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The 43rd International Conference on Ground Control in Mining continues to bring you the leading research on ground control in mining. Hear from recognized industry innovators and specialists from around the world.

Note: Check back often for updates.

TUESDAY
July 23, 2024
WEDNESDAY
July 24, 2024
THURSDAY
July 25, 2024

 

Case Studies

 

8:20 AM

ICGCM China – History, Development, Academic Innovations, and Educational Role

Syd Peng; Henan Polytechnic University, China, Jiaozuo, Henan, China (Mainland),Yang Li; China University of Mining and Technology (Beijing), Beijing, Beijing, China (Mainland), Wenbing Guo; Henan Polytechnic University, Jiaozuo, Henan, China (Mainland), Feng Du; Henan Polytechnic University, Jiaozuo, Henan, China (Mainland), Jinyi Cheng; China University of Mining and Technology, Xuzhou, Jiangsu, China (Mainland)

The annual ICGCM China was initiated in 2014 by the senior author and three senior administration officers for three major coal mining universities. Its objectives and program are patterned after the ICGCM originated and held annually in the US. In the beginning, it was intended to rotate among the three universities represented in the founding group. However, as it developed, more universities continued to join and the conference soon attracted all nine major coal mining schools in China. As a result, it has been held in rotation order among the 9+ major universities with coal mining engineering and related disciplines in China.

Up to 2023, ICGCM China has been held 9 times in that many years and insitutions continuously since 2014, except that due to COVID-19 epidemic, 2020 was skipped, and 2021 and 2022 were online.

In the 9 conferences during the past 9 year, about 420 papers in 17 topical areas were presented and attendance ranged from 200+ to 400+.

The 42nd ICGCM China was held in Xiangtan, Hunan, China, 10/20 – 10/22/2023. There were 76 papers presented in 26 topical areas with speakers from 28 different institutions and operator. In addition, a PhD Dissertation Research Forum was held concurrently with 36 papers presented by PhD candidates in mining engineering from 8 schools. The forum was dedicated to on-going dissertation research presented by individual PhD students. Attendance for the whole conference was well over 400.

In this paper, the 42nd ICGCM China is used to illustrate the current and future development trends of coal mine ground control in China. It will summarize the contents of the 122 papers (including 36 PhD Forum papers) grouped into, and in terms of, 26 topical areas. Its unique and innovative subject aeas, short summary of developments as well as conference strengths and shortcomings will also be presented.

 

8:42 AM

Gob Wells – Is There a Way to Predict Water Makers?

Zacharias Agioutantis; University of Kentucky, Lexington, Kentucky, United States, Julian Brown; University of Kentucky, Lexington, Kentucky, United States,Steve Hicks; Coronado Global Resources, Inc., Beckley, West Virginia, United States, Zachary Wedding; University of Kentucky, Lexington, Kentucky, United States

Vertical gob wells are an efficient method of methane extraction from an actively mined longwall coal panel. These vertical wells are used for degasification of the gob area after mining. They are drilled above the predicted gob area before commencing with mining of the panel to within 50 feet of the top of the coal and become active once the face of the longwall travels far enough past the drilled well for the gob roof to fall  and allow for methane to flow into the well from the gob area. The methane then travels up the well to the surface to be collected or vented to the atmosphere.

At Coronado’s Buchanan mine in Buchanan County, VA, these wells are drilled through 1,500-2,500 feet of overburden. These wells can penetrate up to two previously mined coal seams and are cased below the elevation of the lowest seam. There are approximately 20 vertical gob wells drilled per panel at intervals of about 500 feet. This method of degasification seems to work well for this mine’s requirements. A typical well can initially produce methane at a rate of 1,50 MMcf/day at a volume concentration of 83%

Once the longwall face passes under them, typically 50 to 100 feet, these wells start producing methane; however, about one-third of these wells become a source of water entering the mine. The mine is constrained under its environmental permits to how much water it can discharge to the surface receiving stream. Because of this, many of these wells end up needing to be plugged quickly after becoming active wells to limit the inflow of water into the mine. A gob well that does not introduce water into the mine can be active for decades. A typical gob methane drainage well can cost about $500,000 to site, drill and construct collection infrastructure. Some wells are required to be plugged within three days of becoming active. If it is required to be plugged soon after becoming connected to the mine, a large amount of money is spent to collect a small amount of methane. The gas that is not removed then becomes another challenge to the operation of the mine.

This paper presents and discusses the data that has been acquired as well as the analysis method that was followed and presents preliminary findings with respect to whether it is feasible to predict which wells will become water makers following activation.

 

9:04 AM

The Effect of Overburden Depth on Casing Deformations of Shale Gas Wells in Longwall Chain Pillars — Recent Mine-by Experiences

Peter Zhang; National Institute of Occupational Safety and Health, Pittsburgh, Pennsylvania, United States, Daniel Su; NIOSH, Pittsburgh Mining Research Division, Pittsburgh, Pennsylvania, United States, Zoheir Khademian; NIOSH, Pittsburgh Mining Research Division, Pittsburgh, Pennsylvania, United States, Berk Tulu; NIOSH, Pittsburgh Mining Research Division, Pittsburgh, Pennsylvania, United States, Bo Hyun Kim; NIOSH, Spokane Mining Research Division, Spokane, Washington, United States

Over 2,000 shale gas wells have been drilled in the Pittsburgh seam longwall reserves. As longwall panels are laid out, some of these shale gas wells have to be located in longwall chain pillars. With the constraint of both chain pillar size and gas well location within the pillars, gas wells in chain pillars are subjected to more influence by longwall-induced subsurface ground movements and stresses which could induce deformations in gas well casings. Casing deformations are affected by several factors such as overburden geology, surface topography, setback distance, and casing construction. One important factor is the overburden depth which largely determines the amount of horizontal subsurface movements and abutment pressure over the chain pillars under a given overburden geology. Previous NIOSH gas well research has shown that casing deformations above the coal seam horizon are smaller under deep cover than under shallow cover and that casing deformations could occur at the coal seam horizon under deep cover. Recent mine-by cases have given more insights into the amount and locations of longwall-induced casing deformations as well as potential occurrence of a large casing deformation. This paper presents three mine-by cases with shale gas wells in the chain pillars between two adjacent longwall panels under different overburden depths. Casing deformations were first predicted with numerical modeling and then measured by multi-finger caliper survey after each panel was mined. These mine-by cases provide a general demonstration of how overburden depth can affect longwall-induced stresses and deformations. Based on the measurements and numerical modeling, the effect of overburden depth is further analyzed to investigate the abnormal geologic conditions in which large casing deformations could occur and to show how casing deformations can be minimized through optimal chain pillar layout and casing design. It was found that (1) large casing deformations could occur at the coal seam horizon under a depth of cover greater than 1,100 ft; (2) optimal gas well location is near the center of the chain pillar systems under deep cover; and that (3) uncemented production casing can eliminate or minimize casing deformations both above and in the coal seam horizon. The experience and knowledge gained from these mine-by cases would help longwall operators and gas companies to take appropriate measures to minimize the influence of longwall mining in shale gas wells in chain pillars.

 

9:26 AM

Ground Support Optimization Using a Structed Strata Management Process in Wide Set-up Room Roadways at West Elk Mine

Ry Stone; Agapito Associates, Inc, Lakewood, Colorado, United States, Bob Munz; Arch West Elk, Somerset, Colorado, United States

To facilitate the installation of the longwall equipment for each extraction panel, Mine A develops set-up room roadways that are between 26.5 and 30.5 feet wide. Historically at the mine, the set-up room roadways have been driven in a single 20-foot-wide pass and slabbed to the required width during installation of the shields. The first pass roof is supported with a generic roof support plan consisting of partially encapsulated roof bolts and point-anchored cables. This ground support plan was utilized regardless of the geotechnical conditions encountered in the roadways or consideration of the required stand-up time of the roadway before
the longwall shields were installed. This “blanket” approach tends to result in over conservative or inappropriate roof support designs, particularly in changing geotechnical environments.

Driven by the desire to optimize the ground support plans and increase mining efficiency for future set-up rooms, Mine A and Agapito Associates developed and implemented a strata management program. Strata management, as a formal and structured process, allows ground support and mining methods to be tailored to the anticipated and encountered geotechnical environment in a controlled manner (Thomas, 2007). To arrive at adequate site-specific ground support plans for the set-up rooms at the mine, several structed processes were utilized. Firstly, the geotechnical environment was characterized by examining nearby rock core for roof lithology and geomechanical properties, in conjunction with the results of in-situ stress measurements. To increase both mining efficiency and continuity, and to achieve longer stand-up times before the longwall shields are installed, a two-pass approach was implemented into the design. During mining, the geotechnical conditions of the roadway were mapped, and the roof was strategically surveyed with a borescope. This process was used to ensure that the encountered ground behavior was constrained within the design standards used for the roof support design. To support this process with measured data, roof extensometers were strategically installed throughout the roadway. This data was used to monitor the magnitude of roof displacement at various horizons and record displacement rates up until the longwall shields were installed.
Lastly, a Trigger Action Response Plan (TARP) was used during mining to cater for any unforeseen changes in ground conditions that would warrant additional controls such as increased monitoring or the installation of additional ground support.

This paper presents two case histories at the mine where the above strata management approach was implemented to arrive at a site-specific ground support plan. The main changes to the mine’s ground control plan included a two-pass mining approach, the utilization of fully encapsulated roof bolts, and the migration to a stiffer roof support system. The geotechnical mapping, the roof borescope results, and the roof extensometer data will be presented to demonstrate the effectiveness of the ground support system up until the longwall shields were installed in both of the presented cases.

 

Mine Mapping Techniques

 

10:20 AM

Coal-associated Resources Multi-layer Development: A Technical Framework for Strata Control & ICGCM China – History, Development, Academic Innovations, and Educational Role

Yang Li; China University of Mining and Technology Beijing, Beijing, Beijing, China (Mainland), Nan Wang; China University of Mining and Technology Beijing, Beijing, China (Mainland), Jiachen Wang; China University of Mining and Technology Beijing, Beijing, China (Mainland)

The energy structure and consumption ratio in our country determine the practical demand for the collaborative mining of coal and co-associated resources. The multi-layer mining of coal, uranium, coalbed methane, and oil and gas co-associated resources, represented by the Ordos Basin, Junggar Basin, and Tarim Basin, faces numerous challenges. Additionally, coal has been found to coexist with various mineral resources in 33 coal-bearing basins worldwide. The scientific issues related to the multi-layer development of coal-related co-associated resources urgently need to be addressed. This paper discusses the unique challenges and potential solutions in the multi-layer development of coal-related co-associated resources. The challenges include large extraction space, high mining intensity, intense overburden movement, rapid surface subsidence, and severe overburden damage due to repeated mining disturbances. Proposed solutions include the establishment of a correlation mechanism between multi-layer mining and the carrying capacity of the overburden environment, analysis of the impact characteristics of multiple field couplings, and exploration of their superposition evolution laws. The paper also proposes the development of a comprehensive evaluation and prediction system for overburden environmental capacity loss, a global sensitivity analysis model for overburden environmental capacity, and an intelligent identification and early warning system based on multi-source information fusion. These solutions aim to achieve scientific and precise mining with minimal overburden environmental capacity loss. And the multi-layer development of coal-related co-associated resources is a complex task that requires a multidisciplinary approach and innovative solutions, and further research is needed to validate these strategies and explore new methods and technologies for efficient and sustainable extraction.

 

10:40 AM

Applications of LiDAR in Underground Mines Abstract

Emily Muto; MSHA Technical Support, Pittsburgh, Pennsylvania, United States

The introduction of LiDAR technology has made it possible to accurately and rapidly map large areas of underground mines in three dimensions. MSHA Technical Support’s Roof Control Division began implementing LiDAR technology in conjunction with the agency’s Pillar Collapse Initiative, by using scans to determine actual width to height ratios of pillars adjacent to mass collapse areas. This quickly expanded to change detection, where precise measurements of many pillars show which ones are deteriorating over time. A big advantage of LiDAR is that precise data can be obtained from safe distances. For example, roof fall cavity heights and volumes can be measured from stable ground. Depending on the scanner used it is also possible to collect geologic data, such as joint orientations. The paper will further discuss applications of LiDAR regarding ground control.

 

11:00 AM

From Points to Lines to Surfaces: A Novel Approach to Reconstructing Field-Scale Three-Dimensional Shale Roof Models Using Image Processing

Gaobo Zhao; West Virginia University, Morgantown, West Virginia, United States, Mindi Ruan; West Virginia University, Morgantown, West Virginia, United States,Deniz Tuncay; West Virginia University, Morgantown, West Virginia, United States,Ihsan Berk Tulu; CDC NIOSH, Pittsburgh Mining Research Division, Pittsburgh, Pennsylvania, United States,Yuting Xue; CDC NIOSH, Pittsburgh Mining Research Division, Pittsburgh; Pittsburgh, Pennsylvania, United States,Xin Li; University at Albany, Albany, New York, United States

Most coal mine roofs in the Appalachian region consist of laminated shale, which is prone to brittle failure. Accurate modeling of shale roofs is vital for studying cutter failures of these shale roofs, and ordinary and formational bedding planes play a significant role in the response of the shale roof to mining-induced stresses. This paper presents a robust method for constructing three-dimensional shale roof models using limited borehole cores and leveraging image processing techniques. The approach begins with image extraction from shale cores. Then, we extract the portions that feature the core and employ image-stitching techniques to merge them seamlessly. Once the images are stitched, they are duplicated horizontally and merged to create a cross-sectional plane image representing a shale roof. This roof cross-sectional plane image serves as an input to our proprietary Digital Image Processing (DIP) algorithm, which is adept at extracting ordinary bedding planes (interfaces that represent color transitions between a single shale unit). The extraction process involves transforming discrete core points (ordinary bedding plane pixels) into continuous lines representing ordinary bedding planes. Finally, extending this method into the third dimension, the model is further extrapolated to form a comprehensive three-dimensional shale roof. Through this process, the geometry information of ordinary bedding planes can be extracted for each type of shale in cores, including sandy shale, gray shale, dark shale, etc. This work bridges the gap between limited core data and comprehensive 3D geological modeling, offering valuable insights into identifying and quantifying the variations in different shale roof geologies.

 

11:20 AM

Application of Machine Learning and Explainable AI to Roadway Roof Convergence Data

Jason Emery; Optimum Geotechnics, Bangalee, Queensland, Australia, Ismet Canbulat; UNSW, Sydney, New South Wales, Australia, Chengguo Zhang; UNSW, Sydney, New South Wales, Australia

This paper describes a program of data analytics applied to an industry wide database of roadway roof extensometer data from Australian longwall mines collected between 2014 to 2020. Preliminary analyses with classic machine learning algorithms included multiple logistic regression, K-nearest neighbours, decision tree, random forest, support vector machine, kernel support vector machine, artificial neural network (ANN), naïve Bayes and multiple linear regression. Results indicated that relationships were complex and non-linear. The artificial neural network was found to be the most appropriate ML algorithm for predicting the outcome variable (roof movement). An ANN model was then refined through a standard process of hyperparameter optimisation and data augmentation to arrive at a final model. Due to the black box nature of the ANN further insight into how the parameters interacted was sought and found with Shapley additive explanations (SHAP values) a form of eXplainable Artificial Intelligence (XAI). SHAP values are a type of additive ML model that utilise Game Theory, where each input parameter or feature is a “player” while the dataset is the “team”. The SHAP value is the impact of each player on the target value, essentially establishing the contribution of each input parameter. Application of SHAP proved remarkably valuable when combined with the knowledge of the underlying mechanics in each situation. In most cases the explanations inferred from the AI agreed with the mechanics. This remains an area for further research.

 

11:40 AM

Best Practice Data Management for Extensometers at Australian Underground Coal Mines

Scott Burchmore; Geotechnicoal, Cannonvale, Queensland, Australia, Michael Melville; Geotechnicoal, Cannonvale, Queensland, Australia, Jason Emery; Optimum Geotechnics, Cannonvale, Queensland, Australia

This paper presents best practice data management for monitoring of extensometers in Australian underground coal mines. This work is based on the combined experience of the authors and the available literature. The information and ideas presented herein are a culmination of many years of database development founded from mine site-based ground support design, underground inspections, extensometer data management and data analysis. Each author has more than ten years’ experience as a practicing geotechnical engineer at several operating underground coal mines. In addition to capturing this experience, are the relevant findings in terms of data management, from a current industry wide research project focused on utilizing mechanical extensometer data for data analytics and machine learning. Principal hazard ground control management plans, stipulated in Australian coal mining legislation, outline the mandatory installation of ground monitoring devices during routine mining activities. After 20+ years of data gathering the barrier to implementing modern data analytics remains the challenges imposed by inconsistent data structure and data quality. This inconsistency is still routinely found between sites, companies and mining regions. Through the relatively simple application of a standardized database structure, the potential to shift from simplistic tracking of trigger levels, siloed at individual sites, to an industry standard method for compilation & comparison of monitoring data is enabled.

 

Sesimicity

 

1:00 PM

Quantitative Description and Definition of Soft Rock Tunnel

Demao Guo; Anhui University of Science and Technology, Huinan, Anhui, China (Mainland), Yingming Li; Anhui University of Science and Technology, Huainan, Anhui, China (Mainland), Nianjie Ma; China University of Mining & Technology, Beijing, Haidian District, Beijing, China (Mainland)

Based on the mechanical essence that large-scale plastic failure zone appears in all or part of surrounding rock in soft rock roadway, the numerical simulation method is used to study the rectangular roadway in
layered rock strata. It is clarified that three necessary conditions must be met for soft rock roadway: firstly, the strength condition is that the maximum confining pressure is greater than the uniaxial compressive strength of rock strata. Secondly, the stress environment condition is that the ratio of maximum confining pressure to minimum confining pressure is greater than 3. Thirdly, the angle condition is that the direction of principal stress action enables the plastic zone of weak rock layers to fully develop. At the same time, the quantitative description method of soft rock is given, and the soft rock roadway is redefined. Soft rock roadway refers to the roadway that meets the strength conditions, stress environment conditions, and rock structure angle conditions under certain surrounding rock conditions and in-situ stress environment conditions. After the excavation of the roadway, a large-scale plastic failure can be formed, that is, a butterfly-shaped plastic zone is formed, and the conventional support cannot be adapted. It is difficult to support in engineering. It provides a theoretical basis and engineering analysis method for the identification of soft rock roadway, and the research results have engineering value.

 

1:22 PM

Stress Distribution Characteristics and Energy Evolution Law of Drilling Pressure Relief

Kai Zhang; Anhui University of Science and Technology, Huainan, Anhui, Anhui, China (Mainland), Yingming LI; Anhui University of Science and Technology, Huainan, Anhui, China, Anhui, China (Mainland)

Based on the research background of 1303 working face return air roadway in Jinyuan Zhaoxian Mine, Shaanxi Province, a method of determining the reasonable spacing of boreholes is proposed based on the stress transfer degree of coal above and between boreholes, combined with the law of plastic zone and energy evolution by theoretical analysis and numerical simulation. After drilling pressure relief, the average daily energy of microseismic events decreased by 70%, and those with microseismic energy greater than 104 J decreased by 99.2%. The research has a strong guiding significance and research value for determining the reasonable distance of borehole pressure relief.

 

1:44 PM

Seismic Potential Forecasting in a Deep Longwall Mine

Zoheir Khademian; NIOSH, Pittsburgh, Pennsylvania, United States, Jake Beale; Pilot Geophysical LLC, Riner, Virginia, United States, Steve Hicks; Coronado Global Resources, Inc., Beckley, West Virginia, United States, Josh Fuller; Coronado Global Resources Inc., Mavisdale, Virginia, United States, Zach Agioutantis; University of Kentucky, Lexington, Kentucky, United States, Quintin Justice; Coronado Global Resources Inc., Mavisdale, Virginia, United States

Seismic events can be induced by mining due to unstable rock failures or slips along geologic structures leading to the sudden release of strain energy stored within the rock near underground openings. Depending on their intensity and proximity to the working area, seismic events may raise safety concerns, and thus the forecasting of the seismic potential in advance of mining can mitigate safety hazards. The integration of seismic data into geomechanical modeling can provide a tool for identifying areas with elevated potential for seismic activity. In previous works, a methodology was developed to forecast seismic potentials in a pseudo- 2D geomechanical model. In this paper, seismic events, ranging in magnitude from about -1.0 ML to 3.7 ML, recorded in a deep longwall mine (> 450 m) in Virginia during mining of six adjacent panels, were evaluated to identify areas where larger magnitude events (> 1 ML) had occurred. A three-dimensional geomechanical model of the same area was constructed in the 3DEC software to calculate the state of energy in the system with the progress of mining along the entire length of each panel. The variation in the energy content of the model was monitored, and zones with potentially damaging events with compression-type and slip-type signatures were identified by defining a Seismic Potential Index (SPI). The results show that slip-type events along bedding planes followed by compressive-type events in the sandstone roof are the mechanism for large seismic events in the studied mine. The locations of anomalous events corresponded to the regions where both compression-type SPI (C-SPI) and slip-type SPI (S-SPI) were elevated. The modeling results were compared with the recorded seismic events to evaluate the model performance in forecasting the seismic potentials. The model was able to forecast 100% of regions with elevated and moderate seismic potential and 89% of regions with low seismic potential. This shows the applicability of energy balance calculations for forecasting the approximate location and timing of destructive seismic events in advance of mining.

 

2:06 PM

Research on Microseismic Passive Velocity Tomography Based on Template Matching Technology

Erik Westman; Virginia Tech, Blacksburg, Virginia, United States, Qiankun Zhu; Northeastern University, Shenyang, Liaoning, China (Mainland), Xingdong Zhao; Northeastern University, Shenyang, Liaoning, China (Mainland), Shawn Boltz; NIOSH, Spokane, Washington, United States, Derrick Chambers; Colorado School of Mines, Golden, Colorado, United States

Microseismic passive velocity tomography has become an effective technology for large-scale mining- induced stress monitoring in underground mines, especially in the field of early warning of mining-induced hazards. Aiming at the problems of missing low-magnitude events in traditional microseismic monitoring, as well as the potential to increase the resolution of the tomograms in both time and space, a microseismic passive velocity tomography analysis method based on the template matching method was proposed. First, the template matching method was used to pick microseismic events. Then, the probabilistic, non – linear, global – search earthquake location method was used to locate the events, travel time and travel distance.
Finally, the fast-marching method was used to carry out passive velocity tomography analysis, and verified with the data from a surface microseismic monitoring system mounted above a longwall panel of an underground mine. The results show that the selected templates can identify more microseismic events than the traditional microseismic analysis, and the variation trend of events in each day is consistent with the data from the traditional analysis. Using microseismic event locations, travel times and travel distance can effectively complete microseismic passive velocity tomography analysis in each day during the study period and can effectively identify the front abutment pressure zone and side abutment pressure zones of that longwall panel. This study can provide a reference for realizing the identification of mine-induced high stress zones and mining-induced hazard early warning with increased resolution of the tomograms in time and space.

 

Advances in Ground Control

 

3:00 PM

Ductile Shotcrete Linings for Mining in “Squeezing Ground Conditions”

Manuel Entfellner; Implenia AG, Salzburg, Salzburg, Austria, Helmut Wannenmacher; Implenia AG, Salzburg, Salzburg, Austria, Thomas Fiest; Implenia AG, Munich, Bavaria, Germany, Wulf Schubert; Graz University of Technology, Graz, Styria, Austria

Mining and tunneling in so-called “squeezing ground conditions” at high in-situ stress can result in substantial and enduring ground deformations. The magnitude of deformations is closely tied to the applied excavation- and support concept, though typically, they can reach tens of centimeters.

The yielding principle is based on the idea, that the need for support capacity decreases as deformation increases. To enable controlled ground deformation and safe working conditions, yielding elements as a part of the shotcrete lining are implemented. These types of elements avoid an overstressing of the shotcrete lining. During the deformation process, the support pressure of the yielding elements and lining increases, thus stabilizing the ground. Furthermore, long-term creep deformations of the rock mass can be absorbed with such a system. This economic support technique represents the state-of-the-art infrastructure tunneling practice in squeezing ground condition. A novel yielding element of High-Strength Expanded Polystyrene (HS-EPS) was invented, which overcomes existing systems’ drawbacks. This innovative system is lightweight and allows for safe and rapid installation. Furthermore, the modular setup of the element enables an easy on-site adaption to react to in-situ deformation patterns and changing ground conditions. Recent experiences from applications in Alpine base tunnels in squeezing ground are presented.

 

3:22 PM

Numerical Study on Mining-retention Ratio Optimization in Underground Solid Potassium Salt Mine

Jinwang Zhang; China University of Mining and Technology (Beijing), Beijing, China (Mainland), Jin ZHAO; China University of Mining and Technology(Beijing), Beijing, China (Mainland), Shengli YANG; China University of Mining and Technology(Beijing), Beijing, China (Mainland), Xiaohang WAN; China University of Mining and Technology (Beijing), Beijing, China (Mainland), Weijie WEI; China University of Mining and Technology (Beijing), Beijing, China (Mainland)

Reasonable mining-retention ratio (ratio of room width to pillar width) is vital to recovery rate and stope stability in underground mining of solid potassium salt deposit. Based on the engineering background of a solid underground potassium salt mine in Khammouan Province, Laos, the FLAC3D numerical models under five typical mining-retention ratio conditions (8:8, 8:9, 8:10, 9:9, 9:10) are established respectively. The reasonable pillar size is analyzed from the perspective of stress field, displacement field distribution and the variation characteristics of the plastic zone of the pillar, and the variation of recovery rate and stope stability under different mining-retention ratio conditions are discussed. The results show that compared with current room width (8m) and pillar width (10m), the optimization method of increasing room width from 8m to 9m is more conducive to improving the stope stability than the optimization method of reducing pillar width from 10m to 9m. This is because although the maximum stress in the pillar increases when the room width increased from 8m to 9m, the displacement of overlying strata decreases due to the relatively increase of pillar width and pillar strength, which will result in the improvement of stope stability. The research results are helpful to recover as much solid potash resources as possible under the premise of ensuring the stability of stope.

 

3:44 PM

The Influence of Geologic Province on Rock Mass Jointing and Limestone Pillar Stability

Sandin E Phillipson; USDOL, Triadelphia, West Virginia, United States

Four massive pillar collapses in limestone mines, and one in a marble mine, occurred between 2011 and 2021 in benched areas at underground room-and-pillar mines in the U.S. Despite widespread underground limestone mining, all five collapse events were located in the Appalachian physiographic province. We characterized the rock mass at 43 limestone mines using the Geological Strength Index and, by plotting the results on a physiographic relief map, determined that GSI values between 55 and 70 preferentially occur in the Appalachian and Ouachita Mountains, which were subject to deformation during the Ouachita and Alleghanian Orogenies. Limestone mines located in formations of similar age in the Interior Plains, where deformation was less developed, are characterized by Geological Strength Index values over 80.

We present the results of pillar strength calculations that incorporate the Geological Strength Index from mines that experienced massive collapse, as well as from mines with benched areas that did not collapse, to demonstrate the negative effect that a jointed rock mass has on pillar stability. We suggest that pillar designs, particularly those in which benching will be incorporated, should include allowance for rock mass quality.
Because of the preferential dominance of lower GSI values in the Appalachians, we further suggest that pillar designs in this environment may require additional engineering assessment, especially where benching is intended.  Lower GSI values may often translate into greater overbreak, which results in loss of pillar volume, corresponding wider back spans, and a decreased width-to-height ratio.

 

4:06 PM

Rock Mechanics Database for Coal

Paul Pierce; U.S. Geological Survey, Denver, Colorado, United States, Brian Shaffer; U.S. Geological Survey, Denver, Colorado, United States

The coal mining industry lacks a rock mechanics database from which ground control calculations and related mine planning can be conducted. Safe and productive coal mining relies on proper mining methods and sound roof and rib control techniques. Academics, consultants, and mining operatives their own databases, which they may be willing to share. The Energy Resources Program of the U.S. Geological Survey (USGS) seeks to unify this information through its Evolving Utilization of Solid Energy Fuels Project to organize location, geology, coal beds, rock types, and parametric values into a common publicly accessible database.

The rock mechanics for coal database is to be a browser-based, online data platform of shared multiple sources collated and documented for specificity and accuracy. Continual data collection and management will ensure that the database will be upgraded by adding current research and industry solicited information to traditional ground control knowledge and best practice. The rock mechanics database for coal will be included as an addition to USGS coal data products repositories including the National Coal Resources Data System (NCRDS) and CoalQual. Geomechanical information and geological engineering principles that are currently being collected and organized have a tentative public release in 2025. The publicly accessed database will be available for all conducting ground control study and mining design.

 

 

Operators Session

 

8:00 AM

This session will feature presentations on case studies, solutions, and experiences from an operator’s perspective.

 

 

Support Design

 

8:00 AM

Analysis of Rib Bolt Load and its Impact on Stabilizing Coal Pillar Ribs Using Numerical Simulations

Yuting Xue; NIOSH, Pittsburgh, Pennsylvania, United States, Khaled Mohamed; NIOSH, Pittsburgh, Pennsylvania, United States

Rib stability control is a critical component of underground coal mining operations, and comprehensive rib support design is essential for ensuring the safety of miners. However, there is currently no standardized approach for rib support design in the United States. To tackle this issue, the National Institute for Occupational Safety and Health (NIOSH) has developed a standalone application, Design Of Rib Support (DORS), for rib stability assessment and rib support design under development load. The rib support design in DORS starts with the rib support density, which is determined from the unsupported rib factor of safety (RibFOS). The relationship between rib support density and unsupported RibFOS was obtained from the collected field data. The objective of this research is to validate DORS rib support design by analyzing the extent to which the proposed design capability was utilized to support the coal ribs using numerical simulations. A series of numerical models with varying overburden depth and rib height were built and the ribs were supported with the DORS-recommended rib support design. The bolt load was analyzed under different conditions and the results show that bolt load varies with the overburden depth, the location of the bolt and bolt length. The load in the bolt(s) increases with the reduction in unsupported RibFOS. The bolt(s) start to yield when the unsupported RibFOS falls below a threshold value of 0.8 and secondary support is necessary.

 

8:20 AM

Latest Developments of High Capacity Cable Bolts for Australian Longwall Mines

Peter Craig; Jennmar Australia Pty Ltd, Cooyal, New South Wales, Australia, Jason Emery; Optimum Geotechnics, Bangalee, Queensland, Australia, Matthew Benjamin; Jennmar, Emerald, Queensland, Australia, Matthew Holden; Jennmar, Smeaton Grange, New South Wales, Australia

Over the last 25 years, through adversity and a growing level of risk mitigation, Australian Longwall mines have been using higher and higher capacity cable bolts for secondary support. A recent survey revealed 85% of Australian longwall cable bolts are a 70 tonne capacity pre-tensioned hollow post groutable system. Mines avoiding pumping cementitious grouts are sometimes using pre-tensioned resin encapsulated solid cable bolts of over 90 tonne capacity. Results from various industry and University research has led to manufacturer’s fine tuning the construction of their cable bolts. A review of this research explains how smooth wire construction is now dominant. Aggressive shear has also led to some mines using 8 tonnes pre-tension instead of the previous common 20 tonnes pre-tension. Lower pre-tension acceptance is now leading to a greater use of threaded cable bolt end fittings, these are tensioned to 8 tonne using the drill motor torque.

A recent development is the TEX cable bolt, a slim line threaded end fitting that fits with the drill hole like a standard rock bolt. This cable is being installed at the coal face as primary support off bolter-miners. The laboratory and in-situ testing of the TEX cable is presented.

In a bid to improve gateroad development rates and ground support in the last several years, a 100 tonne tensile capacity Goliath cable system was developed. The latest development in resin anchored solid cables is a 110 tonne capacity cable bolt, with laboratory and in-situ testing results presented.

 

8:40 AM

Investigating the Influence of Lateral Loading on the Vertical Capacity of Coal Mine Standing Supports

Khaled Mohamed; NIOSH/CDC, Pittsburgh, Pennsylvania, United States, Morgan Sears; NIOSH/CDC, Pittsburgh, Pennsylvania, United States, Timothy Batchler; NIOSH/CDC, Pittsburgh, Pennsylvania, United States

The National Institute for Occupational Safety and Health (NIOSH) initiated a testing program to evaluate various standing supports’ lateral loading capacities, focusing on props commonly used in mining applications. The study aims to quantify the lateral loading capacity of standing supports and assess its influence on their vertical loading capacity and yielding mechanisms. This study uses the Mine Roof Simulator (MRS) at NIOSH Pittsburgh to test two types of standing supports: Type-1 with telescopic tubes made from ASTM A-513 steel with a designed locking mechanism and Type-2, comprising a singular component made from ASTM A500 Welded Grade C pipe.

Pure vertical load tests were conducted to evaluate the performance of Type-1 and Type-2 props under controlled loading conditions that simulated roof-to-floor convergence. Type-1 props displayed “constant yielding” performance, with ultimate capacities ranging from 110 kips to 140 kips. In contrast, Type-2 props of different heights exhibited “load shedding” performance, reaching peak vertical loads of up to 191 kips. Buckling analysis indicated that Type-1 props were not susceptible to buckling, whereas Type-2 props failed due to buckling rather than material yielding.

Lateral loading tests were performed on Type-1 and Type-2 props. Lateral loading tests showed that Type-1 props can withstand about 9 kips of lateral load, which is about 6% of their vertical loading capacity. This study reclassified Type-1 props as “load shedding” supports under lateral loading, as they couldn’t maintain their rated vertical capacity but still had a residual capacity of 40 kips, which is 29% of their rated vertical capacity. Type-2 props had a lateral load capacity of 6.3 kips in one test and 10.79 kips in another. When subjected to lateral loading, Finite Element Models reclassified one test as a “constant yielding” support, with remaining vertical loading capacities ranging from 44% to 40% of their rated vertical capacities. These findings provide valuable insights into the behavior of these props under different loading conditions, aiding in their efficient use and design in underground mining operations.

 

9:00 AM

Update of the Support Technology Optimization Program: New Features and a New Interface

Zacharias Agioutantis; University of Kentucky, Lexington, Kentucky, United States, Tom Barczak; Independent Researcher, Venetia, Pennsylvania, United States

The Support Technology Optimization Program (STOP) has been developed by the National Institute of Occupational Safety and Health (NIOSH) to provide a comprehensive tool for evaluating the performance of available secondary roof support systems and designs based on support strength, convergence, cost, installation time and material handling considerations.

This program uses engineering models developed from full-scale testing of numerous supports under controlled loading conditions in the unique NIOSH Mine Roof Simulator load frame to determine the support load-displacement performance as a function of the various support design parameters. Both standing supports such as wood cribs installed within the entry, and intrinsic supports such as cable bolts, can be evaluated. Support systems can be designed and compared for use in a new mining section, or to evaluate potential replacements for an existing design. The support design requirements are defined from: 1) estimating the failure height in the immediate roof, 2) in-mine measurements of support and strata interaction or development of ground reaction curves from numerical modeling, 3) the performance of an existing support system, or 4) from any arbitrary load and convergence criteria. All settings can be saved to permit resuming an evaluation in progress at a later time.

This paper will present the updated MS Windows version of this tool which can be easily installed and run on a personal computer. This Windows implementation will feature a project and application scenario setup where multiple scenarios can be assigned to one project. Scenarios can then be compared on support parameters and cost. Cost parameters can be provided either as individual cost items or using a price grouping feature. Additional support performance curves and/or additional ground reaction curves will be distributed with program updates as new information is developed. Users can also provide their own support and/or ground reaction curves.

 

9:20 AM

Application and Effectiveness Measurement of Ground Consolidation Products in Longwall Mining

Richard Campbell; Blackrock Mining Solutions Pty Ltd, Mackay, Queensland, Australia, Serkan Saydam; University of New South Wales, Sydney, New South Wales, Australia, Mehmet Kizil; The University of Queensland, St Lucia, Queensland, Australia, Ismet Canbulat; University of New South Wales, Sydney, New South Wales, Australia

The design and effectiveness of ground consolidation to regain stability of longwall faces vary widely and are often based predominantly on-site precedence or what were considered successful applications at other sites in similar situations. Little is known regarding product migration characteristics or change in rockmass conditions as a result of the application of consolidation chemicals.

This paper presents the in-situ testing rationale designed and implemented recently across several longwall operations in the Bowen Basin to provide quantitative measurement of the actual zone of influence of various resin injection products. Product migration was physically measured by monitoring the change in rockmass temperature as a result of the exothermic chemical reaction temperature of the various strata consolidation chemicals used. In conjunction with strata coring and Lugeon transmissivity testing pre and post injection to characterise the improvement in rockmass conditions due to consolidation product injection.

The results of the testing programme, migration measurements and rockmass assessment are presented, along with a discussion on how site based rock mechanics engineers can incorporate the data into the design of strata consolidation plans.

 

9:40 AM

Polyurethane Foam and Alternatives for Void Filling Applications

Delbert Hamilton; Mine Safety and Health Administration, Washington, Pennsylvania, United States, Christopher Snyder; Mine Safety and Health Administration, Pittsburgh, Pennsylvania, United States

In the last three years there have been four uncontrolled heating events in mines that have been attributed to the use of polyurethane foam as a void fill product. This is due to the exothermic reaction that occurs during application of polymeric products. These events have led the Mine Safety and Health Administration issue a safety alert on polyurethane products used in void filling and ground consolidation in mining, with the goal of education and outreach to the mining community. This paper provides an overview of various types of polymeric products and best practices, the factors that contributed to the heating events, and case studies involving polymeric products.

 

 

Advances in Mine Design Analysis Techniques

 

10:30 AM

Evaluation of Multiple-Seam Scenarios by Non-Traditional Methods

Sandin E Phillipson; USDOL, Triadelphia, West Virginia, United States

The MSHA Technical Support, Roof Control Division’s primary evaluation tool for coal pillar designs is the Analysis of Coal Pillar Stability (ACPS) program. However, ACPS is limited to evaluating interactions between two seams at a time, which is not ideal for complex multiple-seam scenarios. Further, it does not recognize the influence of strata properties in the interburden. We apply the Rocscience RS2 two- dimensional finite element program as a complement to ACPS. Complex multiple-seam scenarios can be characterized by a modified pillar stability factor where the ACPS single-seam development pillar stability factor is multiplied by the ratio of average single-seam development stress to the stress in the critical pillar at the multiple-seam stage, using the values of σ1 as predicted by RS2.  Several series of test examples involving two-seam analyses with isolated remnants, gob-solid boundaries, and high extraction areas of varying width were used to calibrate simulated gob properties such that the ACPS+RS2 method generated results that matched a traditional ACPS Stability Factor to within 13%. As high-extraction areas become wider and deeper, progressively stiffer gob is simulated by increasing the Young’s Modulus property in RS2. After achieving calibration with the test series, three examples of complex multiple-seam scenarios were evaluated, using actual strata types and thicknesses based on core log data. Resulting modified stability factors are reasonably close to those predicted by ACPS, although substantial units of sandstone in the interburden, as well as gob shadows superimposed with remnant structures, appear to mute multiple-seam interactions.

 

10:52 AM

Application of Statistical-Analytical Methods in Ground Control Engineering

Hamid Maleki; Maleki Technologies, Inc., Spokane, Washington, United States

Starfield and Cundall identify rock mechanics problems as “data-limited,” suggesting that there might be insufficient information about a rock mass for unambiguous use of computational models. Statistical methods are highlighted as uniquely capable in situations where there is good data but a limited understanding of certain natural phenomena. Examples include the creep of rock salt, assessment of escarpment stability, and evaluating elevated risk domains associated with coal burst. Two critical aspects for evaluations are emphasized: having a sufficient number of consistently collected data and incorporating analytical calculations for quantifying geologic, mining, and geotechnical variables.

The paper presents three case studies to demonstrate the use of statistical-analytical techniques in ground control engineering. First case study involves the assessing Castlegate sandstone escarpment stability using historic data collected over 17,000-ft of escarpment exposure in Utah. Second case study focuses on the stability evaluation of a nuclear waste repository in rock salt using the convergence rate measurements at 119 instrumented clusters. The third case study involves ongoing analysis of Coal Burst mechanics and

contributing factors, drawing on geologic, mining and geomechanical variables collected from 30 case studies across U.S. coal mines.

The paper aims to provide a broad review of (1) data collection and variable construction (2) procedures used for multivariable statistical analysis, including stepwise inclusion of independent variables, and (3) a discussion of results from all three case studies, emphasizing the practical application of statistical-analytical techniques in addressing ground control challenges, showcasing the approach through real-world case studies in diverse geological settings.

 

11:14 AM

A Case Study of Path Dependent Calibration and Pillar Stability Analysis Using the LaModel Program

Morgan Sears; NIOSH, Pittsburgh, Pennsylvania, United States

The LaModel program is widely used to calculate stresses and displacements on thin tabular deposits, particularly when multiple seams or complex mining geometry is encountered. The program itself allows the user to create multiple mining steps to show a progressive sequence of mining. However, LaModel considers each individual step as an independent steady-state condition, and any previous loading conditions of the materials are not tracked. It also does not consider any sort of dynamic stress change during the mining process. In certain circumstances, especially in multiple-seam situations, modeling a scenario of the seam of interest without considering the previous mining sequence in the off seams can potentially lead to inaccurate results.

The primary objective of this paper is to present a situation where a potentially dynamic, unstable mining condition was encountered. It was not evident until the previous loading conditions in the off seams and the impact of dynamic stress changes in the active seam were considered. It is important to make the mining community aware of these potential modeling scenarios where the path-dependent nature of the mining sequence is of key importance.

This paper presents a case history where room-and-pillar retreat mining was being conducted in a relatively deep cover stress regime where multiple seam interactions were present from both undermining and overmining. Mining in the active seam was being conducted with room-and-pillar mining techniques consisting of a series of parallel production panels being successively developed and retreat mined along a set of Mains. In this situation, the traditional global LaModel analysis without any path-dependent adjustments did not fully identify the area of poor conditions that were encountered.

This paper explores the impacts of mining in the active seam on the lower seam which, in turn, has a negative impact on the active seam. This provided a solid foundation for the subsequent analysis of the three seams simultaneously. Based on the calibrated model, it is likely that retreat mining in the active seam resulted in increased stresses in the underlying seam that conceivably resulted in additional convergence and, most likely, additionally convergence of the pillars under the panel being developed. This in turn could have caused active subsidence, squeezing of the pillars, floor heave, and significant rib deterioration in the active workings.

The LaModel program is extremely useful for analyzing multiple-seam mining scenarios. As multiple-seam situations become even more prevalent, the potential for encountering a path-dependent mining scenario also increases. To successfully model path-dependent mining scenarios, the ground control engineer will be required to make sound judgments on the condition of pillars in sub-adjacent seams. These engineering judgments should be based not only on the current state of stress, but also on any prior or future states of stress. This means considering the stresses from over or undermining as well as stresses applied to the sub- adjacent seams from actively mining the seam of interest.

 

11:36 AM

Application of Analysis of Coal Pillar Stability (ACPS) Software for Assessment of Pillar Stability in Underground Lignite Mining – A Case Study

Kevin Andrews; Marshall Miller & Associates, Blacksburg, Virginia, United States, Zach Agioutantis PhD, PE; Department of Mining Engineering Stanley and Karen Pigman College of Engineering University of Kentucky, Lexington, Kentucky, United States

Analysis of Coal Pillar Stability (ACPS) software, released in 2018, integrates numerous empirical pillar design techniques. The ACPS program incorporates methodologies originally available as design tools from National Institute for Occupational Safety & Health (NIOSH), including Analysis of Longwall Pillar Stability (ALPS), Analysis of Retreat Mining Pillar Stability (ARMPS), Analysis of Multiple Seam Stability (AMSS), and concepts including Coal Mine Roof Rating (CMRR), Mark-Bieniawski pillar formula, and pressure arch loading. The design methodologies that are the basis of ACPS were developed via analysis of significant amounts of real-world data, and have been standards of the United States coal industry for decades. While there are empirical factors built into ACPS making it ideal for use in U.S. coalfields, the concepts in the program have proven to be applicable in variable mine settings, and the software was developed to allow for user-based, site-specific modifications of key design inputs. Application of ACPS to cases outside the regions for which it was developed must be approached carefully, and continuous development of site-specific data is mandatory. A case study is presented involving application of ACPS to assess pillar stability and assist future design for an underground lignite mine in Eastern Europe. Assessment of in-mine observations, review of geology of the lignite mine, and evaluation of specific conditions associated with a failure event resulted in “calibration” of key input factors to ACPS. Scenarios evaluated with ACPS suggest that pillar strength and overburden depth are key factors for determination of pillar stability and design in future areas.

 

Subsurface Ground Movement

 

1:00 PM

Prediction of Ground Movements for Inclined Seams

Zacharias Agioutantis; University of Kentucky, Lexington, Kentucky, United States, Ernesto Maldonado; University of Kentucky, Lexington, Kentucky, United States, Jesus Romero; University of Kentucky, Lexington, Kentucky, United States

The prediction of ground movements due to underground coal mining has been investigated by numerous researchers worldwide utilizing different analytical, empirical, and numerical models. These studies have primarily focused on the development of prediction methodologies for either flat or gently dipping seams under variable topography, and only a few studies are available that have investigated the prediction of ground movements over inclined seams.

Although the majority of inclined coal seams are in China, India, and other countries worldwide, a few inclined coal seams (with a dip of 10 degrees or greater) are also present in the US. Currently, the prediction of ground movements for inclined coal seams using empirical methods utilizes the same methodology as the one for horizontal seams. It consists of dividing the inclined seam into horizontal segments, calculating deformations due to each segment, and superimposing the calculation results.

In this paper, a new tool is presented that provides a methodology to model subsidence under inclined seam conditions. Examples that are based on subsidence measurements available in the literature are presented. The goal is to implement this methodology into the Surface Deformation Prediction System.

 

1:22 PM

A Review of in Situ Horizontal Stress Characteristics in Coal Measures Strata and the Fundamental Role of Poisson’s Ratio

Russell Frith; Mine Advice Pty Ltd, Brisbane, Queensland, Australia, Guy Reed; Mine Advice Pty Ltd, East Maitland, New South Wales, Australia

In situ or pre-mining horizontal stresses are arguably the least well understood of the principal inputs into underground coal mining geotechnical engineering design, whether analytical, empirical, or numerical. This is a direct result of both the cost and difficulty of obtaining meaningful in situ stress measurements, the various limitations of the measurement method in terms of sourcing measurements from strata types that approximate the assumed conditions of the post-measurement mathematics, and an apparent common propensity amongst geotechnical professionals to prefer to utilise generic values rather than interrogate the available measurement data for cause and effect relationships between horizontal stress magnitudes, directions and a range of associated controls. That numerical modelling simulations attempt to mimic reality but often rely on simplified generic horizontal stress input assumptions is a particular cause for concern.

The paper attempts to further explore the true nature of in situ horizontal stresses using a range of stress measurements from the Australian coal sector supplemented by several international studies addressing the same basic issue, the result being a number of credible and highly relevant cause and effect relationships between the three principal in situ stresses in addition to rock properties (Young’s Modulus and Poisson’s Ratio), cover depth and the larger-scale structural geological environment.
In particular the paper conclusively demonstrates that despite being commonly overlooked as a primary rock/coal material property, Poisson’s Ratio and the associated Ko Effect are intrinsic to understanding 3D in situ stress measurement results and hence predicting in situ stress magnitudes more generally for geotechnical analyses purposes.
As a fundamental question, the paper addresses whether it is feasible and also of engineering value to characterise in situ horizontal stresses according to distinct “domains”, in the same way that more easily identifiable geotechnical properties such as rock mass ratings and cover depth are often treated.

The paper is intended as the first in a series that establishes a fundamental basis for subsequently examining mining-induced ground stresses and their potential controlling impact on a range of operational control strategies that are intrinsic to both safe and productive underground coal mining.

 

1:44 PM

Valley Bottom Ground Movements Above a Longwall Operation with Strong Overburden Strata

Zacharias Agioutantis; University of Kentucky, Lexington, Kentucky, United States, Steve Hicks; Coronado Global Resources, Inc., Beckley, West Virginia, United States, Greg Hasenfus; Barr, Pittsburgh, Pennsylvania, United States, Zachary Wedding; University of Kentucky, Lexington, Kentucky, United States

Most prediction methods used to calculate mining-induced subsidence rely on empirical formulations, which typically assume flat topography and uniform properties in the overburden. It is also well known that when a longwall panel mines below a valley bottom surface ground deformation magnitudes and orientations may be significantly influenced by the presence of the valley.

This paper presents and discusses ground deformation data collected at different surface locations above the Buchanan mine in the eastern United States. Measurements at individual surface points and strata movement measurements using a three-point extensometer have been collected as the area was undermined. Measurements correspond to the mining of the panel immediately under the measurement points and to the mining of adjacent panels. Measurement locations correspond to valley bottom locations.

The measurements are critically evaluated and compared with respect to topography and panel face location. SDPS predictions are also compared to measured movements at different locations. The issue of the fluctuation of GPS measurements is also discussed.

 

2:06 PM

Coal Ecological Protection Mining Technology System and Engineering Practice

Quansheng Li; National Energy Investment Group Co., Beijing 100011, China, Beijing, Beijing, China (Mainland)

Large-scale coal mining will cause ecological problems such as aquifer damage, land excavation and occupation, soil erosion, vegetation damage, and regional landscape damage. The existing coal mine ecological restoration technology is relatively single, and there is a lack of systematic research on ecological total factors. Based on the mechanism of coal mining damage and the laws of ecological natural succession, the concept of “coal ecological protection mining” is proposed, which combines damage reduction mining and ecological element system restoration. Accordance to the ecological protection principle of “source protection, process damage reduction, and systematic restoration”, a technical system of “coal ecological protection mining” is constructed for the two types of mining damage scenarios: underground mining and open-pit mining. In view of the damage characteristics of underground mining, source ecological protection technology based on optimization of mining process parameters, stability maintenance and damage reduction technology for overlying rock bearing arch shell structure, zoning and time-sharing treatment of surface cracks, and direct drainage irrigation technology for mine water have developed.  Accordance to the damage characteristics caused by open-pit mining, land-saving and source reduction damage technology, near-natural stratigraphic reconstruction, topsoil improvement and ecological storage and utilization technologies for seasonal precipitation have developed. Applying the technology in this paper, the maximum surface settlement value of 12401 working face in Shendong Shangwan coal mine was relatively reduced by 25%, the surface cracks have been adjusted from step-type cracks to dynamic small cracks, and since the technical implementation of the Shendong mining area in 2010, the vegetation coverage has increased from an average of 31% to a maximum of 74.1%.Ecological restoration technology has significant effects. The area of land excavation loss and crushing decreased by 90 mu every year, the ecological restoration period of the dump site was advanced by more than one year, and the vegetation coverage rate increased by 41.78% compared with the background value in the semi-arid area of the victory open-pit coal mine demonstration area. A surface reservoir with a water storage capacity of 400,000 cubic meters has been built, and the seasonal and graded utilization of mine water has been realized. A underground reservoir with a water storage capacity of 1.22 million square meters has been built in the Baorixiler open-pit coal mine.

 

Numerical Modeling Applications in Ground Control

 

3:00 PM

NIOSH Gas Well Stability Research: A Summary of Ground Control Engineering Considerations

Wen Su; CDC/NIOSH/PMRD, Jefferson Hill, Pennsylvania, United States, Peter Zhang; NIOSH, Jefferson Hill, Pennsylvania, United States, Berk Tulu; NIOSH, Jefferson Hill, Pennsylvania, United States, Bo Kim; NIOSH, Bruceton, Pennsylvania, United States

This paper summarizes significant findings from the ongoing NIOSH Gas Well Stability research over the past decade; in particular, the important ground control engineering considerations. Longwall-induced surface and subsurface deformations may induce gas well casing deformations and stresses, depending on a few parameters such as overburden depth, overburden geology, topographic relief, strata dip, gas well setback distance, and a gas well casing cementing alternative. Overburden depth to the mining seam is one of the most influential factors; shallow overburden depth induces large horizontal displacement and resulting casing deformation and stress, while deep overburden depth induces large longwall-induced vertical pressure.
Overburden geology is another important factor affecting the longwall-induced casing deformations and stresses; the large contrast of bending stiffness at the soft-to-hard rock interfaces tends to induce large casing deformations and stresses. Large surface topographic relief and the presence of soft-to-hard rock interfaces below the stream valley bottoms may shift longwall-induced subsurface gas well casing deformations closer to the surface, thus having less impact on underground mining operations. Strata dip magnifies longwall- induced deformations by 20% per degree of strata dip for down dip longwall excavations. The gas well setback distance is also a critical geometric parameter; the effect of longwall-induced deformation decreases exponentially as the setback distance increases. Longwall-induced casing deformation and stress will be mitigated or totally uncoupled for uncemented production casing.

 

3:15 PM

Underground Coal and Stone Mining near Oil and Gas Wells

Gregory Rumbaugh; Mine Safety and Health Administration, Pittsburgh, Pennsylvania, United States, Christopher Mark; Mine Safety and Health Administration, Pittsburgh, Pennsylvania, United States, Lon Santis; Mine Safety and Health Administration, Triadelphia, West Virginia, United States

This paper examines relevant theory, experience, and past practices relating to development mining near gas or oil wells and addresses setback distance for both coal and stone room-and-pillar mining. This study also involved review of accident reports involving well interceptions and downhole well surveys. It provides technical considerations for decisions regarding safe setback distances for development mining throughout the United States. The study’s scope is limited to mining near active or inactive (i.e. non-producing, abandoned or inadequately plugged) wells with known surface locations.

 

3:30 PM

Calibration of LaModel In-Seam Material Properties for Underground Stone Mine Benching Operation by Employing Brittle Failure Criteria in FLAC3D

Mustafa Suner; West Virginia University, Morgantown, West Virginia, United States, Alim Elibol; West Virginia University, Morgantown, West Virginia, United States, Rosbel Jimenez; West Virginia University, Morgantown, West Virginia, United States, Deniz Tuncay; West Virginia University, Morgantown, West Virginia, United States, Zach Agioutantis; University of Kentucky, Lexington, Kentucky, United States

LaModel is a displacement-discontinuity variation of the boundary element method, which is utilized to analyze the displacement and stress in flat-lying, tabular orebodies. In coal mining, the accuracy and reliability of LaModel are proven with the utilization of the Mark-Bieniawski coal pillar strength and the stress gradient formula with proposed methodologies. However, the application of LaModel is limited to coal mines due to the default coal pillar strength properties. Recently, the stress gradient functions have been established and used to derive concentric rings of zones to simulate stone mine pillar yielding in LaModel.
Also, to gain a robust understanding of the brittle failure mechanism and its effect on pillar strength, an S- Shaped failure envelope, where rock mass’ cohesive and frictional strength components mobilize as a function of confinement (e.g., minimum principal stress), has been implemented into FLAC3D software. Therefore, by employing brittle failure criteria, the pillar strength stages at various width-to-height ratios and different pillar dimensions are estimated for four benching stages. The estimated pillar strengths and stress gradients for benching conditions are then used to calibrate LaModel in-seam material properties and compare stresses computed by LaModel and FLAC3D. Consequently, this study aims to increase the safety measures in the stone mining industry by implementing the practical use of LaModel for underground stone mines’ initial development to various stages of bench mining.

 

3:45 PM

3DEC Investigation of the Highly Anisotropic Strengths of a Utah Coal Using Discrete Fracture Networks

Bo Hyun Kim; NIOSH/CDC, Spokane, Washington, United States

In this study, 3DEC modeling in conjunction with the Discrete Fracture Networks (DFNs) technique was performed to better understand the true anisotropic behavior of the specimens acquired from a bump-prone underground coal mine. The spatial characteristics of the discontinuities (i.e., cleats and bedding planes) as input data for the 3DEC model are estimated based on the results of the laboratory tests and field observations. The DFNs explicitly generated the coal seam that was poorly or well cleated, indicating the different spacing between cleat apertures using the probability distribution functions on fracture density (or frequency) and size. The heterogeneity of the engineering properties (i.e., cohesion and tensile strength) are also considered by Monte Carlo simulations. As a result, the 3DEC model and DFNs technique demonstrated that the results of the simulations agreed well with the results of the laboratory test. These calibrated results can be used as we seek to evaluate bump risk by modeling at field scale.

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