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2016 | Buch

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Mine Seismology: Data Analysis and Interpretation

Palabora Mine Caving Process as Revealed by Induced Seismicity

verfasst von: S.N. Glazer

Verlag: Springer International Publishing

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik" , Springer Professional "Wirtschaft"

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Über dieses Buch

This book offers an in-depth analysis and interpretation methods applicable to mine-induced seismicity. It is based on over 40 years of experience in mine and exploration geophysics. Another unique feature of this book is the complete history of the caving process as evidenced by the recorded seismicity at the South African copper mine Palabora Lift 1. Until now, the literature has only presented theory and case studies discussing the interpretation of results, and there has been no discussion of the input-data quality or why a certain interpretation technique was applied. This book fills that gap.

This book is a fascinating read, written by one of the world’s leading mine seismologists. It summarises the history and progression of mine seismology. It outlines the practical use of back analysis of data and how it can be used on a daily basis. The book explains how mine seismology can be used as an effective monitoring tool for key events as the mine progresses as well as for future caving operations.Anthony Allman MAusIMM, CP(Min), RPEQ Antcia Consulting Pty Ltd, Director, Mining Engineer
The content of the book is really solid and robust and I have no doubt it is going to be considered a great contribution for the mining community.Raul Fuentes, Former Director of Master Program in Geomechanics Applied to Mining, Universidad de los Andes, Santiago, Chile
This book is long overdue and helps to present some difficult concepts in a way that they can be clearly understood by non-experts in this area. Stefan has personally managed to take mine seismology from being a black-art into a useful tool to help make mines a safer and more controlled environment. Neil Hepworth C. Eng, MIMMM, Geomin Consultorio – Brazil, Consultant Mining and Geotechnics
Seismic monitoring is an important tool in cave management. The information from monitoring allows a number of key production factors to be determined including cave advance rates, the approximate location of the cave back, insight into the size of the air gap and allows the tracking of broad changes in stress. These all assist in the day to day management of a safe and successful cave. Dr. Glazer’s book provides guidance on the application of microseismicity to cave management through a review of appropriate theory and more importantly illustrates its use through case histories, particularly from the Palabora block cave. The text will be a good addition for all practitioners in cave engineering and operations.Allan Moss, General Manager – Grasberg Underground Liaison, Copper Development, Rio Tinto

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract

To start with I was planning to document the South African copper mine Palabora Lift 1 Mine history as evidenced by the recorded seismicity. With time concept of this book changed. From being only a seismic history of a cave mine the book concept evolved into something more complex. This book has three parts. First part is about seismic source parameters, what they mean and about their limitations. This part explains what can be and what can not be done with these parameters. The second part of this book is a seismic history of a cave mine. It describes the caving process from the beginning to the end. This part describes the past. The third part is about the future. Having over 10 years of data (not only seismicity) it seems reasonable to assume that it should be used for the future mine that will be developed below the present one. The underground mine called in this book Lift 1 is located 400 m below the open pit bottom and 1200 m below the surface. A new mine will be developed about 400 m below the present Lift 1 Mine. This will be Palabora Lift 2 Mine.

S. N. Glazer

Chapter 2. Applications of Seismic Monitoring in Combating Rock Burst Hazard

Abstract

This chapter describes the history of mine seismology. This history is not about hardware or software development but about interpretation and practical applications of the recorded seismicity analysis. It indicates that understanding and based on scientific principles analysis of recorded seismicity resulted in practical rock engineering concepts that in consequence improved safety and mining. This is what mine seismology is about. This took place in the age of analogue technology before the digital networks were invented. Practical outcomes of that pre-digital mine seismology are still valid and practiced at present. This establishes the intention of this book, which is to demonstrate that it is possible to make good use of the recorded seismicity. For this reason this book starts from the basis that is from what it takes to understand the input data for analysis and interpretation. It seems to me that at present the concept of understanding the input data is not considered as important.

S. N. Glazer

Chapter 3. Seismic Parameters and Their Physical Meaning

Abstract

This chapter describes the physical meaning of the seismic source parameters. Earthquake source parameters were derived over a long time period in order to get first of all a measure and then a better understanding of them. With time, seismology was introduced to the mines and it was found that there was a lot of similarity between the large earthquakes and the smaller size seismic events recorded in mines. Spectral analysis has become a standard technique used to estimate the source parameters of seismic events recorded by mine digital seismic networks. Simple source models of circular dislocations are used for the interpretation of seismic spectra and for the purpose of deriving source parameters. Seismic moment, corner frequency and seismic energy are inverted from the spectra that are corrected for the instrumental, distance and attenuation effects of each waveform and then averaged. Seismic source parameters are not measured, they are estimated. There is a difference between a measurement and estimation. Understanding these differences results in understanding the limitations of the source parameters. The reliability of seismic data is low. It is my experience that most or a lot of its users do not realise that the seismic source parameters they are using for interpretation purposes are only estimates. Their values are not derived from a process of a measurement. The reality is that the seismic source parameters are just an educated guess.

S. N. Glazer

Chapter 4. Seismic Source Parameter Ranges

Abstract

In this chapter there is a description of the seismic parameter ranges as they are in the mine. Chapter ends with a comparison between natural earthquakes and events experienced in mines. Here I have included some estimates of the released energy in a wide seismic magnitude range. Using seismic efficiency concept I have compared the released energy and seismic energy with TNT explosions and electricity demands of South Africa. Depending on the earthquake size its energy when converted into electricity would be consumed in less time as it takes to blink an aye or could meet the nearly 300 years demand.

S. N. Glazer

Chapter 5. Interpretation Methods of Mine Induced Seismicity

Abstract

Having described parameters the last chapter of part one deals with interpretation methods. This chapter also describes limitations of seismic data and of the interpretation methods. This is a very important part. The presented limitations of the seismic data should not be seen as pessimistic but as a realistic description of the problem. It is still possible to analyse and interpret data which originated in the process of an educated estimate. And what more nothing prevents these analysis and interpretations to be correct. But not all interpretation techniques can be successfully applied to this type of data. Despite the fundamental limitations of the recorded seismic data they still are a source of valid information, not only about the mining but also about the surrounding rock mass in which the mining is taking place. The strength of this data is based on two factors: that it is taking place all around the mine and that there is a lot of them. The fact that there is a lot of seismic data available allows for implementation of specific interpretation methodologies that in turn compensate for the input data limitations.

S. N. Glazer

Chapter 6. Palabora Seismic History

Abstract

At Palabora Mine the seismic system was separated from the Rock Mechanics Department and classified as a cave monitoring tool and consequently the seismic system became part of the Cave Management Section. As a consequence of this, the seismic monitoring priorities were clear, resulting in planning, testing and implementation of interpretation methods specifically for the purpose of cave monitoring and its management. In this chapter there is a description of the Palabora Mine seismic recording system as it was when I arrived at the mine. The following upgrades are discussed together with their influence on the quality of the recorded data. In the further part of this chapter I describe how in real time I have reported the caving progress. Firstly it was the stress caving process initiation followed by the central pillar failure and then its break through into the open pit. Seismic monitoring during production stoppages allowed for estimating the air gap size at the top of the cave. At the time this was very important as every manager at the mine still remembered the tragic consequences of a large in size air gap at Northparkes Lift 1 Mine.

S. N. Glazer

Chapter 7. Palabora Caving Process as Evidenced by Induced Seismicity

Abstract

This chapter is the main part of the book. In this chapter I am presenting how the seismicity was changing with the cave progressing from one milestone to the next one. The stress caving process was initiated in April/May 2002 and the caving process ended by the end of 2012. This chapter is backed by my experience from other cave mines as El Teniente, PT Freeport DOZ Mine or Northparkes Lift 2 Mine. The main value of all presented analyzes is how the interpretation results were achieved. For this reason some of the presented analysis is elaborate and full of details. This part includes the description the open pit North Wall failure. As it was spectacular it attracted a lot of attention. I was often asked if seismicity could be used to predict this failure. That there would be a failure it was expected but its size turned out to be a complete puzzle. It took a couple of years for the modelling research in the back analysis mode to come close to what has happened in reality.

S. N. Glazer

Chapter 8. Caving Process and Seismic Hazard

Abstract

Palabora experience indicates that seismic hazard and seismic risk change with the caving process but these changes are not always corresponding (Glazer 2012). In this chapter I have used the recorded seismic data to describe the methodology for monitoring the seismic risk. It is interesting to note that presented results based on the analysis of independent of each other parameters (for example energy release of small events, time histories and the Peak Particle Velocity of larger size seismicity) resulted in good agreement. It is important to recognize that some of the parameters are derived from the same seismic source values. In such case the analysis results do not complement each other but simply repeat each other. In this paragraph I do not propose an absolute scale for the seismic risk description. All results are relative and describe the changes in seismic risk over time. From presented in this paragraph analysis it emerges that with the caving process the highest seismic hazard is associated with initiation of the caving progress and then with the cave breaking through. This paragraph describes the methodology that allows for monitoring the changes in the seismic risk. As the seismic risk is directly associated with the stress levels then its estimations should result in more accurate seismic risk approximation.

S. N. Glazer

Chapter 9. Problems Related to Software Versions

Abstract

This chapter presents a riddle that for the first time I was confronted with when I was working at the gold mines. All was in place, good quality seismic system, and quality seismic data base and professional and experienced staff employed. The last years were good as the mining management was taking advice and had confidence in our data interpretation results. Unexpectedly the seismicity character changed. In practice one would expect that at this point in time the seismic response to the mining process has changed. This usually is bad news as it means change of seismic hazard. This was not the case. The reason was astonishing as it was the new seismic processing software. There were large differences in the seismic parameter values depending on the version of the software. This illustrated how dependent of the contractor the seismic source parameter values can be and really are. This was a direct prove that their values are not the real thing. This problem repeated itself while I was working for the Palabora Mine. Chapter describing this problem is different from the others as it is not about using seismic data to monitor the caving process or the resulting seismic hazard. Here interpretation was to find what are the differences and then decide are they acceptable or no. In the end one wants to know which software to use that is to assess which one results in data that can be explained by application of basic physical rules. To be honest I enjoyed this analysis as it was different from what I was doing. It was a case when I could use different approaches and have some fun.

S. N. Glazer

Chapter 10. Seismic Preconditioning Below Lift 1 and Its Influence on the Cavability of Lift 2 Cave

Abstract

There is no reason to question the fact that pulling from the cave resulted in fracturing the rock mass around the mine. Above the mine this process is validated by the fact that there was and still by the end of 2015 is production from the cave. If above the mine the rock mass would form one or a limited number of blocks then it would not be possible to mine out such rock mass. This is obvious. The rock mass above the mine was fractured and this fracturing process was recorded in form of seismicity. Seismicity was recorded not only from above the mine but also from below the mine. What more the amounts of recorded seismicity above and below the mine are not random in size and distribution but follow a specific consistent pattern. This pattern is controlled by the caving process and its milestones. From the beginning of 2002 until the end of 2013 about 50 % of the recorded seismicity, released seismic energy and seismic moment took place below the extraction level. This seismicity at some stage migrated down to −1200 m. This elevation will be the future Lift 2 Mine extraction level. In this chapter I have compared the seismicity recorded above the mine extraction level where the caving process took place and the rock mass was successfully mined out with that recorded below the mine. The rock mass below the mine will become Lift 2 cave. The main conclusion from this analysis is that the top volume of the potential Lift 2 rock mass is already de-stressed/preconditioned and fractured so it will cave rather than form an arch that will not cave resulting in the formation of a significant air void.

S. N. Glazer

Chapter 11. Palabora Lift 2 Mine Seismic System

Abstract

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.

S. N. Glazer

Chapter 12. Lift 2 Palabora—Seismic Hazard Monitoring

Abstract

This chapter takes advantage of the recorded and confirmed as bona fide seismic signature of the Lift 1 caving process for monitoring the Lift 2 caving process and related seismic hazard. A detailed and specific proposal how to monitor and report these matters is given. Methods for Lift 2 seismic hazard estimation are easy to list. What more the probability that they will be successful is high. This is due to the fact that the sources of Lift 2 seismic hazard are known because of Lift 1 experience. As always with nature there will be some unknown factors that will influence the Lift 2 seismic hazard. In nature nothing happens twice in exactly the same way. For this reason it must be expected that the seismic hazard history of Lift 2 might not be exactly as it was in case of Lift 1. There will be differences due to the increased depth of Lift 2 extraction level, which will be located 1600 m below the surface. This should result in higher energy release rates and consequently in increased seismic risk. This is not certain as in the early stage of the caving process the induced seismicity is strongly related to the production rates. In case of Lift 2 it is easy to figure out that the initial production rates and their increase with time will be different to these of Lift 1. On the other hand half of the recorded to date seismicity took place in the rock mass volume that will be Lift 2 cave. This seismicity has preconditioned this rock mass volume. Preconditioning decreases the seismic risk. In case of Lift 2 increased depth will increase the seismic risk while preconditioning will decrease this risk. The question remains in what proportions?

S. N. Glazer

Backmatter

Titel: Mine Seismology: Data Analysis and Interpretation
verfasst von: S.N. Glazer
Verlag: Springer International Publishing
Electronic ISBN: 978-3-319-32612-2
Print ISBN: 978-3-319-32611-5
DOI: https://doi.org/10.1007/978-3-319-32612-2