7/29/2019 sismic

http://slidepdf.com/reader/full/sismic 1/6

ROCKBURST AND SEISMIC ACTIVITY IN UNDERGROUND

AUSTRALIAN MINES – AN INTRODUCTION TO A NEW

RESEARCH PROJECT 

Yves Potvin1, Marty Hudyma

1, and Richard J. Jewell

1 

ABSTRACT

Seismicity and rockbursts have been reported in Australian mines since the early 1900’s. The firstmodern seismic monitoring system was installed in an Australian mine in 1994. In the last few years,rockbursts and mine seismicity have become a serious mine safety issue and a constraint to economicviability in several Australian mines. By the end of 1999, there will be at least 14 seismic monitoringsystems installed in Australian mines. The Australian Centre for Geomechanics (ACG) has undertaken aproject entitled “Mine Seismicity and Rockburst Risk Management”. With the support of several of Australia’s largest mining companies, the project aims to address the rockburst and mine seismicity issue inAustralian mines by better defining the nature and extent of the problem and by developing risk analysistools to quantify the hazards associated with rockbursts and mine seismicity. This paper provides anintroduction to rockbursting and the research undertaken in this area to date, outlines the current extent of theproblem in Australia, and introduces the objectives of the new rockburst research project at the ACG.

INTRODUCTION

Rockbursts have been associated with numerous accidents and fatalities in South African, CentralEuropean and North and South American mines. Wagner (1982) wrote that “Rockbursts are the most serious

and least understood problem facing deep mining operations all around the world.” Brady (1990) latercommented “the pervasiveness of rockbursts suggests that they remain the major unresolved ground controlproblem in underground mining”. Despite significant research and progress in the last two decades, theproblem is still not well understood. With more and deeper Australian mines, high stress conditions androckbursts are becoming more common.

BACKGROUND

Distinction between seismic events and rockburstsA seismic event is a transient vibration or stress wave caused by an inelastic deformation in a rock mass.

The deformation may be in the form of physical displacement, intact rock cracking or rockmass degradation.Seismic events are a normal response of a rock mass to stress readjustments near an excavation.

Rockbursts are usually defined as seismic events that cause significant physical damage to excavations.Damage can vary in intensity from minor rock spalling to catastrophic rock mass fracturing. The dynamicnature of rockburst damage means that there is the potential for extensive damage to or complete destructionof supported and unsupported underground excavations.

1 Australian Centre for Geomechanics, 7 Cooper Street, Nedlands, Western Australia 6009

7/29/2019 sismic

http://slidepdf.com/reader/full/sismic 2/6

Rockbursts and Mine Seismicity in AustraliaMine seismicity and rockbursts in Australia have been reported as early as the turn of the century.

Large seismic events and rockbursts with related injuries and fatalities were reported in the Golden Mileunderground workings in Kalgoorlie (Kalgoorlie Miner, 1917). Rauert and Tully (1998) and Mikula andPoplawski (1995), report that mine seismicity was experienced at Broken Hill and Mount Charlotte during(and following) the mid 1960’s.

In 1994, the first modern, commercial seismic monitoring system in Australia was installed at MountCharlotte. MIM commissioned a seismic system in the Deep Copper Mine in 1994, followed by installationsat Pasminco Broken Hill in 1996, and Northparkes in 1996. The operators at Northparkes were notexpecting a rockburst problem, but rather, installed the microseismic system to monitor the initiation andpropagation of block caving. Duplancic and Brady (1999) used data from this seismic monitoring systeminstallation to create a conceptual model of the caving process.

Despite having large open stopes to a depth of 1400 metres, the Deep Copper Mine at Mount Isa has notyet experienced significant mine seismicity. This is primarily due to a locally low stresses, the relatively softore and rock mass, and a mining sequence that minimises the formation of stressed pillars. The mineseismicity recorded to date has been associated with fault related movements in stope crowns.

Rauert and Tully (1998) describe the Southern Cross area of the Broken Hill mine as having “one of the

highest occurrences of microseismic activity recorded in the Australian Mining Industry.” In less than twoyears of seismic monitoring, more than 6000 events have been recorded, albeit many of these are smallmicroseismic events. They have found the microseismic monitoring system to be a useful tool in day to daymine safety management and mine design.

Since 1970, records from the Australian regional seismograph network show the Mount Charlotte Minenear Kalgoorlie to be the source of 16 mining induced seismic events of a Richter magnitude 2.0 or greater(Mikula, 1998). Mount Charlotte has experienced the most severe seismic activity in Australian mines todate and most of the pioneering work in Australia on the use of seismic monitoring systems and managingthe risk associated with a seismically active mine has been conducted there. Poplawski (1997) performedsome advanced seismic parameter analyses at Mount Charlotte, which contributed towards betterunderstanding the seismic response to mining.

Since 1997, with a significant increase in rockbursts and mine seismicity, seismic monitoring systems

being installed at several Western Australian mines, including Forrestania’s (now Viceroy ResourceCorporation) Bounty mine; at WMC’s Long Shaft, Otter, Victor and Junction mines; and KCGM’s Super Pit.Recently, seismic monitoring systems have been installed at Homestake’s Darlot mine and New Hampton’sBig Bell operation.

What are the Conditions Causing the Rockburst Problem

Stress Conditions

High stress is one of the primary causes of rockbursts in mines. High stress conditions are typically acombination of the natural pre-mining in-situ stress and stress changes induced by mining. The pre-miningstresses measured in Western Australia are often high. The ratio of maximum principal in-situ stress(generally horizontal) to minimum principal in-situ stress has been measured near 3:1 in numerous locations

(Lee, 1998). Consequently, many WA mines are encountering high stress related ground conditions at only300 to 400 metres depth.

Mining induced stress changes further exacerbate the unfavourable in-situ stress conditions. Excavationsin rock induce stress concentrations and stress relief, creating biaxial or near uniaxial loading conditions nearopenings. This reduction in confining stresses can initiate rock mass degradation and brittle failure of intactrock. Depending on the nature of the loading system and the properties of the rock, failure may occur in astable yielding manner, or in an unstable dynamic manner. Both stable and unstable failure conditions resultin energy release and the generation of seismicity. However, it is unstable failure that has the greaterpotential to release significant energy release, causing large seismic events and potentially, rockbursts.

Geological Discontinuities

Abnormal stress conditions are rarely the unique cause of unstable failure and rockbursts. Geologicaldiscontinuities often play an equally important role. Many types of geological discontinuities includingfaults, shear zones, joints or bedding, and local variations in rock stiffness contribute to mine seismicity and

7/29/2019 sismic

http://slidepdf.com/reader/full/sismic 3/6

rockbursting. In reality, geological discontinuities play a dominant role in the deformation and failure of arock mass under load. The location, continuity, orientation and material properties of the geological featuresare significant factors in rock mass failure, and these characteristic dictate how energy is stored and releasedin a deforming rock mass.

It is important to note that while geological features play a role in the release of energy and thegeneration of seismicity, rockburst damage may not be coincident with the location or source of a seismicevent. Dynamic stress waves created by the unstable failure are often blamed for causing rockburst damageto nearby mine workings. Kaiser (1994) discussed some of the damage that can be caused by seismic events.These include:

• rock fracturing, resulting in rock bulking and possibly rock ejection,

• kinematic rock ejection due to seismic energy transfer, and

• structurally controlled gravity failure initiated by a seismic event.

Why is Rockbursting an Important Issue In Underground MiningIn the three years 1996 to 1998, three fatalities in WA underground mines occurred as a result of falls of 

ground potentially associated with large seismic events (WA Department of Mines and Energy onlinedatabase). In addition, rockburst related damage and falls of ground are responsible for:

• lost time injuries,• workforce “near misses”,

• equipment damage,

• substantial production delays and losses, and

• costly rehabilitation programs.Clearly, in rockburst prone and seismically active ground conditions, rockbursts are a risk to the safety of theunderground workforce.

The economic consequences of rockbursts are also significant. The consequences of rockbursts (injuries,equipment damage, production losses etc) can have a direct effect on the viability of mining operations.However, proactive measures undertaken to minimise the consequences of rockbursts can also be veryexpensive. These include:

• introducing new equipment to the mine, such as tele-remote loaders, or one pass rockbolters,

• increasing the amount of ground support and rock reinforcement,

• introducing new types of ground support such as fibrecrete or cone bolts, and

• implementing systems to minimise the exposure of the workforce to the rockburst risk, such aspreventing the workforce from entering parts of or the entire mine following mine blasts.

While proactive measures are effective in reducing the risk of rockbursts to the workforce, introducingunnecessary preventative measures impacts the economic viability of the mine.

Many mining operations in Western Australia are going deeper underground as near surface ore reservesare exhausted. It is a reasonable expectation that higher stress conditions will be encountered deeper belowthe surface. As mines go deeper and more excavations are created, the stress conditions and consequently,the conditions conducive to mine seismicity are likely to increase.

ROCKBURST RESEARCH

A Brief History of Rockburst ResearchFor decades, rockbursts have been associated with a large number of fatalities in South African, Central

European and North and South American mines. As a result, rockbursts have been a major topic of researchfor more than three decades in North America and South Africa.

As noted by Hedley (1992), microseismicity was discovered by accident in the late 1930’s duringexperiments with the measurement of shock wave propagation in an underground mine. It was later realisedthat by capturing the shockwaves resulting from mine seismicity, there was an opportunity to locate andmeasure the magnitude of mine induced seismic events. The first microseismic monitoring system wasinstalled in the 1960’s in a South African gold mine (Cook, 1964), and another later in Idaho in the US(Blake and Leighton, 1970). The first commercial microseismic monitoring system, the Electrolab MP-250,

became available in the late 1970’s (Mallot, 1981). These were installed in several US and Canadian mines(MacDonald and Muppalaneni 1983, Davidge 1984, Neuman 1985, Oliver and MacDonald 1985). These

7/29/2019 sismic

http://slidepdf.com/reader/full/sismic 4/6

systems operated as “black boxes”, with automatic data processing, and provided only approximate locationsand magnitudes of seismic events.

Research efforts in the 1980’s in North America and South Africa focussed on the development of newhardware and software to efficiently record and process the full waveforms of seismic events. As a result of this research, two sophisticated South African seismic systems, the ISS (de Kock and Mountfort 1998) andPSS/PRISM (Adams et. al. 1994) and one Canadian system, the ESG/Hyperion (Urbancic 1998) weredesigned to operate in mining conditions. These systems are now available commercially, and are widelyused in the mining industry. The precision in estimating event location and magnitude has improveddramatically. In addition, the application of sophisticated seismological analyses to study the mechanisms of seismic events has been made possible by the new technology (Young et. al. 1989, Gibowicz 1990,Mendecki 1993).

In the 1990’s, research concentrated mainly on data analysis, while refining the seismic system’shardware and software. The research direction in South Africa has been aimed towards rockburst predictionand alarm systems at the mine face (Mendecki, 1995). On the other hand, the Canadian Rockburst ResearchProject (CAMIRO, 1995) attempted to gain further understanding of the factors which generate seismicityand rockbursts in order to control the damage caused by these events, and to minimise their effect on mining.This variance in philosophy can be explained largely by the cultural differences between the two countries,

and by the differences in geological settings and mining methods.Ortlepp (1998) estimated that the South Africans have spent the equivalent of $A15M per annum overthe last few decades on the rockburst problem. The Canadian Rockburst Research projects (Hedley 1992,CAMIRO 1995) were funded to a total of $A10M over the last 10 years. The total Canadian expenditure onrockburst research during this period could easily exceed $A30M, if one included the purchase, installationand monitoring of microseismic systems at operating mines.

Reports of rockbursts and mine seismicity in Australian mines has increased in the last few years. Bythe end of 1999, there will be at least 14 mines with seismic monitoring systems in Australia, with a totalhardware cost in excess of $A2M. While the state-of-the-art technology can be purchased from South Africaand Canada, the Australian mining industry needs to develop local experience in the application of thetechnology to the unique Australian geological and mining environments. The proliferation of microseismicmonitoring equipment in Australian mines will provide an extraordinary opportunity to study the rockburst

phenomenon in local mining conditions.

Mine Seismicity and Rockburst Risk Management ProjectIn 1998, the Australian Centre for Geomechanics (ACG) solicited support for a project that would help

Australian mines deal with rockburst problems being encountered. Support for the project was initiallyreceived from WMC Resources Limited, Kalgoorlie Consolidated Gold Mines, Homestake Australia, andSons of Gwalia Limited. The project is also financially supported by MERIWA (Minerals & EnergyResearch Institute of Western Australia). The project started in July 1999, with the hiring of a full timeproject leader. In September 1999, two PhD students were recruited for the “Mine Seismicity and RockburstRisk Management” (MSRRM) project. Two more PhD students were added to the project in July 2000.

This project is seen to be multidisciplinary and the research team is comprised of a mix of geologists,seismologists, rock mechanics engineers, and mining engineers. The project leader is a rock mechanics

engineer and the PhD students are being drawn from suitable candidates from the full range of disciplines. Anumber of different academic staff will provide expertise directly to the project and through the co-supervision of PhD students, while an advisory panel or steering committee has been establishedincorporating personnel with the required range of expertise from around the world. The objective will be toutilise these personnel to keep the project on track and to expedite access to the outcome of previous work.

The goal of the MSRRM project is to advance the responsible application of seismic monitoring systemsand deliver strategies to quantify and mitigate the risk of mine seismicity and rockbursting. There are threedistinct steps in this goal.

The first step is to optimise the use of microseismic monitoring technology in Australia. This involvesapplying data analysis techniques and methodologies developed overseas and accelerating the application of seismological analyses in Australian mines. Another important component is to help mine-based seismicmonitoring personnel to fine-tune their seismic systems. Microseismic monitoring systems are similar toautomobiles in that they need routine adjustment and tuning to perform optimally. If a seismic system is not

7/29/2019 sismic

http://slidepdf.com/reader/full/sismic 5/6

periodically tuned for the seismicity occurring in a mine, the system will provide less data or less useful data,and ultimately less valuable information.

The second step is to develop a local understanding of the mine seismicity and rockbursting occurring inAustralian mines. Detailed seismic data analysis is time consuming and mine site personnel often do nothave the time and resources to undertake these analyses. In addition, the Australian geological and miningenvironments tend to be small and three dimensional in geometry - generally quite different from theenvironments encountered in many of the overseas mines. Consequently, the key seismic parameters forunderstanding rockbursting in Australia, or the application of these parameters may be different from thoseused overseas. To best understand local rockbursting and mine seismicity, existing parameters will have tobe applied in new ways, or new parameters developed. Ultimately, a comprehensive understanding of thelocal sources of mine seismicity is needed before effective risk analyses and risk mitigation strategies can bedeveloped.

The final step is to develop the link between rockbursting, seismic monitoring, risk assessment and bettermining decisions. Components of this work involve hazard identification, risk assessment and quantificationand risk management tools. When the geological and stress conditions that are conducive to rockburstingand mine seismicity are understood, the most appropriate risk mitigation techniques can be identified. Thesetechniques may include: improved ground support systems, changes to blasting practices, or mining method

modifications.It is understood that the overall objectives are challenging and it is unlikely that all will be completelyachieved. Nevertheless, it is important that they are addressed. It is expected that the comprehensive,multidisciplinary nature of the research team will enable them to make significant progress towardsachieving the objectives.

SUMMARY

The incidence of rockbursting in Australia is likely to worsen as mines go deeper and encounter higherstresses. State-of-the-art microseismic monitoring technologies can provide new insights into themechanisms of rockbursts and mine seismicity. However, successfully applying the new technology inAustralian mining conditions is a complex task. The Australian Centre for Geomechanics has initiated a

project to improve our understanding of these issues and accelerate the application of seismic monitoring inmines. This “Mine Seismicity and Rockburst Risk Management” project will help Australian miningcompanies to maximise the benefit from their investment in microseismic monitoring.

ACKNOWLEDGEMENTS

The authors acknowledge the financial support from WMC Resources Ltd., Kalgoorlie ConsolidatedGold Mines, Homestake Australia, Sons of Gwalia Limited and the Minerals & Energy Research Institute of Western Australia.

REFERENCES

Adams, D.J., Hemp, D.A. and Gurtunca R.G. (1994). “A Seismic System as a Tool in Rock Engineering”.Proc. International Workshop on Applied Rockburst Research , Santiago, pp. 89-100.

Blake, W. (1982). “Microseismic Application for Mining… A practical Guide”, Mining Research ContractReport #J0215002, USBM.

Brady, B.G.H. (1990). Preface of Rockbursts and Seismicity in Mines. Minneapolis, A.A. Balkema.CAMIRO (1995). “Canadian Rockburst Research Program 1990-1995”. Vol 1-6, CAMIRO Mining

Division, Sudbury, Canada.Cook, N.G.W. (1964). “The Application of Seismic Techniques to problems in Rock Mechanics”.

 International Journal Rock Mechanics and Mining Science, Vol. 1, no 2, pp.169-180.Davidge, G.R. (1984). “Microseismic Monitoring at Falconbridge Mine, Falconbridge Ontario”. CIM 

 Bulletin, Vol. 77, no 868, pp.45-59De Kock, E. and Mountfort, P. (1998). “The Integrated Seismic System, in Mine Seismicity and Rockburst

Risk management in U/G Mines”. Australian Centre for Geomechanics Workshop, Notes Section 13,Perth, Australia.

7/29/2019 sismic

http://slidepdf.com/reader/full/sismic 6/6

Duplancic, P. and Brady, B.H. (1999). “Characterisation of caving mechanisms by analysis of seismicityand rock stress.” Proceeding 9th International Congress on Rock Mechanics, Paris, A.A. Balkema, Vol.2, pp. 1049-1054.

Gibowicz, S.J. (1990). “The mechanism of Seismic Events Induced by Mining”. Rockburst and Seismicity inMines, Proceedings of the 2

ndinternational Symposium on Rockburst and Seismicity in Mines,

Minneapolis, A.A. Balkema, pp. 3-27.Hedley D.G.F. (1992). “Rockburst Handbook for Ontario Hardrock Mines”. CANMET Report SP92-1E,

305p.Kaiser, P.M. (1994). “Support in burst-prone ground.” Proc. International Workshop on Applied Rockburst

Research, Santiago, pp. 61-83.Kalgoorlie Miner (1917). “Sensational mining fatality, severe earth tremor causes fall of rock on Great

Boulder mine, one man killed, others injured”. 29 August 1917. Kalgoorlie. Western Australia.Lee, M.F., Pascoe, M.J., and Mikula P.A. (1999) “Stress fields in Western Australia – A

Kambalda/Kalgoorlie Case Study.” Australian Centre for Geomechanics Workshop Notes Section 2,Perth, Australia.

MacDonald, P. and Muppalaneni, S.N. (1983). “Microseismic Monitoring in a Uranium Mine”. RockburstPrediction and Control, IMM, London, pp. 141-146.

Mallot, C. (1981). “Theoretical Limitations of Microseismic Transducer Systems”. Proceedings of the 3

rd

 Conference on Acoustic Emission/Microseismic Activity, Penn State University, pp. 681-693.Mendecki, A.J. (1993). “Real Time Quantitative Seismology in Mines.” 3

rdInternational Symposium on

Rockburst and Seismicity in Mines, Kingston, A.A. Balkema, pp. 287-295.Mendecki, A.J. et al (1995). “Seismology for Rockburst Prevention, Control and Prediction”.

SAIMM/SIMRAC Symposium, Johannesburg, South Africa, September.Mikula, P.A. and Poplawski, F.P. (1995). “The seismic monitoring decision at Mt. Charlotte gold mine.”

Proceedings 6th

Underground Operators’ Conference. Australasian Institute of Mining and Metallurgy,Kalgoolie, WA, pp 79-86.

Mikula, P.A. (1998). “The Australian Perspective: Seismic Risk Management at Mt. Charlotte Gold Mine.”Australian Centre for Geomechanics Workshop Notes Section 2, Perth, Australia.

Neumann, M. (1985). “Microseismic Monitoring at Campbell Red lake Mines Ltd.” Mines Accident

Prevention Association, 54th

Annual Meeting, Ontario, Canada.Oliver, P.H. and MacDonald, P. (1985). “The monitoring system at Creighton Mine, INCO Ltd.”

Proceedings 4th Conference Acoustic Emission/Microseismic Activity. Penn. State University.Ortlepp, W.D. (1998). “The South African Perspective”. Australian Centre for Geomechanics Workshop

Notes Section 4, Perth, Australia.Poplawski, F.P. (1997). “Seismicity underground with particular reference to rockburst problems at Mt.

Charlotte mine.” PhD thesis, The University of Melbourne, Melbourne, pp. 319.Rauert, N.S., and Tully, K.P. (1998). "Integration of a Microseismic Monitoring System in Mining the

Pasminco Broken Hill Southern Cross Area." Seventh AusIMM Underground Operators' Conference,Townsville, Queensland.

Urbancic, T.I. (1998). “The ESG System in Mine Seismicity and Rockburst Risk Management in U/GMines”. Australian Centre for Geomechanics Workshop Notes Section 15, Perth, Australia.

Wagner, H. (1982). Preface of Rockbursts and Seismicity in Mines. Johannesburg, South African Instituteof Mining and Metallurgy.

Young, R.P., Talebi S., Hutchins D.A. and Urbancic T.I. (1989). “Analysis of Mine Induced MicroseismicEvents at Strathcona Mine, Sudbury, Canada”. Pure and Applied Geophysics. Vol.129, pp. 445-474.