scholarly journals In-Situ and Numerical Investigation of Groundwater Inrush Hazard from Grouted Karst Collapse Pillar in Longwall Mining

Water ◽  
2018 ◽  
Vol 10 (9) ◽  
pp. 1187 ◽  
Author(s):  
Dan Ma ◽  
Xin Cai ◽  
Qiang Li ◽  
Hongyu Duan
Keyword(s):  
Coal Pillar ◽  
Lower Probability ◽  
Karst Collapse ◽  
Groundwater Inrush ◽  
Roof System ◽  
Karst Collapse Pillar ◽  
Fractured Coal ◽  
Coal Pillars ◽  
The Stability

Groundwater inrush is a typical hydrologic natural hazard in mining engineering. Since 2000 to 2012, there have been 1110 types of mine groundwater inrush hazards with 4444 miners died or missing. As a general geological structure in the northern China coalfields, the karst collapse pillar (KCP) contains a significant amount of granular rocks, which can be easily migrated under high hydraulic pressure. Therefore, the KCP zone acts as an important groundwater inrush pathway in underground mining. Grouting the KCP zone can mitigate the risk of groundwater inrush hazard. However, the fracture or instability of the coal pillar near KCP can cause the instability of surrounding rock and even groundwater inrush hazard. To evaluate the risk of groundwater inrush from the aquifer that is caused by coal pillars instability within grouted KCP in a gob, an in-situ investigation on the deformation of the surrounding strata was conducted. Besides, a mechanical model for the continuous effect on the coal pillar with the floor-pillar-roof system was established; then, a numerical model was built to evaluate the continuous instability and groundwater inrush risk. The collective energy and stiffness in the floor-pillar-roof system are the two criterions for judging the stability of the system. As a basic factor to keep the stability of floor-pillar-roof system, the collective energy in coal pillar is larger than that in floor-roof system. Moreover, if the stiffness of floor-roof or coal pillar meets a negative value, the system will lose stability; thus, the groundwater inrush pathway will be produced. However, if there is a negative value occurring in floor-pillar-roof system meets, it indicates that the system structure is situated in a damage state; a narrower coal pillar will enlarge the risk of continuous instability in the system, leading to a groundwater inrush pathway easily. Continuous coal pillars show a lower probability of instability. Conversely, the fractured coal pillars have a greater probability of failure. The plastic zone and deformation of the roadway roof in the fractured coal pillar are larger than that of continuous coal pillar, indicating that the continuous coal pillars mitigate the risk of groundwater inrush hazard effectively.

scholarly journals Damage Characteristics and Mechanism of a 2010 Disastrous Groundwater Inrush Occurred at the Luotuoshan Coalmine in Wuhai, Inner Mongolia, China

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 655 ◽  
Author(s):  
Fangpeng Cui ◽  
Qiang Wu ◽  
Chen Xiong ◽  
Xiang Chen ◽  
Fanlan Meng ◽  
...  
Keyword(s):  
Coal Seam ◽  
Inner Mongolia ◽  
In Situ Stress ◽  
Economic Losses ◽  
Karst Collapse ◽  
Great Effort ◽  
Groundwater Inrush ◽  
Collapse Column ◽  
Great Damage

On 1 March 2010, a disastrous groundwater inrush occurred at the Luotuoshan coalmine in Wuhai (Inner Mongolia, China). Great effort was taken during the post-accident rescue. However, triggered by a large amount of groundwater rushed in from the Ordovician limestone aquifer underlying the No.16 coal seam through the fractured sandy claystone and the karst collapse column, it caused great damage, including 32 deaths and direct economic losses of over 48 million yuan. The groundwater inrush originated from the floor heave in the air return gallery of the No.16 coal seam. The peak inflow rate was 60,036 m3/h. The gallery excavation under conditions caused by the incompletely recognized hydrogeological environment induced the accident. The unidentified spatial distribution of the karst collapse column triggered the accident directly. The high-pressure groundwater accumulated in the collapse column and the gallery excavation, which caused the redistribution of the in situ stress, contributing to progressive fractures in the floor of the No. 16 coal seam. Eventually, an intensive water-conductive passage consisting of the fractured floor and the karst collapse column formed. Administratively/technically, that mandatory regulations on gallery excavation were not carried out which contributed the accident. Moreover, the poor awareness about groundwater inrush recognition and quick remediation also contoirbuted to the disastrous extent of the accident.

scholarly journals Modeling the Spatial and Temporal Evolution of Stress during Multiworking Face Mining in Close Distance Coal Seams

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Yong Zhang ◽  
Jinkun Yang ◽  
Jiaxuan Zhang ◽  
Xiaoming Sun ◽  
Chen Chen ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Stress Distribution ◽  
Temporal Evolution ◽  
Coal Pillar ◽  
Coal Seams ◽  
Geological Conditions ◽  
Coal Pillars ◽  
The Stability ◽  
Close Distance ◽  
Close Distance Coal Seams

Mining in close distance coal seams (CDCSs) is frequently associated with engineering disasters because of the complicated nature of stress distribution within CDCSs. In order to establish a layout of a roadway to minimize the occurrence of disasters associated with mining CDCS, here the spatial and temporal evolution of stress distribution during the multiworking face mining of a CDCS was explored through numerical simulation based on the engineering and geological conditions of the Nantun Coal Mine. The numerical simulation results indicate that, after the extraction of adjacent multiple working faces, the spatial distribution of stress can be characterized with areas of increased, reduced, and intact stress. The superposed stress of inclined seams that are very close to each other propagates through coal pillars in the bottom floor, and this propagation follows neither the line along the axis of the coal pillar nor the line perpendicular to the direction of the floor. It instead propagates along a line angled with the axis of the coal pillar. The roadway can be arranged in the area with reduced stress, to improve its the stability. Based on the computed spatial and temporal evolution of stress, an optimized layout of roadway was proposed. This layout features a reasonable interval between the mining roadway and a minimal proportion of increased stress areas along the mining roadway and is aligned with geological structures.

scholarly journals Improvement of the Loading Capacity of Narrow Coal Pillars and Control Roadway Deformation in the Longwall Mining System. A Case Study at Khe Cham Coal Mine (Vietnam)

2020 ◽  
Vol 1 (2) ◽  
Author(s):  
Le QUANG PHUC ◽  
V. P. ZUBOV ◽  
Phung MANH DAC
Keyword(s):  
Longwall Mining ◽  
Coal Pillar ◽  
Rock Bolt ◽  
Mining System ◽  
Pillar Stability ◽  
Roadway Support ◽  
Coal Pillars ◽  
The Stability ◽  
Safe Condition ◽  
Cable Bolt

Currently, the application of coal pillars to protect an adjacent roadway is a common method in Vietnam when exploiting according to the longwall system. Therefore, the width of a coal pillar is an important issue for the stability of a roadway. In order to reduce coal loss in these coal pillars, they tend to be designed in a narrow coal pillar style but still have to ensure that the adjacent roadway can meet safe coal production conditions. The stability of roadways and coal pillars is related to many factors such as technical mechanical characteristics, physical and mechanical properties of coal, stress environment and support methods. The bearing structure of the coal pillar and the around rock a roadway is analyzed and it has been shown that enhancing roadway support and improving the carrying capacity of coal pillars can control the deformation of the surrounding rock. A study related to the stability and safety of roadways and small coal pillars in the longwall mining system has been carried out. Stabilization factors have been considered, especially the state of stress in the coal pillars and the deformation of the roadway. By applying the numerical simulation method, the stress of the coal pillar and the deformation of the adjacent roadway under different supporting solutions were analyzed and evaluated. By using this method, the rock bolt roadway support solution combined with the long cable bolt in the roadway roof and the coal pillar was selected in the safe condition of the mining process. Because cable bolt can improve the flexibility of the coal pillar such as: reducing the size of the plastic area on both sides of the pillar; enhancing coal pillar stability in the core area by providing great drag and tensile for coal pillars; contributing to improving the anchor point fixation of rock bolt. The conclusions obtained may provide a certain reference parameters to improve mining efficiency and labor safety in underground coal mines.

scholarly journals Seismic Response Analysis of Deep Underground Roadways and Coal Pillars under the Influence of the Adjacent Goaf

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Xu Cao ◽  
Xiaoshan Cao ◽  
Tielin Han
Keyword(s):  
Seismic Response ◽  
Numerical Study ◽  
Distinct Element ◽  
Coal Pillar ◽  
Coupling Model ◽  
Response Analysis ◽  
Seismic Load ◽  
Deformation Stress ◽  
Coal Pillars ◽  
The Stability

In this work, a numerical study is conducted on the seismic response of deep-buried roadways in coal mines under the influence of goafs, and a 3D numerical model of the seismic response simulation of deep-buried roadways is established using the coupling model of the finite difference method and the distinct element method. This model simulates the seismic response of different coal pillar widths and the seismic conditions of the deep-buried roadways under the influence of the adjacent goafs. The deformation, stress distribution, and plastic area distribution of roadways and coal pillars are systematically studied, and the situations under the static load and the roadways, which are not affected by the goafs, are compared and analyzed. A reasonable width of the coal pillar is proposed on the basis of the stability of the roadway and the coal pillars. In the end, suggestions for the reasonable setting of coal pillars under seismic load are provided.

scholarly journals Stability of Coal Pillar and Roof Movement Characteristics in Roadway Backfill Mining

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Hai Lin ◽  
Renshu Yang ◽  
Yongliang Li ◽  
Shizheng Fang
Keyword(s):  
Mechanical Model ◽  
Maximum Stress ◽  
Coal Pillar ◽  
Engineering Practice ◽  
Alternate Bearing ◽  
Local Pressure ◽  
Immediate Roof ◽  
Backfill Mining ◽  
Coal Pillars ◽  
The Stability

In order to explore the stability of coal pillar and the characteristics of roof movement during the process of roadway backfill mining (RBM), the 301 backfilling test working face of Ordos Chahasu coal mine is taken as the background. Based on the expansive pressure arch theory, the evolution process of the stope expansive pressure arch in RBM is studied; by establishing a mechanical model for the stability of coal pillars, the interactions between the height, width, and the maximum number of branches are obtained. When the width and height of the branch are both 5 m, the optimal number of the branches is obtained. Then, by establishing a mechanical model for the subsidence of the immediate roof, the process of the immediate roof subsidence is divided into three stages, namely, the formation stage of the local pressure arch, the merge stage of the pressure arch, and the expansion stage of the pressure arch. In addition, using the numerical method, the alternate bearing process of coal pillars and filling bodies and the change of the maximum supporting stress are studied, and the evolution of the pressure arch bearing structure above the stope and the staged subsidence characteristics of the roof are analyzed. The on-site test showed that the coal pillar has a good stability during the mining process. The maximum stress of the coal pillar is 16.5 MPa, and the maximum stress of the filling body is 9 MPa. The maximum settlement of the immediate roof is 102 mm, indicating that the roof control effect is good. This research will play an important role on engineering practice.

scholarly journals Risk Assessment and Control Strategy of Residual Coal Pillar in Room Mining: Case Study in Ecologically Fragile Mining Areas, China

2021 ◽  
Vol 13 (5) ◽  
pp. 2712
Author(s):  
Hengfeng Liu ◽  
Qiang Sun ◽  
Nan Zhou ◽  
Zhongya Wu
Keyword(s):  
Coal Pillar ◽  
Stability Control ◽  
Mining Areas ◽  
Long Term Stability ◽  
Movement Characteristics ◽  
Coal Pillars ◽  
The Stability ◽  
Residual Coal ◽  
Mining Coal ◽  
And Control

Gradual instability of coal pillars left behind underground with room mining is one of the main reasons for sudden roof caving in the gob, surface subsidence, and other significant hazards. Moreover, room mining implies great losses of coal resources. In this paper, the main failure mode and room mining coal pillar process were analyzed according to the coalfield regional engineering geological and hydrogeological conditions. A numerical model was adopted to study the effect of different sizes of coal mining pillars and progressive instability failure of coal pillar on the plastic zone’s evolution characteristics and stress field of coal pillars in the stope. The proposed technologies of cemented paste backfilling and reinforcement of residual coal pillars are applied, and a numerical simulation model is established to study the strata movement characteristics and analyze the stability degree of residual coal pillar and key aquiclude strata in the Pliocene series of Neogene. Consequently, the performance and application prospect were evaluated. The results obtained substantiate a new method for the long-term stability control of coal pillars in room mining and protecting the ecological environment in China’s western eco-environmental frangible area.

scholarly journals Coal Pillar Strength Formula in Indonesian coal mines

2020 ◽  
Vol 1 (1) ◽  
pp. 20-24
Author(s):  
Ratih Hardini Kusuma Putri
Keyword(s):  
Coal Mines ◽  
Coal Pillar ◽  
Research Area ◽  
Pillar Strength ◽  
Coal Pillars ◽  
Indonesian Coal ◽  
The Stability ◽  
Mine Development ◽  
Strength Formula ◽  
Coal Pillar Strength

In underground coal mines, coal pillars play a major rule in sustaining the weight of the overburden and protecting the stability of the entries and crosscut during mine development and production, allowing the miners to safely extract the coal¹. The determination of a coal pillar size is adjusted to the expected load and strength of the coal seam. It needs to consider several factors such as pillar load (stress within the pillar), pillar strength, and safety factors. In this determination, an analysis will be conducted using five similar coal pillar strengths including; Obert-Duvall Equation (1967), Holland Equation (1964), Holland-Gaddy Equation (1956), Salamon-Munro Equation (1967), and Bieniawski (1983). Using AirLaya seam as an example, we can combine the results of various equations. The coal used in the Airlaya research area has a value of k = 425.75, thus the strength of Airlaya insitu seam coal is estimated to be 161,607 Psi.

scholarly journals Stability analysis of hyperbolic coal pillars with peeling and high temperature effects

2020 ◽  
Vol 38 (5) ◽  
pp. 1574-1588
Author(s):  
Youyou Xu ◽  
Huaizhan Li ◽  
Guangli Guo ◽  
Xiaopeng Liu
Keyword(s):  
High Temperature ◽  
Bearing Capacity ◽  
Temperature Effects ◽  
Coal Gasification ◽  
Coal Pillar ◽  
Industrial Test ◽  
Test Area ◽  
Underground Coal Gasification ◽  
Coal Pillars ◽  
The Stability

In this present study, a twice-peeling model was established to analyze the hyperbolic coal pillars stability in underground coal gasification and then propose the concept of stripping degree to show model details for numerical simulation. The data shows that hyperbolic coal pillars stability can be analyzed through the twice-peeling model. Considering the coal pillars peeling and high temperature effects, one side of coal pillars will decrease 3 m, and the stability coefficient is 1.6 which has enough bearing capacity. When the arch depth ratio is 0.6, the critical condition for the coal pillar instability is reached. In this paper, underground coal gasification industrial test area still had strong bearing capacity after twice stripping, and there was no sudden instability. The research results can provide reference for the gasifier design and the stability of non-uniform coal pillars in the future.

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