Abstract The Telfer underground sub-level cave (SLC) operations are located approximately 600 to 1000 m below the west wall of Main Dome open pit at the Telfer Gold Mine, Australia. The Telfer SLC commenced caving in 2006 and broke through to the surface in 2009 forming a large subsidence zone that has progressively developed above the SLC operation. Surface deformations within the subsidence zone continue at a rate of 500 mm to 2000 mm per month and are dependent to the rate of underground mining in the SLC operation. Underground and open pit operations have continued concurrently with the progressive enlargement of the SLC subsidence zone. The stage 4 open pit orebody was solely accessible via the West Ramp, which is located adjacent to the SLC subsidence zone with notable steady state ductile deformation occurring on ramp. Risks were managed by understanding the cave propagation mechanism through modelling and monitoring, and the use of comprehensive TARPs (trigger-action-response-plans) and an array of real-time surface and sub-surface deformation monitoring instruments. This paper discusses the monitoring systems used to track the cave subsidence and monitor ground deformation. These include slope stability radar, automatic total stations with survey prisms, shape-accel arrays, time-domain reflectometers, seismicity monitoring arrays, networked SMART markers, surface extensometers, automated crackmeters and monthly aerial surveys. These monitoring systems were used to determine the cave subsidence zone shape, location, rate of propagation and the direct response in the slopes adjacent to the West Ramp. The monitoring systems and TARPs are critical for identifying approaching hazards and taking proactive risk mitigation measures. 1. Introduction Underground sub-level cave (SLC) operations commenced in 2006 and caving began to propagate towards the surface from approximately 800 m below the pit [1]. In preparation for the SLC operation, a large bench was established in preparation for the initial cave breakthrough area (i.e. ‘Breakthrough Bench’ or predicted subsidence crater extents) as illustrated in Figure 1a. In order to reduce the likelihood of future high wall instability above the subsidence crater, the Breakthrough Bench was backfilled with 1.1Mt of rock fill (Figures 1b & 1c). The life of concurrent open pit and SLC operations was anticipated to be a further five years.

Abstract Processing and interpretation of huge array of mine seismicity data obtained in mines of Norilsk Nickel Mining and Metallurgical Company has revealed the "pulsating" mode of seismic energy release on the background of an increase in the strata pressure and, based on the information on monthly migration of reduced centers of seismic energy release within the mine fields, enabled development of a rockburst hazard criterion for individual rock mass areas. The prognostic criterion of the limiting state of a rock mass area is developed based on the ratio of kinematic characteristics of seismic events, which are the velocity of a reduced center of seismic energy release and the apparent velocity of "migration" of individual seismic events closely timed within the ranges of stress concentration zones inside the mine fields. Verification of this criterion using an ample seismic data base accumulated for a number of years in a mine of Norilsk Nickel has displayed high sensitivity of the criterion towards the change in the stress state of rock mass areas under monitoring. 1. Introduction Currently the largest mines in Russia (in the regions of Norilsk, Tashtagol, Apatity, etc.) run multi-channel control of seismic activity. The acquired data on concentrations of sources of seismic events and on dynamics of their energy are highly essential when selecting mining flow charts or choosing precautions to destress rock mass areas where stress concentration is increased [1, 2] This is specifically important for such a giant of Russia's mining industry as Norilsk Mining and Metallurgical Company situated in the Polar Region. The company's mines develop deposits of Norilsk and Talnakh; the layout of one of such mines - Oktyabrsky Mine - is shown in Fig. 1 [3]. 2. Seismic monitoring in Oktyabrsky Mine Since 1993 seismic monitoring in Oktyabrsky Mine is accomplished by the Center of Automatic Geodynamic Safety Control based on the Norilsk Seismic Station. Oktyabrsky Mine field accommodates 9 underground seismicity monitoring points.

Abstract In the Mediterranean area, cliff slopes represent widespread high-risk landforms as they are highly frequented touristic places often interested by landslide processes. Malta represents a significant case study as several cliffs located all around the island are involved in instability processes, as evidenced by wide block-size talus distributed all along the coast line. These diffused instabilities are related to the predisponding geological setting of Malta Island, i.e. the over-position of grained limestone on plastic clay deposits, that induces lateral spreading phenomena associated to falls and topples of different-size rock blocks and is responsible for a typical landscape with stable plateau of stiff rocks bordered by unstable cliff slopes. The ruins of Għajn Ħadid Tower, the first of the thirteen watchtowers built in 1658 by the Gran Master Martin de Redin, stand out in the Selmun area. Currently the safety of this important heritage site, already damaged by an earthquake on October 12 th 1856, is threaten by a progressive moving of the landslide process towards the stable plateau area. During autumn 2015, a field-campaign was realized to characterize the jointed rock mass. A detailed engineering-geological survey was carried out to reconstruct the geological setting and to define the mechanical properties of the rock mass. Based on the surveyed joint spatial distribution, 58 single-station noise measurements were deployed to cover both the unstable zone and the stable area. The obtained 1-hour records were analyzed in the frequency domain for associating vibrational evidences to different instability levels, i.e. deriving the presence of already isolated blocks by the local seismic response. The here presented results can be a useful contribute to begin to asses defense strategies for the Selmun Promontory, in the frame of managing the landslide risk in the study area and preserving the local historical heritage. 1. Introduction Cliff slopes are high-risk landforms in the Mediterranean area due to the diffused landslide processes that affect sites of touristic relevance as well as buildings which are part of the cultural heritage. Malta Island represents a significant case study as its geological setting, i.e. the over-position of grained limestone on plastic clay deposits, predisposes large lateral spreading processes associated to falls, slides and/or topples of different-size rock blocks. These instabilities interest countryside areas, e.g. the rock slabs where the city of Mdina and Citadel are built [1], as well as sea cliffs all along the coast line, especially in the north-west part of Malta and in Gozo island.

Abstract A first attempt of using the Room and Pillar mining method in the Czech Republic was implemented in the southern part of the Upper Silesian Coal Basin. This stratigraphical unit is well known for its complex geological structure with more than 40 main coal seams vertically distributed in the area of about 122 km 2 of active mines and a complex slide/overlap fault system. The fact that the extraction of coal by this method is realised at a depth around 900 m below the surface has also made it one of the deepest Room and Pillar mining sites in the world. These facts brought lead to several questions. The main question connected to sustaining the safety of the workers before and after the advance of the mining works has resulted in this study of the prediction of unnatural seismological activity based on data that were collected during and after the excavation of the coal seam. Also, we ask whether the methods can be used for the prediction of inhomogeneous stress distributions in this kind of openings. Seismological monitoring, which is the main goal of this paper, was supplemented by stress and deformation measurements in coal pillars and surrounding rocks. More stations were added to the network of seismic stations of the coal mine at different levels surrounding the Room and Pillar site. We give the first results of the evaluation of seismic activity during the driving of the roadway in the first mining panel. We describe the site and mining conditions, details about seismological network, and a comparison of seismic activity with the gate driving advance and creation of coal pillars. This is compared to stress changes in the coal pillars. 1. Introduction Coal mining is still one of the most dangerous branches of all working environments. One of the most useful ways to observe or predict potential rock/coal burst hazardous areas within the rock mass in which mining operations are situated is to monitor the seismological activity in the demarcated area [1]. It is essential to identify the part of the rock mass where there is a higher number of high-energy tremors, or the part with a specific local accumulation of low- and high-energy seismic events [2]. In the Czech part of the Upper Silesian Coal Basin (USCB), a new way of extracting hard coal, the Room and pillar method (R&P), was presented and designed to be put into action for first testing. The R&P mining method as presented was used for the first time in a 200-year history of extracting hard coal in the region of the southern part of the USCB. For the time being the selected mining site, with a depth of around 900 m below the surface in which the extractions are made, makes this the deepest Room and Pillar mining site in the world.

Abstract In the last few years, several approaches and methods have been proposed to improve early warning systems for managing risks due to rapid slope failures where important infrastructures are the main exposed elements. To this aim, a multi-sensor monitoring system has been installed in an abandoned quarry at Acuto (central Italy) to realise a natural-scale test site for detecting rock-falls from a cliff slope. The installed multi-sensor monitoring system consists of: two weather stations; optical cam (Smart Camera) connected to an Artificial Intelligence (AI) system; stress- strain geotechnical system; seismic monitoring device and nano-seismic array for detecting microseismic events on the cliff slope. The main objective of the experiment at this test site is to investigate precursors of rock mass failures by coupling remote and local sensors. The integrated monitoring system is devoted to record strain rates of rock mass joints, capturing their variations as an effect of forcing actions, which are the temperature, the rainfalls and the wind velocity and direction. The preliminary tests demonstrate that the data analysis methods allowed the identification of external destabilizing actions responsible for strain effects on rock joints. More in particular, it was observed that the temperature variations play a significant role for detectable strains of rock mass joints. The preliminary results obtained so far encourage further experiments. 1. Introduction In the last few years, more attention has been focused on the monitoring of fast to very fast failures, which include landslides from rocky slopes, e.g. rock falls, topples and wedge sliding. The relevance of such events is mainly related to the short time available for taking action in the case of exposed infrastructures (i.e. highways and railways) as no significant displacements are generally detected before failure. To create a comprehensive detection strategy, a coupled monitoring system can be adopted: monitoring precursors by using micro- or nano-seismometric devices as well as acoustic emissions [1–3] and monitoring the rock fall source areas as well as the threatened infrastructures, by using optical devices able to detect fast to very fast changes of the observed scenario or the presence of anomalous objects that can clutter the infrastructure [4–9].

Abstract The practical algorithm for determination of burst hazard zones using data from an automated system of mining pressure control is suggested. A procedure of an emergence prognosis is designed using the index of burst hazard, KUD, that characterizes the geo-mechanical state of rock stratum. A computer experiment is presented which illustrates the possibility of a suggested prognosis procedure. 1. Introduction The field development and underground mining works at difficult geological conditions and at great depths requires the effective methods and tools of prognosis and prevention of the manifestations of rock pressure, the most dangerous form of which are rock and rock-tectonic bursts. To predict the dangerous manifestations of rock pressure, multi-channel automated geo-mechanical monitoring systems are widely used in the global mining practice. In Russia, the geo-acoustic measuring complex "Prognoz ADS" is installed on a number of burst hazard fields [1, 2]. It operates to measure and process the parameters of the geo-acoustic activity, which reflects changes in processes of deformation and redistribution of stresses in the rock massif under the influence of mining. To identify the potentially bump hazardous areas in rock massif where the sites of destructive geodynamic phenomena are formed, we used / applied the cluster analysis methods. Algorithm of determination of potentially hazardous areas is based on graph theory. It uses a representation of observations in the form of a graph, whose nodes are the point sources of sound. We introduce edges in the graph, if the "distances" between two points are smaller than some critical value. The graph connectivity components characterize the attribution of micro seismo-acoustic events to clusters. The initial data for the clusters construction is an array of coordinates of the point sources of sound. Thus, these data allow us to create a film that shows the dynamics of the development of hazard zones. To implement this algorithm, the software was developed which traces the formation of the sites of destructive geodynamic events in rock massif according to seismo-acoustic monitoring. The software analyzes the information after a certain interval of time and identifies potentially dangerous areas. Graphical output of software is represented interactively as 3D images. The size and displacement of the zones found can be assessed. The proposed algorithm and software in conjunction with the automated system of geo-mechanical monitoring were tested in the mining industry in the Far Eastern Russia and has shown to be effective for the identification of potentially hazardous areas in the mountain range. A preliminary version of the algorithm is presented in [3].

Abstract Understanding changes in slope geometry and knowledge of underlying engineering properties of the rock mass are essential for the safe design of man-made slopes and to reduce the significant risks associated with slope failure. Recent advances in the geomatics industry have provided the capability to obtain accurate, fully geo-referenced three-dimensional datasets that can be subsequently interrogated to provide engineering-based solutions for monitoring of deformation processes, rock mass characterization and additional insight into any underlying failure mechanisms. Importantly, data can also be used to spatially locate and map geological features and provide displacement or deformation rate information relating to movement of critical sections or regions of a slope. This paper explores the benefits that can be obtained by incorporating different remote sensing techniques and conventional measurement devices to provide a comprehensive database required for development of an effective slope monitoring and risk management program. The integration of different techniques, such as high accuracy discrete point measurement at critical locations, which can be used to complement larger scale less dense three-dimensional survey will be explored. Case studies using a combination of aerial and terrestrial laser scanning, unmanned aerial vehicle and hand-held scanning devices will demonstrate their ability to provide spatial data for informing decision making processes and ensuring compliance with Regulations. 1. Introduction In recent years, there has been considerable advancements in the geospatial industry, with focus placed on capturing the real world in an unprecedented amount of detail. This increased focus on capturing large datasets has exposed engineers in the mining and minerals industry to data that would have been previously unimaginable. Different remote sensing technologies are now available, each having specific benefits for engineering geology-based applications: such as rock mass characterization, spatial analyses and monitoring of deformation processes. Nevertheless, despite the potential advantages of each remote sensing technique, there are associated limitations that should be considered depending on the nature of the problem one is dealing with. This could lead to the necessity to integrate different techniques to obtain complete and detailed data to be used for different purposes.

Abstract In Germany geothermal energy production plays an important role in the area of renewable energies. The Upper Jurassic (Malm) aquifer beneath the Molasse Basin is predestinated for hydro-geothermal energy. As part of the research program PrognosPermae several laboratory tests were performed on Malm limestones and dolomites. The rock samples were characterized by uniaxial compressive strength (UCS), tensile strength, Young's Modulus, Poisson's ratio, bulk density, porosity and ultrasonic p- and s-wave velocities. Additionally water-permeability was measured in a triaxial cell under varying stress conditions. Ultrasonic wave velocities were investigated on dry and saturated samples, free to leak. The aim of this study is to ascertain a correlation between the lithology of the target horizon, permeability and the ultrasonic wave velocities. Furthermore, the influence of different stress levels on water-permeability of the specimens is investigated. 1. Introduction Planning the exploitation of hydro-geothermal systems requires geophysical parameters from seismic and borehole measurements as well as the quantification of rock (hydro-) geomechanical properties in the laboratory. Many studies have already been performed on carbonate rocks (e.g. [1–6]). Nevertheless since geomechanical properties of carbonates depend strongly on depositional, diagenetic and tectonical processes it is essential to investigate these properties for the present conditions. One of the main hydro-geothermal energy targets is located in the South German Molasse Basin. The aim of the presented research project is to develop a workflow to improve the potentiality diagnosis of the Upper Jurassic (Malm) aquifer. Therefore (hydro-) geomechanical parameters of carbonate samples were examined. For the study borehole and seismic data of the investigation area close to Kirchweidach are available. Three wells, one of them a side-track, were drilled until a target depth of around 3,800 m (TVD). The characteristics of the Malm reservoir in a depth of 3,500 to 3,800 m is qualified by cuttings, thin sections and geological maps. For laboratory tests analog outcrop material with similar properties was chosen. To cover the range of possible rock formations detected in the cuttings limestone and dolomite of the Franconian Alp were selected. This work presents the first results of the experimental laboratory program.

Abstract A real-time monitoring system was established for 10-channel acoustic emission (AE) in hydraulic fracturing in the laboratory, with a hydraulic fracturing test conducted on two different sizes of natural outcrop cores under unconfined pressure and confining pressure respectively. Then, a discussion was carried out on the microscopic response in rock to the formation and growth of hydraulic fracture under confining pressure and unconfined pressure. The study of AE parameters shows that the change of RA (Rise Angle) in hydraulic fracturing process is always opposite to that of AF (Average Frequency). Also, AE parameters have higher dispersion under unconfined pressure. With breakdown pressure as a dividing point, as pumping pressure changes under unconfined pressure, the dominant internal fracture mechanism of rock will turn from tensile failure to shear failure. But under confining pressure, the transformation of the dominance is reversed, namely from shear failure to tensile failure. This phenomenon indicates that despite the same hydraulic fractures in macro scale under both confining pressure and unconfined pressure, there may be a large difference in microstructure between the hydraulic fractures formed under both pressure conditions respectively. 1. Introduction Hydraulic fracturing technology has become the primary means of reservoir stimulation since its first application in North America in 1949 [1]. At present, as the conventional oil and gas resources are increasingly exhausted, and the yield of unconventional oil and gas resources rises gradually, hydraulic fracturing has grown into a more critical factor to artificial production's increase [2]. From the perspective of theoretical research, with the constant development of fracture mechanics and its application to rock engineering, scholars have come to realize that the nonlinear areas have an important influence on the mechanical behavior of a hydraulic fracture before and after its formation, while the occurrence of micro cracks is an important sign of nonlinear rock failure [3].

Abstract Coal seams in the Upper Silesian Coal Basin are currently extracted under more and more disadvantageous geological and mining conditions. Mining depth, geological dislocations and mining remnants are factors which affect the rockburst hazard during underground mining to the greatest extent. This hazard can be minimized by employment of active rockburst prevention, where long-hole destress blasts in roof rocks (torpedo blasts) have an important role. The main goal of these blastings is to either destress local stress concentrations in rock mass and to fracture the thick layers of strong roof rocks to prevent or minimize the impact of high energy tremors on the excavations. Sometimes, these blastings are performed to make the roof rocks caving behind the longwall face easier. The efficiency of blasting is typically evaluated from the seismic effect, which is calculated based on seismic monitoring data (seismic energy) and the weight of the charged explosive. This method, as used previously in the Czech Republic, was adopted in a selected Polish hard coal mine in the Upper Silesian Coal Basin. This method enables rapid and easy estimation of destress blasting effectiveness, adjusted to conditions occurring in the designed colliery. Destress blasts effectiveness may be evaluated via the seismic source parameters analysis as well, as was carried out in the selected colliery in the Polish part of the Upper Silesian Coal Basin. These parameters provide information, for example, on its size, state of stress and occurrence of slip mechanism in the source of provoked tremors. Long-hole destress blasting effectiveness in selected colliery has been evaluated using the seismic effect method and seismic source parameters analysis. The results were compared with each other and conditions were observed in situ. 1. Introduction Rockburst is a dangerous phenomenon occurring during deep underground hard coal mining in the Upper Silesian Coal Basin (USCB). To minimize this hazard, special prevention techniques are applied. One of them are destress blasts in the rocks surrounding the coal seam, especially in roof rocks. The main purpose of such blasts is to reduce stress concentrations in these rocks, and to reach a new advantageous energy equilibrium state by the rock mass due to stress drop. Fracturing the thick layers of strong roof rocks to prevent or minimize the impact of high energy tremors on the excavations is important too. Sometimes blasts are performed to facilitate roof rocks caving and goaf formation. Hanging-up of strong roof rocks behind longwall face may be responsible for high-energy tremors occurrence in close distance from the longwall face, which is dangerous for the working crew.

Abstract The main aim of this study was to determine the variation of the P- wave velocity of carbonate rocks over time. Samples of carbonate rocks like dolomite and limestone were carried out from three quarries. The study was done in May and November 2015. To test equipment Pundit Lab+ was used, which measure the transmission time of ultrasonic wave. On the base on the transmission time P- wave seismic velocities were calculated. It allows to compare the results obtained for one time interval and to calculate, using the Student's t test, if differences of P- wave seismic velocity values are significant. 1. Introduction Determination of the physical and mechanical properties of rocks is the most interesting problem which is still not definitely solved despite of a lot of scientists who try to do it. It seems to be very important to make an assessment of the elastic properties of rocks which can be studied in laboratory using cylinder samples [3–5, 7–9, 13] and also directly in quarries using geophysical methods [10, 14]. The rock under the influence of external forces undergoes compression and decompression. The deformation of the body is the result of moves of its particles relative to each other. Rocks within the rock mass there are under the pressure of the surrounding rocks. Depending on the pressure size, rocks there are in a specified state of compression and a specified state of deformation [1, 2, 6]. At the moment of output from the deposit and remove the existing pressure, annealing process begins and elastic strain decays. The decompression of rock causes the change of properties such as hardness, grindability, porosity and strength. In addition to decompression phenomena, another process takes place like moisture loss. In the process of deposit documentation the tests are done immediately after extraction of the rock from the rock mass but in many cases, these tests are carried out after a certain time when the analysed samples were stored by some time under certain conditions.

Abstract The paper presents a seismic data interpretation approach to reconstruction of stress fields in rocks at any stage of coal mining. The approach involves: thee-axial compression testing of coal in order to find an empirical relation between elastic wave velocity and stresses; coal bed tomography using standard monitoring systems and taking signals generated by dynamic events (with the energy higher than the background level) as the probing signals; formulation and solving of a boundary inverse problem within a geomechanical model of an object under analysis where the input data is the velocity field reconstructed in the illuminated area of coal bed by tomography. The laboratory data of the coal specimens tested by the von Karman scheme have been approximated to plot analytical relationships between P-waves velocity, axial stress and confining pressure. The numerical experiments performed for a typical underground layout at coal producer "Vorkutaugol" have shown that given the accepted array of seismic pickups, the single-valued solution of the inverse problem requires good illumination of coal bed areas with the spatial stress gradient. 1. Introduction Modern seismology has accumulated extensive experience in the field of using seismograms recorded after earthquakes for the location of the hypocenters and focal mechanisms as well as, assisted by 3D tomography, for the reconstruction of spatial distribution of seismic velocities. Combined with the geological data, this allows an insight, in a varying degree of fidelity, into the structure and properties of a lithosphere area under investigation [1, 2]. There are a few causes of uncertainty of this information. The first cause is the scale of a study object which makes lab experimentation aimed at data refinement impossible. Second, the physical properties of rocks are variable with pressure and depth (up to the change of the physical state) [3]. And third, selection of a reference model for the tomography research is performed on a relatively random basis [4, 5]. In mineral mining, linear size of geomechanical objects is as a rule not more than 1–3 km. This abates uncertainty and enables deterministic modeling when analyzing the evolution of physical fields and predicting the rock mass condition in the course of mining [6]. All metal and coal mines hold microseismic monitoring systems [7, 8] recording acoustic emission signals. Each signal is associated with an event of destruction (initiation of a new microcrack or growth of an existing one); for this reason, interpretation of such stochastic information uses:

Abstract A near field network with 11 acoustic emission (AE) sensors was installed for the in situ underground experiment (Nova project 54–14–1) that took place 410 m below surface in the Äspö Hard Rock Laboratory, Sweden. The acquisition system for the piezoelectrical sensors has been improved to record signals with 1 MHz sampling rate, to detect signals produced by weaker sources and enhance the microseismic catalogue. The acquisition system was capable to operate in trigger and continuous mode. The basic idea of the experiment was to compare hydraulic fracturing growth and induced seismicity under controlled conditions for different loading scenarios as conventional versus progressive, and pulse-like water injections. In this work, we consider continuous recordings and apply recently developed automated full waveform detection and location algorithms which are based on the stacking of characteristic functions calculated from squared amplitudes. Waveform stacking and coherence techniques are adapted to detect and locate AE signals for massive datasets with extremely high sampling. We significantly increase the detection rate in comparison to trigger mode routines. Most detection concentrated during the fluid injection occurred around the fracking stages. Frequency-magnitude distribution characteristics are investigated using a relative magnitude scale estimated from the amplitude recorded at AE sensors. We demonstrate that the stacking of characteristic functions yields to a significant improvement of the detection and location also in presence of noisy records, supporting the adoption of similar techniques for other induced and natural seismic activity monitoring systems. 1. Introduction An in situ hydraulic fracturing experiment was performed at Äspö Hard Rock Laboratory (Sweden) aiming at optimizing geothermal heat exchange in crystalline rock mass [1]. A near field network with 11 acoustic emission (AE) sensors was installed 410 m below surface to map the seismic response of hydraulic fractures for different fluid injection scenarios (Figure 1). The location of the experimental tunnel TASN is seen from which four long boreholes were drilled sub-parallel to orientation of minimum horizontal compressive stress. The middle borehole (Figure 1, blue line) serves as hydraulic testing borehole and was drilled to a total length of 28.40 meter, down dipping −4°. The rest of monitoring boreholes were drilled with inclination upwards to allow water outflow from AE sensor chains. This geometry in the predetermined stress state allows propagating hydraulic fractures perpendicular to the hydraulic testing borehole, in the direction of maximum horizontal compressive stress, and in a direction towards the monitoring boreholes.

Abstract More than 450 rockbursts, many of them with fatal consequences, have been monitored in Ostrava-Karvina Coalfield since the start of the last century. Right from the start of their appearance, miners have made efforts to avoid them or at least to reduce their consequences. Many researchers and geomechanical experts have explored the rockburst mechanism, its regularities and natural relations. Nevertheless, there are many things about rock mass properties and rock mass behavior that we do not know yet. Together with gaining valuable knowledge, the development of rockburst protection methods was achieved. The development of prognosis and prevention methods as well as a contemporary system for their application in the coal mines in Ostrava-Karviná Coalfield is described in the contribution. It considers the history of rockburst cognition, reflecting new experience and consequently new opinions on the mechanism of different types of rockburst in the specific geological conditions in the Upper Silesian Coal Basin. Geomechanical methods comprising destress drilling, destress blasting and seams watering as well as geophysical methods of rockburst prediction and prevention are presented. All are supplemented by examples of the application of protection methods in coal mines where there is a risk of rockburst. Opinions on the effectiveness and usability of individual methods of rockburst prevention based on practical experience are stated in conclusion. 1. Introduction Rockburst is a phenomenon which has accompanied coal mining in Ostrava-Karviná Coalfield (OKCF) as well as in Polish mines generally for more than one hundred years. OKCF is the southernmost part of the Upper Silesian Coal Basin (USCB), which is the easternmost part of the Bohemian massif. It is one of the well-known hard coal deposits in Central Europe and it is currently the largest one in Europe. It lies on the border between the Czech Republic and Poland, where only one third of the whole deposit belongs to the former. Coal mining there started in the 18 th century and since then more than 50 coal seams have been mined out. From the last decade of the past century, a major restriction of coal production occurred in OKCF. Reduction of the annual coal production from about 24 million tons to about 10 million tons was caused mainly by the abandoning of the mines in the Ostrava part of the coalfield. Mining openings caused changes of primary stress field distribution. Owing to these changes and with regard to discontinuities of rock massive the stress field is heterogenic. They are the places with great concentration of stress, which can reach limit state of deformation. In this case, sudden release of accumulated deformation energy origin and their transformation in other forms of energy, (changes of potential energy of rock blocks, seismic energy etc.). From point of seismology, these events are named as mining induced seismic events. Part of them, which caused damages and destructions of mining openings, are called rockburts.

Abstract In this study we analyze the nano- and picoseismicity recorded during the Fatigue Hydraulic Fracturing (FHF) in situ experiment performed in Äspö Hard Rock Laboratory, Sweden. The fracturing experiment composed of six fractures driven by three different water injection schemes (continuous, progressive and pulse pressurization) was performed during the year 2015 inside a 28 m long, horizontal borehole located at 410 m depth. The fracturing process was monitored with two different seismic networks covering a wide frequency band between 0.01 Hz and 100000 Hz, including broadband seismometers, geophones, high frequency accelerometers and acoustic emission sensors. The combined seismic network allowed for detection and detailed analysis of nearly 200 seismic events with moment magnitudes M W < −4 that occurred solely during the hydraulic fracturing stages. We relocated the seismic catalog using double-difference technique and calculated the source parameters (seismic moment, source size, stress drop, focal mechanism and seismic moment tensor). The derived physical characteristics of induced seismicity are compared with the stimulation parameters as well as with the geomechanical parameters of the site. 1. Introduction The geothermic Fatigue Hydraulic Fracturing (FHF) in situ experiment (Nova project 54–14–1) was performed in the Äspö Hard Rock Laboratory/Sweden situated in granitic to dioritic rocks with an age of about 1.8 Ma [1]. The experiment aimed at optimizing geothermal heat exchange in crystalline rock mass by multistage hydraulic fracturing. At a depth of 410 m, six fracture stages were initiated using three different water injection schemes (continuous, progressive and pulse pressurization) inside a 28 m long, horizontal borehole (Figure 1), with up to 30 dm 3 during each fracture stage. The rock volume surrounding the hydraulic fracturing tests was monitored by three different and independent networks equipped with Acoustic Emission (AE) and accelerometers, short and long-period geophones as well as electromagnetic sensors (Figures 1, 2). The monitored volume was about 30 m × 30 m × 30 m in size. The 16-channel in-situ AE monitoring network manufactured by GMuG [2–5] predominantly used in this study monitored the rupture generation and propagation in the frequency range from 1000 Hz to 100000 Hz using combined 11 acoustic emission sensors and 4 high-frequency accelerometers (1 channel spared for time synchronization between different networks). The acquisition system operated at 1 MHz sampling rate. This monitoring setup was successfully used before [2, 6, 7] to detect and analyze seismic events with rupture dimensions from a few cm- to m-scale [6]. However the environment in Äspö Hard Rock Laboratory was a different one; we had 4–5 Liters/minutes inflow and sensors and equipment had to be adapted to the wet facility. The additional microseismic network covered the lower frequency range from hundreds of hertz to 100 seconds (Figure 2) targeting potentially stronger seismic events. The in-situ AE monitoring system detected and analyzed AE activity in-situ in online mode (P- and S-wave picking, localization). To locate earthquakes, an isotropic velocity model was used. After each stimulation, the results of monitoring were reviewed in order to assess the ongoing microfracturing activity and adjust/improve the monitoring strategy.

Abstract We present a combined study of a classical rock sample from Val Malenco, Italy, by investigating the microstructure and texture with state-of-the art synchrotron X-ray, neutron diffraction methods and measuring ultrasonic velocities both with a multianvil apparatus and a novel instrument to measure P and S velocities on spheres. Petrological properties were studied by thin section analysis in three basic structural planes. We discuss advantages and disadvantages of texture measurements and compare them with ultrasonic velocities results. Elastic tensor properties (Cij parameters) can be derived from spherical velocities by inversion. From quantitative texture measurements, elastic properties can be modelled by self-consistent averaging. Comparison of experimental and model Cij parameters is done based on micro structures. Good agreement between the velocity and microstructural models is observed. Similar methods can now be applied to more complex geological materials, where anisotropy is more significant. 1. Introduction The goal of this contribution is to quantify the microstructure and particularly crystallographic preferred orientation (CPO) in serpentinate with modern diffraction methods, time-of-flight neutron diffraction and synchrotron X-ray diffraction. We will then compare ultrasonic velocity measurements in three orthogonal directions on cubes with new 3D velocity determinations on spheres. The samples used for the seismic as well as for the texture measurements were prepared from the same block of serpentinite. Finally, we will predict elastic properties of the serpentinite based on CPO data and compare them with those that were actually measured. 2. Sample, experimental techniques and results 2.1. Sample The sample is a serpentinite from Val Malenco, N-Italy, where ultramafic rocks constitute the subcontinental mantle of the Adriatic lithosphere [1]. The serpentinite is mined in a quarry near the locality Castellaccio. The sample displays a pronounced foliation and lineation. Antigorite is the main component with flat grains (e.g. Fig. 1A). There are some relic olivine grains from which antigorite transformed. Fragments of sheared olivine grains are observed locally, and small relics of olivine grains are distributed throughout the antigorite matrix. Aspect ratios of antigorite grains obtained from length of minor and major axes are in the range 0.3–0.1. At ambient conditions bulk density of the serpentinite, as derived from the volume and the mass of the sample cube, is 2.71 g/cm 3 . The optically identified minerals are antigorite, olivine, magnetite, and chromite. Magnetite and chromite compose less than 5 % of the volume.

Abstract Strong mining seismic events are the source of very high values of peak particle velocity (PPV) recorded in near wave field. The high value of PPV and in low frequency band can exert high dynamic load on the support and underground excavation. As a result of significant increase in dynamic load on the support there is instability and the rockburst phenomena in excavations are observed. The stress concentration zones linked to edges or remnants of the old exploitation are the places where rockbursts have occurred most often. The performed numerical modeling showed, that under the some level of PPV, an important increase in the calculated load on the arch steel support were observed in the stress concentration zones. These results are in good correlation with numerous cases of rockbursts occurred in the Polish mines. In our opinion, continuous measurement and controlling the level of PPV and numerical modeling of dynamic loads in the stress concentration zones allow us for better forecasting of potential rockbursts hazard in mines. 1. Introduction The statistics of rockbursts in the Upper Silesia Coal Basin (USCB) in Polish part shows that the sources of mine seismic events leading to destruction of a mine excavations were usually located no farther than 300 meters away [10]. Such data indicate that the vibrations originate from the near-field wave and are characterized by high values of the amplitudes of peak particle velocity (PPV), [9]. The mechanisms of the rockbursts indicate that they occurred as a result of the summation of static stresses and dynamic stresses and in case of exceeding level of the critical stress in the zone around the tunnel [4]. In Chinese coal mines there are similar rockbursts mechanisms [8, 5]. The article [11] presents a system for monitoring, recording and processing the results of velocity vibration and the calculation of dynamic loads in the arch profiles support at the field study in gateroad 4/510 in Bobrek mine. In the article was proved that only the PPV recorded in low frequency band (mostly below 30 Hz and named PPV W ) has influence on the increase of load exerted on arch support. Applying data on geological and mining conditions in the area of the field study and the record of the tremor on 5 November, 2013 and seismic energy E=3E5 J, numerical calculations were conducted using FLAC software. Maximum value PPVw = 0.110 m/s (in situ measurement) was analysed; in addition, increased values of PPVw=0.250, 0.500, 0.750 and 1.0 m/s were analysed too. The vibrations in each case caused a specific increase in reduced stress in the profile of an arch support. Maximum increase for PPV W =1.0 m/s was nearly 25% compared with the static phase. When the values of PPV W were just one fourth (0.25 m/s), the increase in reduced stress was approximately 5% compared with the static phase, while for the PPV W =0.11 m/s the increase in reduced stress reached 2.5%. The results presented in the article [11] indicated that for analyzed values of PPV W , absolute values of the reduced stresses ranged from 250 to 450 MPa. They were below permissible stress for steel arch support, amounting to σ max = 623 MPa. The vibrations registered for seismic events at Bobrek field site were safe to maintain the stability of the excavations.

ABSTRACT: Granite is well known as an anisotropic rock. It usually has three planes normal to each other being called the rift, grain and hardway, and these planes have different physical properties and strengths. In this study, Pocheon granite in Korean was selected to investigate its elastic anisotropy and strength anisotropy. According to scanning electron microscope observations, Pocheon granite has a higher density of microcracks in the rift plane compared to the other two planes. Elastic characteristics and indirect tensile strength of Pocheon granite were measured through free-free resonant column testing and Brazilian tensile strength (BTS) tests. It is found that the ROD wave is the smallest for the rift plane (3180 m/s) whereas it is the highest for the hardway plane (3761 m/s). S wave has no obvious difference among the three planes. BTS test results show that the average values for the rift, grain and hardway planes are around 6.1 MPa, 8.3 MPa and 8.8 MPa, respectively. Moreover, the failure plane of Pocheon granite in BTS tests were scanned by X-ray CT and roughness of the failure planes were evaluated. Analysis results show that roughness of failure plane is lower for the rift, and higher for the grain plane. Minerals ratio, and their distribution along failure planes influence roughness. No clear relation between BTS and roughness was found at this scale. 1 INTRODUCTION Granitic rocks are characterized by three orthogonal planes of weakness that present different mechanical and physical properties (Dai & Xia 2013). Since a long time ago, quarryman have identified and named them as rift, grain, and hardway planes (Dale 1923). They have taken advantage of these planes of weakness because the rock mass can easily split along the rift plane than along the other two (Takemura et al. 2003). Various researches have studied the mechanical properties along these planes and have found on them distinctive characteristics (Lee et al. 2001). Porosity, density, permeability, wave velocities, and unconfined compressive strength of granites have been reported to exhibit significant anisotropy (Zhang & Takeda 2003). Moreover, changes in ultrasonic wave propagation speed have been used to study different properties of granites. A recent study of Pocheon granite, in South Korea, reported anisotropic characteristics with different values of primary wave velocity for each plane (Kang et al. 2014). Additionally, roughness assessment of natural and manmade surfaces has been conducted for more than four decades (Rengers 1970), and although roughness is a not well defined property, it is generally accepted as any superficial deviation from an ideal plane, and it is scale dependent (McCarroll 1996).

ABSTRACT: Rocks typically show inherent anisotropic characteristics originated from various reasons. It is one of the most long-standing issues of rock mechanics field and of great importance for many engineering purposes. Anisotropic material that has remarkable planar structure is called transversely isotropic. Transversely isotropic material has quite different properties and behavior comparing with isotropic one. In this paper, cracking behavior as well as degree of anisotropy of transversely isotropic mortar cement samples was investigated experimentally. 1 INTRODUCTION Rocks typically show inherent anisotropic characteristics originated from various geological processes and environment. In many engineering fields, anisotropy of rock is one of the most important issues to be addressed and a lot of researches have been carried out for figuring out its behavior (Amadai 1996, Cho et al. 2012). Among several models for anisotropy, transversely isotropy is the most frequently encountered model, especially in sedimentary rock formations. Failure pattern and cracking behavior of transversely isotropic media are quite different from those of isotropic case and understanding them is of great importance for several engineering purposes. In order to investigate the cracking behavior of transversely isotropic material, a series of experiments was carried out with acoustic emission (AE) measurements and high speed camera recording. Cement mortar samples containing clear planar structure in the middle were prepared for better repeatability of the tests. Because of its simplicity, Brazilian tensile test was carried out mainly to observe cracking behavior and other fundamental experiments were conducted as well. Angles between the direction of loading and isotropic plane of sample were selected so that the effect of transversely isotropy on strength as well as cracking could be investigated. During experiments, AE was measured by multiple sensors. Cracks could be defined by source locating technique based on the measurements. In the transversely isotropic material, AE generation and propagation were influenced by anisotropic feature. A new source locating technique that is capable of dealing with anisotropy was developed in this study based on partition approximation method. Cracking behavior as well as variation of mechanical properties of the samples could be experimentally investigated.

ABSTRACT: As historic monuments become more vulnerable to seismic hazard with time, it becomes essential to be able to assess the seismic hazard in a quantifiable manner. For soft soil foundations, a computer program such as SHAKE may be utilized. For stiff rocks comprised of layers and joints a discontinuous approach must be utilized. This approach can be extended to masonry structures, so as to find by means of numerical analysis the peak ground acceleration and frequency at which the historic monument is most vulnerable and to predict the anticipated failure modes. The numerical, discrete element discontinuous deformation analysis (DDA) method is used here for this purpose. We begin by demonstrating DDA's ability to model wave propagation through layered media using a theoretical example and a real case study. We proceed with comparing between thermally and seismically induced irreversible block displacements in jointed rock slopes at the foundation of Masada world heritage site, and finally we present two case studies of masonry structures in Israel that are prone to seismically induced deterioration due to their proximity to the active Dead Sea rift. 1 INTRODUCTION We model here the vulnerability of historic monuments in rocks to earthquake hazards using the numerical, discrete element, discontinuous deformation analysis (DDA) method (Shi 1993). The basic principles of DDA are relatively well known and will not be reviewed here, for the sake of brevity. Interested readers are referred to review papers and text books that describe the theory, its verification, and application (Jing & Stephansson 2007, Jing 1998, Jing 2003, Yagoda Biran & Hatzor 2016, Ohnishi et al. 2006). To demonstrate the applicability of DDA for modeling wave propagation through discontinuous media we shall begin with checking the accuracy of DDA in modeling P and S wave propagation in an elastic bar and a stack of layers, respectively. We shall check the ability of DDA to compute accurately two-dimensional site response in masonry structures by comparing between DDA and a field scale site response study performed on a historic multi-drum column founded on stiff rock foundation. We will demonstrate the applicability of the approach in historic monuments that are prone to seismically induced damage due to their proximity to the active Dead Sea rift: the rock slopes of Masada world heritage site, and Byzantine period cathedrals in Mamshit and Susita , located in the southern and northern segments of the Dead Sea rift.