Articles

Hazards and Risks associated with shotcrete/ applied sprayed concrete as part of a ground support system – EAGCG Meeting May 2017

W Hartman

This presentation describes the hazards and risks associated with shotcrete or applied sprayed concrete as part of a ground support system. A number of incidents have been associated with shotcrete as part of the ground support system being subjected to strong ground motion. The presentation highlights certain deficiencies (e.g. design approach) in assessing the capability and performance of shotcrete as an appropriate containment system in pseudo-static to dynamic ground conditions. The presentation highlights the urgency for all ground support systems to be re-evaluated which are expected to perform and endure the effects of violent ground motion. The ground engineering principals will emphasize the important underlying factors when a ground support system is designed or selected. In this presentation I’ve urged that assessing the energy capacity of ground support systems is an important process in determining whether a specific surface support and reinforcement system is able to withstand the total energy that the rock mass could exert for a specified location, deformation, velocity, acceleration and displacement. Thus the presentation addresses the hidden dangers of applied sprayed concrete as part of a ground support system subjected to strong ground motion.

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Brown Coal Open Pit Mechanisms of Failure Geotechnical or Administrative? – Geotechnical Engineering in Brown Coal – October 2014

W Hartman

A number of significant historic ground failure incidents have occurred in the Latrobe Valley, some of which have prompted changes to operating arrangements and legislation. The historic incidents varies between overburden clearance, coal mining activities and overburden waste dumping activities. One of the most recent and famous failures associated with coal mining activities occurred at the Yallourn Open Cut Mine in November 2007. The alleged failure mechanism associated with this batter failure was that it was structurally controlled.

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Hazelwood Mine – Filling in the Cracks – Mine Subsidence Conference – August 2014

M Nicholson, R Polmear, J Faithful, W Hartman and G Wilkinson

Hazelwood Mine is located in Victoria’s Latrobe Valley, mining almost 20Mt / annum of brown coal for electricity production and steaming coal for briquette production. Mining commenced in the mid-1950s as a State owned and operated venture to support Morwell Briquette and Power and subsequently the Hazelwood Power Station. Both the power production and mining operations were privatised by the Victorian Kennett Government in 1996. GDF Suez Australian Energy currently own and operate Hazelwood Mine and Power Station. There are two other major brown coal mining and power station operations in the Latrobe Valley, both in the immediate vicinity of Hazelwood. Within the Latrobe Valley, over the past decade there have been a number of significant mine related ground movement events. Some of these events have resulted in significant impacts to operations, the landscape, infrastructure, surrounding communities and the environment. The details around these historical events and the degree to which the various Latrobe Valley mining operations contributed are beyond the scope of this paper. However, in reviewing these events GDF SUEZ Australian Energy identified opportunities for improvement in the monitoring and management regimes employed at the mine. These realisations prompted Hazelwood to go right back to the drawing board with the aim to develop a completely new risk based Ground Control Management Plan (GCMP) developed by Geohart. Ground movement events of the past have highlighted the need for rigorous ‘risk based’ Ground Control Management Plans (GCMP). Survey (spatial) monitoring plays a major role in Hazelwood’s GCMP GIS, used to aid in the development of understanding the correlations between ground movements and other site factors e.g. coal extraction, hydration levels survey system is now providing Hazelwood Management with high confidence ground movement data, in combination with other site monitoring data sets to facilitate timely, informed decision making.

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Brown Coal Structural Mapping with I-Site – Latrobe Valley Geotechnical Group Meeting – April 2014

B Pang, J Sidhu and W Hartman

Geohart Consultants was engaged by GDF Suez Hazelwood to develop a ground control management plan (GCMP). A structural geological model was developed for the mine as part of the GCMP.

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Brown Coal Open Pit Mechanisms of Failure Geotechnical or Administrative? – Geotechnical Engineering in Brown Coal – October 2014

W Hartman

A number of significant historic ground failure incidents have occurred in the Latrobe Valley, some of which have prompted changes to operating arrangements and legislation. The historic incidents varies between overburden clearance, coal mining activities and overburden waste dumping activities. One of the most recent and famous failures associated with coal mining activities occurred at the Yallourn Open Cut Mine in November 2007. The alleged failure mechanism associated with this batter failure was that it was structurally controlled.

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Non Destructive Integrity Testing of Rock Reinforcement Elements in Australian Mines – Wollongong 2010

W Hartman, B Lecinq, J Higgs and D Tongue

Non-destructive testing, used to study the integrity of the bolting systems in underground mining and civil construction industries, as an alternative method to the current hydraulic pull testing practice, is described. Non-destructive tests were carried out on a total of 227 bolts, comprising 89 rebar type bolts, 124 cable bolts and 14 split sets were tested in four mines across Australia. The purpose of these tests was to confirm the validity of the testing methodology for rock reinforcement systems used in mines and provide reassurance on bolt’s integrity, which could have been compromised during installation or affected by in-situ aggressive conditions causing corrosion. A complex stress wave analysis package, based on the processing of clear seismic signals imparted into the rock reinforcement element, was used. The seismic signals are processed by “Fourier Transform” into various criteria, which can be used to produce models of the elements, such as mechanical admittance, frequency spectra and velocity. These components are then used in the final modelling of the rock reinforcement element under analysis. The non-destructive integrity testing of rock reinforcement at these mines indicated that there is opportunity to further investigate the potential in effectively managing the risk of ground failure incidents in underground openings.

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Managing Geotechnical Risk through Non-Destructive Rock Reinforcement Testing Trialed at the George Fisher Mine, Mt. Isa – Sydney 2010

W Hartman, F Harvey, B Lecinq, J Higgs and D Tongue

Corrosion affects the performance of rock support and reinforcement at various underground mines, including the George Fisher Mine, where recent studies showed that this risk to mining operations is generally not well understood. Corrosion reduces the capacity and life expectancy of ground support and generally is undetected unless the traditional destructive pull out test is employed to detect defect bolts. Where it is still acknowledged that the pull out test has still an important role to play in determining critical bond lengths for static and quasi static ground support designs, it does not provide an underground operation with any reassurance regarding its bolt‟s integrity, which has been compromised by in-situ aggressive conditions. Non-destructive rock reinforcement calibration testing on single and twin strand cable bolts, rebar bolts and friction bolts at the George Fisher Mine enabled the testing team to detect bolts with compromised integrity in one area of the mine. The non-destructive rock reinforcement integrity testing conducted uses a complex “Stress Wave Analysis“ package based on the processing of clear seismic signals imparted into the rock reinforcement element that is being tested. The seismic signals are processed by “Fourier Transform” into various criteria which can be used to produce models of the element such as mechanical admittance, frequency spectra and velocity which are all being used in the final modelling of the rock reinforcement element under analysis. This paper highlights the enormous potential to effectively manage the geotechnical risk that corrosion presents for an underground mining operation.

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Understanding the Performance of Rock Reinforcement Elements under Shear Loading through Laboratory Testing – A 30-year History – AGCM Conference 13 Nov 2003

W Hartman and B Hebblewhite

This paper outlines the history of the developments over the last 30 years in understanding the performance of rock reinforcement elements under shear loading through laboratory testing and where the research stands today. Shear testing of rockbolts was fi rst conducted at the Swedish Rock Mechanics Research Foundation in 1974 in hard rock reinforced by rockbolts and was followed by a series of other research attempts around the world over the last 30 years. The factors looked into included the size (length and diameter) and number of bolts, the inclination of the bolts, the relative displacements in joints, joint roughness, the effect of compression, relative strength of rock and grout and elastic modulus of rock and grout. Analytical and numerical solutions were also proposed based on these experiments.

The paper takes the reader through these developments and critically analyses their achievements and shortcomings. It highlights the current understanding and its shortcomings, and identifies the need for further research. It then introduces the state of the art facility being established at The Mining Research Centre at UNSW for shear testing of reinforcement elements and the anticipated outcomes from this experimentation exercise.

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Block modelling for the purpose of visualising geotechnical borehole data at Tritton Mines

S. Hayes, M. C. Pang, W. Hartman, and S. Fitzgerald

Borehole logging data from Tritton Mine is utilised to develop a block model in which geotechnical data is interpolated to enable visualisation in 3D. Traditionally, geotechnical data such as Rock Quality Designation (RQD) and Modified Rock Mass Quality Tunneling Index (Q’ value) obtained from borehole logging is used in analysing the stability of underground openings (e.g. Mathews Stability Graph Method). The most representative data point from a borehole is chosen based upon the data considered closest to the point of interest. At Tritton Mine, an alternative approach has been used in a number of geotechnical block models to aid in the interpolation of geotechnical data amongst boreholes. The applicability of a block model is dependent on the choice of block size, search parameters and on developing appropriate geotechnical domains for use as constraints for such a model. A large block size can be useful for regional geotechnical understanding, while small block sizes are considered to be more appropriate for looking at localised scale. A number of block models using differing block sizes and search parameters were created and the block models were visually assessed together with the borehole data for optimum representation.

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Endeavor Mine Shines With an Integrated Geotechnical Service

Wouter Hartman

Consolidated Broken Hill (CBH) Resources is accessing new primary ore sources at their Endeavor Mine in Cobar, New South Wales. During this development phase the bulk of production is obtained from pillar extraction. This presents a technically challenging environment, especially considering the backlog of open voids inherited by CBH from the previous mine operators.

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Is Mining Coal at a 900M Below Surface at the Xuandong Coal Mine in China Challenging or Just Interesting Rock Mechanics?

Wouter Hartman, Mark Everson, Ben Pang, Sarra Hayes

Xuandong Coal Mine is mining coal in one of the most challenging underground environments in the world. This work has found that it is not only challenging but it also has the
composition for some interesting rock mechanics and ground control conditions. The paper highlights the extreme mining and rock mass behavior conditions encountered when mining coal at 900 m below surface. It was found that the ground control environment associated with geological weakness, low coal material strength and stiffness, was reasonably well controlled; however, the chain pillar geometry and design did not take these geological weaknesses into consideration. Some of the chain pillars employed were quite large, which resulted in floor punching and secondary floor heave, which causes extreme difficulty for production. No barrier pillar has been employed except for the
center 164-m-wide main headings pillar with a w/h ratio in excess of 40.

After assessing the location and geometry of a 200-m-thick dolerite sill overlaying the coal measures, we found the probability of it breaking up into to smaller fragments and producing a larger goaf to be low. Therefore, the influence of the dolerite sill on chain pillar loading is considered small compared to the low coal, immediate floor and roof rockmass strength.

It is further recognized that horizontal stresses could be locked up within the dolerite sill, which would likely result in regional bending that would be distributed through the chain pillars. This has, to some extent, already occurred, and the effects have been seen and felt through excessive floor heave, pillar punching, and coal bumps (seismicity). We’ve also found that there was a need to employ basic rock mechanics principals in assessing the stability of future multiple seam mining layouts.

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The Application of the Q Tunneling Quality Index to Rock Mass Assessment at Impala Platinum Mine

W. Hartman, M.F.Handley

Publications on hard rock tunnel support design in the South African mining industry have originated primarily from the gold mines during the last 50 years. Little has been
published to date on the platinum and chrome mines of the Bushveld Complex. This paper covers the search for a suitable design methodology for off-reef tunnels at Impala Platinum Mine, situated on the Western Lobe of the Bushveld Complex. The fall of ground accident statistics for off-reef excavations of the mine are presented and the available rock mass quality evaluation systems are reviewed. The Q Tunnelling Quality Index (or Q-Index) is selected because it assesses the important driving factors behind falls of ground at Impala. Two off-reef excavations are evaluated using the Q-Index, and it is shown that minor modifications are required for implementation at Impala. It will take some time before support design throughout the mine is based on the outcome of proper geotechnical investigations based on the Q-Index. Widespread implementation of such support designs should help to solve the fall of ground problem in off-reef excavations while at the same time reducing support costs.

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The Risk Management Process for Practicing Geotechnical Engineers

Wouter Hartman

A structured Geotechnical Risk Management Process will assist you and your geotechnical team in defining and exploring pathways to minimise and even eliminate geotechnical risk situations. Experience in managing rock related risks shows that existing practices had various degrees of harm and a number of hazards are disregarded and sometimes not included in mining organisations global risk management strategy. The geotechnical risk management process will allow practising geotechnical engineers to identify key rock related risks to the operation and / or organisation. This process should be associated with previous experiences and whereby the human factor involved in each of the rock related activity process is defined. A mine wide baseline geotechnical risk assessment where all the rock related activities, which include a rock related incident and accident analysis, are processed analysed, will identify the geotechnical hazards and their expected severity associated with a specific re-occurring mining practice. The subsequent control underlining the assessment and analysis process are all part of the geotechnical risk management process.

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The influence of mix design on boundary conditions of applied sprayed concrete for underground mine and civil tunnels.

W. Hartman

Sprayed concrete or typical known as shotcrete in the world of civil and mine tunnels has been used for a number of years and for various problematic issues. The issue that intrigues me most, is the fact that boundary condition is inevitably, neglected by most tunnel and geotechnical design engineers. It is without a doubt the most important aspect of implementing a proper design including the acquisition or control of boundary conditions from design to application.

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