Key Strata Inducing Dynamic Disasters Based on Energy Condition: Criterion and Application

The thick and hard rock strata (THRS) exist widely in coal measure strata, which control the movements of overlying rock strata in stopes. When THRS break, great energy is released, which could aggravate the risks of coal and gas outburst, rock burst, and other dynamic disasters. Therefore, the foundation and key of preventing dynamic disasters are to distinguish the THRS that could induce coal-rock dynamic disasters and to analyze the laws of rock stratum breaking and energy releasing. The paper proposed the theoretical calculation methods of the energy accumulation and attenuation of rock breaking which is greatly affected by the hanging length of rock strata and the spreading distance. One or more roof strata that play a leading role in inducing dynamic disasters of the underlying coal mass are defined as the key disaster-inducing strata (KDIS). The disaster-inducing coefficient (DIC) is defined and used as the criterion of KDIS. The greater the source energy, the shorter the spreading distance, and the smaller the attenuation coefficient are, the easier the roof strata are to become KDIS. The disaster-inducing ability of the main THRS was analyzed, and the igneous sill was judged as KDIS, taking the Yangliu Coal Mine as project background. The breaking laws of the igneous sill were obtained by the methods of UDEC numerical simulation and microseismic monitoring, which verified the criterion of KDIS.

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Study on Mechanism of Influence of Mining Speed on Roof Movement Based on Microseismic Monitoring

Advances in Civil Engineering ◽

10.1155/2020/8819824 ◽

2020 ◽

Vol 2020 ◽

pp. 1-9

Author(s):

Ke Ma ◽

Su-jian Wang ◽

Fu-zhen Yuan ◽

Yi-lin Peng ◽

Shi-min Jia ◽

...

Keyword(s):

Load Transfer ◽

B Value ◽

Microseismic Monitoring ◽

Surrounding Rock ◽

Working Face ◽

Final Failure ◽

Variation Characteristics ◽

Microseismic Events ◽

Roof Strata ◽

Rock Strata

Based on the study of the movement rule of the rock strata under the influence of the mining speed in the typical working face of Dongjiahe coal mine, the distribution of microseismic events and the variation characteristics of microseismic parameters in the slow and fast advancing stage are compared and analyzed, and the mechanism of the rock strata activity under the influence of the mining advancing speed is revealed from the perspective of the microfracture. The results show that the movement of the roof strata and the stress adjustment of surrounding rock have certain timeliness. The maximum advanced distance of microseismic events in the slow and fast stages is 185 m and 130 m, respectively, and the maximum lag distance of microseismic events in the goaf is 120 m and 180 m, respectively. The time of stress adjustment of surrounding rock is short, and the load transfer of the roof is insufficient. The advanced distance of microseismic events is increased, and the lag distance decreases. The percentage of microseismic events in the total number of events is 47% and 38%, respectively, in the slow and fast stages of advancing. With the increase of mining speed, the intensity of roof strata activity in the goaf is weakened. The rock failure decreases and the volume of broken block increases, and roof collapse and rotary subsidence are insufficient. During the nonpressure period, the maximum development elevation of microseismic events is +350 m and +300 m, respectively, in the slow and fast stages, while with the development elevation of microseismic events in the roof pressure near +390 m, increasing the mining speed cannot change the final failure height of the overburden. During the analysis period of roof pressure, the concentrated release of microseismic energy in the faster stage is 183% of that in the slower stage. The increase of large moment magnitude event frequency leads to the decrease of b value. The risk of roof instability and strata behavior increases.

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Rock Breaking Performance of Two Disc Cutters of Tunnel Boring Machine for Safe Tunneling in Unstable Coal Rock Stratum

International Journal of Safety and Security Engineering ◽

10.18280/ijsse.100508 ◽

2020 ◽

Vol 10 (5) ◽

pp. 639-646

Author(s):

Zhenggang Guo ◽

Juan Wang ◽

Shuai Lv ◽

Deyue Yu ◽

Xu Zhang

Keyword(s):

Specific Energy ◽

Tunnel Boring Machine ◽

Rock Breaking ◽

Rock Stratum ◽

Deployment Strategy ◽

Disc Cutters ◽

Rock Formations ◽

Coal Rock ◽

Cutter Spacing ◽

Cutter Head

In unstable coal rock formations, the rescue channels should be constructed through safe and efficient tunneling. The rock breaking performance of the tunneling equipment directly hinges on the cutter-head layout. Focusing on the conditions of unstable coal rock formation, this paper adopts the extended Drucker-Prager (D-P) plastic model to define the properties of bedrock materials of the coal rock with low mechanical strength and poor homogeneity. Then, a finite-element model was established on ABAQUS for the coal rock cut by two disc cutters, and used to simulate the breaking of the coal rock and the peeling of slags from the bedrock. On this basis, the authors analyzed the influence of cutter spacing (30, 35, 40, and 45mm) over cutting force, rock breaking amount, and specific energy under two cutting methods: simultaneous cutting and sequential cutting. Finally, a cutter deployment strategy was designed for safe and efficient tunneling in unstable coal rock formations. The results show that: Under simultaneous cutting, as the cutter spacing increased from 30 to 35mm, the rock breaking amount increased, while the specific energy declined; as the cutter spacing further rose from 35 to 45mm, the rock breaking amount dropped, while the specific energy increased. Under the coal rock conditions in our research, the optimal cutter deployment strategy is: simultaneous cutting with cutter spacing of 35mm. The research results provide theoretical support for the cutter-head design of rescue equipment for collapsed coalmines.

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Failure Mechanism of a Coal-Rock Combined Body with Inclinations of Structural Planes and a Calculation Model for Impact Energy

Advances in Civil Engineering ◽

10.1155/2019/3735427 ◽

2019 ◽

Vol 2019 ◽

pp. 1-18

Author(s):

Yi-Chao Zhao ◽

Ming-Shi Gao ◽

Yong-Liang He ◽

Dong Xu

Keyword(s):

Mechanical Properties ◽

Failure Mechanism ◽

Impact Energy ◽

Coal Mines ◽

Calculation Model ◽

Engineering Practice ◽

Test Results ◽

Failure Characteristics ◽

Coal Rock ◽

Rock Strata

A coal-rock (CR) combined body can be used to simulate structures of coal and rock strata, and its impact-induced failure characteristic conforms more close to engineering practice. Exploring the mechanical properties and impact energy in a CR combined body contributes to better predictions of rock bursts in coal mines. In the study, the mechanical properties of CR combined bodies with four different inclinations (0°, 15°, 30°, and 45°) of structural planes were measured, and also their failure mechanism was analysed. Based on the theory of particle mechanics, a calculation model for impact energy in a CR combined body with inclinations was established and then verified by using monitored acoustic emission (AE) data. The test results showed that inclination affected mechanical properties and failure characteristics of the CR combined body, i.e., the larger the inclination, the lower the strength and impact energy in the CR combined body and the lower the level of damage. The proposed calculation model for impact energy revealed the mechanical essence of energy accumulation and release of a CR combined body, providing a reference for investigating rock burst in coal mines.

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Movement Law and Discriminant Method of Key Strata Breakage Based on Microseismic Monitoring

Shock and Vibration ◽

10.1155/2019/8652894 ◽

2019 ◽

Vol 2019 ◽

pp. 1-19 ◽

Cited By ~ 1

Author(s):

Yang Li ◽

Tianhong Yang ◽

Weidong Song ◽

Ling Yu

Keyword(s):

High Intensity ◽

Microseismic Monitoring ◽

Geological Structure ◽

Western China ◽

Dynamic Monitoring ◽

Ecological Environment ◽

Environmental Damage ◽

Key Strata ◽

Key Stratum ◽

Working Face

Because of the unique natural geography, geological structure, and ecological environment, there are serious geological disasters and environmental damage caused by the high-intensity mining in Western China. It seriously restricts the development of coal resources and the protection of ecological environment. In order to fully capture the law of key stratum breakage with high-intensity mining, the IMS microseismic system was introduced into Xiaojihan coal mine which is a typical high-intensity mining mine in Western China, and the whole process dynamic monitoring was carried out. The process of key stratum breakage was analysed by MS data, which were in agreement with the pressure analysis results of the hydraulic support of the working face. The results showed that there were the obvious forewarning characteristics in microseismic event number, energy release, energy index, Schmidt number, coefficient of seismic response, and b value when the key stratum was breaking. Then, a method to discriminate the breakage of key stratum was proposed by using the forewarning characteristics, which could provide the guidance for prevention and control of geological hazards in the working face with high-intensity mining.

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Theoretical Study and Numerical Simulation Research on the Effect of Coal-Rock Interface on Multistaged Fracturing in the Roof of Outburst Coal Seam

Shock and Vibration ◽

10.1155/2021/5529884 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Fan Zhang ◽

Yang Tang

Keyword(s):

Elastic Modulus ◽

Coal Seam ◽

Hydraulic Fracture ◽

Mechanical Parameters ◽

Multiple Fractures ◽

Rock Stratum ◽

Gas Drainage ◽

Rock Interface ◽

Coal Rock ◽

Outburst Coal Seam

Multistaged fracturing in the roof of outburst coal seam is an efficient and creative technology for coalbed methane (CBM) drainage, which can effectively improve the permeability of coal seam. To reveal its mechanism of permeability enhancement, the effect of coal-rock interface on multistaged fracturing in the roof of outburst coal seam was simulated and discussed in this paper. Firstly, the lithological difference between outburst coal seam and roof was compared, and the concept and significance of multistaged fracturing in the roof of outburst coal seam were explained. Then, the mechanical conditions of multiple fractures in the roof traversing coal-rock interface were analyzed. The effects of mechanical parameters on multiple fractures were numerically simulated. The results indicated that fracturing borehole in adjacent rocks of outburst coal seam is much easier to drill and maintain gas drainage. Considering gas drainage efficiency and avoiding being blocked by coal fines, multistaged fracturing borehole is generally drilled in the stable rock stratum of roof. Whether the multiple fractures in the roof can traverse coal-rock interface is related to mechanical parameters of coal and rock, friction factor of coal-rock interface, angle between horizontal profile and coal-rock interface, cementing strength of coal-rock interface, minimum horizontal stress, and other factors. Higher fracturing fluid pressure contributes to propagating from the reservoir with low elastic modulus to the one with high elastic modulus for hydraulic fracture. Hydraulic fracture is more likely to propagate in the rock stratum with high brittleness index. The research results can improve multistaged fracturing theory and provide technological support for field test.

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Coal Rock Breaking Simulation and Cutting Performance Analysis of Disc Cutters

Tehnicki vjesnik - Technical Gazette ◽

10.17559/tv-20210423115559 ◽

2021 ◽

Vol 28 (5) ◽

Keyword(s):

Performance Analysis ◽

Rock Breaking ◽

Cutting Performance ◽

Disc Cutters ◽

Coal Rock

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Modelling igneous rock mechanics parameter based on logging data in Shunbei oil field

Journal of Physics Conference Series ◽

10.1088/1742-6596/2076/1/012008 ◽

2021 ◽

Vol 2076 (1) ◽

pp. 012008

Author(s):

Wenxia Li ◽

Weiqiang Song ◽

Jingtao Liu ◽

Xiuping Chen ◽

Huidong Mu

Keyword(s):

Tensile Strength ◽

Compressive Strength ◽

Rock Mechanics ◽

Igneous Rock ◽

Friction Angle ◽

Rock Breaking ◽

Oil Field ◽

Rate Of Penetration ◽

The North ◽

Rock Strata

Abstract In order to improve the rate of penetration (ROP) in Permian igneous rock strata, the rock mechanics is modeled based on the continuous logging data (acoustic, density, caliper, resistivity and gamma logging) and confirmatory indoor experiments. The model considers the influence of well collapse and expansion on logging data in igneous rock formation to improve the calculation accuracy. Based on this model, the continuous profile of Permian compressive strength, tensile strength, mud content, internal friction angle are calculated, and then the differences of Permian strata in the north, middle and south of the oilfield are further compared and analyzed. The results can provide support for the optimization of efficient rock breaking and reservoir fracturing technology.

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MODELING OF STABILITY OF SIDE ROCKS IN A COAL MASIFWITH DIFFERENT METHODS OF SUPPORT THE WORKINGS

Labour protection problems in Ukraine ◽

10.36804/nndipbop.37-3.2021.28-34 ◽

2021 ◽

Vol 37 (3) ◽

pp. 28-34

Author(s):

V. Yu. Dovhal

Keyword(s):

Static Field ◽

Rock Massif ◽

Shear Stresses ◽

Support Structures ◽

Coal Seams ◽

Rock Stratum ◽

Static Loads ◽

Flexible Support ◽

Coal Rock ◽

The Stability

Purpose of work. Determine the conditions of the side rocks stability in a coal massif with different ways of support coal-rock stratum to ensure safe working conditions for miners in the excavation areas of a coal mine with steep coal seams. To achieve this goal, laboratory studies were carried out on models of optical and equivalent materials. The modeling of the stability of side rocks in a coal-rock massif was carried out with the methods of support roadways with vertical timber setsand wooden crib supports: 4-point chock.On models made of optical materials in the analysis of the static field of the distribution of shear stresses in side rocks, the regularity of the change in hazardous manifestations of rock pressure, depending on the deformability of support structures, was recorded. On equivalent models of support structures, the deformation characteristics of experimental samples were determined and their effect on the integrity of the roof under the action of static loads was established. When using rigid support structures in the form of vertical timber sets made of wooden racks to protect sliding drifts, there is a deterioration in the stability of side rocks and destruction of the roof. When using flexible support structures in the form of wooden crib supports: 4-point chock, a smooth deflection of the roof and its integrity are observed. A decrease in the size of the stress concentration zone in the model of a coal-rock massif with workings after the compaction of flexible support structures located above the haul roadway, due to a change in their rigidity, when as a result of the convergence of side rocks, a smooth deflection is provided and the movement of the roof is limited. To ensure the stability of side rocks and development workings, as well as reduce the level of injuries of miners from landslides and collapses in the excavation areas of coal mines that develop steep seams, it is advisable to use flexible support structures, when using which, a smooth deflection of side rocks and their integrity in the mined-out area is ensured coal massif.

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Research of Safe Distance between Concealed Karst Cave and Tunnel

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.405-408.1283 ◽

2013 ◽

Vol 405-408 ◽

pp. 1283-1287

Author(s):

Yong Biao Lai ◽

Chun Sheng Qiao ◽

Chen Guang Bai

Keyword(s):

Catastrophe Theory ◽

Total Potential Energy ◽

Karst Cave ◽

Safe Distance ◽

Rock Stratum ◽

Distance Calculation ◽

Total Potential ◽

Concealed Karst Cave ◽

The Stability ◽

Rock Strata

Based on the catastrophe theory, a research method of safe distance between concealed karst cave and tunnel is put forward. The stability of rock stratum between concealed karst cave and tunnel is evaluated by the catastrophe theory, the catastrophe mode of rock strata system destabilization is established through the research of rock stratum total potential energy between karst cave and tunnel, then the safe distance calculation formula between concealed karst cave and tunnel are deduced, which is veried by an engineering example.

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