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A new watersoluble binder for mineral ore pellets has been developed by the sulfonation of bituminous materials. A highly effective binder for iron ore pellet making is obtainable from bituminous materials produced in the hightemperature cracking of crude oils. This paper deals with production process and basic properties of this binder as well as new applications in the field of iron ore pelletizing.

Jan 1, 1974

By de Bruin J H

A method new to Australia was used for sinking a vertical shaft at Broken Hill in the development of Pasminco Southern Operations No 5 Ventilation Shaft. The 6 m diameter shaft of 820 m depth was planned with a construction method which allowed access for ground support as sinking proceeded by mechanical excavation.The vertical shaft boring machine, known as the V-Mole, was originally developed in West Germany. The machine operates in a manner similar to a full face TBM but vertically and the cuttings drop down a previously constructed raise. The raise is subject to stringent tolerance on verticality and must remain stable for the duration of reaming.

Jan 1, 1993

By Grady B. V, Ault A. R, Newman O. M G, Fraser R. J, Malcolm J. McPhersqn

In all electrolytic zinc plants cadmium is removed as an impurity prior to the zinc electrowinning stage of the process. Cadmium metal is the favoured form of this by-product and most plants use an electrolytic route for its production. The formation of dendrites in cadmium electrowinning processes is the major limitation to deposition rates. There is an economic incentive, therefore, to better understand the factors affecting their growth. A technique that has been used by others to examine fundamental aspects of dendrite growth has been applied to industrial strength electrolytes. It involves potentiostatic deposition in a cell containing the electrolyte of interest. The variation in the current with time at a given overpotential allows the determination of the dendritic growth induction time. A method was developed (the Locus method) from the investigation of a set of such potentiostatic curves, obtained over a range of applied overpotentials, that appears to give a measure of electrolyte quality with respect to dendritic growth in galvanostatic deposition. The Locus technique predicts that zinc at industrial concentrations in cadmium electrolytes should have a significant effect on morphology and that deterioration of morphology will occur as the zinc concentration in the electrolyte is increased. This effect is consistent with literature prediction and was shown to relate to a reduction of the diffusion limiting current density. Magnafloc R333 is used as an additive at Pasminco Metals-EZ to control the morphology of cadmium deposits and the Locus method was successful in predicting its dendrite inhibiting properties. A possible mechanism is discussed. This work has opened avenues for future research with respect to a technique that may have an industrial application in electrolyte characterisation and has pointed to a direction in which better understanding of galvanostatic dendritic growth may be found.

Jan 1, 1993

By Segnit ER, Boow J

The start up operations of Western Mining Corporation's Kalgoorlie nickel smelter encountered troubles due to the high magnesia content of the concentrates. The flash smelter slags, with higher than normal magnesia content, had a much higher melting point than the normal low-magnesia, predominantly fayalite slags usually produced in nickel smelting. Investigations were made of the structures, melting points and viscosities of the Kalgoorlie smelter slags, as produced, and with additions of silica or lime.

Jan 1, 1980

By D Henderson, K Howie

In 2005, Glass Earth Limited (GEL) commissioned two large area detailed airborne geophysical programmes in the Taupo Volcanic Zone (TVZ). In the first survey Bell Geospace Ltd of Scotland conducted an Air-FTG« (airborne Full Tensor Gravity Gradiometry) survey covering 2338km2 at 300m line spacing. The second survey by UTS Geophysics, Australia included detailed airborne magnetic, radiometric and digital terrain data capture covering 5341km2 at 150m line spacing.   From the detailed geophysical data collected it is possible to identify major deeply penetrative crustal structures within the TVZ, as well as define subsurface geological features, such as intrusive bodies and alteration zones. These major deep crustal structures are thought to have a controlling influence on the distribution of epithermal gold mineralising systems, and along the corridors defined by these deep crustal zones, the chances of discovery of an economic epithermal gold discovery are greatly increased.   In this paper GEL gives some examples of the application of its integrated data driven approach to exploration in the TVZ at both regional and project scale. The paper focuses on how GEL identifies regional scale highly prospective deep crustal structures. Then, using the Horohoro epithermal gold system as an example, we show how GEL applies innovative geological and geophysical data processing to model and understand detailed subsurface geology, focusing subsequent exploration to ensure the best opportunity for a new economic epithermal gold discovery.

Jan 1, 2007

By Hagan T. N

Quite apart from economic considerations, the following performance parameters must be considered when selecting an explosive for a particular blasting operation. 1. total energy yield/kg, and more particularly, strain energy/kg and bubble energy/kg of charge 2. charge weight/m of blasthole 3. sensitivity of the charge 4. water resistance of the charge The effective division of an explosive's total energy into strain energy (SE) and bubble energy (BE) is explained as is the influence of each energy component on blast results. Because some rocks require a high strain energy for effective breakage, while others are most satisfactorily fragmented by bubble energy, values of SE and BE are more meaningful than those of total energy. Unfortunately, our extensive knowledge of the effects of certain variables on total energy has not yet been completely supplanted by the influence of these variables on SE and BE values. Relative SE/kg and BE/kg values are presented for a range of explosives. The 'charge density of ammonium nitrate/ fuel oil (ANFO)-type explosives is essentially constant throughout the length of the charge; because of their compressibility, slurry

Jan 1, 1974

By A J. Burchell

The introduction reviews the tunnelling carried out in Singapore since the early 1980s. Between 1983 and 1990, Phases 1 and 2 of the mass rapid transit system were constructed. These included some 20 km of bored and cut and cover tunnels together with 18 underground stations. Some particular points of interest in this massive project are briefly commented upon. Reference is also made to other underground or underwater schemes undertaken during this period such as the proposed large caverns project and the submerged tunnel to Pulau Seraya. A description of the subsurface works, now under construction in Singapore, follows. This includes an all underground North-East railway line 20 km long with 16 stations. At a budget of US$ 3 billion, this is a major civil engineering undertaking. Another project is the extension of the railway to Changi Airport which involves 3.5 km of twin tube tunnelling together with a major underground station which is fully integrated into the airport terminals. An on-going program of further major railway extensions over the next 10 to 15 years is in place and an outline is given of some of the most important underground sectors. Other proposed projects such as the underground roads system and the deep level sewers are briefly described. Together they demonstrate the very significant volume of underground construction scheduled for the next century in Singapore.

Jan 1, 1999

By J Andrina, D Richar, R Smart, A Neale

The Grasberg is a large copper and gold open pit mine operated by PT Freeport Indonesia and located in the high equatorial mountains of Papua Province, Indonesia. The climate is alpine/sub-alpine with little seasonal variation in temperature and rainfall. The annual precipitation varies from about 3000 to 5000 mm over short distances around the Grasberg, but in general, an average daily precipitation of 10 mm per day applies and leaching of the overburden is continuous throughout the year. Mining commenced in 1988, and almost all of the overburden mined up to 2003 was potentially acid forming. From 2003 to the end of the Grasberg pit operation in 2014, approximately 70 per cent of the overburden will be potentially acid forming and 30 per cent limestone. A major focus of the investigations is developing strategies to maximise the beneficial use of the limestone that will be mined. Laboratory columns and field test pad investigations have been ongoing for six years examining limestone blends. Trial dumps utilising truck placement and conveyor/stacker placement and blending of limestone and acid generating rock have recently been constructed. In addition, based on initial results, investigations aimed at further evaluating the performance of limestone covers in this high rainfall environment have commenced. A significant finding has been the identification of strong armouring layers on sulfide surfaces within well-blended material and under limestone covers. These layers effectively isolate sulfides and thus progressively slow the oxidation rate to a level where the alkalinity load from the limestone exceeds the rate of acid generating. ARD is controlled and neutral low metal drainage results. The results have demonstrated that although limestone blending is effective, it is necessary to ensure that all size fractions within the blend receive adequate acid neutralising capacity to buffer the potential acidity. Because the sulfur content generally increases and the acid neutralising capacity decreases with decreasing particle size in limestone blends, the amount of limestone required greatly exceeds the stoichiometric requirement. This paper describes the development of limestone blending specifications for potentially acid forming overburden and presents the results of the ongoing limestone cover trials at the Grasberg mine.

Jan 1, 2003

By D P. Blair

Rio Tinto’s Hope Downs Operations are currently mining iron ore in their South Central Pit. Prior to the commencement of mine operations, Hope Downs carried out an extensive archaeological investigation and identified an ancient rock shelter lying within the proposed mine boundaries. The site is significant to the traditional owners/custodians of the land in this part of the Pilbara, and thus the final pit design was changed to preserve the rock shelter, which now lies 30 m outside the mine boundary. In order to further preserve this ancient dwelling from blast-induced damage, blast design procedures were improved over time to minimise the vibration impact when blasting close to the shelter. Blasting and vibration monitoring commenced in May 2008 using pyrotechnic delay sequences and normal-direction firing. In October 2009 electronic delays were used to reverse-fire blasts close to the shelter in order to create a damage zone between the initiating holes and the rock shelter. A detailed statistical analysis of the vibration data shows a reduction in the higher levels of vibration for blasts fired after October 2009, which is most likely caused by the created damage zone. In May 2010, a site-specific vibration model was developed and implemented, and based on Monte Carlo waveform superposition. This model was used to give a further insight and improvement to the blast delay sequences when blasting close to the shelter. However, such models are expensive to implement and have limitations, which reduces their potential for estimating the probability of getting an excessive vibration due to a given blast design. In this regard, it is more realistic and significantly less expensive to use a recently developed probabilistic analysis based on simple charge weight scaling. This analysis shows that there was a higher probability of exceeding prescribed vibration limits at the rock shelter for blasts fired before October 2009 than there was for blasts fired after October 2009.

Nov 8, 2011

By Lawson E, Purkiss S. A R, Van Ashwegen p C

It is only in the past decade or so that industrial exploitation of biological resources and techniques has become regarded as a distinct discipline. Commonly referred to as Biotechnology, it embraces biochemistry, microbiology and the engineering sciences and is mainly aimed at the biological conversion of suitable raw materials into desired end products. The catalytic agents are more often than not bacteria although other micro-organisms such as fungi are used. The range of micro-organisms used is wide and the choice depends upon the desired end product, which in turn depends upon the metabolic attributes, genetically engineered or otherwise, of the cells. The metabolic diversity of micro-organisms has been applied to processes such as antibiotic production, food processing, brewing and chemical production, and of course extraction of metals from ores. Metabolic diversity is, to a certain extent, based on nutrition, which, in its simplest form, can be divided into energy source, carbon requirements and nature of the electron donor producing reducing power to the cells. The source of energy may be light, in which case the organisms are phototrophic (eg green plants, algae). The carbon requirements and reducing power may come from organic sources. These organisms are then called heterotrophic (eg man and most bacteria, including the well known Escherichia colt). However, there is a group of bacteria whose energy metabolism depends upon chemical redox reactions, use inorganic carbon (CO2) and obtain their reducing power from reduced chemicals such as metal sulphides. These are known as chemolithotrophs. They play an important role in mineral recycling in nature and are also ideal for extraction of metals from ores. This is because they are extremeophiles being acidophilic (grow at very low pH) and sometimes also thermophilic (grow at very high temperatures). These bacteria operate in such hostile environments that competition, or contamination, by other organisms does not occur. Extraction of metals from ores by chemolithotrophic bacteria is commonly referred to as biohydrometallurgy. Other related areas are bioadsorption of metals from dilute solution,- microbial treatment of metal contaminated wastes and removal of toxic chemicals produced or used during mineral processing. This paper basically reviews the work that Gencor has undertaken in the field of biohydrometallurgy and the advancements it has made in commercialising the technology, but also touches on certain long-term areas of research that are currently under investigation.

Jan 1, 1995

By Hommert P. J, Brown B

Early attempts at estimation of stress wave damage in blasting by use of finite element analysis met with limited success due to numerical instabilities that prevented calculations from being carried to late times. An improved damage model based on microcrack growth in tension allows finite element calculations which remain stable at late times. Estimation of crater profiles for blasting experiments in granite demonstrate successful simulations with this model.

Jan 1, 1990

By M Stephens, T A. Sutra

Currently, there are several open pit mines with production rates of about 200 000 tpd of ore that are reaching the end of their economic lives. In most cases, the remaining orebody extends to depths greater than 300 m below the pit limit, leaving hundreds of millions of tons of reserves that can only be recovered by means of an underground mining method. One such method used for mass production is block caving. This paper presents a ventilation system for a four-zone block cave mine operation developed on a footprint 1000 m wide and 1200 m long. The system is designed for a mine with a nominal production rate of 120 000 tpd of ore using diesel powered units on the production and reduction levels. It discusses the air quantity requirements for the worst case scenario, which is anticipated to occur five years after the mine has reached its full production capacity. Finally, it summarises the results of computer modelling exercises that were carried out to determine an economic ventilation infrastructure that includes shafts, drifts, main fans, and ventilation control devices.

Jan 1, 2005

By K E. Mudzanani, T A. M Msagati, D T. Maiga, T T. Phadi, M R. Letsoal, B M. Chabalala, S W. Limani

This paper addresses critical environmental, health, regulatory and scientific concerns related to gold mining activities in the specific area of Barberton, Mpumalanga, South Africa. The paper thus calls for informed decisions to be made by the authorities to safeguard both the environment and people’s health. The novelty of this study is based on its comprehensive nature of the simultaneous assessment of both cyanide and potential toxic elements (PTEs) in tailings, while taking into account their composition variability over time. By combining these aspects, it is then possible to provide a holistic understanding of the contamination risks associated with mining tailings and thus justify the need for regular monitoring and supervision to ensure compliance against regulatory limits. Additionally, this paper considered investigating the dynamic nature of tailings, which are subject to changes in their chemical composition due to exposure to weathering by various agents. In this study, the determination of weak acid dissociable (WAD) and free cyanide in tailings was performed using a validated method employing the South African Council for Mineral Technology (MINTEK) Laboratory Cynoprobe. The PTEs in tailings were determined by an inductively coupled plasma optical emission spectrometer (ICP-OES). The results revealed that the tailings contained primarily substantial amounts of PTEs, including Fe (87 566 to 37 800 mg/L), Cu (271 to 110 mg/L), Mn (2100 to 680 mg/L), Ni (400 to 390 mg/L), Zn (180 to 68 mg/L), Cr (645 to 510 mg/L), As (450 to 128 mg/L), and Pb (up to 35 mg/L). The cyanide concentrations in tailings varied between 0.20 mg/L and 0.26 mg/L for free CN (with a mean of 0.23 mg/L in water leaching), 0.23 mg/L to 0.28 mg/L for free CN (with a mean of 0.25 mg/L in alkali leaching), 0.24 mg/L to 0.35 mg/L for WAD CN (with a mean of 0.28 mg/L in water leaching), and 0.31 mg/L to 0.39 mg/L for WAD CN (with a mean of 0.35 mg/L in alkali leaching). The measured concentration of cyanide and the PTEs was compared to the minimum permissible levels enforced by the South African Department of Water and Sanitation (DWS) and the Water Research Commission (WRC) regulations that govern the disposal of hazardous constituents into the environment. Additionally, it was observed that the concentrations of contaminants in the tailings exceeded the acceptable minimum limits for hazardous waste exposure, posing risks to the environment and human health.

Apr 16, 2024

By T McConachy

New opportunities for miners are beginning to appear through new discoveries, improved knowledge and access to vast unexplored areas of the deep sea and continental shelf. Recent discoveries of undersea hydrothermal deposits show evidence of high-grade mineralisation, although in many instances the extent of the resource is still unknown. The promise and the difficulties of undersea mining have been evident since attempts were first made to mine manganese nodules in the 1960s. The physical nature of the undersea resource is a key influence on its mining potential; and environmental issues will also become increasingly important. This paper explores these issues and concludes with a description of the immediate to medium term applied research required to develop this industry and the spin off that such research can provide.

Jan 1, 2000

By W L. Daniels, C Stilson, C Zimmerman

Mineral sands mining for ilmenite, rutile and zircon has disturbed over 1000 ha of prime farmland in Virginia (USA) since 1997 and additional areas are likely to be disturbed in Virginia and North Carolina (USA) over the next 15 years. Full-scale mining operations at the Old Hickory Project in Virginia were initiated in 1997 by Iluka Resources Inc. and restoration protocols have continued to evolve in response to a variety of economic, technical and social issues. Early on, the return of these lands to agricultural row-crop production was complicated by vertical stratification of tails + slimes and lateral variability in soil physical conditions in the reclaimed pits and by limited topsoil return. Virginia Tech and Iluka have worked cooperatively with all stakeholders for over 20 years to review the pre-existing research base, conduct new and innovative site-specific research and thereby provide reasonable expectations of post-mining soil productivity levels. In 2004, Virginia Tech, Iluka Resources and a local leaseholder (Carraway-Winn family) agreed to jointly manage a 45 ha research demonstration farm where the long-term effects of alternative soil reconstruction practices are being rigorously monitored for both row crops (corn and wheat) and forage production. All mined land crop yields are also compared to an adjacent undisturbed exceptional quality prime farmland soil. Row crop yields between 2005 and 2010 were significantly above county average yields (regulatory target level) and approximately 75 - 80 per cent of undisturbed adjacent prime farmlands. The state regulatory authority has recently relaxed its position on the necessity of topsoil return versus use of topsoil substitutes based on appropriate on-site research results and the ability of the reclaimed soils to meet comparative local county crop yield targets. This cooperative effort allows all clientele groups to objectively assess the post-mining productivity of these mined lands while providing an invaluable educational opportunity for the mining industry. CITATION:Daniels, W L, Stilson, C and Zimmerman, C, 2012. Development of effective rehabilitation protocols for mineral sands mining in Virginia, USA, in Proceedings Life-of-Mine 2012 , pp 97-104 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 10, 2012

By S Hapugoda

Iron ore oxide and oxyhydroxide minerals such as haematite (eg various types of martite and microplaty haematite), different forms of goethite, magnetite, hydrohaematite and kenomagnetite were analysed using optical microscopy, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) techniques, to determine the type and proportion of deleterious elements present and the chemistry of associated gangue minerals. The aim was to characterise elements potentially deleterious for agglomeration and steelmaking, eg sulfur, phosphorus, aluminium and silicon and correlate their distribution with mineral texture and association, to provide feedback on downstream processing performance and product quality.Examples of characteristic mineral associations are shown from various genetic styles of iron ores, including magnetite banded iron formation (BIF), BIF-derived martite-goethite and skarn-type magnetite ores.A number of examples are presented demonstrating the benefits of the use of combined techniques of reflected optical microscopy, SEM and EPMA data to reliably identify ore and gangue minerals and their associations in different types of iron ores.

Jul 11, 2011

By A Boucher, M Baudin, P Androszczuk, I Minniakhmetov, A Rigby, P Machado, M Wright, B Van Dijken

IGO Ltd’s (IGO’s) Nova Operation (Nova), which is 160 km east-north-east of the town of Norseman in Western Australia (WA), mines and processes nickel-copper-cobalt (Ni-Cu-Co) sulfide ore from the magmatic Nova-Bollinger Deposit (Nova-Bollinger), which is hosted by the Mesoproterozoic age high-grade metamorphic rocks of the Albany Fraser Orogen. Over its 56-month life-of-mine (LOM) operations to 31 December 2020, Nova has processed 5.63 Mt of ore grading 2.04 per cent Ni, 0.86 per cent Cu and 0.07 per cent Co from its underground mine. At the end of 2020, both the Nova-Bollinger JORC Code reportable Mineral Resource estimate (MRE) and Ore Reserve estimate (ORE) were >90 per cent classified in the highest JORC Code confidence categories of Measured Mineral Resource and Proved Ore Reserve respectively. The high JORC Code classification confidences assigned to the Nova-Bollinger MRE and ORE results from the 386 km of surface and underground diamond drill testing of the deposit to a nominal 12.5 by 12.5 m pierce point spacing in mineralisation. The close spaced high-quality drilling and bulk mining method employed at Nova has effectively removed the need for any grade control modelling outside of the MRE process. Importantly, having only the one fully drilled out deposit being mined and only the one process plant, Nova’s reconciliation process is in the fortunate situation of not being confounded by issues such as external ore sources and constant updates as new grade control information becomes available. IGO’s Nova reconciliation processes are focused on reconciliation ratios that quantify operational period differences between the MRE and ORE head grade and tonnage forecasts and the process plant head actuals. These metrics have been used to identify key reconciliation issues and have initiated several studies into the causes for specific reconciliation results, which are discussed in the paper. In late 2020, a period of sustained poor reconciliation results led to the recognition that increasing the understanding of risk between the MRE and ORE should be investigated. To assist with modelling stope level risk within the mine plan and subsequent reconciliation, an attempt was made to develop a formula to quantify ‘stope risk’ from MRE metrics such as sample spacing, kriging efficiency and so on

Mar 22, 2022

By F Owusu-Mensah, F Nsarko

The Obuasi Mine has been in operation for the past 100 years. Within this period a host of mining methods have been employed during its various changing phases. The causes for the changes are multiple, ranging from orebody capability, dynamics, technology, safety, economics, production levels, geotechnical, etc. Mining methods applied have also ranged from timber square setts, conventional cut-and-fill, shrinkage stoping, sublevel caving, mechanised cut-and-fill, longitudinal and transverse open stoping, and lately longitudinal retreat mining method (LRMM).The Obuasi Mine has a world class underground resource potential of about 27 million ounces. A third of this is in reserve. The orebody is subvertical, with multiple lodes and with widths ranging from 1.5 - 40 m. It stretches along 8.5 km N/S strike. A cursory statistical analysis on the various resource ore widths show a higher percentage (60 per cent) of the resource being within the range of about 1.5 - 10 m. Thus a high proportion of the resource is amenable to narrow vein mining methods. This has enhanced the choice of LRMM as an alternative method. Also, with the increasing cost of mining over time, LRMM, which eliminates expensive and time consuming footwall drives, will become far more advantageous as compared to the transverse/longitudinal open stoping methods which currently constitute about 40 per cent of the total underground production.The LRMM currently delivers about 20 per cent of the Obuasi Mine production. Plans are underway to improve total underground production from the current average of 160 000 tpm to about >180 000 tpm in the next few years and about 20 - 40 per cent more in the foreseeable future. Recoverable ounces will also increase from 26 000 to about 34 000 ounces per month. The proportion of LRMM in the business plan is also expected to increase from the current modest level to about 50 per cent. Despite its tremendous advantages in terms of economics and productivity, the method is facing some challenges during its inception. The objective of this paper is to highlight some of the emerging challenges and their effect on production and offer possible remedies that could mitigate the current and possible future challenges.CITATION:Nsarko, F and Owusu-Mensah, F, 2012. The Obuasi mine - longitudinal retreat mining method application and challenges, in Proceedings Narrow Vein Mining 2012 , pp 59-70 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Mar 26, 2012

By M McGrory, A Rodolfo, J Paredes, L E. Manguba, K A Villaspir, G Webb, R Setiagani, H Cardenas

"OceanaGold’s Didipio operation has been in operation for three years. Integral to the flow sheet design is a flash flotation circuit treating a portion of cyclone underflow, consisting of an Outotec SK-500 flash rougher and an Outotec TC10 flash cleaner and a SB-2500 falcon treating flash rougher concentrate to recover fine free gold.Flash copper recovery has been holding steady at 60 per cent, while flash gold recovery at 50 per cent. Gold recovery from the gravity circuit is 22 per cent, bringing the overall flash plus gravity gold recovery to 72 per cent.Operation of the flash rougher is mainly by pulp level control. Control of copper grade in the flash cleaner is mainly controlled by air inflow and flash cleaner pulp level control drives copper recovery. Gold recovery around the circuit is mainly driven by gold head grade.SB-2500 concentrate is scalped with a 250 micron screen with the coarse fraction reporting to a SB-250 falcon, concentrate of which combines with the screen fine fraction to a Gemini table.Citation:Cardenas, H, McGrory, M, Webb, G, Paredes, J, Setiagani, R, Villaspir, K A, Manguba, L E and Rodolfo, A, 2016. Didipio Flash Flotation and Gravity Recovery Circuit, in Proceedings 13th AusIMM Mill Operators’ Conference 2016, pp 123–126 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Oct 10, 2016

By G Gopinath, R Balachander, H S. Venkatesh

This paper describes in detail the controlled blasting adopted and the measurements undertaken for the successful excavation of large twin tunnels under a shallow cover for a six-lane highway project in India. The tunnels are D-shaped, each 15 m in diameter, and the cover between the tunnels and the existing railway track was about 14 m. These twin tunnel tubes were characterised by two separate three-lane carriageways for each direction of traffic, and were planned with about 25 m of reinforced cement concrete (RCC) portals at the entrance and exit of the tunnels. The major challenge of the project was the blasting of tunnels in rock below an operating railway line. As the tunnels approached the area below the railway line, the ground vibrations were monitored vertically above the blasting faces and on the railway track sleepers. Vibration intensities between those generated from tunnel blasting and those from the movement of the trains were compared, and it was found that the vibrations from blasting were lower than those from the moving trains. Though the permissible level of ground vibration based on the Indian Standard (IS) code happens to be 70 mm/s, the maximum charge per delay was calculated restricting this limit to 50 mm/s. This ensured that the vibrations in the vicinity of the railway tracks never exceeded the prescribed limit of 70 mm/s. The surface ground settlement before and after the blasts were also measured using an optical levelling instrument, which confirmed that there was no significant impact on the surface movements due to blasting. Extensometer readings inside the tunnels showed that there was no deformation in the tunnel. These twin tunnels are now operational and are providing faster connectivity with safety.CITATION:Gopinath, G, Venkatesh, H S and Balachander, R, 2015. Controlled blasting for twin tunnels with a shallow cover under an operating railway line, in Proceedings 11th International Symposium on Rock Fragmentation by Blasting, pp 801–808 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 24, 2015