scholarly journals Mechanism of Hard-Roof Rock Burst Control by the Deep-Hole Blasting: Numerical Study Based on Particle Flow

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Anliang Lu ◽  
Linming Dou ◽  
Jinzheng Bai ◽  
Yanjiang Chai ◽  
Kunyou Zhou ◽  
...  
Keyword(s):  
Rock Burst ◽  
Roof Rock ◽  
Force Chain ◽  
Particle Flow ◽  
Hydraulic Pressure ◽  
Deep Hole ◽  
Key Strata ◽  
Hard Roof ◽  
Single Hole ◽  
Working Resistance

In underground coal mines, the deep-hole blasting (DHB) technology is generally adopted for thick hard-roof control. This technology uses the energy released by explosives to weaken the energy storage capacity of hard roof so as to prevent hard-roof rock burst disasters. In this paper, a numerical simulation model of roof DHB was established based on particle flow and the damage range of single-hole blasting with concentrated cylindrical charge was studied. The temporal and spatial evolutions of overlying strata, the distribution of the force chain structure, and the working resistance of hydraulic pressure in the mining process before and after the application of DHB were contrastively analyzed. The following beneficial conclusions were drawn. The blasting-induced single-hole damage range is generally characterized by annular zoning. After the application of DHB, overall the collapse morphology of the key strata in the mining process changes from long-distance instantaneous slipping instability to stratified short-arm stepped synergistic subsidence. The density and strength of force chains in the overburden are notably reduced; the peak value of compressive force chain strength in the key strata in the mining process falls by 17.85% as a result of DHB. The monitoring results of the working resistance of hydraulic support reveal that the DHB technology can effectively shorten the step distance of periodic weighting and reduce the variation amplitude of overburden load during weighting. In summary, the mechanism of hard-roof rock burst control by DHB is reflected by both static load reduction and dynamic load reaction.

scholarly journals Analysis and Application on Controlling Thick Hard Roof Caving with Deep-Hole Position Presplitting Blasting

2018 ◽  
Vol 2018 ◽  
pp. 1-15 ◽  
Author(s):  
Baobao Chen ◽  
Changyou Liu
Keyword(s):  
Large Scale ◽  
Mining Area ◽  
Field Application ◽  
Deep Hole ◽  
Mining Operations ◽  
Hard Roof ◽  
Measurement Analysis ◽  
Mining Safety ◽  
Strata Behavior ◽  
Working Resistance

For the thick hard roof (THR) in Datong mining area, mining operations often led to large-scale hanging-roof and frequent and strong strata behavior, threatening mining safety seriously. Based on the instability mechanism, the fracture model for THR was established, including rock blocks articulation and combined cantilever beam, and the limit initial and periodic intervals of THR were determined to be 36.0 m and 8.0 m, respectively. The study proposed the deep-hole presplitting blasting (DPB) for weakening THR for mitigating strong strata behaviors. Blasting-induced fracture characteristics were calculated, determining the charging coefficient and holes spacing. LS-DYNA was employed for establishing a DPB model to analyze crack evolution under the synergistic action of blasting stress wave and detonation gas and the attenuation characteristics for rock peak particle velocity, verifying the rationality of blasting parameters. Field measurement analysis indicated that the immediate roof induced a timely collapse to fill the goaf and the THR was effectively cut off near the presplitting line. Meanwhile, the working resistance was utilized with safety allowance. The field application showed the DPB on controlled THR caving achieved the significant effect.

scholarly journals A case study of the periodic fracture control of a thick-hard roof based on deep-hole pre-splitting blasting

2021 ◽  
pp. 014459872110362
Author(s):  
Baobao Chen ◽  
Changyou Liu ◽  
Bing Wang
Keyword(s):  
Distinct Element ◽  
Good Control ◽  
Mining Area ◽  
Deep Hole ◽  
Control Effect ◽  
Roof Collapse ◽  
Hard Roof ◽  
Fracture Evolution ◽  
Distinct Element Code ◽  
Working Resistance

A thick-hard roof implies a large hanging-roof and high-frequency dynamic strata behaviour during mining, which may jeopardise personnel safety and equipment. To alleviate these hazards, deep-hole pre-splitting blasting is employed to control periodic fractures in thick-hard roof seams in Datong mining area. Based on loading and instability characteristics, a mechanical model of thick-hard roof periodic collapse is established to investigate the relationships and optimal parameters among the collapse interval, fracturing angle and support working resistance. LS-DYNA was employed to analyse the fracture evolution to determine the optimal charge parameters. The minimum weakening width and average fragmentation of the pre-split roof are obtained. Universal distinct element code simulations were used to determine the thick-hard roof collapse morphology and strata behaviour to confirm the optimal pre-splitting parameters. The deep-hole pre-splitting blasting on-site implementation reduces thick-hard roof collapse intervals, and the supports loading is verified to be safe with sufficient allowance, which show a good control effect on thick-hard roof seams.

scholarly journals Study on Rock Burst Event Disaster and Prevention Mechanisms of Hard Roof

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
Nan Zhou ◽  
Hengfeng Liu ◽  
Jixiong Zhang ◽  
Hao Yan
Keyword(s):  
Rock Mass ◽  
Energy Release ◽  
Rock Burst ◽  
Strain Energy ◽  
Roof Rock ◽  
Coal Mass ◽  
Energy Evolution ◽  
Hard Roof ◽  
Working Face ◽  
Coal Rock

Coal mining under hard roofs is jeopardized by rock burst-induced hazards. In this paper, mechanisms of hard roof rock burst events and key techniques for their prevention are analyzed from the standpoint of energy evolution within geological conditions typical of the hard roofs found in Chinese coal mines. Equations used to calculate the total strain energy densities of the coal-rock mass and hard roof working face are derived. Moreover, several failure-causing energy evolution rules are analyzed under various conditions. Various rock roof and coal mass thicknesses and strengths are considered, and a method of preventing hard roof rock burst events is proposed. The results obtained show that rock burst events can be facilitated by high stress concentrations, significant accumulation of strain energy in the coal-rock mass, and rapid energy release during roof breakage. The above conditions are subdivided into two classes: energy accumulation and energy release. The total strain energies of the coal mass and working faces in the roof are positively correlated with the roof thickness, roof strength, and coal mass strength. The coal mass strength primarily influences the overall accumulation of energy in the working face, and it also has the largest effect on the total energy release (i.e., the earthquake magnitude).

scholarly journals Cooperative Control Mechanism of Long Flexible Bolts and Blasting Pressure Relief in Hard Roof Roadways of Extra-Thick Coal Seams: A Case Study

2021 ◽  
Vol 11 (9) ◽  
pp. 4125
Author(s):  
Zhe Xiang ◽  
Nong Zhang ◽  
Zhengzheng Xie ◽  
Feng Guo ◽  
Chenghao Zhang
Keyword(s):  
Coal Seam ◽  
Cooperative Control ◽  
Field Tests ◽  
Surrounding Rock ◽  
Deep Hole ◽  
Coal Seams ◽  
Thick Coal Seam ◽  
Structure Damage ◽  
Hard Roof

The higher strength of a hard roof leads to higher coal pressure during coal mining, especially under extra-thick coal seam conditions. This study addresses the hard roof control problem for extra-thick coal seams using the air return roadway 4106 (AR 4106) of the Wenjiapo Coal Mine as a case study. A new surrounding rock control strategy is proposed, which mainly includes 44 m deep-hole pre-splitting blasting for stress releasing and flexible 4-m-long bolt for roof supporting. Based on the new support scheme, field tests were performed. The results show that roadway support failure in traditional scenarios is caused by insufficient bolt length and extensive rotary subsidence of the long cantilever beam of the hard roof. In the new proposed scheme, flexible 4-m-long bolts are shown to effectively restrain the initial expansion deformation of the top coal. The deflection of the rock beam anchored by the roof foundation are improved. Deep-hole pre-splitting blasting effectively reduces the cantilever distance of the “block B” of the voussoir beam structure. The stress environment of the roadway surrounding rock is optimized and anchorage structure damage is inhibited. The results provide insights regarding the safe control of roadway roofs under extra-thick coal seam conditions.

scholarly journals A Case Study of Effective Support Working Resistance and Roof Support Technology in Thick Seam Fully-Mechanized Face Mining with Hard Roof Conditions

2017 ◽  
Vol 9 (6) ◽  
pp. 935 ◽  
Author(s):  
Wei-bin Guo ◽  
Hong-sheng Wang ◽  
Guo-wei Dong ◽  
Lei Li ◽  
Yao-guang Huang
Keyword(s):  
Thick Seam ◽  
Hard Roof ◽  
Working Resistance ◽  
Roof Support

scholarly journals Study of the Stability Control of Rock Surrounding Longwall Recovery Roadways in Shallow Seams

2020 ◽  
Vol 2020 ◽  
pp. 1-22
Author(s):  
Cheng Zhu ◽  
Yong Yuan ◽  
Zhongshun Chen ◽  
Chaogui Meng ◽  
Shengzhi Wang
Keyword(s):  
Rock Pressure ◽  
Coal Mine ◽  
Stability Control ◽  
Control Effect ◽  
Support Design ◽  
Key Strata ◽  
Key Stratum ◽  
Discriminative Approach ◽  
The Stability ◽  
Working Resistance

The rock pressure appearance of longwall faces in shallow seams is generally violent, and roofs and supports are susceptible to damage during equipment extraction. Stability control of the rock surrounding longwall recovery roadways allows safe and rapid equipment extraction. Herein, via theoretical analysis, numerical simulations, and field observations, the stability control of the rock surrounding recovery roadways is studied to ensure the release of the accumulated rock pressure on the roof, the working resistance of the supports and the reasonableness of the recovery roadway support design. Pressure-relief technology is introduced to release the accumulated rock pressure before equipment extraction, and a discriminative approach is proposed to determine the breaking and articulated forms of key strata and broken blocks, respectively. On this basis, mechanical models of roof instability are established based on four key stratum structures in the overburden of shallow seams. Methods for calculating a reasonable working resistance for supports are discussed. Finally, Liangshuijing Coal Mine and Fengjiata Coal Mine are taken as research objects to evaluate the roof stability of recovery roadways based on observations of weighting characteristics. The support working resistances and reasonable recovery roadway widths under three key stratum structures are determined. Considering the time effect of plastic zone development, the support design of recovery roadways is optimized. FLAC2D software simulates the surrounding rock control effect of two support designs, and roof subsidence curves are obtained. The results show that the key to equipment extraction in shallow seams is to ensure that supports have reasonable working resistances and to improve the support of recovery roadways. The results provide a reference for the selection and extraction of supports in shallow seam faces.

scholarly journals Study on Stress Relief of Hard Roof Based on Presplitting and Deep Hole Blasting

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Peng Gong ◽  
Yongheng Chen ◽  
Zhanguo Ma ◽  
Shixing Cheng
Keyword(s):  
Stress Distribution ◽  
Coal Mine ◽  
Coal Pillar ◽  
Deep Hole ◽  
Hard Roof ◽  
Formation Conditions ◽  
Coal Pillars ◽  
Mining Coal ◽  
The Impact ◽  
Pillar Size

For the problem that the hard roof causes wider end-mining coal pillar, and the roadway is greatly affected by mining, this paper took Shanxi Luning Coal Mine as the engineering background; based on the stress distribution characteristics of the coal pillar, the calculation method of the limit end-mining coal pillar size was given; considering the formation conditions and transmission forms of the advanced abutment stress, a method combining presplitting and deep hole blasting was proposed to weaken the advanced abutment stress. The numerical simulation was used to analyze the stress distribution of coal pillars, which was verified by on-site industrial tests. The results showed that the presplitting can achieve the blocking of stress. The closer it is to the peak of the abutment stress, the better the blocking effect. Deep hole blasting can weaken the source of the advanced abutment stress and reduce the peak of abutment stress. With the combination of the two blasting methods, the end-mining coal pillar size of Luning Coal Mine can be reduced to 60 m. The method combining presplitting and deep hole blasting can effectively reduce the end-mining coal pillar size and reduce the impact of mining on the deformation of the dip roadway.

Study on Damage of Rock Samples with Single-Hole under Uniaxial Compression Condition

2012 ◽  
Vol 446-449 ◽  
pp. 3810-3813
Author(s):  
Bing Xie ◽  
Huai Feng Tong ◽  
Xiang Xia
Keyword(s):  
Compressive Strength ◽  
Uniaxial Compression ◽  
Uniaxial Compressive Strength ◽  
Particle Flow ◽  
Particle Flow Code ◽  
Compression Tests ◽  
Rock Samples ◽  
Single Hole ◽  
Compression Condition

Numerical specimens with single-hole is established by particle flow code PFC2D and uniaxial compression tests are conducted. Studies have shown that uniaxial compressive strength of specimen with single hole is less than complete specimens. As the holes move to the end of specimen, the uniaxial compressive strength first increases and then tends to decrease.

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