Ground Control In Mining Research Articles

Deformation-based support design for highly stressed ground with a focus on rockburst damage mitigation

As mines go deeper, mine designs become more fragile and effective rock support becomes a strategic element for ground control to facilitate timely construction and cost-effective access for uninterrupted production. This article focuses on the design of integrated support systems for brittle ground when large displacements due to gradual bulking of stress-fractured rock or sudden violent bulking during rockbursts are induced by static and dynamic loading. It provides an overview of support design principles for a rational approach to ground control in deep mines when large deformations are anticipated near excavations. Such designs must not only account for load equilibrium but also for deformation compatibility. Most importantly, the design approach must account for the fact that the support's displacement capacity is being consumed as it is deformed after support installation. It is therefore necessary to design for the remnant support capacity, i.e. the capacity remaining when the support is needed. Furthermore, if the support capacity can be consumed, it can also be restored by means of preventive support maintenance (PSM). The PSM concept for cost-effective ground control is introduced and illustrated by quantitative and operational evidence. Contrary to other design approaches, the deformation-based support design (DBSD) approach provides the capacity of an integrated support system as a function of imposed displacements. Reduction in this support capacity due to mining-induced deformation renders excavations increasingly more vulnerable if located within the influence of active mining and seismic activity. Because deformation measurements are robust indicators of the decay in support capacity, scanning and other displacement monitoring technologies enable measurements to verify the DBSD approach, to assess the remnant safety margin of the deformed support, and to make operational support maintenance decisions.

An operational approach to ground control in deep mines

As mines go deeper and get larger, mine designs become more fragile largely due to the response of the rock mass to mining. Ground control and rock support become important levers in the mine construction schedule, production performance, and excavation health. For example, in cave mines, the production footprint together with associated mine infrastructure are significant investments in a modern caving operation. This investment must be protected and maintained to reduce the risk of ground-related production disruptions. It is necessary to preserve the health of these excavations and their maintenance through an effective rock support design. Rock support thus becomes a strategic element in asset management. This article focuses on support design for brittle ground when displacements induced by stress-fracturing consume much of the support's capacity. It deals with the functionality of the support in deforming ground. Several interlinked concepts are important when assessing excavation health. Designs must not only account for load equilibrium but also for deformation compatibility and capacity consumption. Most importantly, the support's displacement capacity is being consumed when the rock mass is deformed after support installation. Hence, it is necessary to design for the support capacity remaining at the time when the support is needed. If support capacity can be consumed, it can also be restored by means of preventive support maintenance (PSM). This concept for cost-effective ground control is introduced and illustrated on operational evidence. Furthermore, how design can impact construction costs and schedule are discussed. Support is installed to provide a safe environment and preserve an operationally functional excavation. It also must assure senior management that investments in high quality support and its maintenance will substantially reduce delays and with it, costs. It is demonstrated that the use of ‘gabion-like’ support systems can achieve these goals. A technical summary of the ‘gabion panel’ support system design is presented.

Guest editorial–special issue on ground control in mining in 2020

Guest editorial–special issue on ground control in mining in 2020

Numerical Investigation on the Mechanism of Rock Directional Fracturing Method Controlled by Hydraulic Fracturing in Dense Linear Multiholes

Rock directional fracturing is one of the difficult problems in deep mines. Directional fracturing controlled by hydraulic fracturing in dense linear multiboreholes is a novel directional fracturing technology of rock mass, which has been applied to the ground control in mines. In this paper, a physical model experiment was performed to study the fracture propagation process between multiboreholes. The results show that the intersecting of fractures between boreholes caused the sharp fluctuation of injecting water pressure. A directional fracturing plane was formed along with the direction of boreholes layout, and the surface of the fracturing plane is relatively flat. The dynamic initiation and propagation process of cracks between boreholes during directional hydraulic fracturing were simulated. The evolution of poroelastic stress and pore pressure between multiboreholes was analyzed. The numerical results indicated that a poroelastic stress concentration zone and pore pressure increase zone appeared between boreholes in the direction of boreholes layout. The pore pressure distribution is generally an elliptical seepage water pressure zone with the long axis along the direction of the boreholes layout. After the hydraulic fractures are initiated along the direction of the boreholes layout, the poroelastic stress on both sides of fractures decreases.

New insights on ground control in intelligent mining with Internet of Things

The conception of Smart city has been gaining momentum in recent years. Coal mines as a part of city should be characterized with smart or intelligent features. Production and safety are two major themes in coal mining. With the development of automation, Internet of Things (IoT), big data, artificial intelligence, and cloud computing in Fourth Industrial Revolution, Intelligence Mining has been put forward by Chinese Academy of Engineering to achieve the goal of unmanned workface production. However, safety is not highlighted in the novel idea. In this paper, ground control in intelligent mining with IoT is studied. An architecture of ground control with IoT is proposed. The previous research on theoretical modeling and on-site monitoring methods are reviewed. Then the IoT based ground control method is proposed. An on-going dynamic platform on ground control are proposed based on our research of nondestructive testing (NDT) on rock bolt anchorage quality assessment. The research progress is introduced with equipment introduction, principles, and an on-site experiment. Future developments on combination of NDT and IoT of ground control is discussed. The ideas, frameworks, and results in this paper can make efforts on safety control and spark new ideas in the much-anticipated Intelligence Mining.

Monitoring and Characterization of Mining-Induced Overburden Deformation in Physical Modeling With Distributed Optical Fiber Sensing Technology

Facing increasingly large and discontinuous structural evolution under the influence of extensive mining activities, some traditional geophysical technical methods of monitoring overburden deformation have become of restricted use. As an advanced sensing technology, the distributed optical fiber sensor has been introduced into rock deformation monitoring by virtue of its good adaptability and high precision. In this paper, an overburden stratum deformation monitoring experiment was performed within a physical model test to explore the deformation characteristics of mining-induced overburden stratum based on distributed optical fiber sensing. The results indicate that distributed optical fiber monitoring is effective, and the Brillouin frequency shift (BFS) variation distribution reflects every aspect of the space-time and movement laws of the overburden stratum. The comparison of measurements of the distributed optical fiber, fiber Bragg gratings, and dial gauges proved the feasibility and reliability and revealed the ability of optical fiber measurement to monitor large-scale macroscopic deformation, and capture subtle deformation along the entire overburden stratum. More importantly, the BFS variation distribution presents a three-step form, which explicitly identifies the zoning development of overburden stratum. In turn, a conceptual model for describing the overburden deformation process is provided; it illustrates the inversion mechanism of the BFS variation distribution in reaction to the typical overburden deformation structure. This study aims to provide a theoretical and methodological foundation for the application of distributed optical fiber sensing (DOFS) measurement in mining ground control research.

Shield-Roof Interaction in Longwall Panels: Insights from Field Data and Their Application to Ground Control

The shield-roof interaction as mining proceeds in longwall panels remains unclear, hindering the further increase of longwall productivity. To uncover the mechanisms of shield-roof interaction, using our self-developed Status of Shield and Roof IntelliSense (SSRI) system, we investigated the effects of idle time, retreating rate, setting pressure, yielding, and shearer’s cutting, as well as neighboring shields’ advance on the spatial-temporal evolution of leg pressure and leg closure of shields. Our results show that the shield-roof interaction is not only dependent on the shield capacity, but also collectively determined by the time-related factors, the geological condition, the setting pressure, yielding characteristics, and mining method. Understanding the shield-roof interaction in longwall panels enables us to apply the SSRI system for ground control in longwall coal mines. Early warning of severe roof weighting can be achieved by establishing a warning model based on the decision tree algorithm. Apart from this, we can also assess the working condition of yield valve and diagnose fluid leakage of shield cylinder using the SSRI system. Finally, we propose the research prospects on shield-roof interaction in longwall panels to achieve a more reasonable determination of shield capacity, prediction of roof fall and coal wall spalling, and self-adaptive control of the shield.

Geotechnical characterization of red shale and its indication for ground control in deep underground mining

Geotechnical properties of red shale encountered in deep underground mining were characterized on both laboratory and field scale to reveal its unfavorably in geoenvironment. Its constituents, microstructure, strength properties and water-weakening properties were investigated. In situ stress environment and mining-induced fractured damage zone after excavation were studied to reveal the instability mechanism. The results show that red shale contains swelling and loose clayey minerals as interstitial filling material, producing low shear strength of microstructure and making it vulnerable to water. Macroscopically, a U-shaped curve of uniaxial compressive strength (UCS) exists with the increase of the angle between macro weakness plane and the horizon. However, its tensile strength reduced monotonically with this angle. While immersed in water for 72 h, its UCS reduced by 91.9% comparing to the natural state. Field sonic tests reveal that an asymmetrical geometrical profile of fractured damage zone of gateroad was identified due to geological bedding plane and detailed gateroad layout with regards to the direction of major principle stress. Therefore, red shale is a kind of engineering soft rock. For ground control in underground mining or similar applications, water inflow within several hours of excavation must strictly be prevented and energy adsorbing rock bolt is recommended, especially in large deformation part of gateroad.

Strain energy analysis of floor heave in longwall gateroads.

Floor heave in longwall gateroads is a severe issue that affects mining safety and efficiency. Researchers, however, have limited understanding on the floor heave mechanism because the deformation of post-failure rocks in the floor was seldom considered previously. In this study, we developed a theoretical model using the strain energy theory to investigate the post-failure deformation of rocks. This model was validated before being implemented into a numerical modelling package, FLAC3D, for floor heave analysis. Based on a case study of a longwall entry employing a stiff–yield pillar configuration, we observe that massive floor heave occurs at the entry rib that takes less loads (yield pillar) and eventually propagates towards the other rib bearing a significant amount of loads (stiff pillar). This observation sheds light on the floor heave mechanism in longwall gateroads and has major implications for coal mine ground control.

Experimental Investigation on the Basic Law of Directional Hydraulic Fracturing Controlled by Dense Linear Multi-Hole Drilling

Directional rupture is a significant and routine problem for ground control in mines. Directional hydraulic fracturing controlled by dense linear multi-hole drilling was proposed. The physical model experiment, performed by the large-scale true triaxial hydraulic fracturing experimental system, aims to investigate the basic law of directional hydraulic fracturing controlled by dense linear multi-hole drilling, the impact of three different pumping modes on the initiation and propagation of hydraulic fractures among boreholes are particular investigated. The experimental results indicated that there are mutual impacts among different boreholes during crack propagation, which leads to a trend of fracture connection. Furthermore, during propagation, the fractures not only exhibit an overall bias toward the direction in which the boreholes are scattered but also partially offset against the borehole axes and intersect. The directional fracturing effect of equivalent pumping rate in each borehole is better than the other two pumping modes. In practical applications, because of rock mass heterogeneity, there may be differences in terms of filtration rate and effective input volume in different boreholes; thus, water pressure increase and rupture are not simultaneous in different boreholes. Additionally, if the crack initiation directions of different boreholes at different times are not consistent with each other, more lamellar failure planes will occur, and the mutual influences of these lamellar failure planes cause fractures to extend and intersect.

Ground control in mining steeply dipping coal seams by backfilling with waste rock

Ground control in mining steeply dipping coal seams by backfilling with waste rock

Stability Assessment of Open Stope under Overlaying Mined-Out Regions at Modi Taung Gold Mine, Myanmar

Stability assessment is one of the most important issues in mining ground control. Mine development and/or production instability can cause production delay, loss of reserves, as well as injury to miners. Within the scope of this study, a series of open stope’s instability under the influence of overlaying mined-out regions were carried out with different mining scenarios at Modi Taung gold mine which is operated by National Prosperity Gold Production Group Limited (NPGPGL) in Myanmar. NPGPGL has been developing stopes up to 150 m from the surface at Shwesin vein system, and the mining activities are going to continue to deeper levels to fulfill the ore mineral supply. Creating a new stope opening under overlaying mined-out regions is not easy considering the instability of mined-out regions can affect the stope. The instability of new stope opening is not only due to its own induced stress but also the strong influence by the mined-out regions situated on upper part of the stope. Therefore, the understandings of ground behaviors and failure mechanisms of new stope opening due to the influence of overlaying mined-out regions are paramount to be studied. This paper describes in detail the strength factor and failure zones under the overlaying mined-out regions with different mine conditions by using numerical simulations, 3D finite difference software (FLAC 3D).

A New Closed‐Form Solution of the Side Abutment Pressure Distribution of Roadway

Instability of coal wall is one of the hot‐button and difficult issues in the study of coal mine ground control. The shallow side coal of roadway in the coal measures is usually weak and consequently easy to bring about failure. Hence, the side abutment pressure redistributes and dramatically influences the roadway stability. Since the previous closed‐form solutions of the side abutment pressure do not take into account all the necessary parameters which include the properties of the coal and the interface between coal and roof/floor, the roadway height, and the support strength, a mechanical model is established based on the equilibrium of the plastic zone, and a new closed‐form solution is derived in this paper. Moreover, a numerical investigation is conducted to validate the accuracy of the closed‐form solution. The numerical results of the side abutment pressure distribution are in good agreement with the closed‐form solution. Afterwards, a parametric analysis of the width of the plastic zone is carried out, and the results show that the width of the plastic zone is nearly negatively linearly correlated with the friction angle and the cohesion of the coal, the interfacial cohesion, and the support strength. By contrast, it is positively linearly correlated with the roadway height and negatively exponentially correlated with the interfacial friction angle. The results obtained in the present study could be useful for the evaluation process of roadway stability.

Numerical investigation of the effects of coal seam dip angle on coal wall stability

Instability and failure mechanism of coal wall at coalface is one of the hot-button and difficult issues in the study of coal mine ground control. Research to date has mainly focused on the macro-characteristics of coal face failure whereas few efforts have been devoted to the micro aspects or to the mechanisms behind these failures. The work described here takes coal face 8102 in the Wolonghu Mine, China, as an example and employs distinct element numerical software (UDEC) to investigate the distribution of abutment stress in front of the coal face at different mining dip angles from micro and macro perspectives, and reveal the main failure form and location of coal rib. The numerical results indicate the following six points. (1) The distance between the location of the peak abutment stress and the coal face increases with greater mining dip angles. (2) The rank by angle of abutment stress concentration factors is horizontal >up-dip> down-dip coal faces.(3) Tensile fractures dominate the failure of horizontal and up-dip coal faces and the only difference between the two is the form of the failure. (4) Shear fractures are the dominant failure components of down-dip coal faces. (5) The coal face failure forms include integral rib spall and a combination of upper-rib shear failure and roof caving. (6) Tensile fractures are mainly responsible for roof failures. The difference in roof movement between up-dip and down-dip coal faces is reflected in the forms of failure of their coal faces and of their roofs. Moreover, the effect of coalface depth, mining height, panel advance velocity and coal strength on the stability of coal rib is studied. The conclusions obtained from numerical simulation are consistent with engineering result, which verifies the reasonability of simulation analysis by UDEC. Finally, we propose measures to avoid coal face failure in the Wolonghu mine considering the numerical outcomes, the monitored strata behavior, and the recorded setting support resistance.

A numerical modelling study of longwall face stability in mining thick coal seams in China

Longwall face failures remain a major ground control and safety hazard in Chinese coal mines. This paper develops a better scientific understanding of stress and displacement distribution in the face area through 2-D finite element modelling of a typical longwall face in China. The results show: 1) most of the yielding occurs in the upper part of the face; 2) most vertical displacement occurs near the upper part of the coal face, while most horizontal displacement occurs around the centre part; 3) most face falls should, therefore, occur in the upper part of the coal face; 4) face stability is most affected by the load carrying characteristics of caved gob; 5) increased loading capacity of shields has limited effect on the stress distribution ahead of the face; 6) currently used face plate pressure distribution does not have a major effect on the redistribution of stress in the face area.

A numerical modelling study of longwall face stability in mining thick coal seams in China

Longwall face failures remain a major ground control and safety hazard in Chinese coal mines. This paper develops a better scientific understanding of stress and displacement distribution in the face area through 2-D finite element modelling of a typical longwall face in China. The results show: 1) most of the yielding occurs in the upper part of the face; 2) most vertical displacement occurs near the upper part of the coal face, while most horizontal displacement occurs around the centre part; 3) most face falls should, therefore, occur in the upper part of the coal face; 4) face stability is most affected by the load carrying characteristics of caved gob; 5) increased loading capacity of shields has limited effect on the stress distribution ahead of the face; 6) currently used face plate pressure distribution does not have a major effect on the redistribution of stress in the face area.

Science of empirical design in mining ground control

Many problems in rock engineering are limited by our imperfect knowledge of the material properties and failure mechanics of rock masses. Mining problems are somewhat unique, however, in that plenty of real world experience is generally available and can be turned into valuable experimental data. Every pillar that is developed, or stope that is mined, represents a full-scale test of a rock mechanics design. By harvesting these data, and then using the appropriate statistical techniques to interpret them, mining engineers have developed powerful design techniques that are widely used around the world. Successful empirical methods are readily accepted because they are simple, transparent, practical, and firmly tethered to reality. The author has been intimately associated with empirical design for his entire career, but his previous publications have described the application of individual techniques to specific problems. The focus of this paper is the process used to develop a successful empirical method. A six-stage process is described: identification of the problem, and of the end users of the final product; development of a conceptual rock mechanics model, and identification of the key parameters in that model; identification of measures for each of the key parameters, and the development of new measures (such as rating scales) where necessary; data sources and data collection; statistical analysis; and packaging of the final product. Each of these stages has its own potential rewards and pitfalls, which will be illustrated by incidents from the author’s own experience. The ultimate goal of this paper is to provide a new and deeper appreciation for empirical techniques, as well as some guidelines and opportunities for future developers.

Experimental Study On The Effect Of Micro-Cracks On Brazilian Tensile Strength

Abstract For coal mine ground control issues, it is necessary to propose a failure criteria accounting for the transversely isotropic behaviors of rocks. Hence, it is very helpful to provide experimental data for the validation of the failure criteria. In this paper, the method for preparing transversely isotropic specimens and the scheme of the Brazilian tensile strength test are presented. Results obtained from Brazilian split tests under dry and water-saturated conditions reflect the effect of the development direction β of the structural plane, such as the bedding fissure, on the tensile strength, ultimate displacement, failure mode, and the whole splitting process. The results show that the tensile strength decreases linearly with increasing β. The softening coefficient of the tensile strength shows a sinusoidal function. The values of the slope and inflection point for the curve vary at the different stages of the Brazilian test. The failure mode of the rock specimen presented in this paper generally coincides with the standard Brazilian splitting failure mode. Based on the test results, the major influencing factors for the Brazilian splitting strength are analyzed and a mathematical model for solving the Brazilian splitting strength is proposed. The findings in this paper would greatly benefit the coal mine ground control studies when the surrounding rocks of interest show severe transversely isotropic behaviors.

Topical areas of research needs in ground control – A state of the art review on coal mine ground control

Ground control is one of the four subsystems of underground mining. It covers not only roof control, but also rib control, floor control, pillar design, shield design, overburden failures and subsidence. In the past three decades, ground control has made a tremendous advancement and many case studies have demonstrated its important role in the daily mining operations. However, there are plenty of room for improvements. This paper discusses the research needs in 12 subject areas including research approach, rock property, geology, computer modeling, in-situ stresses, roof bolting, coal pillars, field instrumentation, failures, surface subsidence, shield supports and coal bumps.

3D topographic stress perturbations and implications for ground control in underground coal mines

It is well known that the perturbed stress field beneath valleys can result in roof instabilities in shallow underground coal and stone mines. Quantitatively predicting the magnitude of these stress perturbations, particularly beneath complicated three-dimensional (3D) topography, has not become commonplace in mine planning, perhaps due to the complexity and time-consuming nature of the problem. Here we utilize 3D digital elevation models and the 3D boundary element method (BEM) approach to efficiently calculate the pre-mining topographically perturbed stress field in the vicinity of the Carroll Hollow coal mine in eastern Ohio. We find that regions of elevated compressive stress in the mine correspond to areas in which cutter roof failure is a common source of roof instability. Furthermore, both the magnitude and inclination of the principal stresses calculated from the 3D topographic BEM model are found to be consistent with observed failure distributions within the mine. We propose that the approach outlined in this study can be efficiently applied to the mine planning process in order to mitigate or avoid potentially hazardous mining conditions.