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By S. E. Phillipson

Four massive pillar collapses in limestone mines, and one in a marble mine, occurred between 2011 and 2021 in benched areas at 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.

Jun 25, 2024

By Thomas Fiest, Helmut Wannenmacher, Wulf Schubert, Manuel Entfellner

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.

Jun 25, 2024

By Yuting Xue, Khaled Mohamed

Rib 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.

Jun 25, 2024

By Lon Santis, Gregory M. Rumbaugh, Christopher Mark

This paper examines the relevant theory, experience, and past practices relating to development mining near gas or oil wells. It addresses setback distance for both coal and stone room-and-pillar mining. This study also involved a 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.

Jun 25, 2024

By Bob Munz, Ry Stone

To facilitate the installation of the longwall equipment for each extraction panel, West Elk mine 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, then incrementally widened to the required width during installation of the longwall 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. Guided by the desire to optimize the ground support plans and increase mining efficiency for future set-up rooms, the West Elk mine and Agapito Associates, Inc. have 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 con- trolled manner (Thomas 2007). To arrive at adequate site-specific ground support plans for the set-up rooms at the mine, several struc- tured processes were utilized. Firstly, the geotechnical environment was characterized by examining the roof lithology and geomechanical properties from nearby rock core obtained from exploration boreholes. To increase both mining efficiency and continuity, and to achieve longer stand-up times before the longwall shields are installed, a multi-pass approach was implemented into the design. During mining, the geotechnical conditions of the roadway are mapped, and the roof is strategically surveyed with a borescope. This process was used to ensure that the encountered ground behavior was in alignment with 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 con- trols 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 multi-pass mining approach, the utilization of fully encapsulated roof bolts, and the transition 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 presented cases.

Jun 25, 2024

By Quansheng Li

Large-scale coal mining will cause environmental problems such as aquifer damage, land excavation and occupation, soil erosion, vegetation damage, and regional landscape damage. The existing coal mine environmental restoration technology is relatively simple, and there is a lack of systematic research on environmental total factors. Based on the mechanism of coal mining damage and the laws of environmental natural succession, the concept of “coal environmental protection mining” is proposed, which combines damage reduction mining and environmental element system restoration. In accordance with the environmental protection principle of “source protection, process damage reduction, and systematic restoration,” a technical system of “coal environmental 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 environmental 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. In accordance with the damage characteristics caused by open-pit mining, land-saving and source reduction damage technology, near-natural stratigraphic reconstruction, topsoil improvement, and environmental storage and utilization technologies for seasonal precipitation have developed. By applying the technology in this paper, the maximum surface settlement value of 12401 working face in 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 loss and crushing decreased by 0.06 km2 every year, the environmental 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. An underground reservoir with a water storage capacity of 1.22 million square meters has been built in the Baorixiler open-pit coal mine.

Jun 25, 2024

By Yuting Xue, Xin Li, Ihsan Berk Tulu, Gaobo Zhao, Deniz Tuncay, Mindi Ruan

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 off 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.

Jun 25, 2024

By Christopher Mark

Area wide pillar failures, or “squeezes,” were once fairly common in underground coal mines. While rare today, they do occur. This paper describes seven case histories that were investigated by MSHA Technical Support. They occurred across the range of US coalfields, in both longwall and room-and-pillar mines, and involved development mining, pillar recovery, longwall panel extraction, and multiple seam interactions. Significant lessons from each are discussed.

Jun 25, 2024

By Timothy Batchler, Khaled Mohamed, Morgan Sears

The National Institute for Occupational Safety and Health (NIOSH) initiated a testing program to assess the effects of lateral loading on various standing supports used in underground coal mines. This study is not intended to endorse a particular type of standing supports nor to provide a comparison between different types of standing supports. This paper aims to measure the lateral loading capacity of two types of standing supports and evaluate how it affects their vertical loading capacity and yielding mechanisms. The study utilizes the Mine Roof Simulator (MRS) at NIOSH Pittsburgh. Type-1 support is characterized by telescopic tubes made from ASTM A-513 steel with a specified locking mechanism, and Type-2 support comprises a single component constructed from ASTM A500 Welded Grade C pipe. Vertical load tests were carried out to assess the designed performance of Type-1 and Type-2 props. Type-1 props demonstrated a "constant yielding" behavior, achieving an ultimate capacity of up to 140 kips. Type-2 props showed a "load shedding" behavior, reaching peak verti- cal loads of up to 191 kips. Buckling analysis revealed that Type-1 props were not designed to buckle, and Type-2 props failed due to buck- ling rather than material yielding. Under vertical pre-loading, lateral loading tests showed that Type-1 props can withstand about 9 kips, and Type-2 props can withstand about 10.79 kips of lateral load. This represents roughly 6% of their vertical loading capacities. Testing props under lateral loads in addition to their intended vertical loads showed that the lateral loads could influence their loading mechanisms. Type-1 props did not exhibit the expected "constant yielding" behavior under lateral load but instead showed "load shedding" decreasing their rated vertical capacity by 70%. At high vertical pre-loading, Type-2 props demonstrated "constant yielding" behavior instead of the anticipated "load shedding," leading to a 60% reduction in their rated vertical capacity. 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.

Jun 25, 2024

By J. Fuller, J. Beale, Q. Justice, Z. Agioutantis, S. Hicks, Z. Khademian

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 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.

Jun 25, 2024

By Emily Muto

LiDAR technology has made it possible to map large areas of underground mines accurately and rapidly in three dimensions. MSHA Technical Support began implementing LiDAR technology in conjunction with the Agency’s Pillar Collapse Initiative, using scans to determine width-to-height ratios (w/h) of pillars adjacent to mass collapse areas and to conduct risk assessments for global pillar stability in U.S. stone mines. This work quickly expanded to include change detection, such as measuring many pillars to show which are deteriorating over time. Change detection has also been used in ground falls and squeeze areas to see if they have continued to propagate. LiDAR technology supports accurate data acquisition of unstable mining conditions from safe distances. For example, once the LiDAR scan has been processed, it can measure roof fall cavity heights and volumes with the user at a stable ground location. Some LiDAR scanners can collect geologic data, such as joint orientations.

Jun 25, 2024

By Alim Elibol, Rosbel Jimenez, Mustafa Can Suner, Deniz Tuncay, Zach Agioutantis

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.

Jun 25, 2024

By Syd Peng, W. B. Guo, F. Du, L. Yang, J. Yw. Cheng

The annual ICGCM China was initiated in 2014. Up to 2023, ICGCM China has been held 9 times. In the 9 conferences during the past 10 years, about 559 papers in 17 topical areas were presented and attendance ranged from 200+ to 400+ each conference. The 42nd ICGCM China was held in Xiangtan, Hunan, China, 10/20–10/22/2023. There were 86 papers presented in 26 topical areas. In addition, an MS and PhD Research Forum was held concurrently with 36 papers presented by MS and PhD candidates in mining engineering from 8 schools. The conference plays an important role in cultivating advanced degree student talents. In this paper, all 559 papers reviewed previously were summarized. In addition, the 42nd ICGCM China is used to illustrate the current and future development trends of coal mine ground control in China. It summarizes the 122 papers (including 36 MS and PhD forum papers) grouping into, and in terms of, 26 topical areas. In addition, its unique and innovative subject areas, short summary of developments as well as conference strengths and shortcomings will also be presented.

Jun 25, 2024

By Delbert Hamilton, Christopher Snyder

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. These heating events are due to the exothermic reaction that occurs during application of these polymeric products. These events led the Mine Safety and Health Administration to issue a safety alert on polyurethane products used in void filling and ground consolidation in mining, with the goal of educating the mining community about this potential hazard. 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.

Jun 25, 2024

By Jin Zhao, Weijie Wei, Jinwang Zhang, Xiaohang Wan, Shengli Yang

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 deposits. Based on the engineering background of a solid underground potassium salt mine in Khammouan Province, 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 (8 m) and pillar width (10 m), the optimization method of 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.

Jun 25, 2024

By Shawn Boltz, Erik Westman, Derrick Chambers, Xingdong Zhaoa, Qiankun Zhua

Microseismic passive velocity tomography is becoming 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 and calculate travel time and travel distance. Finally, the fast-marching method was used to carry out passive velocity tomography analysis to image the movement of the abutment stress associated with the longwall. 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 forward and side abutment stress zones of that longwall panel. This study provides a reference for the identification of mine-induced high stress zones, which has implications for hazard identification and mitigation, with increased resolution of the tomograms in time and space.

Jun 25, 2024

By I. Abdullayev, M. Soberano Capistran, J. Garcia

The application of post-tensioning in segmental structures was introduced in the early 1900s and has been successfully applied in different types of structures including immersed tunnels, bridges, buildings, metro stations, and stadiums. There are, however, only five known circular concrete tunnel projects where the post-tensioning approach has been adopted. This paper discusses the application of post-tensioning to mitigate the high internal operating pressures in an effluent outfall tunnel project 7 miles, 11.3 km long, currently under construction for the Los Angeles County Sanitation Districts, LACSD. This project will be the first use of post- tensioned segmental concrete tunnel linings in North America.

Jun 23, 2024

By Irwan Halim, Bhoshaga Mitrran Ravi Chandran, Kevin Huynh

Tunnel segmental lining design constitutes a significant iterative process where modeling and numerical analysis are factors in deciding the number of segments, their dimensions, gasket placements, as well as the locations of dowels and bolts. Consequently, these modifications lead to revisions in the final drawing details. However, the current tunnel engineering practices lack systematic solutions that effectively bridge the gap between the iterative design process and efficient visualization of completed drawings due to the time- consuming nature of redrawing. This paper presents a pioneering application of AI-driven solutions including using Autodesk's API, for the Northside Interceptor Tunnel (NSIT) Project. It showcases the automation of drawing design and the real-time visualization of modifications, thereby streamlining the drawing process.

Jun 23, 2024

By Rob Herr, Irwan Halim, Heather Marsh

This project will expand sanitary sewer within the City of Columbus. It consists of 2.5 mile long, 72-inch finished diameter pipe grouted inside 10.8-foot diameter tunnel excavation in shale. This paper describes the multi-faceted geotechnical exploration to minimize the underground risks. The tunnel will cross below a buried valley with minimum cover of highly weathered rock. The risk mitigation to cross the valley includes contingencies and cost allowances. Provisions to prevent impact on adjacent groundwater resources will be described. Latest construction updates will be provided including contractor alternate shaft support and pre-excavation probing to mitigate tunneling risk below the valley.

Jun 23, 2024

By Colin Irwin, Adrian Naranjo-Castillo, Christopher Petta, Eric Zarobila

The Shoreline Consolidation Sewer is a CSO control project in Cleveland, Ohio that requires the installation of 5,000 feet of 72-inch inside diameter pipe using microtunneling methods. After award, the contractor submitted a value engineering proposal to eliminate two deep shafts and install the tunnel in two drives instead of four. In an example of successful collaboration, owner, contractor, and engineer worked together during the initial construction stages to modify the design and update the contract documents. This paper examines the importance of exible requirements in contract documents and a collaborative environment between all parties to successfully deliver a project.

Jun 23, 2024