The SPE has split the former "Management & Information" technical discipline into two new technical discplines:
- Data Science & Engineering Analytics
The SPE has split the former "Management & Information" technical discipline into two new technical discplines:
|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
The development of a software code for simulation of the impact of mining layouts on stress fields and rock mass deformation or displacement is a demanding process, even after a mathematical framework for the code has already been established. The initial version of the limit equilibrium code, TEXAN, has been expanded to include features such as off-reef structures (bedding planes and faults) as part of a larger research project at the University of Pretoria that has the aim to derive an appropriate mine design criterion for deep-level, seismically active mines. Deep-level mining environments are characterized by a highly discontinuous rock mass. In most cases, the environment includes varying mining depths, mine spans, and layouts as well as different rock types and geological structures. At the same time, the vast areal extent of the typical ‘tabular’ orebodies in South Africa suggests highly variable rock mass and structural properties across the mining tenure. The updated version of the code will require substantial calibration to test the proposed design criterion against actual recorded rock mass responses. This is expected to be a complex process due to the vast number of variables that should be accounted for. Calibration of numerical codes to actual rock mass response should, in theory, consider the impact of these potential conditions or environments. However, numerical modelling must apply a process of eliminating unnecessary details. The selection of the critical factors that must be included should follow a scientific approach or process. It is suggested that the code calibration should be an iterative process through which the code's sensitivity to specific input parameters and conditions is tested against the selected rock mass responses. To start the planned calibration process, the behaviour of the TEXAN code based on certain input parameters was evaluated as a sensitivity study. The results include the identification of parameters/conditions that are ‘critical’ to future calibration of this code by ensuring that the following is clear:the importance of establishing accurate values (or ranges of values) to some parameters and which parameters/conditions need to be included in the models. INTRODUCTION In the physical world, there are often a vast number of factors that may influence the outcomes of a specific situation or act. At its simplest, each of these factors may impact significantly, moderately, or have no noticeable impact on the situation or act. It is often the case that only the factors that can be shown to have a considerable impact are considered ‘critical’ and are applied in evaluating the possible outcomes of a situation or act. Frequently, also, no real process is applied in selecting these critical factors, or the values allocated to them, but a subjective selection is made based on what is thought to be important.
Durrheim, R. J. (University of the Witwatersrand, Johannesburg) | Ogasawara, H. (Ritsumeikan University, Kusatsu, Japan) | Nakatani, M. (The University of Tokyo, Japan) | Yabe, Y. (Tohoku University, Japan) | Naoi, M. (Kyoto University, Japan) | Moriya, H. (The University of Tokyo, Japan) | Cichowicz, A. (Council for Geoscience, South Africa) | Satoh, T. (AIST, Japan) | Kawakata, H. (Ritsumeikan University, Kusatsu, Japan) | Milev, A. (CSIR, South Africa) | Kgarume, T. (CSIR, South Africa) | Brink, A. vZ. (CSIR, South Africa) | Ward, A. K. (Seismogen CC, South Africa) | Ribeiro, L. (Seismogen CC, South Africa) | Manzi, M. S. D. (University of the Witwatersrand, Johannesburg, South Africa) | Mngadi, S. (Ritsumeikan University, Kusatsu, Japan) | Team, SATREPS (SATREPS)
Mining-induced earthquakes pose a risk to workers in deep mines, while large earthquakes that occur near plate boundaries (and occasionally in stable continental regions) pose a risk to the public. A five-year Japanese–South African collaborative project ‘Observational studies in South African mines to mitigate seismic risks’ was concluded in 2015. Acoustic emission sensors, accelerometers, strain meters, and controlled seismic sources were installed in three deep Witwatersrand gold mines to monitor the deformation of the rock mass, the accumulation of damage during the earthquake preparation phase, and the propagation of the rupture front. A surface array of accelerometers was installed in the Far West Rand mining district. This data was integrated with measurements of stress, in-stope closure, and strong motion, as well as data recorded by the mine-wide seismic networks. New insights into the physics of earthquakes were gained, and technologies developed or adapted to assess seismic hazard and mitigate rockburst risks. INTRODUCTION Earthquakes pose a significant risk to workers in deep and overstressed mines and people residing near to these mines (such as gold mines in South Africa), and inhabitants of regions close to plate boundaries (such as Japan). While the earthquake hazard is less in stable continental regions, rare large earthquakes can occur and cause considerable damage if buildings are not designed to withstand shaking. The risk posed by seismicity in South African mining districts is exemplified by the M5.5 seismic event that struck the North West Province at 12:22 p.m. (local time) on 5 August 2014. It was the largest event ever to occur in a South African mining district. Dwellings and other buildings in the nearby towns of Khuma, Stilfontein, and Orkney suffered extensive damage (Figure 1). Strong shaking was experienced in Johannesburg and Pretoria, and was felt as far away as Durban and Cape Town. One person died as a result of the collapse of a garden wall, and many others suffered minor injuries. The cost of damage was estimated to be R130 million (B. Manzunzu, Council for Geoscience, personal communication, 2015).
ABSTRACT We have developed an optimization method for automatic dyke delineation from observed magnetic and gravity gradient traverse data. A non-linear least squares algorithm is used to find model dyke parameters that best fit the computed gradient tensor data to the observed data. The eigen-system of the observed magnetic gradient tensor data is used to provide starting model dyke parameters for an iterative non-linear least squares solver. This greatly enhances the ability of the solver to find a plausible dyke model for matching observed and synthetic tensor gradients locally. The method works well on synthetic examples. Multiple surveys using a Full Tensor Magnetic Gradient (FTMG) signal instrument from IPHT, have been made in Southern Africa. A real case study with remanence, taken from the Platreef near Pretoria, shows that the gross observed gradient features can be recovered by our procedure, but the residuals in the gradient fit hint strongly at the need for more complex dyke models. There is more directly inferable structural geology in this tensor signal than can be found in a conventional TMI signal.
Abstract Steeply dipping rockhead and cavities provide extreme challenges for design and construction of foundations in karst dolomite terrain. The Gautrain Rapid Rail Link will connect Johannesburg, Pretoria and the OR Tambo International Airport along approximately 80 km of align-ment with 10 railway stations. Approximately 15 km of the alignment is underlain by dolomite with nearly 6 km elevated on a viaduct. To facilitate detailed design and choice of foundation method for the viaducts founded in dolomitic bedrock or overlying residual soils the Bombela Civils Joint Venture opted to include single-hole reflection borehole radar surveys as part of the ground investigation works. First arrival time, signal attenuation and reflectors were assessed from radargrams to locate karst structures and geological discontinuities for distances up to 12 ms around each borehole. This paper describes procedures together with examples demonstrating the merit of borehole radar surveys combined with conventional ground investigation in karst dolomite.
Abstract The Gautrain Rapid Rail Link is an 80 km rail network between Pretoria, Johannesburg and the OR Tambo International Airport in South Africa. The stability of the rail constructed over dolomitic ground was classified as a major project risk and obtaining geotechnical parameters for design presented a unique challenge as development in this area has been kept to a minimum. The ground investigation employed numerous investigation techniques in an attempt to obtain consistency between different methods and hence obtain a representative data set in very heterogeneous ground conditions. To further understand the performance of the ground full scale surcharge loading tests and pile load tests were carried out. As a result of the extensive investigations, a suite of foundation solutions was designed and validated. These solutions comprised piles to rock, large diameter shafts to rock, floating foundations over grout treated ground and spread footings founded on rock close to the surface.
ABSTRACT: The Bushveld platinum group metal deposits in South Africa are the largest in the world. These deposits occur as two distinct stratiform tabular ore bodies and strike for many hundreds of kilometres. Mining is extensive, with depths ranging from close-to-surface to 2300 m. The mining method is a variation of planar open stoping. Crush pillars are widely used to support the open stopes. These pillars are designed to fail and the residual strength provides the required support resistance to stabilize the stoping excavations. This paper describes the in situ measurement, of stress within a pillar, and provides a stress-strain curve including pre and post failure behaviour. 2D FLAC modelling, with strain softening, was done to show how damage expands into the hanging- and/or footwall. Although the so-called ?squat? effect is still present at larger width to height ratios, the modelling suggests that it does not dominate the pillar system behaviour. The paper investigates the behaviour of a system that incorporates the immediate hanging- and footwall, as well as the pillar itself. 1. INTRODUCTION The Bushveld Complex is a large layered igneous intrusion which spans about 350 km from east to west. This region is situated north of the city of Pretoria in the northern part of South Africa (see Fig. 1). This remarkable geological phenomenon hosts not only the majority of the world?s platinum group metals but also contains nickel and gold. There are also vast quantities of chromium and vanadium in seams parallel to the platinum ore bodies some hundreds of metres in the footwall and hangingwall respectively. The platinum group metals are concentrated in two dipping planar ore bodies known as the Merensky Reef, a mineralised pegmatoidal pyroxenite 0.7 m to 1.4 m thick, and, underlying this, the UG2 Reef comprising one or more chromitite seams of similar thickness. The strata generally dip toward the centre of the complex at 8° to 15°. The k ratio varies from about 0.8 to over 2.5 and locally the relatively high horizontal stress can cause severe strata control problems, particularly in tunnels. The depth of mining ranges from outcrop to 2300 m. If a sufficiently large mining span is achieved, or the stope abuts a geological feature, a large volume hangingwall rock can become unstable, resulting in a stope collapse, or colloquially, a "backbreak." Fig. 1 The extent of the Bushveld platinum exposure. (available in full paper) In order to prevent these backbreaks a high support resistance support system is required. This is universally achieved by the use of small in-stope chain pillars oriented either on strike for breast mining (see Fig. 2) or on dip for up or down dip mining. Fig. 2 Plan view of a typical stope on one of the planar platinum ore bodies (available in full paper) The pillars are known as crush pillars and they are required to fail in a stable manner soon after being cut. The residual strength of the pillars provides the required support resistance to prevent backbreaks and keep the stope hangingwall stable. These pillars provide an ideal opportunity to study the in situ behaviour of small pillars.
ABSTRACT: In South Africa, the Bushveld platinum group metal deposits are unique in that they are the largest platinum group metal deposits in the world. These deposits occur as two distinct stratiform tabular ore bodies and strike for many hundreds of kilometers. Mining is extensive, with depths ranging from close-to-surface to 2000 m. The mining method is a variation of planar open stoping. Pillars are widely used to support the open stopes. Crush pillars are commonly used in this role, where the residual pillar strength provides the required support resistance to stabilize the stoping excavations. This paper describes the direct measurement of stress within these crush pillars, and describes the stress ? strain behavior of these pillars. These findings indicate that the measured pillar failure stress is too high. The implications of these findings are that roof damage and pillar bursting could occur, and some examples of this type of damage are shown. The paper concludes that this problem could be mitigated if the three dimensional pillar geometry was modified and the pillars were cut smaller. INTRODUCTION The Bushveld Complex is a large layered igneous intrusion which spans about 350 km from east to west. This region is situated north of the city of Pretoria in the northern part of South Africa (see Fig. 1). This remarkable geological phenomenon hosts not only the majority of the world?s platinum group metals but also contains nickel and gold. There are also vast quantities of chromium and vanadium in seams parallel to the platinum ore bodies some hundreds of metres in the footwall and hangingwall respectively. The platinum group metals are concentrated in two dipping planar ore bodies known as the Merensky Reef, a mineralised pegmatoidal pyroxenite 0.7 m to 1.4 m thick, and, underlying this, the UG2 Reef comprising one or more chromitite seams of similar thickness. The strata generally dip toward the centre of the complex at 8o to 15o. The k ratio varies from about 0.8 to over 2.5 and locally can cause severe strata control problems, particularly in tunnels. The depth of mining ranges from outcrop to 2300 m. In the mining depth range from surface to about 1400 m there is a vertical tensile zone in the stope hangingwall. If a sufficiently large mining span is achieved, or the stope abuts a geological feature, a large volume of hangingwall rock can become unstable, resulting in a stope collapse, or colloquially, a backbreak. In order to prevent these backbreaks a high support resistance support system is required. This is universally achieved by the use of small in-stope chain pillars oriented either on strike for breast mining (see Fig. 2) or on dip for up or down dip mining.
ABSTRACT: Around 20% of Gauteng Province and most of the gold mining districts of the Far West Rand are underlain by dolomitic formations. Ground surface instability may occur in such areas. Dewatering associated with mining in the gold bearing reefs of the Far West Rand, which underlie dolomite and unconsolidated deposits, has led to the formation of sinkholes. Sinkholes formed concurrently with the lowering of the water table in areas which formerly, in general, had been free from sinkholes. Hence, certain areas became unsafe for occupation and were evacuated. In addition, the risk of sinkholes occurring is greatly increased by development, where interrupted natural surface drainage and leakage from water bearing services can result in the concentrated ingress of water into the subsurface. In the area underlain by dolomite which extends around Johannesburg and Pretoria the problem has been accentuated in recent years because of housing development and the growth of informal settlements. Dolomite at shallow depth, that is, occurring at less than 15 m beneath the ground surface, has been associated with the appearance of significant numbers of small sinkholes. When dolomite is located at depths greater than 15 m, the sinkholes usually have larger diameters. INTRODUCTION Sinkholes can take place due to the collapse of voids and cavities in dolomite rock which has been subjected to prolonged dissolution, this occurring when the roof rocks are no longer thick enough to support themselves. Alternatively, the downward movement of unconsolidated deposits into cavities in the top of dolomite as a result of excessive ingress of water at the surface or due groundwater lowering also can lead to the appearance of sinkholes at the surface. In fact, most induced sinkholes (i.e. those caused or accelerated by human activity) are formed as a result of roof failures in unconsolidated deposits.
ABSTRACT: The fitting of synthetic seismograms to locally-recorded, broad-band, wide dynamic range seismic data is a very effective means of determining both seismic source parameters and focal mechanisms of mine tremors. Using data from a single three-component surface station, in conjunction with a seismic location network, a comprehensive description of the seismic source process can be obtained by the trial and error calculation of synthetic seismograms, for a point source in a homogeneous half-space, until the ground motion observed at the surface is matched. This methodology was applied to two tremors located in the Vaal Reefs Gold Mine, near Klerksdorp, South Africa, and was used to relate these events to the geological and mining situation in the environs of each hypocenter. INTRODUCTION This paper reports an analysis of seismograms recorded at a single station situated on the surface of a gold mine in the Klerksdorp mining district, about 150 km WSW of Johannesburg, South Africa. The purpose of this report is to demonstrate the usefulness of synthetically calculated seismograms for gaining insight into the source processes of locally-recorded tremors. Langston (1979) demonstrated the effectiveness of this approach for the analysis of body waves recorded teleseismically at a single station and Spottiswoode (1980) was able to constrain the source mechanisms of tremors at the ERPM gold mine by fitting synthetic seismograms to the long period records at Pretoria, 54 km north of the mine. The results reported here, however, are the first application of synthetic seismogram modeling to mine tremors recorded locally using broad-band wide dynamic-range instrumentation. Such seismograms, recorded at hypocentral distances typically in the range of 2 to 5 km, contain a wealth of seismic source information, much of which can be extracted by means of synthetic seismograms. The network included four GEOS digital event recorders (Borcherdt et al., 1985), one of which was situated in each of the four districts that account for nearly all of the mine induced seismicity. Each GEOS unit recorded three components each of ground acceleration and velocity at 200 samples/second/channel. The two events analyzed in this study were recorded at GEOS station HBF, situated adjacent to the border between the Hartebeestfontein and Vaal Reefs gold mines, and were each located within Vaal Reefs (Figure 1). The Klerksdorp mining district which consists of four gold mines including the two just mentioned, is characterized by major through going faults that offset the strata, including the gold-bearing reefs, often by 200 m or more (e.g., Gay et al., 1984). Because this gold field is noted for its exceptionally large tremors a seismic location network, consisting of both underground and surface geophones, was installed during the 1970s to investigate the nature of the large-magnitude seismicity and the extent to which it is controlled by the major faults. The main objective of this report is to indicate the utility of synthetic seismogram modeling of locally-recorded tremors for relating these events to either geological faults or to the mining, or both.
SYNOPSIS: A geotechnical investigation is described in which the rock mass was classified from geotechnical logging of surface outcrops and cores and limited exploration development. Critical structures were identified and their influence on pillar stability was assessed using numerical techniques. The ore zone varied from 2.5 m to 20 m thick at depths of 60 m to 100 m below surface. The objective of the analysis was to obtain basic design criteria from which the extraction percentages could be estimated so that further financial evaluation of the deposit could be carried out. RESUME: On decrit une investigation geotechnique au cours de laquelle une masse rocheuse a ete classee à partir d'une etude geotechnique des affleurements de surface, de carottes et de developpements exploratoires limites. Les structures critiques ont ete identifies et leur influence sur les piliers a ete evaluee par des techniques numeriques. L'epaisseur de la zone de minerai varie de 2,5 m à 20 m pour une profondeur de 60 m à 100 m. Le but de l'etude a ete d'obtenir des critères de conception fondamentaux à partir desquelles les pourcentages d'extractions puissent être estimes, ce qui permettra de realiser une evaluation financière complementaires du gisement. ZUSAMMENFASSUNG: Eine geotechnische Untersuchung wird beschrieben, in der das Gebirge durch die geotechnische Aufnahme von Gesteinsaufschluessen und von Bohrkernen und durch begrenzte Erkundungen untertage klassifiziert wurde. Kritische Gefuege wurden festgestellt und deren Einfluß auf die Stabilitat der Pfeiler mittels numerischer Methoden bestimmt. Die Erzzone variierte von 2,5 bis zu 20 m Machtigkeit bei einer Teufe von 60 bis 100 m. Das Ziel der Analyse war es, grundlegende Entwurfsparameter zu gewinnen, die Erzhöffigkeit abzuschatzen und weitere Kostenanschlage der Erzlagerstatte auszufuehren. 1 INTRODUCTION The geotechnical feasibility investigation described in this paper was carried out for an underground fluorspar deposit situated in the Marico district of the Western Transvaal. Due to the paucity of data, the investigation was primarily concerned with establishing lower limits for ore recovery. These lower limits would be used in a financial evaluation in the knowledge that when further underground development took place, further information would enable a more optimistic assessment of the potential recovery. The investigation attempted to classify the rock mass in terms of structure, strength and, using empirical classification techniques. From this analysis, a sensitivity approach was adopted in order to qualify the potential response of the rock mass to a room and pillar system. Geology The fluorspar deposits occur within the upper part of the Dolomite Series of the Transvaal System which is overlain unconformably by the cherts, shales and quartzites of the Pretoria System Series of the same system. The entire sequence has been metamorphosed by the later intrusion of the Bushveld Igneous Complex which has subsequently been eroded. A representative lithological profile based on available borehole information is shown in Figure 1. The stratiform mineralisation of the deposit is of the replacement type with the fluorspar concentrating along the more permeable zones in the dolomites, such as algal mats and stromatolitic structures, vugs, cavities and joints. In this way, the stratiform mineralisation can also be very erratic, and contains much barren or low, grade dolomite. The dip of the ore zone varies from 0° to 15° and the thickness of the economic zones varies from 2,5 m to 20 m. The footwall of the economic zones is situated within 60 m to 100 m of the surface. 2. ROCK MASS CHARACTERISATION The assessment of the rock mass characteristics was derived from analysis of: -aerial photographs for an initial structural analysis -engineering geological mapping of surface outcrops -structural logging of vertical and inclined boreholes -engineering geological mapping of the shaft and test room -field and laboratory testing of selected rock samples -statistical analysis collected data for Index (Barton, 1974) 2.1 Engineering geological mapping Engineering geological mapping of the quartzite and chert outcrops and of the dolomite exposures underground was carried out. The properties recorded for each surface were: -rock type -rock hardness -structure of discontinuity -continuity, both down dip and along strike -infilling type and thickness -surface roughness by recording amplitudes and base length of asperities -water seepage -surface compressive strength by use of the Schmidt hammer The discontinuity orientation was plotted on an equal area polar projection and contoured to identify the major discontinuity sets. Figure 2 was derived from the mapping of the shaft and trial room. It was possible to make a direct correlation between the range of bearings of the surface features and the underground features. This enabled prediction to be made concerning the continuity of the various sets. The underground development, although extremely limited, was of the utmost value. It illustrated the true interrelation of the identified joint systems and enabled conclusions to be drawn regarding the critical structures. The continuity of this joint set was up to 155 m.