ISRM 2023 - PUBLICATIONS

T04: Deep mining and tunnellingSanjay SINGHHarmony Gold, South AfricaDynamic response of the rock mass where the orebody dip changesMining at depth in a South African gold mine, poses common risks and hazards. Many seismic events have, in the past and present, resulted in the loss of life of several employees. Most of these were inexplicable, and no consideration was given in any study where the orebody being normally weaker in relation to the surrounding rock mass is a result of a catastrophic event, merely by the change in its dip. From the investigations it was deduced that when there is a change in the dip of the orebody the surrounding rock mass characteristics allow the orebody to behave in a similar manner as a steeply dipping fault. The following is an attempt to set the scene, analyze and draw conclusions when an orebody dip changes and thus ensuring the transfer of knowledge. | Dynamic, response, rock, orebody, dip, change
T04: Deep mining and tunnellingAlexey SHARIPOV, Amoussou ADOKOSchool of Mining and Geosciences, Nazarbayev University, KazakhstanAn investigation of the effect of rock brittleness on rockburst prediction in seismically active minesThe aim of this paper is to investigate the effect of the brittleness indices (B1 and B2) on the rockburst damage potential classification performance using Artificial Neural Network classifiers. Rockburst incident cases from seismically active mines are used to implement the proposed ANN models. Several scenarios were considered. The performance of the models was evaluated and the results indicated that the brittleness index has a great influence on the predictive performance of the models, especially for severe rockburst cases. The classification rates vary between 60-88% depending on the scenarios. Overall, showed a slight higher impact on the model accuracies compared to. The classification results showed some superiority over existing studies. It is concluded the results of the present study can be useful in managing ground prone to rockburst. | Rockburst potential damage, rock brittleness, ANN classifiers, rockburst intensity, mine seismicity
T04: Deep mining and tunnellingKamilya OMIRZHANKYZY, Ali MORTAZAVISchool of Mining & Geosciences, Nazarbayev University, Astana, KazakhstanA numerically based geomechanics risk assessment of the cut and fill underground mining methodThe study of rock pillar stability is a common concern in mining engineering. It is critical to enhance predictive research of the mining effect and improve design to avoid catastrophic failures in mines operating at great depths. This results in the creation of pillars that must be retrieved during subsequent phases of excavation, typically under conditions of extreme stress. The purpose of this work is to examine the geomechanical parameters affecting pillar stability and behavior under the complicated nature of the rock mass in-situ, boundary conditions, and operational complexities associated with the cut-and-fill mining method at great depths. To evaluate the pillar deformation mechanisms, a comprehensive Finite Element Analysis was conducted. The obtained results are discussed and presented in terms of pillar stress and displacement fields. A parametric analysis was conducted to compare and determine the significance of geomechanical design parameters on pillar behavior, stability, and bursting potential. | Geomechanics Design, Pillar Stability, Risk Assessment, Cut and Fill method
T04: Deep mining and tunnellingYuehan WANG, Guangyao SI, Joung OHSchool of Minerals and Energy Resources Engineering, University of New South Wales, Sydney, AustraliaCoupled Geomechanical CFD Modelling of Goaf under Goaf Gas Drainage: Impact of Goaf CharacteristicsAustralian mines heavily relied on a series of boreholes to control goaf gas emissions. The use of these boreholes not only reduces greenhouse gas but also recovers a large amount of energy. However, high suction pressure applied on boreholes may cause ventilation air migration from the working face to enter the goaf. The leaked air containing rich oxygen would react with the residual coal in the goaf and accumulate heat, which may cause spontaneous combustion and gas explosion risks. This paper developed a goaf CFD model to analyse the goaf gas distribution and leaked air flow pathways under the impact of intensive goaf gas drainage. Besides, the associated gas explosion risks will be quantified using Coward’s triangle based on the CFD modelling simulation results. Therefore, this CFD model can be used to optimise the drainage efficiency of intensive boreholes while ensuring mining safety during the operation period. | Goaf gas drainage, CFD modelling, goaf permeability, coal oxidation, gas explosion risk
T04: Deep mining and tunnellingYuepeng SUN (1), Biao LI (2), Nuwen XU (1), Qi WANG (3), Bei JIANG (3)1: Sichuan University, Sichuan, China; 2: Southwest Petroleum University, Sichuan, China; 3: China University of Mining & Technology (Beijing), Beijing, ChinaStability analysis of surrounding rock mass in underground powerhouse based on octree and catastrophe theoryBased on the underground cavern engineering of the left bank of Shuangjiangkou hydropower station, Octree theory is used to define the indexes of the MS spatial aggregation degree and the deviation values of MS frequency and energy, establishes the relationship with surrounding rock mass instability from three aspects of "time, space and strength". The cusp catastrophe model of the MS spatial aggregation degree and the deviation values of MS frequency and energy is established to quantitatively describe the early warning state of surrounding rock mass instability of underground cavern. The results show that the multi-level tree structure and voxels generated based on Octree theory is higher goodness of MS point set in three-dimensional space. The cusp catastrophe model based on the MS spatial aggregation degree and the deviation values of MS frequency and energy can effectively identify the early warning interval and potential damage area of surrounding rock mass, The warning time zone and potential damage zone quantified by this method are highly consistent with the characteristics of MS precursors with high recognition and field investigation results, which fully proves the rationality and applicability of this method. The research results can provide basis and reference for the early warning of surrounding rock instability in the later excavation of underground powerhouse. | Underground caverns; MS monitoring; early warning; Octree theory; Catastrophe theory
T04: Deep mining and tunnellingJörg-Martin HOHBERGIM/IUB Engineering AG, SwitzerlandPrediction of long-term deformation and dimensioning of support in squeezing rock under high overburdenLarge infrastructure projects such as the railway base tunnels crossing the Alpine ridge are designed for a minimum service life of 100 years. The running tracks are adjustable to a few centimeters only and may be replaced after 50 years, but the tunnel lining must stay intact over the entire life span with secured clearance. The primary feature of such tunnels is their flat alignment for energy-efficient high-speed traffic of heavy trains, accepting long tunnel drives with high overburden of 1,500 m or more. Despite optimization of the horizontal alignment to avoid difficult rock conditions at best, the scarce geological reconnaissance leaves ample room for surprises such as faults, carst or squeezing rock. | Deep tunnels, squeezing rock, numerical methods, FEM, long-term behaviour
T04: Deep mining and tunnellingYang ZOU, Ping ZHANGLuleå University of Technology, SwedenAssessment of energy release and redistribution on excavation instabilities for underground miningEnergy considerations are essential for the evaluation of violent failures which are commonly encountered as mining goes deeper. To address the relationships among different energy components, a series of numerical models were conducted by using 3DEC and a script was developed for energy visualization. The theoretical and numerical results of the ratio between the released kinetic energy and the excavated strain energy were compared under elastic and plastic models. The distribution of stored elastic strain energy and dissipated plastic strain energy in the vicinities of openings with different shapes were also investigated. Furthermore, the efficiency of a latest destressing method as a proactive measure for seismic management was evaluated based on the energy redistribution patterns. This research can improve the understanding of the energy evolution near excavations and contribute to the evaluation of burst-proneness of excavations as well as effectiveness of rockburst mitigation measures. | Rock burst, Released energy, Dissipated energy, Destressing, Seismic management
T04: Deep mining and tunnellingAli HASHEMI, Neda DADASHZADEH, Kathy KALENCHUKRockEng Inc., CanadaAn implicit numerical modeling approach for destress blasting design optimization for tunneling and mine development in high stress conditionsTunnelling and underground mine development in high-stress conditions are exposed to potential rockburst hazards. Rockburst risk management may include multiple hazard control and/or exposure management strategies. Rockmass preconditioning, such as destress blasting, is a tactical approach to hazard control by introducing blast-induced fractures to the rockmass. Introducing fractures softens the rockmass and reduces potential stored strain energy. This paper explores a case study where a large-magnitude rockburst occurred in the floor of a mine tunnel located approximately 2km below the surface, in a strong, massive rockmass. Subsequently, destress blasting was implemented in all active development headings for risk mitigation. This paper presents a geotechnical study to optimize the utilization of destress blasting. A detailed numerical modeling investigation with implicit representation of blast damage is done using a calibrated FLAC3D model. The influence of destress blast design on rock burst hazard potential is numerically studied and discussed. | Rockburst, Destress Blasting, Risk Management, Numerical Modeling
T04: Deep mining and tunnellingEmeline LHOUMAUD (1), Yann GUNZBERGER (1), Jannes KINSCHER (2), Marianne CONIN (1)1: GeoRessources lab, Université de Lorraine - CNRS, Mines Nancy, Campus ARTEM, Nancy, France; 2: Institut National de l’Environnement Industriel et des Risques (INERIS), Campus ARTEM, Nancy, FranceOrigin of seismic repeaters in a deep mine: what do we learn from in-situ investigation coupling geology, geomechanics and geophysics?Seismic repeaters (i.e. seismic events with highly similar waveforms) have been observed in the deep mine of Garpenberg, Sweden. In natural seismology, repeaters are commonly associated with the presence of aseismic slip (i.e. creep) on fault planes, loading seismogenic asperities. This raises questions regarding what these asperities and creeping zone consist of and how they behave from a mechanical point of view. A local monitoring network has been installed in situ, close to the source area of one family of repeaters at 1km depth, with the objective of identifying the origin of these repeaters. The network comprises boreholes, geophones and strain cells. We show that the presence of a fault plane with creeping portions and an asperity is compatible with field data. We also discuss the difficulty of clearly identifying the origin of the repeaters, as we couldn’t reach the seismic asperity itself, even with such a local network. | Induced seismicity, seismic repeaters, deep mining, in-situ investigation
T04: Deep mining and tunnellingHongpu KANG, Yanjun FENG, Fuqiang GAOChina Coal Research Institute, People's Republic of ChinaApplication of hydraulic fracturing for destressing mining-induced stresses in underground coal minesHydraulic fracturing (HF) has emerged as a widely used ground control strategy in Chinese coal mining practice, often employed in combination with ground support techniques. HF campaigns can be broadly categorized into two types based on the size of the targeted region: local campaigns, which are applied to smaller areas such as the roof above a coal pillar, and large-scale campaigns, which encompass a broader area, such as the entire width of a longwall panel. This paper presents two case studies that examine the use of both local and regional HF as a ground support strategy in Chinese coal mines. The field studies demonstrate that HF is effective in reducing or redistributing mining-induced stresses, preconditioning hard rock strata, and, in some cases, decreasing mining-induced microseismicity. | hydraulic fracturing, underground coal mine, destressing, case study
T04: Deep mining and tunnellingFuqiang GAO, Guiyang YUAN, Xiangyuan PENGChina Coal Research Institute, People's Republic of ChinaExperimental study of coal bursts caused by decrease of local mine stiffnessThe crucial role played by local mine stiffness (LMS) in the occurrence of rock strainbursts has been widely acknowledged. To prevent rockbursts, it is essential to comprehend the evolution of LMS during mining operations. Unfortunately, existing studies on this subject are largely limited to theoretical and numerical methods. To address this research gap, we conducted an experimental investigation using an in-house developed equipment. The aim was to generate strainbursts resulting from excavation-induced stress concentration and LMS reduction. In this study, we simulated the excavation process and associated disturbances using real coal blocks in a laboratory setting. The results of our experimental investigation provide a novel approach for producing strainbursts that arise due to the progressive reduction of local mine stiffness during mining operations. | strainbursts, local mine stiffness, experimental study, stress concentration
T04: Deep mining and tunnellingGilles ARMAND, Carlos PLUA, Minh-Ngoc VUAndra, France18 years of monitoring pore pressure evolution during and after excavation in the Callovo-Oxfordian claystone: the main insightsIn France, the Callovo-Oxfordian claystone (COx) formation is considered as the host rock for the geological disposal for radioactive waste due to its very low hydraulic conductivity, low molecular diffusion, significant retention capacity and its self-sealing capacity. The hydromechanical behavior around underground openings in such claystone is also of importance for the short- and the long-term. At the short-term, the front advancement in “quasi-undrained” conditions modifies the stress field and create volumetric strains leading to pore pressure disturbance. If the effective stresses reach the failure criterion, the induced damage around these excavations might change the favorable properties of such formation. At the long-term, the geomechanical characteristics of the formation control the evolution of the induced fracture network and the time-dependent behavior around the openings which are key issues to design drift supports. This paper presents a comprehensive field monitoring study at two different scales conducted in the COx since 2004. | Callovo-Oxfordian claystone, hydromechanical behavior, mine-by-test, pore pressure
T04: Deep mining and tunnellingKrzysztof FUŁAWKA, Piotr MERTUSZKA, Marcin SZUMNY, Lech STOLECKI, Izabela JAŚKIEWICZ-PROĆKGHM CUPRUM Ltd. R&D CentreNovel method of multi-face destress blasting efficiency assessmentIn this paper, the newly formulated solution of multi-face destress blasting efficiency assessment is presented. The developed method is relevant for near and far-field effect evaluation and is improved by the duration, amplitude, and frequency characteristics of blast-induced seismic waves. The proposed approach is based on the advanced analyses of the waveforms generated by blasting, ground motion prediction equations and data describing the technological parameters of blasting in terms of the amount of explosives, delay times, and spatial location of mining faces. The proposed solution was validated in deep underground mines in Poland in which the room-and-pillar mining method is applied. Based on the performed analysis, it is shown that a new method may be used as an element of rockburst hazard control in underground mines. However, the developed method may also be successfully implemented in other engineering practices, including open pits and quarries. | Destress blasting, seismic waves, blasting efficiency, mining seismology, underground mining
T04: Deep mining and tunnellingTatsuya YOKOYAMA (1), Akira MITO (2)1: Fukada Geological Institute, Tokyo, Japan; 2: Shimizu corporation, Tokyo, JapanEvaluation of rock stresses measured in a long water tunnel at deep depthThree different methods were used to measure stress in a deep tunnel under excavation, and the obtained values were compared. At two locations at a depth around 200m, the stress relief method (CCBO) and the hydraulic fracturing method (HF) were used. The stress states measured at these points have large horizontal stress components, and the maximum principal stresses were greater than the overburden stress. The stress states measured by CCBO and HF agreed well with each other. At a depth of location of 1,130m, CCBO and the Borehole Wall Strain method (BWS) were used. Assuming that the tunnel itself is a large borehole, stress measurements by BWS were obtained by gluing strain gauges directly to the tunnel wall and releasing stress only in that part. This BWS is a very unique and challenging method. Interestingly, the stress states measured by two different methods were in good agreement with each other. | Rock stress. Stress relief method (CCBO). Hydraulic fracturing method (HF). Borehole wall strain method (BWS)
T04: Deep mining and tunnellingSevda DEHKHODA (1), David BECK (1), Vladislav LEVKOVITCH (2)1: Beck Engineering, Australia; 2: Beck Engineering, GermanyNumerically simulated Rate of Energy Release and its correlation with measured seismic potencyAs mines are getting deeper, mining induced seismicity becomes a major hazard threatening the health, safety, and security of operations. In today’s mines, seismicity is well measured and documented. However, the ability to foresee events lags behind. This paper will discuss the correlation between numerically simulated Rate of Energy Release (RER) and measured seismic potency in the real rock mass. RER is defined as the rate of elastic strain energy emitted into the surrounding rock as a result of abrupt fracture or deformation. RER has proven to be a good candidate for probabilistic forecasting of seismic potential (the capacity to develop seismogenic activity) in the rock mass. In the following sections, we will describe a computational framework for simulating RER and subsequent analyses for evaluating the likelihood of mining induced seismic events. We will present example results from mines where model predictions matched measured seismicity. | Mining induced seismicity, rate of energy release, RER, hazard management, seismicity forecast
T04: Deep mining and tunnellingDavide MERLINI (1), Matteo FALANESCA (1), Gianluca BELLA (1), Antonio SPAZIANI (2), Antonio VOZA (2)1: Pini Group SA, Switzerland; 2: BBT-SE, Bolzano, ItalyNumerical modelling and tunneling experience of the Emergency Stop in Trens, Lots Mules 2-3 (Italy) - Brenner Base TunnelThe present paper focuses on the design and the construction experience related to Emergency Stop in Trens as a part of the Brenner Base Tunnel (BBT). This underground work consists in a 470 m long central tunnel excavated by conventional tunnelling connected through cross-passages every 90 m to the main tunnels excavated by TBMs-shield. The main design issues and construction challenges are represented by the complex interaction between underground structures located at two different elevations in combination with the high overburden about 1100 m and medium-low strength rock mass composed mainly of schists. The design involved 2D and 3D numerical analyses and also included swelling and creep. A comparison between the forecast geology and the cross-check will be analyzed also considering the data from the in-depth monitoring system. The comparison between Design and As-Built in terms of installed rock-supports, timing and costs will be examined in detail. | TBM and conventional tunneling, deep and long tunnel, BBT, numerical analysis
T04: Deep mining and tunnellingLinard CANTIENI (1), Alexandros N. NORDAS (2), Dennis MOROSOLI (2), Georg ANAGNOSTOU (2)1: National Cooperative for the Disposal of Radioactive Waste (Nagra), Wettingen, Switzerland; 2: ETH Zurich, Zurich, SwitzerlandOn the short-term response of Opalinus Clay to tunnellingOpalinus Clay is the host rock for the Swiss deep radioactive waste repository. Effective stress analyses have been performed for a first assessment of hazards related to the short-term ground response to the excavation of the repository drifts and caverns. The analyses were performed assuming that the rock either remains saturated or completely desaturates under the negative pore pressures developing short-term around the tunnels due to cavity unloading. The results show that the risk of shield jamming during construction of the repository drifts can be mitigated by providing an over-cut in the range of just a few centimetres. Yielding support is planned for the construction of repository caverns in order to accommodate deformations and reduce rock pressure. An over-excavation of one to two decimetres, in combination with adequate structural detailing, must be planned to accommodate the short-term convergences. | radioactive waste repositories, Opalinus Clay, brittle softening, squeezing ground, short-term, negative pore pressure cut-off
T04: Deep mining and tunnellingFedilberto J. GONZALEZ (1), Peter K. KAISER (2), Mark S. DIEDERICHS (1)1: Queen's University, Miller Hall, Kingston, Ontario, K7L 3N6, Canada; 2: Laurentian University, Sudbury, Ontario, P3E 6H5, CanadaDisplacement and energy demand imposed by rapid bulking and tunnel shape changeIn burstprone ground, sudden and violent failure of hard brittle rock dynamically loads and deforms ground support. Failure of underground excavations comprises two processes: bulking of stress-fractured rock and shape changes of the excavation in response to the fracturing process. For demonstration purposes, a case with a stress ratio k < 1 is examined. Brittle failure of sidewalls occurs if induced stresses exceed the crack propagation stress level, leading to a rupture process and rock mass convergence in which the bulking rock moves rapidly toward the excavation. At the same time, the roof and floor converge rapidly induced by the sudden shape change due to wall rupture. This article presents estimates of kinetic energy demands that would be imposed on support by self-induced strainbursts and associated sudden and violent shape change. The effects of confining pressure at the tunnel surface on the violence of this process are explored using FLAC. | Rapid bulking, self-induced strainburst, shape change
T04: Deep mining and tunnellingMrityunjay JAISWAL (1), Resmi SEBASTIAN (1), Ravibabu MULAVEESALA (2)1: Department of Civil Engineering, Indian Institute of Technology Ropar, Rupnagar, Punjab, India, Pin; 2: Centre for Sensors, iNstrumentation and cyber-physical Systems Engineering (SeNSE), Indian Institute of Technology Delhi, Hauz Khas, New DelhiModulated thermal wave imaging approach to detect subsurface microcracks and their coalescence in deep mines for rock burst (strain burst) predictionRock burst, which is exceptionally powerful and abrupt, is one of the most dangerous geological hazards in deep mines. Although it is difficult to prevent rock explosions, it can be predicted with continual monitoring. Traditional monitoring systems produce a large quantity of data and false signals. Most methods are affected by blasting and other mining activities. This study used modulated thermal wave imaging to locate the high damage zone in a rock sample containing artificially implanted subsurface microcracks prior to any rock bursting. Finite element (FE) simulations were used to examine the infrared thermal response of a rock sample to a fixed-frequency sinusoidal heat wave. To automate detection, a cutting-edge deep-learning technique was used to identify, localize, and segment cracks. A sizable dataset of images with a resolution of 640×480 was produced for the algorithm training and validation. The F1 score and precision of the applied method were considerably high. | Rockburst, thermal monitoring, infrared thermography, deep learning
T04: Deep mining and tunnellingMax JOHNZT John, AustriaAre trigger levels useful for tunnels at high rock pressure?For rock tunnels under high overburden and/or squeezing ground stable conditions may be obtained at a wide range of displacements depending on the support stiffness and rock mass characteristics. The ground reaction curve (Fenner-Pacher curve) depends on complex geologic and surrounding conditions which may never be known beforehand. It may also be noted, that once the rock mass strength is exceeded, the rock mass curve is changed. This has rarely been noted in the literature. The fracture processes within the rock mass determines if critical situations may occur. Therefore, rock bolting is most important in order to control the development of failure surfaces. As long as displacements tend to cease, a stable condition is approached. Because displacements depend on excavation rate and sequence (heading/bench/invert) as well as on the stiffness of support including deformation slots and/or yielding elements, displacements are not decisive as trigger values. | Rock pressure, trigger levels, fracture process, displacements, monitoring
T04: Deep mining and tunnellingMiguel Angel BERROCALGEOMECANICA DEL PERU EIRL, PeruIn situ stress evaluation according to the Drillhole detonation method, applied to the geometric design underground excavationsThe rock mass is composed of homogeneous and heterogeneous rocks, generating stresses of different orientation and magnitude. One of the techniques to evaluate the state of stress in situ is the Drillhole detonation method; the procedure consists of detonating a drillhole with explosives to obtain radial cracks and with this result analyze the ellipse generated, called stress ellipse. The data to evaluate the magnitude of the stresses σ1, σ3, and σ2; are based on the analysis of the stress ellipse, from which are obtained: the orientation (α) of the major stress σ1, the coefficient k, and the Correction factor (CF). The Drillhole detonation method provides the appropriate technique for the design of underground excavations, according to the profile of the horizontal and vertical trend stress ellipse. | K coefficient, Design of underground excavations, Drillhole detonation method, In situ stress evaluation, Stress ellipse
T04: Deep mining and tunnellingMohammad MOHAMMADI, Johan SPROSSDivision of Soil and Rock Mechanics, KTH Royal Institute of TechnologyModeling uncertainty of activity duration in probabilistic time estimation of tunneling projectsThe PERT distribution may be a suitable distribution for modeling activities’ duration in probabilistic time estimation of tunnel projects as it puts more emphasis on the mean value of the distribution. In this paper, we compared the outcome of time estimations for a tunnel, using the triangular and PERT distributions for modeling the uncertainty of activities’ duration. The results indicate that the choice of the distribution affects the total estimated time considerably. In addition, the skewness of the distribution also affects the results of estimation meaning that realistic assessment of the parameters of the distributions is important. | Time estimation, probabilistic approaches, tunneling, activity duration, production effort
T04: Deep mining and tunnellingTuo CHEN, Hani S. MITRIMcGill University, CanadaUnplanned ore dilution control in longhole mining using sill pillars – A case studyThis paper discusses the main causes for unplanned ore dilution in longhole mining and possible mitigation measures. It reports on the results of a case study of an underground mine that uses the longitudinal retreat method for the extraction of a narrow gold-silver orebody. The study is conducted with finite difference software FLAC3D. The modelling technique tracks and fills the cavities created by progressive overbreak with cemented rockfill in bottom-up sequence. In this work, a strategic measure of ore dilution control is explored by incorporating a sill pillar in the mine plan. Comparison of two mine plans - with and without sill pillar - reveals the benefits of sill pillar on unplanned ore dilution control, especially in the three mining levels immediately above the sill pillar. The findings of this work could be equally applicable to similar mining systems with one or more sill pillars in each mine plan. | Underground mining, sill pillar, unplanned ore dilution, numerical modelling
T04: Deep mining and tunnellingTobias LADINIG (1,2), Patrick GAMS (1), Horst WAGNER (1), Matthias WIMMER (2), Michal GRYNIENKO (2)1: Chair of Mining Engineering and Mineral Economics, Montanuniversität Leoben, Austria; 2: Rock Engineering Kiruna Mine, LKAB, SwedenAddressing rock engineering challenges faced in the development of a novel, deep mining methodRaise Caving is a novel mass mining method utilizing an active stress control approach for the foresighted, strategic and systematic control of rock pressure. The active stress control approach is based on a slot-pillar system, which is established prior to large-scale mineral extraction. From a rock engineering point the challenge is to design initially strong pillars, which are required to provide and maintain a favorable stress environment for establishing the de-stress slots. As large-scale mineral extraction commences, the pillars have to be weakened stepwise to create a regional de-stressed area for mineral extraction. The critical issue is to manage this process such that pillar strength degradation takes place in a stable controlled manner. The paper discusses rock engineering considerations related to pillars. The investigations show that the design of pillars and the regional extraction sequence are crucial and that design criteria for infrastructure and mining-induced seismicity need to be developed. | Deep mining, Rock Mechanics, Cave Mining, Raise Caving, Stress Control, Pillars
T04: Deep mining and tunnellingZulfiqar ALI (1), Murat KARAKUS (1), Giang D. NGUYEN (1), Khalid AMROUCH (1,2), Chris CHESTER (3)1: The University Of Adelaide,Adelaide, Australia; 2: Mohammed VI Polytechnic University, Benguerir, Morocco; 3: OZ Minerals, Adelaide Airport, SA 5950, AustraliaIn-situ stress measurement using non-destructive and relief methodsOver the past many decades, in-situ stress measurement using overcoring (OC) and hydraulic fracturing (HF) methods has been scientifically accepted and commercially adopted worldwide. However, with the mines getting deeper, their application has become more cumbersome and costlier. This paper presents the use of non-destructive techniques like the secant modulus method (SMM) and acoustic emission (AE) for in-situ stress measurement. Cyclic tests were performed on sub-cores extracted in six independent directions from the oriented main core having a trend and plunge of 285o and 75o respectively in the mine grid. The cores were retrieved from a mine site in South Australia where the OC method was applied. A minimum of two sub-cores were tested in each direction to get the complete stress tensor. The deformation was monitored using strain gauges and AE monitoring system. Results show a very good estimate of in-situ stresses that compares well with the OC method. | Kaiser Effect; Stress Memory; Secant Modulus Method (SMM); Acoustic Emission (AE); Overcoring (OC)
T04: Deep mining and tunnellingTao LIN (1), Zhihong ZHAO (1), Wen MENG (2), Xingguang ZHAO (3)1: Department of Civil Engineering, Tsinghua University, Beijing, China; 2: Key Laboratory of Neotectonic Movement and Geohazard, Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing, China; 3: CNNC Key Laboratory on Geological Disposal of High-level Radioactive Waste, Beijing Research Institute of Uranium Geology, Beijing, ChinaCoupled thermal and unloading-induced permeability of rock fracturesThe behavior of fluid flow through rock fractures is a critical issue in many subsurface rock engineering projects. Previous studies focused more on the permeability evolution of rock fractures under loading stage, while the change of fracture permeability under unloading stage is more consistent with the actual engineering excavation. To examine the unloading-induced changes in fracture permeability under different temperatures, we performed flow through tests on fractured core samples subjected to decreasing confining pressures and constant temperatures. The results show that the permeabilities of fractures under unloading confining pressure increase but decrease with increasing temperature because of fracture closure caused by asperity damage and thermal expansion. A coupled thermal-mechanical model considering asperity damage is used to explain the unloading-induced changes in fracture permeability. The coupled thermal-mechanical model properly predicts the experimental results. | Unloading, Permeability, Rock fracture, Temperature
T04: Deep mining and tunnellingLorenzo MILAN, Monica BARBERO, Mauro BORRI-BRUNETTOPolitecnico di Torino, ItalyApplication of a new brittleness index to estimate the proneness to brittle failure of rock around a deep tunnelA major problem that may arise during the excavation of deep tunnels is the incidence of brittle failure of rock, induced by the stress release in a particularly heavy natural state of stress. The severe energy release is often associated to rapid fracturing and to projection of rock blocks inside the opening, phenomena commonly referred to as spalling or rockburst, which endanger personnel and equipment. Thus, the proper prediction of the occurrence of brittle failure is paramount in underground excavations. This paper presents the application of a new rock brittleness index based on the response of two mechanical models of rock damage, which allows the estimation of the proneness to brittle failure of rock around deep tunnels. For this purpose, the competition between ductile and brittle failure is analyzed. The calculation and usage of the index is described considering a real case study of brittle failure in a deep tunnel. | Brittleness index, Rockburst, Spalling, Tunneling
T04: Deep mining and tunnellingRicardo Isidro FERREIRA, Pinkie NDABA, Richard MASETHESibanye-Stillwater, South AfricaThe implementation of ‘automatic’ polygons for relevant data selection in short-term seismic analysisMining at depth and high rock-stress environments can induce unanticipated dynamic rockmass deformation, posing a serious risk to the workforce. Time-trend analysis of certain seismological parameters has been used for many years to produce daily workplace seismic risk ratings which are meant to characterise rockmass behaviour and enable the identification of developing or imminent rock instability, allowing timeous ameliorating action to be taken – pro-actively and successfully. The impracticality of the daily reviewing of dozens of prior user-defined data selection polygons has meant that often an inappropriate assessment of the seismic hazard is done. Depending on the methodology or application of data analysis and interpretation, some of the information may not be relevant and even detract from the objective. By using the spatial event clusters associated with active workplaces to define the shape and size of the polygons for data selection for subsequent analysis, a problematic subjective component can be eliminated. | seismicity, risk, warning, short-term, ratings
T04: Deep mining and tunnellingRicardo Isidro FERREIRA, Richard MASETHE, Pinkie NDABASibanye-Stillwater, South AfricaRationale for the quick withdrawal of the underground workforce following (large) dynamic ground motions – how extensive should the exclusion zone be?The mining of the tabular auriferous reefs on the rim of the Witwatersrand Basin in South Africa is very extensive, and even within individual mines, underground workplaces are often widespread. There is just cause not to evacuate an entire operation’s workforce following the unanticipated occurrence of a large mining-induced seismic event. We present the rationale for the quick withdrawal of the possibly affected underground workforce following such seismic events and the calculation methodology based on the damaging peak particle velocities (PPV) of the past seismicity. A minimum PPV from the source at which observable damage to the underground excavations is no longer apparent was inferred. The radii from the source within which ground velocities exceed this amount are then calculated for all recorded events with local magnitudes ML1.0 and greater. Those workplaces located within these negatively affected volumes are deemed at risk and the workforce is withdrawn. | seismicity, risk, workforce, evacuation, safety
T04: Deep mining and tunnellingRodolfo Enrique CABEZAS (1), Adeline DELONCA (2)1: SRK Consulting, Chile; 2: Universidad Técnica Federico Santa María, ChileReliability of Predicting damage in hard rock mass around deep tunnels in terms of its convergenceIn deep excavations, mechanical instabilities may appear, inducing damage to the rock mass. These instabilities may be difficult to identify but are inferred as convergence of the walls over time. This magnitude and evolution may provide valuable information for tunnel stability analysis, as the extent of the damage affects where the ground support is installed. This study proposes a simple model to relate convergence with the depth of failure within the rock mass. A normalized damage curve is obtained as a function of the total deformation measured, for compressed and tensile areas around the excavation. The parameters are defined according to the stress state and the strength properties of the rock mass. The influence of the variability of the properties is considered, extending the analysis to a probabilistic case using Montecarlo method and obtaining reliability ranges for different rock masses expected in deep orebodies, for example in hydrothermally altered conditions. | Deep mining, tunneling, Damage, Depth of failure, Reliability
T04: Deep mining and tunnellingRichard MASETHE (1), Raymond DURRHEIM (2), Musa MANZI (2)1: Sibanyestillwaters, South Africa; 2: University of the Witwatersrand, South AfricaSource mechanisms of mining-induced seismicity at Kloof Gold Mine, South Africa – moment tensor analysis of ML≥1.5 eventsMining-induced seismic events in South African deep-level gold mines cause hazardous working conditions, damage infrastructure, delay production and pose a risk to miners. A good understanding of seismic source mechanisms is needed for seismic data to be used efficiently and effectively for mine planning purposes. A comprehensive study of mining-induced seismic events (ML1.5 – 3.3) that caused damage to stopes at Kloof Gold Mine is described. The source mechanisms of 88 events were calculated. All events were located within the central part of the in-mine seismic network, enabling reliable moment tensors to be determined. It was found that approximately equal numbers of events were related to mining-related structures (such as pillars and abutments) and to geological structures (such as faults and dykes). | seismicity, mining-induced, moment tensors, Kloof Gold Mine
T04: Deep mining and tunnellingXu LI, Guangyao SI, Joung OH, Ismet CANBULATUNSW, AustraliaA modification of the nearest neighborhood triggering mechanism in longwall mining: do seismic events only triggered by its closest neighbors?A common approach in seismology is to use the nearest neighbours method to identify the spatial and temporal relationships between events and select the closest event pairs to identify the triggering cascade. However, in mining engineering, due to the continuous triggering from dynamic mining development as well as the complex geological conditions (e.g., faults), the mining seismic events may not be purely triggered by one prior event, but by a triggering group of a few different events. In this study, we modify the event-event triggering identification approach applied in longwall seismic events. We find that high-energy events can be triggered by previous low-energy events, with clear foreshadowing events. High-energy events can be related to a few low-energy events whose mechanism is based on mining activities. | Longwall mining, Seismicity, rock mechanics
T04: Deep mining and tunnellingJoel CHIWARA (1), Ioannis VAZAIOS (2), Chrysothemis PARASKEVOPOULOU (1)1: University of Leeds, United Kingdom; 2: Ove Arup & Partners Ltd, London, United KingdomThe influence of brittle failure and its impact on face stability in high-stress tunnelling conditionsIn deep hard rock environments under high-stress conditions, rockmasses behave in a brittle manner resulting in spalling and strain bursting. This paper examines the occurrence of brittle failure and its impact on face stability. Generalised Hoek-Brown failure criterion modified after the Damage Initiation and Spalling Limit (DISL) approach is adopted in 2D and 3D numerical models to capture the mechanical response of brittle rocks in underground excavations. Unsupported circular tunnel models are used to investigate brittle failure at the tunnel face. Excavation induced stress and deformation results show that under anisotropic in-situ stress conditions, models become unstable, and relaxation rapidly increases within 3 m behind the tunnel face, while within a distance of 0.85 times the tunnel radius, the tunnel relaxes 85% to 95%. This demonstrates the rapid loss of confinement in hard rock masses within the face vicinity which yields instabilities in the tunnel. | brittle failure, high-stress, tunnel face stability, strain bursting, hard rock tunnelling, deep mining
T04: Deep mining and tunnellingChen XU (1,2), Lingxiao ZHENG (1), Gecheng ZHANG (1), Qing YAO (1), Shikang QIN (3)1: Institute of Rock Mechanics, Ningbo university, People's Republic of China; 2: Ningbo Key Laboratory of Energy Geostructure, Ningbo, China; 3: College of Civil Engineering, Tongji University, Shanghai, ChinaApplicability of stress release method in soft rock tunnel with high geostressThe Deformation Reserved (DR) method is a commonly used stress release method in the construction of weak rock tunnel with high geostress. The excavated tunnel section is usually larger than its design size, a space is reserved outside the design excavation boundary of the tunnel. The behavior of the double-layer support structure was investigated through theoretical derivation, and the applicability of the DR method in controlling the large deformation of soft surrounding rock during tunnel construction in high geostress was discussed. The calculated results by proposed method were verified by the in-situ monitoring data of field test. It is found that the DR method is capable of releasing the high geostress when tunnelling in squeezing rocks, and the double-layer support structure is necessary to resist the high ground stress. | large deformation, in-situ monitoring, multi-layer support, Deformation Reserved method, stress release
T04: Deep mining and tunnellingRajashekar Yadav AVULA, Sreenivasa Rao ISLAVATHIIT KHARAGPUR, IndiaAnalysis of the behaviour of the Barrier Pillars and Gateroads of the deep Longwall Panel of India using the 3D Finite Element Modelling approachIn Longwall mining, gateroads play a major role in transporting men and materials and providing ventilation. Barrier pillars lie between two adjacent panels to support the face and gateroads. During the retreating, these gateroads and barrier pillars are subject to mining-induced stresses and may cause the failure of the face, barrier, roof and floor of gateroads. The behaviour of barrier and face must be assessed to extract the panel successfully. For this, a longwall panel of 250 m x 2500 m size lying at 530 m depth is analysed using 3D finite element modelling technique. This study considers the variations in retreat distance, coal properties, and barrier size. All the numerical models are analysed considering Mohr-Coulomb criterion. The vertical displacement in gateroads and stress on the barrier and longwall face, abutment zone and yield zone are analysed, and the safety factor of the barrier pillars and longwall face are determined. | Barrier pillar, Gateroad, Development of load, Goaf, Safety factor
T04: Deep mining and tunnellingTawanda ZVARIVADZALuleå University of Technology, SwedenA conceptual study on the prediction of destress blasting efficiency using geostatistical approachesAs underground mines go deeper, it is of utmost importance to manage increased stresses to minimise occurrences of rockbursts. Rockbursts have several documented devastating economic, social and safety consequences such as fatalities, loss of mine assets or production sections, social uproar, force majeure etc. Among several approaches which can be adopted to manage rockbursts is the practice of destress blasting. It is necessary to evaluate the efficiency of any adopted destress blasting design. This can be done through the measurement of physical parameters such as changes in deformation, local seismic magnitude, stress; fracturing intensity etc. at different locations where destress blasting has been implemented. This entails physical exposure of workers to mining excavations, increasing their exposure to harm when safety fails. This paper presents a conceptual study on geostatistical approaches which can be utilized to estimate unmeasured locations using measured locations, thereby reducing the mining personnel's exposure to harm. | Deep mining, Rockburst, Destress blasting, Geostatistics, Semi-variogram modelling, Cross-validation
T04: Deep mining and tunnellingTobias BACKERS, Simon KATTENBECK, Mandy DUDARuhr-University Bochum, GermanyThe Brown-Hoek stress-depth relation revisitedIn 1978 Brown and Hoek published their well-known paper on the relationship between measured in-situ stress and depth. The key figure of this paper can be found in many textbooks related to rock mechanics and rock engineering and the given relationships are used frequently. In this paper we use the World Stress Map data to check if the more than 40 years old interpretation of the limited dataset at that time is still valid. The presented analyses clearly shows that the general trends are, but that some details need to be tuned in future. In an ongoing initiative more measured stress data is included into the analysis. | in-situ stress, horizontal stress, depth-related, stress gradients
T04: Deep mining and tunnellingYousef GOLABCHI, Matthew A. PERRASYork University, CanadaComparison of regression and classification Machine Learning algorithms for determining excavation damage zones depthsDuring the construction of underground excavations, the development of excavation damage zones (EDZs) is a crucial factor in designing permeability-sensitive excavations, such as deep geological repositories for nuclear waste. In this study, regression and classification machine learning (ML) models were employed. Specifically, k-nearest neighbors (KNN) and multi-layer perceptron (MLP) were used for both models. The aim of the regression ML models was to predict the depth of damage based on the maximum tangential stress around the opening and the crack initiation (CI) threshold. In contrast, the classification ML models aimed to determine different EDZ zones using the same features. After comparing the ML models with each other and with the traditional regression approach, it was concluded that MLP outperforms KNN for both models. Moreover, MLP exhibits consistency with the traditional regression lines. Thus, MLP can be effectively utilized for regression in higher-dimension modeling with a greater number of features. | Excavation Damage Zones, Machine Learning, Regression, Classification, K-Nearest Neighbor, Multi-Layer Perceptron
T04: Deep mining and tunnellingPengxuan JI (1), Qianbing ZHANG (1), Gisela VIEGAS (2)1: Monash University, Melbourne, Australia; 2: Newcrest Mining Limited, Melbourne, AustraliaMechanical and fracturing characteristics of defected cement mortar samples under biaxial confinementsIn this study, quasi-static biaxial compression tests are conducted on rock-like cement mortar materials to examine the effect of shape, orientation, and interaction of pre-existing defects representing the rock mass with fissures created by nature or hydrofracturing. The mechanical and fracturing characteristics are investigated by stress-strain response, acoustic emission, digital image correlation and synchrotron X-ray computed tomography techniques. Results show the biaxial compression strength (σ_BCS) increases with confinement and restricts the development of cracks compared to uniaxial tests. In terms of hole samples, the confinement squeezes the tensile stress concentration area at the crown and invert of the hole. The orientation of the flaw impacts the failure characteristics and σ_BCS reaches its lowest value when the inclination angle is 45 degrees. The proposed integrated analysis framework is proven to be feasible for samples with more complicated geometry and the findings would benefit underground civil and resource-related projects. | Biaxial compression, Cement mortar, Pre-existing defect, Fracturing characteristic, Integrated analysis framework, Analytical solution
T04: Deep mining and tunnellingArpan NANDY, K Seshagiri RAO, Tanusree CHAKRABORTYIndian Institute of Technology Delhi, IndiaDevelopment of failure criterion for extensile fracturing of Kannur limestone under triaxial stressesThe classic rock mechanics is limited to evenly fractured rock mass at shallow depths wherein works of Mohr, Coulomb, Hoek and Brown, Drucker-Prager, Wiebols and Cook and more consider isotropic structural effects of joints seen at shallow depths. However, hardly any failure criterion is applicable to massive rocks available at deep depths. At deep tunnels, as one moves from the excavation surface into the rock, the fracture mechanism changes from extensional to shear cracking. The representative Kannur limestone is observed to exhibit exquisite extensile fractures as columnar shards are blown away in a manner much similar to strainburst in deep tunnels. The aim of the paper is to discuss the confinement dependency of limestone when subjected to triaxial stresses. Also, an improvement is suggested to Mogi criterion. This will further help to decide upon the multistep unloading of confining pressure observed during an excavation process in tunnels. | Brittle, triaxial, extensile, principal stress, crack
T04: Deep mining and tunnellingAtsushi SAINOKIKumamoto University, JapanNumerical modelling of induced seismicity considering metre-scale stress heterogeneity in a fault damage zoneIt is of paramount importance to gain a better understanding of induced seismicity taking place in deep underground for sustainable energy developments. Notwithstanding the effort made in the numerical simulation of induced seismicity, there is still a large gap between analysis results and field observations. The present study aims at simulating spatially and temporally distributed fault-slip events whilst considering metre-scale stress heterogeneity. The result indicates that the heterogeneous fault confining stress is crucial in the occurrence of fault-slip. The analysis of b-values computed from multiple seismic events simulated on the fault plane demonstrated that the b-value decreases with the reduction of the effective normal stress, showing consistency with the characteristic of induced seismicity in the field. This implies the possibility of applying the simulation method developed in this study to the risk evaluation for seismic hazards through the b-value analysis based on the advanced fault-slip modelling approach. | Induced-seismicity, stress heterogeneity, b-value, dynamic analysis