by this method are few. Rockburst occurs in hard thick strata with a higher probability, larger scale, and higher risk. To better understand the GERPOHR method is beneficial for rockburst mitigation. In this paper, the design of GERPOHR was first introduced. And the layout of the working face was optimized. Then, based on the numerical simulation, the stress and displacement distribution characteristics were compared under the condition of conventional mining and GERPOHR method. The research shows that the intervals of main roof weighting could be decreased through the precut overhanging hard roof method. And the peak value of abutment pressure decreased. Meanwhile, the energy accumulation and the stress fluctuation could be alleviated in roadway surrounding rock.

scholarly journals Analysis on Catastrophe Theory during First Weighting Sliding Instability and Support Crushing of Main Roof with Large Mining Height in Shallow Coal Seam

2020 ◽  
Vol 10 (16) ◽  
pp. 5408
Author(s):  
Dengfeng Yang ◽  
Yongjun Zhang ◽  
Zhonghui Chen
Keyword(s):  
Catastrophe Theory ◽  
Sufficient Conditions ◽  
Main Roof ◽  
Mining Area ◽  
Stiffness Ratio ◽  
Working Face ◽  
Cross Section Area ◽  
Immediate Roof ◽  
Support Resistance ◽  
Mining Height

Roof sliding and instability along the coal wall usually occur in the working face at large mining heights during the process of the first weighting, which causes roof cutting and support crushing. A mechanical model consists of the main roof, immediate roof, and support based on the nonlinear characteristics of the failure and instability of the immediate roof under the abutment pressure, which we constructed to study the step sinking of the main roof, as well as to assign the reasonable value of the support resistance during the first weighting. The instability mechanism of the system was studied by the catastrophe theory and the principle of energy conservation. A conclusion was drawn that the combined cantilever beam structure for the immediate roof will form with the increase of the mining height, and the instability of the immediate roof causes the catastrophic instability of the system. The system instability was found to be related to the stiffness ratio K, material parameters, the load Q, and the first weighting interval of the main roof by analyzing the necessary and sufficient conditions for system instability. The influence degree of each parameter on the stiffness ratio K was as follows: elastic modulus E > support stiffness k1 > cross-section area a > immediate roof thickness H. The calculation equations of support resistance and subsidence of roof step were obtained. The method of judging the roof instability using catastrophe theory was proved as reasonable on the basis of the monitoring example of no. 12401 working face in Shendong mining area, China. On this basis, a reasonable value of support resistance was further calculated, and the working face was maintained safely when the support resistance exceeded 19,232 kN.

Analysis on Instability of Surrounding Rock in Gob-Side Entry Retaining with the Character of Soft Rock Composite Roof

2012 ◽  
Vol 524-527 ◽  
pp. 396-403 ◽  
Author(s):  
De Chuan Yang ◽  
Ming Zhong Gao ◽  
Yun Hai Cheng ◽  
Wu Sheng ◽  
Jia Sheng Chen
Keyword(s):  
Coal Mine ◽  
Soft Rock ◽  
Main Roof ◽  
Wide Distribution ◽  
Economic Security ◽  
Surrounding Rock ◽  
Mine Pressure ◽  
Working Face ◽  
Immediate Roof ◽  
Plastic Zones

The filling belt of gob-side entry retaining with the character of soft rock composite roof,deforms violently,affected by the fracture and rotation of the main roof,and is prone to instability.This essay,considering characteristecs of coal mine pressure behavior on -790m 1311 (1) working face ventilation roadway at DingJi coal mine in HuaiNan,puts forward structural mech -anics model of the key block of gob-side entry retaining,which is used to forecast the position of the fracture line of the main roof, and analyze the roof subsidence at the side of the filling belt;It applies FLAC and UDEC to simulate distribution of plastic zones of surrounding rock of gob-side entry retaining,and stress variation law of the immediate roof and the main roof along coal seam inclination.The results show that:stress concentration factor of the immediate roof on the filling belt is about 1.6,first decreasing and then increasing with increasing width of the filling belt,which indicates that reasonable width of the filling belt is 3.0 m in accordance with the requirement of economic security requirment. The filling belt has significantly wide distribution of the plastic zones,with its four corners obviously plasticized,and overlying strata above the filling belt at side of goaf suffering upward plasticization,which is the result of rotation of the main roof; Deform- ation instability of filling belt is mainly caused by fracture rotation of the main roof;Finally, the measures to reduce the instability of gob-side entry retaining with the character of soft rock comp- osite roof are put forward.

scholarly journals Comprehensive technical support for safe mining in ultra-close coal seams: A case study

2021 ◽  
pp. 014459872110093
Author(s):  
Wei Zhang ◽  
Jiawei Guo ◽  
Kaidi Xie ◽  
Jinming Wang ◽  
Liang Chen ◽  
...  
Keyword(s):  
Coal Seam ◽  
Technical Support ◽  
Surrounding Rock ◽  
Coal Seams ◽  
Deformation Control ◽  
Hard Roof ◽  
Working Face ◽  
Close Coal Seams ◽  
Safe Mining

In order to mine the coal seam under super-thick hard roof, improve the utilization rate of resources and prolong the remaining service life of the mine, a case study of the Gaozhuang Coal Mine in the Zaozhuang Mining Area has been performed in this paper. Based on the specific mining geological conditions of ultra-close coal seams (#3up and #3low coal seams), their joint systematic analysis has been performed, with the focus made in the following three aspects: (i) prevention of rock burst under super-thick hard roof, (ii) deformation control of surrounding rock of roadways in the lower coal seam, and (iii) fire prevention in the goaf of working face. Given the strong bursting tendency observed in upper coal seam and lower coal seam, the technology of preventing rock burst under super-thick hard roof was proposed, which involved setting of narrow section coal pillars to protect roadways and interleaving layout of working faces. The specific supporting scheme of surrounding rock of roadways in the #3low1101 working face was determined, and the grouting reinforcement method of local fractured zones through Marithan was further proposed, to ensure the deformation control of surrounding rock of roadways in lower coal seams. The proposed fire prevention technology envisaged goaf grouting and spraying to plug leaks, which reduced the hazard of spontaneous combustion of residual coals in mined ultra-close coal seams. The technical and economic improvements with a direct economic benefit of 5.55 million yuan were achieved by the application of the proposed comprehensive technical support. The research results obtained provide a theoretical guidance and technical support of safe mining strategies of close coal seams in other mining areas.

scholarly journals Automatic Roadway Backfilling of Caving Gangue for Cutting Roofs by Combined Support on Gob-Side Entry Retaining with No-Pillars: A Case Study

2019 ◽  
Vol 2019 ◽  
pp. 1-13
Author(s):  
Shengrong Xie ◽  
Xiaoyu Wu ◽  
Dongdong Chen ◽  
Yaohui Sun ◽  
Junchao Zeng ◽  
...  
Keyword(s):  
Longwall Mining ◽  
Control Process ◽  
Coal Pillar ◽  
Main Roof ◽  
Control Effect ◽  
Mining Technology ◽  
Thick Coal Seam ◽  
Immediate Roof ◽  
Seam Mining ◽  
And Control

Automatic roadways on gob-side entry retaining with no-pillars are used for longwall mining technology. The mining technology with no-pillars can recover coal pillar resources and reduce the amount and cost of roadway excavations. Automatic roadway technology for cutting roofs by combined support on gob-side entry retaining with no-pillars is adopted for the condition of thick immediate roof and medium-thick coal seam mining, cutting off the immediate roof and the main roof on the gob by combined support. The fractured roof forms gangue blocks to fill the gob and loads the overlying strata. The gangue control system is placed on the roadside, which controls the caving gangue to form a gangue rib. In this paper, the viewpoints and key technologies (the roof-cutting technology, the reinforcement and support technology, the gangue rib control technology, and the auxiliary support technology) of automatic roadway technology for cutting roofs by combined support on the gob-side entry retaining with no-pillars are introduced. Furthermore, the formation and control process are explained. The numerical simulation is used to simulate and analyze the roof hanging and the roof cutting structures. In addition, a field engineering test is performed. The field test shows that automatic roadway technology for cutting roofs by combined support on gob-side entry retaining with no-pillars is feasible. This process uses construction techniques and technologies to meet on-site production needs. The combined support has high resistance strength and is shrinkable. In engineering applications, the combined support has a low damage rate. The deformation of the automatic roadway with gob-side entry retaining is small, and the control effect is significant.

scholarly journals Rebound Mechanism and Control of the Hard Main Roof in the Deep Mining Roadway in Huainan Mining Area

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Denghong Chen ◽  
Chao Li ◽  
Xinzhu Hua ◽  
Xiaoyu Lu ◽  
Yongqiang Yuan ◽  
...  
Keyword(s):  
Slope Angle ◽  
Bending Moment ◽  
Main Roof ◽  
Mining Area ◽  
Calculation Model ◽  
Surrounding Rock ◽  
Tensile Failure ◽  
Damage Area ◽  
Critical Range ◽  
Working Face

Taking the occurrence conditions of the hard main roof in the deep 13-1 coal mining roadway in Huainan mining area as the research object, based on the mechanical parameters of the surrounding rock and the stress state of the main roof obtained by numerical simulation, a simply supported beam calculation model was established based on the damage factor D, main roof support reaction RA, RB, and critical range C (9 m) and B (7 m) at the elastoplastic junction of the solid coal side and mining face side (hereinafter referred to as “junction”). Considering that the damage area still has a large bearing capacity, the vertical stress of the main roof at the junction is K1γH (0.05γh, 0.15γh, and 0.25γh) and K2γH (0.01γh, 0.10γh, and 0.2γh). The maximum deflection is 21 mm, 324 mm, and 627.6 mm, respectively. According to the criterion of tensile failure, the maximum bending moment of the top beam is 209 mN·m at the side of the working face 3.1 m away from the roadway side when K1 = 0.15 and K2 = 0.10, and the whole hard main roof is in tensile failure except the junction. To control the stability of the top beam and simplify the supporting reaction to limit the deformation of the slope angle, RC and RD are used to construct the statically indeterminate beam. By adding an anchor cable and advance self-moving support to the roadway side angle, the problem of difficult control of the surrounding rock with a large deformation of the side angle roof is solved, which provides a reference for roof control under similar conditions.

scholarly journals Safe and Efficient Coal Mining Below the Goaf: A Case Study

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 864 ◽  
Author(s):  
Weidong Pan ◽  
Shaopeng Zhang ◽  
Yi Liu
Keyword(s):  
Abutment Pressure ◽  
Theoretical Calculations ◽  
Distribution Law ◽  
Working Face ◽  
Strata Behavior ◽  
Working Resistance ◽  
Behavior Characteristics ◽  
Theoretical Analyses ◽  
Important Significance

Mining at the fully mechanized working face below the goaf of the short-distance coal seam is influenced by the upper goaf. To address this problem, methods such as theoretical analyses, numerical simulation, and on-site measurement are used to study the strata behavior characteristics of the Ningxia Lingxin Coal Mine 051508 working face in this study. The roof weighting intervals of the working faces below the goaf and the non-goaf are obtained via theoretical calculations. The stoping processes of the working faces below the goaf and the non-goaf are simulated with FLAC3D to obtain the distribution law of the bearing pressure and plastic zones before the working face. Based on the statistical analysis of the measured working resistance of the supports and its distribution, the roof weighting interval of the working face mining below the goaf is obtained. The results show that the roof weighting interval and the advanced abutment pressure during mining at the working face below the goaf are smaller than those below the non-goaf, providing a reasonable theoretical basis for mining below the goaf, and having important significance for safe and efficient mining.

scholarly journals Study on the Fracture Law of Inclined Hard Roof and Surrounding Rock Control of Mining Roadway in Longwall Mining Face

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5344
Author(s):  
Feng Cui ◽  
Shuai Dong ◽  
Xingping Lai ◽  
Jianqiang Chen ◽  
Chong Jia ◽  
...  
Keyword(s):  
Energy Release ◽  
Longwall Mining ◽  
Coal Pillar ◽  
High Energy ◽  
Mechanical Analysis ◽  
Engineering Practice ◽  
Analysis Model ◽  
Hard Roof ◽  
Working Face ◽  
The Stability

In the inclination direction, the fracture law of a longwall face roof is very important for roadway control. Based on the W1123 working face mining of Kuangou coal mine, the roof structure, stress and energy characteristics of W1123 were studied by using mechanical analysis, model testing and engineering practice. The results show that when the width of W1123 is less than 162 m, the roof forms a rock beam structure in the inclined direction, the floor pressure is lower, the energy and frequency of microseismic (MS) events are at a low level, and the stability of the section coal pillar is better. When the width of W1123 increases to 172 m, the roof breaks along the inclined direction, forming a double-hinged structure, the floor pressure is increased, and the frequency and energy of MS events also increases. The roof gathers elastic energy release, and combined with the MS energy release speed it can be considered that the stability of the section coal pillar is better. As the width of W1123 increases to 184 m, the roof in the inclined direction breaks again, forming a multi-hinged stress arch structure, and the floor pressure increases again. MS high-energy events occur frequently, and are not conducive to the stability of the section coal pillar. Finally, through engineering practice we verified the stability of the section coal pillar when the width of W1123 was 172 m, which provides a basis for determining the width of the working face and section coal pillar under similar conditions.

scholarly journals Deformation Rules for Surrounding Rock in Directional Weakening of End Roofs of Thin Bedrocks and Ultrathick Seams

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Fei Liu ◽  
Zhanguo Ma ◽  
Yongsheng Han ◽  
Zhimin Huang
Keyword(s):  
Abutment Pressure ◽  
Main Roof ◽  
Stability Control ◽  
Surrounding Rock ◽  
Western China ◽  
Resource Exploitation ◽  
Failure Characteristics ◽  
Key Strata ◽  
Working Face ◽  
Geological Conditions

With the deployment of China’s energy strategy in the western regions, complex geological mining conditions such as thin bedrock and ultrathick seams in western China have caused a series of problems such as serious deformation of the surrounding rock at the ends of the working face and the increase in the lead abutment pressure of the roadways; the research on end roof deformation in the resource exploitation in western China has become one of the great demands of the industry. Based on the failure characteristics of rock mass, relying on the actual mining geological conditions of a coal mine in Inner Mongolia, the failure characteristics of the overlying rock strata under the influence of mining were simulated and analyzed using similar material simulation experiment, which intuitively reproduced the failure and deformation processes of the immediate roof, main roof, and key strata and revealed the mechanical mechanism of the directional weakening of the end roof. It is of great significance for the stability control of the surrounding rock at the end of the fully mechanized caving face in the thin bedrocks and ultrathick seams, reducing the abutment pressure of gate roadway and controlling the spontaneous combustion of residual coal in the goaf.

Cutting Roof Roadway Parameter Optimization Simulation Analysis

2015 ◽  
Vol 741 ◽  
pp. 179-182
Author(s):  
Yan Min Shu ◽  
Yong Li Liu
Keyword(s):  
Shear Stress ◽  
Stress State ◽  
Rock Strength ◽  
Simulation Analysis ◽  
Main Roof ◽  
High Impact ◽  
Mine Pressure ◽  
Working Face ◽  
Optimization Simulation ◽  
Concentration Degree

Contrast simulation analysis under different cutting distance between top lane, cut the top lane area stress state, according to different stress state analysis of the optimal cutting top lane spacing, so as to realize the optimization of cutting top lane setting parameters.Results show that due to the inhomogeneity of rock strength, the main roof breaking are mainly shear stress play a role, as a result, the vertical stress of roof fracture need conditions may be much smaller than mine pressure strength limit.Considering cutting top lane for the larger spacing, cutting the top coal lane area of stress concentration degree is higher, easy to cause impact danger, from this aspect to consider cutting the top lane spacing should be small as far as possible, but the spacing is too small and cut the top lane roadway of quantities will increase, at the same time has the potential to cut two top lane of the superposition of stress, high impact and increase the working face danger.

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