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The load variation during three-point bending (TPB) tests on prismatic Nestos (Greece) marble specimens instrumented by piezoelectric sensors is predicted using acoustic emission (AE) signals. The slope of the cumulative amplitude vs the predicted load curve is potentially useful for determining the forthcoming specimen failure as well as the indirect tensile strength of the material. The optimum artificial neural networks (ANN) model was selected based on a comparison of different machine learning techniques with respect to the root mean square error (RMSE) and the coefficient of determination (CoD). The top three best-performing techniques were decision trees, random forests and artificial neural networks. Results show that decision trees and random forests have a coefficient of determination of 98.8% and 99.2%, respectively. The artificial neural network has an accuracy of 99.6% with a root mean square error of 0.022. The comparison of results with experimental data shows that ANNs can potentially be utilized to predict rock behavior and/or establish a failure index.

During the past 15 years, roof fall rates have fallen dramatically in US coal mines, particularly in regions where the roof is weakest. The remarkable reduction in the number of roof falls has been accomplished with more effective roof support systems. The purpose of this paper is to present a design methodology that builds on and quantifies the basic roof support concepts that have been successful in the USA. The methodology starts by defining three modes of roof support, based on the roof strength relative to the stress level: (1) suspension, where roof bolts mainly provide skin control for strong roof; (2) beam building, where moderate strength roof can be supported by roof bolts alone; and (3) supplemental support for weak roof. Next, a large database of roof fall histories at a number of mines is used to define the approximate boundaries of these three regimes based on the coal mine roof rating and the depth of cover. Finally, guidelines are presented for site-specific design of support systems within each regime. The new computer package, analysis of mine roof support (AMRS), implements the design methodology.

During the last few decades, the mining industry has increasingly turned to autonomous systems in its efforts to modernize and advance mining methods and techniques. Vehicle automation in such complex working environments can play a critical role in improving worker safety and mine productivity. Moreover, as the global demand for minerals continues to increase, such technologies will enable access to deeper and more difficult to mine orebodies. The research reported in this article seeks to demonstrate the feasibility of autonomous batch haulage vehicles in the underground coal mining production cycle. By introducing autonomous shuttle cars, the operator can be removed from dusty, noisy, and potentially dangerous conditions and be placed in a relatively safe location, while supervising the machine rather than operating it. This article presents an overview of the approach taken, a description of a lab-scale model and mock mine environment, and preliminary results for autonomous navigation of the prototype shuttle car.

The pillar stability factor (PSF) is calculated in three different mining stages for a sublevel open stoping mining project located in northern Botswana. Several three-dimensional finite element models were developed by varying the stope span. Pillar strength was estimated using the Lunder and Pakalnis equation and pillar stress was obtained from the numerical models. As mining progresses, both the first and second mining stages meet the rib pillar stability factor requirement for safe extraction. Geometrical improvements are suggested in the mining layout for the third mining stage to achieve the required PSF, which is based on international practices.

Rare earth elements (REEs) are considered critical minerals for industrial and defense sectors. REEs are not as rare as the word “rare” portrays; yet, the exploitable and/or profitable deposits of REEs may be found only in certain geographical areas. The political and social conditions characterizing these areas may not always be in favor of mining operations. These conditions are imposing the need for extra consideration on the geopolitical constraints prior to any decision-making and before any mining project begins. This study assesses the risk related to mining projects for areas that feature REE deposits based on a geopolitical viewpoint. Probable ranking differences between the current assessment and a 2015 assessment are discussed. The comparative indicators used and the appraisal procedure applied in this comparison are based on a number of different geopolitical indicators. Several ranking changes occurred between 2015 and 2019.

Summarization: Two series of uniaxial and triaxial compression tests including unloading-reloading cycles were performed under different confining pressures, in order to study the stress-strain and the deformation behavior of a pozzolanic lime mortar subjected to cyclic loading. Each test included a cyclic loading sequence using five loops in the pre-peak region. The experimental results showed that the specimens exhibit a strain-softening behavior for uniaxial and low pressure triaxial tests and a strain-hardening behavior for higher triaxial compression tests. The mortar specimens subjected to triaxial compressive cyclic loading at higher confining pressures failed along a single or conjugate shear planes accompanied by considerable lateral expansion. The marked Young’s modulus degradation behavior in the prepeak region is related to damage that occurs in each specimen. Παρουσιάστηκε στο: Frattura ed Integrità Strutturale

Highlights • Granting of the Social License to Operate (SLO) is extremely important at the prefeasibility or bankable feasibility phase of a mining or a coal mining project. Feasibility studies typically focus on technical aspects of a mining project • Loss of the SLO can result in disruptions of the Value Chain business model. • A Mining Operational Risk Management Model (MORMM) was developed to incorporate risk probabilities and risk severities evaluated by experts. • Hazard categories, hazards and hazard indicators are identified and evaluated for a hypothetical coal mining project., The Social License to Operate (SLO) and the Value Chain business model are basic elements that need to be considered both at the planning and operation stages of mining operations and in particular in coal mining projects. If a coal mining enterprise loses its SLO, it may face risks in operations, which may lead to value chain risks. One of the causes of enterprise failure as related to coal mining operations is the inability to reliably assess/manage risk holistically and the inability to understand that lack of SLO is a critical risk. Although financial risks are typically assessed for mining projects, lack of SLO risk should also be taken into account starting as early as the bankable feasibility study. Furthermore, as it is difficult to establish a proactive decision-making policy for SLO risk in coal mining operations, the Operational Risk Management (ORM) methodology is probably a good tool to apply towards that goal. For this reason, a Mining Operational Risk Management Model (MORMM) was developed to incorporate risk probabilities and risk severities evaluated by experts. The final risk assessment is coded using Risk Assessment Codes (RACs). A hypothetical scenario was developed utilizing the MORMM model in order to illustrate how risks can be managed during the SLO granting process. This scenario describes a hypothetical coal mining project evaluated by virtual risk evaluators under specific hazard categories. Risk evaluation involves the assessment of risk probability and risk severity. Through this scenario this paper presents ways: (i) to establish a baseline ORM process that will be applicable to any coal mining operation environment, and (ii) to provide a theoretical example to demonstrate how the method can be applied to coal mining operations. The resulting RACs can provide critical information to decision makers regarding the rejection, acceptance or re-engineering of the mining business plan.

“Web ground control” (webGC) provides users with instantaneous access to mine design applications anywhere, at any time, through a web browser. Utilizing a web-based multiple-tier architecture, users are able to easily access ground control designs, perform on-demand calculations in the field, as well as facilitate project collaborations across multiple users, devices, and operating systems. Currently, the webGC platform contains five ground control related design applications previously developed and distributed by the US National Institute of Occupational Safety and Health (NIOSH), that is, analysis of roof bolt stability (ARBS), analysis of longwall pillar stability (ALPS), analysis of retreat mining stability (ARMPS), analysis of retreat mining stability–highwall mining (ARMPS-HWM), and analysis of horizontal stress in mining (AHSM). With respect to design decisions made by the webGC development team, the webGC platform will be able to further integrate future mine design applications providing the mining industry with one of a kind umbrella suite of ground control related software available at ones fingertips. The following paper provides a detailed overview on the current state of the webGC platform with discussions ranging from back-end database development and design to the front-end user-platform interface. Based on current progress in platform development as well as beta testing results, the webGC platform is scheduled for release in the fall of 2018. Keywords: Ground control, Stability, Web application, Cloud computing

Two series of uniaxial and triaxial compression tests using unloading-reloading cycles (cyclic loading) were performed under different confining pressures, in order to study the stress-strain and the deformation behavior of pozzolanic lime mortar subjected to cyclic loading. A cyclic loading scheme with five loops in the pre-peak region was performed for each test. The experimental results showed that the ratio of plastic strain to total strain is very large in the case of the triaxial compression tests. The marked Young’s modulus degradation behavior in the pre-peak region is related to damage that occurs in each specimen. Future work will aim to experimentally investigate the post-peak region behavior of the material.

Summarization: This work aims to identify geotechnical characteristics at selected sites in Crete, Greece where strong ground motion stations of the Hellenic Accelerometric Network are installed. Particular emphasis was given in the determination of shear wave velocity profiles, so that the geotechnical classification of the sites in relation to their seismic response can be defined. The shear wave velocity was estimated using the multichannel analysis of surface waves (MASW) method along survey lines close to boreholes, drilled for site investigation purposes. In order to verify the reliability of MASW results, published relationships between shear wave velocity and standard penetration test values were considered. In addition, shear wave velocity measurements were conducted through laboratory tests using bender elements on undisturbed soil samples obtained during drilling. Results indicate that a combination of techniques for shear wave estimation may minimise the effects of uncertainties involved in application and assumptions of the MASW method. Παρουσιάστηκε στο: International Journal of Geotechnical Engineering

This paper focuses on the experimental investigation of the mechanical properties of the Alfas natural building stone. Two series of uniaxial compression tests and indirect tensile tests (Brazilian tests) were performed in order to determine the uniaxial compressive strength and the indirect tensile strength respectively. Different sets of cylindrical specimens and circular discs were prepared by varying their geometry in order to examine the size effect on the respective strength values. Also, the size effect was investigated with respect to the calculated intact rock modulus and Poisson’s ratio. All specimens were prepared by following the ISRM suggested methods and the load was applied using a stiff 1600 kN MTS hydraulic testing machine and a 500 kN load cell. Strain was measured using biaxial 0/90 stacked rosettes appropriately attached on each specimen.

The last few decades, the mining industry has turned to autonomous systems in its efforts to modernize and advance its methods and techniques. Automation in such complex working environments can play a critical role in improving worker safety and mine productivity. Moreover, as the global demand for minerals continues to increase, such technologies will enable access to deeper and more difficult orebodies. The research in this paper seeks to demonstrate the feasibility of autonomous machinery in the underground coal mining production cycle. By introducing autonomous shuttle cars, the operator can be removed from dusty, noisy, and potentially dangerous conditions and be placed in a relatively safe location while supervising the machine instead of operating it. This paper presents preliminary results for autonomous navigation of shuttle cars in the underground coal mining cycle. A lab scale prototype equipped with several exteroceptive and proprioceptive sensors has been developed and is being tested in a mock mine plan, simulating several navigation scenarios within a room and pillar section.

This paper discusses the potential of using advanced satellite remote sensing techniques such as radar interferometry for millimeter-accuracy structural health monitoring over abandoned mines. Images covering the broader Springfield, IL, USA area were used to determine the potential of radar interferometry products from several satellite missions (e.g., Sentinel-1) by employing diverse processing techniques. The methodology and results for permanent scatterer interferometric synthetic aperture radar (PS-InSAR) solutions is presented in detail. The vertical movements calculated using PS-InSAR are validated using high precision in-situ surveying measurements. The practical limitations and considerations for utilizing PS-InSAR as an accurate and cost-effective operational procedure for the subsidence insurance industry are presented.

The occurrence of rockfall incidents on the transportation network may cause injuries, and even casualties, as well as severe damage to infrastructure such as dwellings, railways, road corridors, etc. Passive protective measures (i.e., rockfall barriers, wire nets, etc.) are mainly deployed by operators of ground transport networks to minimize the impact of detrimental effects on these networks. In conjunction with these passive measures, active rockfall monitoring should ideally include the magnitude of each rockfall, its initial and final position, and the triggering mechanism that might have caused its detachment from the slope. In this work, the operational principle of a low-cost rockfall monitoring and alerting system is being presented. The system integrates measurements from a multi-channel seismograph and commercial cameras as the primary equipment for event detection. A series of algorithms analyze these measurements independently in order to reduce alarms originated by surrounding noise and sources other than rockfall events. The detection methodology employs two different sets of algorithms: Time–frequency analyses of the rockfall event’s seismic signature are performed using moving window pattern recognition algorithms, whereas image processing techniques are utilized to deliver object detection and localization. Training and validation of the proposed approach was performed through field tests that involved manually induced rockfall events and recording of sources (i.e., passing car, walking people) that may cause a false alarm. These validation tests revealed that the seismic monitoring algorithms produce a 4.17 % false alarm rate with an accuracy of 93 %. Finally, the results of a 34-day operational monitoring period are presented and the ability of the imaging system to identify and exclude false alarms is discussed. The entire processing cycle is 10–15 s. Thus, it can be considered as a near real-time system for early warning of rockfall events.

Development of failure in brittle materials is associated with microcracks, which release energy in the form of elastic waves called acoustic emissions. This paper presents results from acoustic emission measurements obtained during three point bending tests on Nestos marble under laboratory conditions. Acoustic emission activity was monitored using piezoelectric acoustic emission sensors, and the potential for accurate prediction of rock damage based on acoustic emission data was investigated. Damage localization was determined based on acoustic emissions generated from the critically stressed region as scattered events at stresses below and close to the strength of the material. Keywords: Acoustic emissions, Three point bending test, Indirect tensile strength, Crack localization, Nestos marble

Energy resources are distributed in space. Models of spatial variability thus greatly contribute to the optimal exploitation of such resources. This paper concentrates on modeling the spatial distribution of energy content based on geostatistical interpolation and simulation methods. We focus on lignite, a fossil fuel which plays a key role in the energy budget in several parts of the world. Nonetheless, geostatistical tools are also relevant for the analysis of renewable and other fossil-based energy resources. Quantitative understanding of the spatial variability of lignite energy reserves helps to optimize mine exploitation and to reduce fluctuations in the quality of the fuel supplied to power plants. We also introduce the spatial profitability index as an analytical tool for the design and medium-term exploitation of multiseam mines. Based on this index we propose an empirical equation which allows fast and practical estimation of changes in energy reserves due to variations in expected costs or revenues. We illustrate the proposed modeling framework using lignite data from the Mavropigi mine in Northern Greece.

Perfluoromethylcyclohexane (PMCH) is a member of the perfluorocarbon tracer (PFT) group of compounds. PMCH has been widely used in various tracer gas studies to characterize ventilation systems, atmospheric transport patterns, and pollution distribution schemes. PMCH exists as a volatile liquid at room temperature and pressure, a characteristic that prevents PMCH from being deployed using traditional means. This paper presents a design for a permeation plug release vessel (PPRV) for PMCH. The PPRV is designed to passively deploy PMCH vapor at constant rate as a function of temperature and plug thickness for quantitative tracer gas studies. Details regarding the development process and the release rate analysis are included.

A common result of Environmental Impact Assessments associated with mining projects is the construction of new wetlands in areas disturbed by mining operations. Where appropriate, this mitigation may be considered an integral part of the mine reclamation process under the principles of sustainable development in the minerals industry. Wetbud is a new tool for estimating wetland water budgets using available weather data and site-specific topographic, soil and geohydrologic data, coupled with mass balance mathematics. Wetbud is primarily intended as a planning tool for use in the design of created wetlands, but it can also be applied to native wetlands or wetland restoration sites where the required input parameters can be specified. Wetbud can be run in its basic form where wetland topography, soil parameters and groundwater flux are simplified, or in the advanced form, where these parameters are included in a more complex approach via integration of the MODFLOW package, a free 3D program that was developed by the United States Geological Survey. Both versions can also include overbank flow hydrology sources and the advanced form can also model sloping and irregular topography. The program downloads weather data from the nearest applicable station and selects appropriate wet-normal-dry (W-N-D) years following a modest user data clean-up step. Wetbud also has the ability to utilize existing short-term (e.g. 6 to 9 months) groundwater data from an up-gradient well to simulate longer-term groundwater level inputs for the selected W-N-D years. In addition, Wetbud features a “Wizard” version that comes pre-loaded with 14 pre-selected weather data sets for all areas of Virginia that can develop a simple monthly water budget in less than 15 minutes – a feature that could be expanded anywhere geographically with historic weather data.

This paper presents a data management application driven by real-time events, which has been developed as a productivity and maintenance planning software application to be used in the surface lignite mines in Northern Greece. The mines operate using a continuous mining system comprised of multiple bucket wheel excavators, belt conveyors, spreaders and stackers. There is a control centre for each mine, comprising of aspect servers, OPC servers and a SCADA system which interfaces with PLCs at each equipment unit in the field. The overall data management infrastructure is installed on the main network system and draws data from the OPC servers at each mine. In order to collect the data, the application is developed using event driven functionality as well as data polls. Data can then be modified by the control tower personnel. The application generates reports on a daily basis for production monitoring, productivity, equipment performance and utilisation as well as various maintenance tasks. The system has been in operation at the surface lignite mines in northern Greece since 2011 and has been embraced by mine personnel for decision making and planning.

A cloud-based near real-time data management system for geotechnical monitoring that can efficiently record, transfer, store, manage, process, analyse and evaluate monitoring data and generate easy to view and use information is presented. The database structure and manual of the system functionalities for addressing issues during data upload and processing, record handling for multisensory devices, data visualisation using common reference dates, data error correction and parametric handling of import files are presented in detail. New features that are in development include a more robust warning system and a journaling system for visual observations. The system can reliably and quickly generate alarms and information about excessive movements with respect to mining and other operations that require monitoring.

More than 350 Mm 3 of materials are excavated annually from the mines of the Ptolemais basin which produce about 50 Mt of lignite. This lignite is subsequently supplied to Thermal Power Plants located in the vicinity of the mines. Mining activities currently occupy a total of 16,000 ha. Unless appropriate preventive and mitigation measures are applied, environmental conditions will deteriorate in numerous ways due to the scale of the operations and the applied surface mining method. From calendar year 2002, it is required that the Ptolemais mining complex complies with environmental permits set by Ministerial Decisions signed in common by the Ministers of Environment, Development, Culture and Agriculture. For the core mining activity, which consists of four pits with an annual lignite production of more than 35 Mt, the permits were signed eight years after the submission of the relevant Environmental Impact Assessment study. During this long period of negotiations, the mine operator was called many times to submit supplementary information that was deemed necessary in order to agree to the terms and conditions that were finally included in the permit. This paper presents the main terms and conditions of these permits, which provide a framework for developing and implementing an integrated environmental management system. This system comprises several preventive and mitigation measures related to waste management and monitoring of environmental quality, which are applicable from the early stages of mine operation. The implementation of this system is completed after the mine closure with a series of site-specific land rehabilitation and post-mining monitoring activities. Based on the experience gained so far from the implementation of the terms and conditions prescribed in the permits, this paper also presents some critical aspects regarding the benefits of this process, the regular implementation of auditing procedures and the effective settlement of conflicts between mining companies, supervising authorities and other stakeholders. Additional

Summarization: The application of seismic reflection and electrical resistivity methods (2D and 3D) in geotechnical investigations is explored through a case study in Northern Greece. These methods were employed to Mavropigi lignite open pit mine and the surveyed area is the next step in mining expansion. The main aim of the geophysical survey was to map the bedrock, the contact between the Neogene and Schist/Carbonate formations as well as to estimate the thickness of the carbonate rocks on top of the Schist formations in order to study the stability of the final mine slopes. These geophysical data provides a geotechnical model which will be used in mine planning from Greek Public Power Corporation. Παρουσιάστηκε στο: 11th Congress of the Balkan Geophysical Society

Summarization: A two-dimensional numerical investigation concerning the effects of the interfacial transition zone (ITZ) on the mechanical behavior of concrete is presented in this paper. The ITZ lies between the cement paste and the aggregates. Considering elastic two-dimensional models of the cement paste, the aggregate material and the ITZ, which is modeled as a thin band around each grain of aggregate, the response of the composite material was calculated using the finite element method. A parametric analysis was conducted for different model geometries as well as varying model parameters for the dilute limit, i.e. when the aggregate volume fraction is very small. Results indicate that the maximum tensile stresses which could lead to the development of microcracks, as well as larger displacements, tend to develop mainly in the ITZ. The distribution of stresses and displacements along appropriate sections of these models are also presented. Presented on: Cement and Concrete Research

Summarization: The Alfas porous stone (porolithos) excavated in Rethimnon, Crete, Greece, often features two material bands with similar mineralogical but different depositional characteristics and therefore different mechanical parameters. The present study compares the experimental and numerical results for uniaxial compressive tests of the banded Alfas porous stone. Cylindrical specimens with a diameter of 54 mm were prepared and tested in the laboratory. Testing revealed complex failure modes/patterns under uniaxial compressive loading. Experimental tests were simulated numerically using the bonded particle model (BPM) available in the PFC2D code. The PFC2D microparameters of the BPM were indirectly determined, and the experimental fracture load and the failure pattern are compared with the numerical results. The simulation results demonstrate that both the macromechanical response and the failure process can be modeled using BPMs. The strong influence of the weaker band on the mechanical behavior and failure mode of the Alfas porous stone is confirmed. The differences between the numerical results and the macroscopic behavior are discussed. Παρουσιάστηκε στο: Material Design & Processing Communications

Summarization: Marble beams were subjected to gradually increasing three-point bending from low loading levels up to levels that significant damage was observed. After each loading step the permittivity was measured at three characteristic locations: the tensional, middle and compressional zone of each sample. The permittivity measurements were conducted in the frequency range from 1kHz to 1MHz. The permittivity values were compared for the three locations at the frequency of 10kHz. The experimental results indicate that the permittivity values decrease after each loading at the three selected locations. More specifically, the permittivity variation is more intense at the tensional zone (due to intense cracking processes) than the compressional zone, while the middle zone exhibits the lowest variation in permittivity. Thus, the damage magnitude of each sample can be estimated by permittivity measurements before the fracture of the sample. Presented on

Summarization: This paper focuses on the experimental and numerical investigation of the size effect and the fracture process on the uniaxial compression strength (UCS) of the banded Alfas porous stone. This natural building material excavated in Rethimnon, Crete, Greece often features two material bands with similar mineralogical properties, but different depositional characteristics and therefore different mechanical parameters. The experimental tests were simulated numerically using the Bonded Particle Model (BPM) available in the PFC2D code. The noticeable unusual increase of UCS with increasing specimen diameter as well as the strong influence of the weaker band on the mechanical behavior of the banded Alfas porous stone are confirmed by the numerical results. Future work will focus on the direct measurement of the weak/strong material band properties and will investigate the effect of the loading rate and boundary conditions on the mechanical response of the BPMs. Παρουσιάστηκε στο: 1st Mediterranean Conference on Fracture and Structural Integrity