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Controlling induced seismicity at El Teniente mine: The sub-6 case history
... Rock masses of primary copper ore at the El Teniente mine have been described as very competent and massive during caving operation (Rojas et al., 2001). This is because caving performance has resulted in larger than expected fragmentation, and these rock masses have exhibited brittle, often violent failure under a high stress conditions (Rojas et al., 2000). Moreover, it is currently believed that induced seismicity during caving operation 'has more relation to the rock mass characteristics (competence) rather than other factors' (Araneda and Sougarret, 2007). ...
... At the same time panel caving develops a continuous front cave, which sometimes can be 600 metres long. Pre-undercut caving mainly differs from panel caving, called conventional according to Rojas et al. (2000), because the undercut (UCL) is developed ahead of all development below the undercut levels (Figure 1c). El Teniente is the largest known copper-molybdenum deposit in the world; main rock types include andesite, diorite and hydrothermal breccias of the Miocene era (Skewes et al., 2005). ...
... El Teniente Mine is the biggest underground caving operation in the world currently mining around 140,000 tons per day, 80% of this within primary copper ore (Araneda and Sougarret, 2007). Moreover, such competent rock masses have achieved caving with a small hydraulic radius of around 25m at both the Esmeralda mine sector (Rojas et al., 2001) and Reno mine sector (former Ten Sub-6) during its experimental operation (Rojas et al., 2000). These experiences are contrary to the description of a competent and massive rock mass. ...
The primary copper ore at the El Teniente Mine is a very competent and massive rock mass with almost no
open discontinuities. Nevertheless, there is a network of high frequency, small scale healed veins coupled
with widely spaced faults. In addition, recent work has found that veins filled with particular mineralogical
infill and thicknesses are more likely to define blocks during the fragmentation process. The occurrence of
weak vein data from Esmeralda mine sector has been assessed and correlated with observations of
fragmentation. Analysis between structural data and moment tensor estimates of seismic events located in
the seismogenic zones, show that it is not only the large scale, weak faults, but also weak veins that are
mobilised and seismically active during caving propagation. Modelled moment tensors using modern non
linear Finite Element modelling (ABAQUS) are in agreement with the findings, and confirm this
phenomenon throughout all structural domains at the Esmeralda mine sector. The research work presented
here describes how such competent rock masses are being disassembled during caving propagation. The
results are relevant during the assessment of cavability and fragmentation in block caving operations.
... Rockbursts have been documented worldwide for nearly a century. In the South African gold mines, which can reach depths in excess of 3,500 m with up to 800 km of subsurface tunnels, the rockbursting phenomenon is exacerbated in that several contiguous mines exploit a single continuous ore body (Cook 1976;Ortlepp 2005;Cranswick 2011;Bennett and McLaughlin 1997;Cook 1964;Spottiswoode and McGarr 1975;Notley 1983;Kaneko et al. 1990;Krishnamurthy and Shringarputale 1990;Dunlop and Gaete 1997;Li and Guo 2001;Båth 1984;CMRO 1988). In this case, large areas of the earth's crust are effectively weakened and stresses within the rock are redistributed by mining operations, a similarity observed in current unconventional hydrocarbon production within the Central United States at depths exceeding 2000m (Kisslinger 1976;Cook 1976;Maury et al. 1976;McGarr 2014;Horton 2012;). ...
... Rockbursts are not unique to South African gold mines and have been observed in conventional mining activities throughout Canada, Australia, Japan, India, Chile, China, United States, and Western Europe (Ortlepp 2005;Cranswick 2011;Bennett and McLaughlin 1997;Notley 1983;Kaneko et al. 1990;Krishnamurthy and Shringarputale 1990;Dunlop and Gaete 1997;Li and Guo 2001;Båth 1984). Large shear fractures, 30-m vertical by 100-m longitudinal, with shear displacements of a few centimeters have been observed in conventional mining; these dimensions yield a potential seismic moment on the order of 5,000 GJ associative with M2.0 earthquakes (Cook 1976). ...
Unconventional hydrocarbon development-induced seismic hazard in historically aseismic regions is more frequent and concentrated than seismicity in established tectonic high-hazard zones. A significant increase in seismicity within historically aseismic regions and in close proximity to federal infrastructure has been observed within Arkansas, Kentucky, Missouri, Oklahoma, Tennessee, Texas, and Virginia. Seismological events M2.0 and greater, spanning 02/08/1950 until 10/20/2013, were analyzed to identify and assess the hazard potential. Geospatial and temporal observations correlate the seismic increase to the rise of unconventional hydrocarbon development, which has become more analogous with deep ore mining in terms of energy release. Thus, unconventional hydrocarbon is subjected to the same causality phenomena and associative hazards with significant implications towards quantifying the risk to infrastructure health and longevity. Furthermore, the current standard of practice for risk assessment is not applicable for this highly variable, induced hazard. Additionally, this research investigated the cumulative seismic potential, based on injected fluid volume, of co-located hydraulic fracturing wells wherein the seismic potential of such wells are equivalent to the seismic potential of conventional wastewater injection wells. This cumulative seismic potential of multiple hydraulic fracturing wells could explain the seismicity within regions of Arkansas, Oklahoma, and Texas, wherein no other regional geo-engineering activity has been reported. Additionally, this study presents a power-law relation, useful for all injected fluid activities irrespective of the injection purpose, and applies the cumulative potential to the largest known UHP hydraulic fracturing volumes an event up to Mw5.5 can reasonably expect with a maximum potential of Mw6.5.
... The ultimate purpose of rockburst research is to predict and control the occurrence of rock burst and relieve its damage to working face, equipments, and miners. Destressing (Stress control method) mining mainly consists of two kinds of methods such as: Regional destressing and local destressing (Dunlop and Gaete, 1997;Scott, 1997; Dubinski and Mutke, 1997; Wu and Zhang, 1997; Blaha, 1990;Glazer, 1997 ...
... The primary hypogene copper ore of the El Teniente deposit is described as being a very competent massive rock mass, exhibiting brittle and often violent failure under high stress conditions (Rojas et al., 2000) that can temporarily result in the closure of localized mine sectors. Geological discontinuities recognized within the primary copper ore are mainly widely-spaced, large scale faults as well as a high frequency network of smaller scale veins (stockwork), of which only a sub set of weaker low tensile strength veins behave as fractures (Brzovic and Villaescusa 2007). ...
At the El Teniente mine, most observed cases of rock damage during rock bursts in tunnels and mine drives are the result of structurally controlled wedges. Therefore during tunnel development it is critical to firstly obtain detailed rock structure descriptions and to then secondly characterise and understand the rock structure surrounding the excavations. Discrete Fracture Network (DFN) modeling has been introduced in the mining industry as a way to generate a better statistical representation of a fractured or structural controlled rock mass, such as the primary ore at the El Teniente mine. As the parameters needed to build a DFN (discontinuity orientation, size and intensity) can be accurately measured digitally, the final result would be comparing these results with the use of traditional classification systems. Recent technological innovations for tunnel geological mapping introduced at El Teniente such as 3D digital photogrammetry allow a detailed description of the rock structure of the larger rock mass to be digitally obtained. A single photogrammetric file or image, named Digital Terrain Models (DTM), represent between 3 and 4 meters of a tunnel development and more than 200 geological structures can be described in term of their basic parameters from a single image (dip direction, observed trace length and location in mine coordinate system). By using detailed data collected from more than 90 DTMs from different mine sectors (Esmeralda, Reno and New Mine Level project), a methodology to construct a DFN for each single tunnel advance is described and presented in this study. Following the simulated sampling technique to obtain the discontinuity size and intensity whilst considering different truncation bias, a DFN that honors the observed structural data was determined. The main results indicate that vein intensity known as P 32 m 2 /m 3 (fractured area/volume) surrounding the excavation within the Cmet rock mass varies from 2 to 7 m 2 /m 3 considering a sampling cut off by 0.5 meters.
... Rockbursts have been documented worldwide for nearly a century. In the South African gold mines, which can reach depths in excess of 3,500 m with up to 800 km of subsurface tunnels, the rockbursting phenomenon is exacerbated in that several contiguous mines exploit a single continuous ore body [Cook 1964[Cook , 1976Spottiswoode and McGarr 1975;Notley 1983;Båth 1984; Chamber of Mines Research Organization (CMRO) 1988; Kaneko et al. 1990;Krishnamurthy and Shringarputale 1990;Bennett and McLaughlin 1997;Dunlop and Gaete 1997;Li and Guo 2001;Ortlepp 2005;Cranswick 2011]. In this case, large areas of the Earth's crust are effectively weakened and stresses within the rock are redistributed by mining operations, a similarity observed in current unconventional hydrocarbon production within the CeUS at depths exceeding 2,000 m (Cook 1976;Kisslinger 1976;Maury et al. 1976;Frohlich et al. 2011;Horton 2012;McGarr 2014). ...
Unconventional hydrocarbon development-induced seismic hazard in historically aseismic regions is more frequent and concentrated than seismicity in established tectonic high-hazard zones, and the current standard of practice for risk assessment for infrastructure is not applicable for this highly variable, induced hazard. A substantial seismic increase has been observed in historically aseismic regions and in close proximity to federal infrastructure within Arkansas, Kentucky, Missouri, Oklahoma, Tennessee, Texas, and Virginia. Seismological events M2.0 and greater, spanning February 8, 1950 until October 20, 2013 were analyzed to identify and assess the hazard potential. Geospatial and temporal observations correlate the seismic increase to the rise of unconventional hydrocarbon development, wherein all production components contribute to weakening of the subsurface and induced seismicity. Unconventional hydrocarbon production hazard has become more analogous with deep ore mining in terms of energy release and is subjected to the same causality phenomena and associative hazards with significant implications towards quantifying the risk to infrastructure health and longevity.
... The Southern African Institute of Mining and Metallurgy 1 st International Symposium on Block and Sub-Level Caving Cave Mining W D Ortlepp rockbursts can be an additional major threat e.g. Simser et al (2001) and Dunlap et al (1997). ...
In hard-rock mining, cable anchors and grouted rockbolts have long been used for the support of both short-term and long-life excavations. Sub-level and block cave-mining operations are now being pursued at greater depths and subjected to higher stresses than previously. Some of these operations experience severe stress and seismic damage. In these instances it is possible to improve safety and to minimize production losses, by ensuring greater effectiveness and improved service life of the support tendons. Recent developments in South Africa have greatly improved the dynamic capacity and extended the service life of both rock bolts and cable anchors. These improvements offer significant benefits in safety and economy particularly where large displacements occur or where seismicity causes violent failure of the surrounding rock. The tendons are effectively unbreakable in tension and more resistant to shear failure than conventional fully-grouted anchors. The mode of operation of these innovations is described and the results of quasi-static and dynamic tests are presented. Displacement velocities up to 10 metres per second and single-pulse extension of a few hundred millimeters were sustained by the tendons with no reduction in capacity. The device can also be applied to cladding and containment with major benefit compared to conventional steel straps and mesh or screening. So far the statically-elastic / dynamically-ductile principle (SEDD) which defines these innovations, has been applied only to deep tabular mining. However, the author believes that it could be of great benefit in cave mining. It might also have application in the fields of earthquake engineering and explosion-resistant concrete barriers.
This chapter deals with designing the seismic monitoring system for Lift 2 Mine. Seismic network consists of specialised hardware and software. An important part is the communication system which allows transferring recorded data to the central computer. This is the widespread understanding of what is the “system”. Sometimes this understanding goes a bit further and accepts the fact that an additional part of this structure is means of recorded data visualisation. Still the differentiation between visualisation and interpretation of recorded data is not clear and often not regarded as something of importance. The same applies to the network managing. Professional management of the seismic network and expert analysis of the recorded data are important parts of the “system”. These parts of the seismic network are there to make sure the system records as it should, the recorded data is processed properly so the seismic data base is of high quality. This is critical for analysis and data interpretation to be reliable. When comparing hardware and software with human skills and know-how this second element is more important. It is easy to imagine that old technology combined with professional knowledge will result in more reliable results than the combination of the best technology with lack of skills. This is common sense but difficult to apply in practice.
During the past several years, seismic monitoring has been expanded in several mining districts, a number of new techniques have been introduced, and new significant results have been obtained in studies of the seismic events induced by mining. New techniques in seismic monitoring in mines, geological and mining factors affecting seismicity, source parameters and their scaling relations, and shearing versus non-shearing source mechanisms are briefly described in the chapter. Statistical techniques and methods that are used extensively in recent years in studies of seismicity in mines, especially for seismic hazard assessment are discussed. This chapter provides an overview of the seismic discrimination between underground explosions and seismic events originating in deep mines. Seismic events induced by mining are not uniformly distributed in either space or time. Extensive studies performed on the space-time-energy distributions of seismic events in mines show that the tendency to form nests, swarms, and clusters is commonly observed. Seismicity in mines is strongly affected by local geology and tectonics, and by interaction between mining and crustal state of stress on a local and regional scale.
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