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Goodenough and Fergusson Islands, in eastern PapuaNew Guinea, lie in an area of crustal extension on the western end of the Woodlark Basin seafloor spreading system. The islands are made up of a number of mountainous domes of complexely deformed basement, and these are intruded by large bodies of granodiorite. The domes are bounded by curved shear zones and faults dipping outwards at angles of around 25 to 45¦. The cores of the domes contain lower crustal rocks of eclogite and granulite facies, these rocks have undergone retrograde metamorphism in the outer sheared zones. Movement indicators on the shear zones indicate a complex moverm.-It geometry which does not fit the models proposed by earlier workers. These dome-like structures are similar to the metamorphic core complexes of the western United States Cordilleran region, however there are a number of aspects which do not fit with the models proposed for the development of metamorphic core complexes. Uplift of the metamorphic basement probably resulted from a combination of forces associated with the extension of the crust and the intrusion and emplacement of granodiorite plutons.

Jan 1, 1990

By S Morgan, L C Pagdalian, S Serdzeff, C Malaloy-on

It is widely accepted that mineral deposits are decreasing in metal grades. To remain profitable and meet market demand, mining companies are expanding their operations by increasing the tonnage treated. These expansions may include new concentrators with higher nameplate tonnages or upgrading the capacity of existing ‘brownfield’ operations. In many cases, the brownfield upgrade route is preferred as it is less capital intensive; however, brownfield upgrades are never straightforward and present many metallurgical and engineering challenges.For example, to increase feed throughput at a brownfield site, there will be a requirement to modify the mine development plan. This may result in the ore mineralogy varying beyond the current feed fluctuation range. To accommodate these ore variations, a combination of mineralogical analysis and small scale testwork can be used to develop a new process flow sheet to achieve the product recovery/concentrate grade requirements. In general, however, flow sheet development does not usually consider site specific layout constraints and equipment requirements. At sites where future expansions were never considered, taking this silo approach could lead to project delays and compromise the circuit design.Engaging an experienced technology partner ensures the nominated project team is involved throughout all stages and aspects of a given brownfield upgrade – from conceptual flow sheet development, through to detailed engineering, construction and commissioning. The recent Carmen Copper Corporation (Carmen Copper) circuit upgrade has been completed in technology partnership with Outotec. The circuit upgrade was extensive and included new equipment additions to the comminution, flotation and dewatering circuits. Carmen Copper’s intimate knowledge of the ore characteristics, in conjunction with a trusted, knowledgeable technology partner, facilitated a robust circuit design, and fast-tracked the project execution. This paper deals specifically with the flotation circuit upgrade and highlights the benefits to Carmen Copper of this holistic approach.CITATION:Morgan, S, Serdzeff, S, Malaloy-on, C and Pagdalian, L C, 2014. The benefits of technology partnerships during brownfield upgrades, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 471–476 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By R H. Sibson

Magmatic and/or hydrothermal fluid systems in island or mountain arcs self-organise to critical states subject to perturbation by changes in the regional stress, which plays a controlling role in the containment of overpressured fluids. Whether the magmatic arc is under compression (eg Andes, northern Honshu) or extension (eg Taupo Volcanic Zone, New Zealand) is a key factor controlling the ease of magmatic or hydrothermal fluid ascent. Abrupt changes in the stress regime have the potential to induce major episodes of fluid redistribution. Large earthquake ruptures along plate boundaries may induce such changes over broad areas, also contributing to fluid redistribution by renewing fault permeability along the causative rupture zone or reactivating distant fault-fracture permeability by shaking from radiated waves. High-resolution geophysical investigations of active arc systems and the subduction thrust interface underlying their fore-arcs reveal repositories of overpressured hydrothermal fluids. In active magmatic arcs under compression such as NE Honshu or Cascadia, there is evidence for a heterogeneous distribution of overpressured hydrothermal fluids in the middle-to-lower crust trapped around the base of the upper crustal seismogenic zone. Investigations of the subduction thrust interface responsible for great (Mw = 8.0) ‘megathrust’ earthquake ruptures has revealed in some instances (Cascadia, SW Japan) the existence of a belt of non-volcanic tremor (NVT) with accompanying slow slip episodes defining the base of the megathrust interface at 40 ± 5 km and 350°C??-??550°C. Aqueous fluid at these depths is likely derived from dehydration reactions accompanying the basalt-eclogite transition in subducted oceanic crust. NVT sequences in the hanging-wall above the interface may be defining migration pathways into the overlying crust.The potential for eruptive episodes in magmatic arcs and redistribution of hydrothermal fluids is assessed in the light of the stress changes that followed the 2011 Mw9.0 Tohoku subduction thrust rupture which extended along strike for over 500 km and down-dip for over 150 km, with maximum slip of c 50 m.

Aug 22, 2011

By J Harmse

This paper deals with the modernisation of the brakes on an electrically coupled Blair multi-rope hoist and covers the removal of the old calliper brakes and hydraulic control system, and its replacement with brake discs, disc braking units and hydraulic control systems. The paper covers the braking requirements of the hoist, which is made up of two electrically coupled single-drum hoists, together with the theory behind the choice of brakes and control systems supplied. The paper also covers the project logistics that were required in order to install and commission the new brakes and control systems with the minimum disruption to production on the only rock hoist on a major production shaft. Items covered include the modifications to civil works, pre-installation of bearing lubrication systems, brake discs and hydraulics and the interfacing of the new hydraulic control system to the existing electric control system. It had to be designed to be compatible to a new electric drive and control system due for installation at the end of 2005.

Jan 1, 2005

By R J. Butcher

Many deposits have been evaluated as potential block caves over the last 20 years due to the perceived benefit of low operating costs. However, block cave projects are typically capital intensive, with mass mining providing high throughput rates that required large investments in mining, processing and utilities infrastructure. While the key economic metrics in deciding to proceed with a caving project are typically net present value (NPV) or internal rate of return, these may not represent the best decision metrics for some companies. Where a caving project is competing for scarce capital amongst other projects in a company’s portfolio or where the caving project is the only project being evaluated by a company trying to raise capital, other metrics may be more appropriate. This paper explores the use of present value ratio and the minimising of maximum negative cash flow as suitable metrics in determining alternative strategies. Trade-offs between optimising for economic value and capital efficiency measures allow for decision-makers to evaluate potentially higher-risk, higher-capital and maximum NPV projects against lower-risk, lower-capital projects.CITATION:Stewart, C A and Butcher, R J, 2016. Block cave evaluation, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 809–816 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By N Javati, G D. Carman, D Kikiha, B Likia, K Dala, J McPhie, R Johnstone, D R. Cooke, J L. Blackwell

The 40 Moz Ladolam gold deposit on Lihir Island, Papua New Guinea is the worldÆs largest, low-sulfidation, epithermal gold deposit, in terms of contained gold. The deposit has average grades of 2.42 g/t Au (LGL Resources Reserves Update, 2008) and gold is hosted primarily in refractory pyrite. Lihir Island is part of the 150 km long, Tabar-Lihir-Tanga-Feni, alkalic, volcanic island chain located in the New Ireland basin. Five volcanic blocks comprise Lihir; Plio-Pliestocene Huniho, Kinami and Luise volcanic edifices are built on top of remnant Pleistocene Wurtol Wedge and Londolovit Block (Wallace et al, 1983). The Ladolam gold deposit is located in the central portion of the dissected Luise volcanic edifice and is composed of four main orebodies: 1. Minifie, 2. Lienetz, 3. Coastal, and 4. Kapit. An active geothermal system is overprinted on the ore deposit, localised along north-trending lineaments, and is expressed as hot mud pools and fumaroles. The focus of open pit mapping and drill core logging, as part of ongoing PhD research, has been in the Minifie and Lienetz orebodies. The deposit geology is grouped into four main phases: 1. volcano-sedimentary host rocks, 2. porphyry-style biotite alteration and related hydrothermal breccias and veins, 3. epithermal-style breccias and veins, and 4. modern geothermal alteration. Gold is associated with epithermal-style alteration and mineralisation. Ongoing observations of the Minifie and Lienetz orebodies are highlighting differences in the geology and paragenetic histories. An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation.

Jan 1, 2008

THE paper is principally eoncerncd with experimental work carried out the author whilst a number of the metallurgical staff at the Cockle Creek works. The metallurgical has been discussed sufficiently for the reader to follow the course of the experiments but the actual plant has only been described in so far as it effected metallurgical treatment, since the arrangement of such a smelter is a matter of common knowledge.The lead-roasting plant consisted of Godfrey roaster, Dwight-Lloyd maehines and Huntingdon-Heberlein pots. The usual treatment was in the Godfrey furnaces, followed by sintering in the Huntingdon- Heberlein pots. The paper is divided into two parts in the Godfrey furnaces and Huntingdon-Heberlein pots. An account of experiments on the utilization of the hood gases from the Huntingdon-Heberlein pots for acid making...

Jan 1, 1924

By Tarvainen M, Mattila O

Outokumpu Oy has systematically developed the automation of mineral flotation covering the technology of both new devices and control methods, and as a practical result of this effort currently produces two on-stream X-ray analyzers. The Courier 300 system basing on conven- tional X-ray technology is applied to complex or large processes. The newer Minexan 202 dis- tributed probe system based on radioisotope technology is developed mainly for simple or small scale applications. In this paper aspects and experiences of these analyzer systems and their applications for flotation control are discussed with particular reference to the role of the computer

Jan 1, 1977

By B E. McCarthy

Red Dome Mine was a highly complex gold copper operation developed over a number of phases between mid-1986 to October 1997. With only three years of production ahead at any time, a proactive practical approach to mine closure was necessary. In 1989 the Domains Concept to life-of-mine planning and mine closure was created as a response to the proposed changes to legislation.The Domains Concept, a relatively simple idea developed to integrate mine closure during production at Red Dome, has been broadly adopted by both government agencies and industry in the intervening 20 year period. Over time the author has observed that the concept has been poorly applied, misunderstood and in some cases even misrepresented. As a consequence, the potential opportunities from applying the concept, including the optimisation and minimisation of life-of-mine costs, mitigation of long-term financial liability exposures and building credibility with the general community, have been missed.This paper examines the many benefits, advantages, applications and perceived barriers to developing and integrating a fully costed life-of-mine plan. Integrating the Domains Concept early in the project, within the operational budgeting, allows the production of a meaningful and useful document, representative of a whole life-of-mine, cradle to grave, with measurable rehabilitation and closure outcomes when the concept is used to full effect.The Domains Concept serves to optimise cost-effective, whole of mine, life cycle planning which provides beneficial outcomes for the community, significantly mitigates legacy issues and contributes to the attainment of compliance and sustainability principle objectives.CITATION:McCarthy, B E, 2014. The domains concept – 20 years on retrospective, obstacles and opportunities for effective life-of-mine implementation, in Proceedings Life-of-Mine 2014 , pp 621–636 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 16, 2014

By Scales PJ

Fatigue is the primary cause of failure of structural and mechanical components subject to dynamic loading. Recognition of this basic fact and the development of appropriate techniques and details are important in the design and repair of off highway trucks (OHTs). The frames and appendages of OHTs and other mobile plant used in the Pilbara are subject to tough operating conditions. Any fatigue-prone details quickly show up and become a maintenance liability of considerable concern. Much of this equipment is approaching the limit of its fatigue life and maintenance managers face decisions on whether to repair or replace. Even new equipment often contains some poor details which suffer distress soon after commissioning. In those cases a repair is required which will reinstate the detail to its original intended design life. Repair details must be practical and cost effective. They must also be tailored to the capability and expertise available in the field or in local manufacturers' establishments. This is particularly important where original equipment was manufactured overseas and long delivery times are involved. Lessons are drawn from components which have failed, using the evidence constructively, to provide an upgraded part or an improved substitute. With the experience now available it is relatively easy to extrapolate to cover new problem areas. This paper describes specialised techniques of mechanical fastening and detailing for low fatigue susceptibility, built up over many years of experience with OHTs and other mining plant and equipment in the Pilbara.

Jan 1, 1982

A co-operative research project, combining Commonwealth Scientific and Industrial Research Organisation (CSIRO) research scientists findings and company iron ore geologists' expertise, resulted in new concepts about the origins, distribution and complexitie of iron ores and their parent rocks (banded iron-formation or BIF) in the Hamersley Iron Province of Western Australia. Understanding these problems was important to the efficiency of exploration, development and ultimate mining of iron ores. This genetic model, based on a detailed mineralogic background, was modified by Mt Newman geologists to obtain a user oriented classification for practical application in the field.The proposed Pilbara Iron Ore Classification (PIOC) gives iron ore geologists a basis from which to understand, identify and record the various mineralogic and physical characteristics of the many genetically different ore types occurring within and between orebodies in the Pilbara. More definitive quality control over ore products can be achieved based on the detailed understanding of ore types which the PIOC allows, compared to current classifications which deal only with the physical nature of ores. Of equal importance, the classification remains sufficiently simple to enable owners, operators and buyers to achieve a basic appreciation of ore type variations.With little modification, it is believed the classification has applications beyond the Pilbara, to iron ore worldwide.

Jan 1, 1984

The sulphide ores of the Kalgoorlie goldfield have long been looked upon as' refractory, involving special metallurgical treatment. For many years two kinds of treatment have been practised-(l) wet treatment, including fine grinding, amalgamation or concentration of the free gold, concentration of the sulphide minerals with subsequent roasting and cyanidation, and cyanidation or bromo-cyanidation of the residue from the concentrating operation; (2) dry-crushing of the ore and roasting the whole of thecrushed ore, amalgamation of the gold in the calcine during fine grading, followed by cyanidation. The wet treatment was advanced a stage further when, in 1929, the Lake View and Star Ltd. adopted large scale flotation. As a consequence, however, further metallurgical problems were introduced. This paper covers the investigation, ,of one of the most prominent of these problems.Flotation preceded by strakes was satisfactory to a point.The flotation concentrate consisted largely of auriferous pyrite and tellurides, and the gangue minerals in the concentrate were practically barren.Several sources of loss of gold values were, however, found to be associated with this circuit, viz.-(a) There was the loss of gold in the flotation tailing.(b) Loss by dusting during roasting of the flotation concentrate.(c) Loss of gold in the cyanided residue.

Jan 1, 1937

By X L. Liu, W Huang, J M. Zhu, S L. Wu

The shape, position and thickness of the cohesive zone have a great influence on the operational performance of the blast furnace. Many researchers have found that the high temperature properties of iron ores determine the formation of the cohesive zone. The results of this work show that sinter of high basicity interacts with lump ores and acid pellets due to the difference in chemical compositions. The softening and melting properties and the primary slag formation behaviours in the cohesive zone are improved by the high temperature interactions. The high temperature interaction is mainly influenced by the chemical compositions, porosity, interfaces and so on. Although the softening and melting properties and primary slag formation behaviours of lump ore A (a typical limonite lump ore from Australia) is the poorest of the iron ores studied, the high temperature properties of integrated burden A (consisting of sinter and lump ore A) is no worse than the other integrated burdens due to the high interaction between the sinter and lump ore A. It is useful to apply the results in the optimisation of blast furnace burden.CITATION:Liu, X L, Wu, S L, Huang, W and Zhu, J M, 2015. High temperature interactivity of iron ores in the cohesive zone of the blast furnace, in Proceedings Iron Ore 2015, pp 363–366 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 13, 2015

By A Madera, R Watt

The Tampakan deposit is a strongly telescoped high-sulphidation-epithermal/ porphyry deposit pair which is hosted by a sequence of probable Pliocene age subaerial andesite flows. These host units lie on the western flank of a deeply dissected andesitic stratovolcano within the northernmost portion of the Sangihe Arc in southern Mindanao. The deposit was discovered by WMC geologists in 1992 and is currently undergoing resource evaluation. Preliminary resource estimations indicate a total inferred metal content of 12 million tonnes of copper metal and 16 million ounces of gold. Using a 0.2 per cent Cu cut-off grade, the deposit has a current mineral resource of approximately 2.5 billion tonnes with an estimated grade of 0.48 per cent copper. At a higher cut-off grade of 0.5 per cent Cu, the mineral resource is approximately 900 million tonnes with an estimated grade of 0.75 per cent copper. Mineralisation is open both to the west and at depth. The Tampakan district is centrally located with respect to a 100 km wide zone of left-lateral strike-slip deformation represented by the trans-Mindanao Cotabato Fault Zone. The district is transected by several WNW-striking wrench faults which represent strands of the regional Cotabato Fault Zone. High-sulphidation epithermal mineralisation within the Tampakan deposit is strongly controlled by NNE-trending faults which lie along a dilational orientation within the Pliocene stress field associated with the Cotabato strike-slip fault zone. The mineralisation is broadly hosted by a gently-dipping, tabular zone of partial to massive silicification which displays multi-phase brecciation, acid-leaching, related vuggy porosity and which is developed within a district-scale advanced-argillic and argillic lithocap exceeding 90 km 2 in area. High-sulphidation epithermal mineralisation is associated with a silica-pyrophyllite-dickite-alunite-diaspore¦sericite alteration assemblage which is transitional downward to sericite-chlorite alteration and relict potassic biotite-chlorite-magnetite-anhydrite alteration associated with pervasively developed but weakly mineralised porphyry quartz stockwork veins. The high-sulphidation mineralisation is dominated by disseminated, vein and vug-filling enargite-bornite-digenite-chalcocite-covellite ¦ molybdenite which has overprinted an earlier phase of porphyry copper stockwork veins associated with high-level porphyritic hornblende diorite stocks. The distribution of high-sulphidation alteration and mineralisation reflects strong stratigraphic and structural controls. The high-sulphidation mineralisation covers a surface area of approximately 1.6 km by 2.0 km and forms a tabular, flat-lying to gently-dipping body between 200 and 500 metres thick. It is intersected at RL-1200 m ASL (at surface) in the northern portion of the deposit and extends down to RL-600 m ASL at the southern end. The deposit has been diamond-drill tested to a depth of 400 - 500 metres where low-grade chalcopyrite-bornite-pyrite mineralisation is hosted by pervasive quartz stockwork veins. This deep-level mineralisation represents the outer portion of a porphyry Cu system hosted by both andesite flows and the uppermost portions of high-level hornblende diorite stocks. Deep drilling to test for higher tenor porphyry Cu mineralisation is planned.

Jan 1, 1999

By G F. Johansen

The erratic and localised occurrence of economic gold grades is a common feature of high-nugget effect gold veins. The nugget effect is a consequence of small-scale geologically controlled enrichment, and the inclusion or exclusion of sparse gold particles because of the sampling process. Such deposits do not always contain visible or coarse gold, and can be characterised by fine gold particles. Economic grade accumulations are generally contained within discrete oreshoots, which are surrounded by barren to low-grade material. Problems are often encountered where small sample types (eg drill core or channel samples) often vastly understate in situ grade, due to their general inability to intersect rare gold particles. As a result, the definition of grade and its distribution is often challenging, and leads to substantial resource uncertainty. Proxies, or indicators for grade, can help the geologist gain a better understanding of grade distribution and grade potential. These are based upon geological (eg mineralogical, textural, etc) and/or geochemical (eg specific elemental ratios, fluid inclusion compositions, elemental correlations, etc) criteria. The paper discusses the use and application of such proxies through three case studies.

Jan 1, 2004

By R G. Reddy, A Yahya

The sulfur distribution ratio (Ls) is an expression of the amount of sulfur in slag to the amount of sulfur in molten metal. The sulfide capacities calculated from Reddy-Blander (RB) model were used to calculate the sulfur distribution ratio (Ls). A new Reddy model for sulfur distribution ratio (Ls) was developed for modelling Ls for ironmaking, steelmaking, and secondary steelmaking conditions. Besides calcium oxide, the major component in the ladle furnace (LF) slags is alumina. The Ls was calculated for typical LF slags as a function of temperature and composition. The model calculated Ls values are in good agreement with the experimental and industrial slags data. The extremely low oxygen potential in these furnaces after fully-killed steel is favourable for desulfurisation. For any given slag’s composition and temperature, its sulfide capacity can be calculated a priori. The equilibrium sulfur distribution ratio between this slag and liquid metal in a particular vessel can also be calculated a priori. The Ls for ladle furnace (LF) slags is about twice those for blast furnaces (BF) slags and ten times those of basic oxygen furnace (BOF) slags. The desulfurisation of pig iron in BF and desulfurisation of steel in LF during secondary steelmaking are recommended. Steel desulfurisation in steelmaking furnaces is not effective. Since the model used to calculate the sulfur distribution ratio (Ls) is a priori, it is a useful tool for the iron and steel makers in improving the product quality and optimisation of the industrial furnace operations.

Aug 21, 2024

The Health Tracking project is one of five projects being undertaken as part of the Minerals Industry Cooperation Initiative (MICI) û a national initiative sponsored by the Minerals Council of Australia. The aim of the Health Tracking project is to assess the practicality of ways to demonstrate the monitoring of hazardous exposures and the occurrence of related occupational illness and disease and development of management systems and strategies at a national level. This second stage of the project will be completed in 2005 and will cover four areas: pilot development of a comprehensive job exposure matrix (JEM) for the minerals industry; development of both proactive and reactive occupational illness and disease metrics; recommendations regarding appropriate health tracking models; and provision of best practices guidelines for management of occupational health. The synergies between these areas will establish the path towards an effective national occupational health surveillance system and the development of effective prevention strategies and policies.

Jan 1, 2005

By J T. Smit

The theory of froth flotation developed slowly, in almost all cases lagging behind practical developments in the operation of flotation processes. This was largely the result of a lack of understanding of the required basic principles of chemistry and physics, many of which were being developed at the same time. A review of some of the early theories propounded is worthwhile, and should encourage those who are presently studying or practicing flotation to exercise some care in claiming a complete understanding of the underlying phenomena in the art. This paper considers theories presented up to and including those in Principles of Mineral Dressing by Antoine M Gaudin (1939). Of course, developments since that time are important, but they are beyond the scope of this discussion.

Jan 1, 2005

By G K. N Subasinghe

Metallurgists operating Knelson Concentrators (KC) often rely on manufacturerÆs recommendations for selecting operating parameters, such as fluidising water flow rate and cycle time. Recent studies have shown that these parameters are not only dependent on the machine parameters but also on the feed characteristics, such as size distribution of the gold and gangue particles and the composition of its constituent minerals. It is known that a particle entering a KC initially traverses a circular path within the bowl. For a particle to maintain a given orbit, the required centripetal force must be supplied by external means. It has been argued that this centripetal force, which is dependent on the mass of the particle, its radial position and the rotational speed of the bowl, is provided by the fluid drag force created by inwardly moving fluidising water and the BagnoldÆs force created by the particle/particle collisions. Depending on the fluidising water flow rate, one of two situations can occur where the porosity of the bed increases or decreases, which influences the amount of material retained within the bowl. The amount of material of a given size and density retained in the bowl is thus dependent on the extent of the centripetal force provided. Based on the above concept, a criterion that can be used to predict the amount of material recovered in the bowl has been derived and validated by experimental data. It may also be construed that this criterion demarcates the transition of the bed from a packed-bed state to a fluidised state. By identifying the transition values for the different constituent mineral particles in the feed, it is possible to estimate the optimal fluidising water flow rate that would maximise gold recovery while minimising gangue recovery. In addition, the kinetics of gangue displacement by incoming heavy mineral particles were also studied using synthetic mineral mixtures. The experimental data suggests that this process follows first order kinetics and that the build-up of heavy mineral reaches a maximum. A model has been proposed to predict the optimal batch cycle time for a KC in terms of the feed characteristics and machine operating parameters.

Jan 1, 2006

Hard rock TBMs are very often open machine layouts, with just a part roof shield over the front of the machine. The whole system is designed for fast face advance and the economy of the project often depends entirely on the rate of advance. Typically, hard rock conditions will demonstrate stable and good ground for a major part of the tunnel. However, short sections of crushed shear zones with clay and gouge material may cause serious time delays. Spiling rock bolting has been proven to be very efficient under such circumstances, provided the fully grouted rebar bolts can be placed in a controlled and practical manner.Environmental restrictions are becoming more and more a part of tunnel excavation projects. Even hard rock TBM tunnelling may require a strict ground water control, because of consequences on the ground surface from lowering the ground water level. Such consequences may be surface settlement, negative influence on ground water resources or damage to vegetation.Pressure injection ahead of the advancing tunnel face (in this paper named pre-injection), using microfine cement and chemical grouts, is today a proven technology. As examples can be mentioned (Garshol, 1997) about 100 km of pre-injected tunnels below Oslo City and about the same length of subsea tunnelling elsewhere in Norway. Examples from other parts of the world are also available, like below Stockholm, Sweden, the Inland Feeder project and Hollywood Metro both in Southern California.To take advantage of spiling rockbolts and pre-injection, it is an obvious prerequisite to be able to drill the necessary boreholes in the right positions and at the correct angle. In drill and blast excavation this is simple, but in TBM projects it has repeatedly turned out to be difficult. More than once owners have accepted bids containing reassurance from the contractor that the drilling method will be sorted out later. Experience shows that if ælaterÆ means after start of the TBM operation, it is often too late.

Jan 1, 1999