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By A. F. McKown, P. E. Sperry, W. L. Fourney, D. E. Thompson

INTRODUCTION Underground drill and blast excavation is usually accomplished with small diameter holes loaded with high energy explosives. The detonation pressures are extremely high and an extensive amount of energy is dissipated in the process; however, very little of this energy is used to create the specified fracture planes required for excavation. The available energy is expended in producing radially outgoing stress waves, in crushing the adjacent rock, and in producing a dense, randomly oriented radial crack pattern about the holes. This causes several undesirable effects: 1. Overbreak at the perimeter, which results in more muck to remove and extra concrete or shotcrete to fill the voids. 2. Damage to or loosening of the remaining rock at the perimeter which may result in the need for additional support measures. 3. Ground vibrations and/or airblast, which could result in damage to nearby structures and complaints by people living or working in the area. Several steps may be taken to minimize these effects. Where control of the perimeter is desired, smooth blasting techniques are generally employed in which the spacing and burden of perimeter holes are reduced and lighter, decoupled charges are used. Where vibration damage to structures is feared, control is generally exercised by limiting the charge weight per delay period so that the ground vibrations at the nearest structure do not exceed a peak particle velocity of two inches per second. Where blasting complaints may be a problem, con-

Jan 1, 1979

By K. Kavouridis

Coal is broadly recognized as sure, competitive, diversified, not vulnerable and predictable in price energy resource. In power generation coal is playing a dominant role in the EU-27 with 25% of installed capacity and almost one third of the power generation. The role played by the domestic resources and especially by coal are increasingly becoming the focus of the EU energy strategy. There is a strong pressure for the decarbonization of the energy mix. The Emission Trading system (ETs) can have an impact on the shift to lower carbon-intensity fuels. The impact of ETs on coal can be important, because it is very short sighted and only defines the period up to 2008-2012. The ETs CO2 regime must ensure that investment in coal-fired plants in the long term are supported. EU Research Institutes and Coal Industry identified an important CO2 reduction potential by improving the efficiency of the conversion of solid fuels into electricity. Highly efficient clean coal technologies can contribute to reasonable costs and challenge the issue of climate change. It must be pointed out that the EU Energy policy should now concentrate on the necessity to effectively support demonstration projects and to create the legal framework for the integrated approach of efficiency enhancement and CCS. It is not a right approach to implement CCS before the technology is demonstrated and before it is clear that it will be commercially viable.

Jan 1, 2007

By B. R. Utz

The goal of the DOE Coal Preparation Program is to provide industry with the scientific and engineering knowledge base to produce economically competitive and environmentally acceptable clean coal products for both existing and new markets. The DOE/PETC in-house program continues to conduct fundamental, exploratory, and applied research in the areas of physical, chemical, and microbial coal beneficiation to assist in meeting these goals and objectives. The Coal Preparation Division now has a new Coal Preparation Process Research Facility that allows continuous bench-scale testing of emerging coal cleaning technologies and ancillary coal preparation equipment at feed rates up to 1,250 kilograms (1.25 tons) per hour. Bench-scale and laboratory-scale research projects at PETC cover areas such as 1) the use of micronized-magnetite for fine-coal, 2) heavy-media cycloning, 3) fine coal reconstitution, 4) development and testing of coal preparation process flowsheet simulators, 5) dry coal beneficiation using electrostatic methods, 6) tracer methods to determine the efficiency of density-based separations, 7) selective oxidation of organic sulfur, and 8) microbial removal of pyrite and organic sulfur from coal. This paper will discuss several of these research areas.

Jan 1, 1993

By R. H. Mozley

It is not my intention in this paper to review recent developments in the mineral processing industry which might fall under the above heading, but to refer to some of the research that I have done over the past 25 years or so. To begin with then, my student days at the Camborne School of Mines, the year 1952. Equipment from the last century was still in everyday use at the local tin mines. At South Crofty Ltd a steam beam engine 100 years old was pumping mine water from 2000 feet, the motive force being conveyed from surface to the pump at the bottom of the mine by a 14 inch square pitch pine rod joined with forged iron straps, steam winders were still in use, and in the mills, stamps ground the ore, and the cassiterite was recovered by equipment with exotic names like "buddies, kievs, and round frames." And to equip us students for the brave new world, we included in our practical mineral dressing a day's test programme with a Californian stamp -- experience that I am still waiting to put to good use!

Jan 1, 1984

By P. J. Rua

The Piedras Verdes copper mine is a new run-of-mine (ROM), heap leach, solvent-extraction/electrowinning (SX-EW) operation located 21 km (13 miles) north-northwest of the town of Alamos in the state of Sonora, Mexico. The Piedras Verdes copper mine is wholly owned by Frontera Copper Corp. (FCC), a Canadian corporation, through its 100 percent beneficial interest in Cobre del Mayo S.A. de C.V. (CDM), a Mexican registered company. The January 2008, minable reserves were estimated to be 193.6 Mt (213 million st) at a grade of 0.36 percent copper. The overall recovery of total copper was estimated to be 61.9 percent. The property has an additional 17-year life and is designed to produce 31.7 kt/a (70 million lbs/year) of cathode copper. Construction commenced in early October 2005. The first copper cathode was produced 12 months later at a total capital cost of $100 million. Elevations at the site range from 150 to 300 m (490 to 985 ft) above sea level. The area has excellent infra-structure in the form of towns, power, water, roads, rail, airfield and access to the deepwater port of Guaymas (Fig. 1). The surrounding area is also famous for its numerous polymetallic (lead, zinc, copper, silver and gold) epithermal veins. Some of these were mined for more than 200 years and provided the wealth on which the town of Alamos was built. The original village of Piedras Verdes was located in the area of the proposed openpit mine and, consequently, it was necessary to construct a new townsite 6 km (3.7 miles) to the south before project development could commence. The new town site (Fig. 2), complete with power and water supplies, roads, sewer system, schools, clinic and recreational facilities, was completed and occupied by 49 families in September 2005. CDM received its remaining permits from the Mexican environmental authorities on Sept. 20, 2005. This enabled the company to proceed with full-scale development. CDM owns or controls 27 mining concessions covering the resource. Surface rights to the Piedras Verdes project were controlled by four Ejidos (communal agrarian and/or ranching societies) and five individual landowners. CDM has acquired all surface rights necessary for its mining operations and associated facilities either through outright purchase or long term lease agreements.

Jan 1, 2008

By J. A. Lombardi

Acid-Minesite-Solutions (AMS) are defined as copper-containing pit lake, tailing pond, acid-mine-drainage, and heap and waste dump irrigation solutions. All of these solutions are characterized by copper, acid and water contents that have value as individual commodities. HW Process Technologies, Inc. (HWPT) has developed nano- and hyper-filtration membrane methods for the separation of copper and other base metals, acid and water from AMS. These treatments are collectively called HWPT?s Engineered Membrane Separation® (EMS®) systems. The EMS® method of copper recovery produces small volumes of higher-concentration copper solution from large-volume, copper-dilute AMS. A case study of the 4,000 gpm Cananea EMS®-AMS plant for the recovery of copper from an acid-pit-lake resource is described. The EMS® method of copper removal from AMD and tails pond waters has been bench-scale demonstrated and are described, complete with projected budgetary capital and operating costs. Additional treatments for the recovery of sulfuric acid and high-quality water from the permeate (membrane passing) waters for the above-described AMS treatments are presented, with budgetary capital and operating cost estimates. [ ]

Jan 1, 2009

By Alfred Weiss

Selecting a minicomputer is not unlike selecting a costly piece of mining equipment such as a truck, shovel, crusher, or conveyor belt system. A marked difference might lie in the frequency at which such selection takes place; another difference might be mine management's familiarity with mining equipment vis a vis a minicomputer. These basic differences might prompt a mining company to seek the aid of a consultant when selecting a minicomputer system. Advantages and Disadvantages The fundamental advantage of employing an independent consultant is that it provides management with a source of knowledge and breadth of experience not readily available within the organization. If the consultant has a minerals background, such knowledge and experience are further enhanced by actual experience in exploration, mining, and mineral processing. If the consultant has worked within a mining company, such hands-on experience is supplemented with a meaningful understanding of the client's business; this facilitates communication between the consultant and members of the client organization. The consultant has been, so to speak, "in the client's shoes." There are several other advantages. Since computer systems cut across organizational boundaries, the independent consultant may be able to move within the organization more easily than an inside staff person to collect necessary information. Also, detachment from any manufacturer should provide the client with an objectivity and a set of recommendations as near optimal as feasible. The principal disadvantages lie in the area of continuity and accountability. Once the consultant's report has been submitted and his recommendations implemented, a discontinuity might occur. Also, if implementation does not provide the desired results, the consultant might not be available to correct the situation or account for actions taken. Proper selection of consultant services, relative to kind and duration, and the consultant's method of operation, will often prevent many of these aftereffects. Services Offered The professional consultant can help a client: •Define and summarize information systems technology* needs; • Evaluate alternatives such as in-house capability and capacity, time-sharing, or service bureaus; • Prepare a formal request for proposal (RFP) to be submitted to vendors; •Evaluate vendor proposals; •Evaluate the economics of lease vs. purchase; and •Assist in the conversion and installation. Thus, consulting services may range from evaluating an existing system and upgrading to a larger piece of equipment, to selecting a new first-for-the-organization computer. First, Define and Summarize Needs Regardless of circumstances, the most valuable document required before equipment selection is the information system plan (I/S plan). It helps insure that the company's information needs are met in a cost-effective manner. An I/S plan is usually a comporient of the mining company's overall business goals. Since an I/S plan is a formal vehicle for establishing and communicating the direction the organization intends to take to satisfy information requirements needed to achieve goals and objectives, most initial systems services are likely to center around creating such a document or updating an existing document. The trend toward company-wide I/S planning is increasing in the mining industry; however, smaller scale efforts focused at the information systems needs to support an individual

Jan 11, 1981

By John L. Halls

INTRODUCTION In this section, it is assumed that the reader is an engineer with sufficient training in underground mining work, preferably with budgetary control, to understand the mining methods outlined in other sections of this handbook. The mining-method descriptions are not repeated herein; only sufficient information is provided to enable the reader to comprehend the development of the costs presented. All costs are in 1977 US dollars, except where explicitly stated otherwise. CAPITAL INVESTMENT The capital investment in the underground mining portion of any mining property includes the following: 1) The development of original access involving adits, shafts, declines, etc. It includes the necessary equipment for transporting men, materials, and rock. 2) The purchase of mine equipment including loaders, underground haulage equipment, fans, pumps, electrical distribution, surface facilities associated with the underground mine, etc. 3) Sufficient preproduction mine development to assure steadily increasing production after startup. De- pending upon the mining method used, the preproduction development should provide a supply of three months to one year of ore that is developed and is ready to be stoped. Underground development also includes excavations other than shaft stations, loading pockets, sumps, etc., which usually are associated with the means of access and are excavated by the contractor. These excavations could include a crusher cavern, an ore- storage pocket, and underground workshops that may or may not be included by the shaft-sinking contractor. Portions of these could be delayed until after production begins, but it is preferable to complete them during the development phase, so there is no interference with the production buildup. 4) The staff and labor costs for all phases from inception through final production. 5) The provision of mine-surface equipment and facilities strictly applicable to the underground portion of the operation. The required facilities include a changehouse with a lamp room, a first-aid station, compressors, an electrical substation, workshops, a ware- house, water pipelines to the concentrator, water storage tanks, explosive storage, etc. A concrete-batch plant, a sand-fill plant, and boilers for heating may be required. 6) Other direct and indirect costs. 7) Engineering, design, and procurement costs. 8) Contingency allocations. 9) Contractor's fees, startup costs, and owner's costs. Original Access As part of a study for the US Bureau of Mines, Dravo Corp. conducted an extensive literature research survey covering underground operations in the United States between 1963 and 1973. Table 1 is compiled from the section of that study pertaining to the types of access to underground mines. Table 1 does not include distances attributable to the deepening of existing shafts, nor does it include shafts bored by raise drills or downhole machines that need existing underground workings for the disposal of the cuttings. During the period under review in the report ( 1963 through 1973). concrete-lined circular vertical shafts were the predominant means of providing the first access to a new underground mine; these shafts accounted for 80% of the original access in terms of the number of accesses completed, and 75% in terms of the total verti- cal linear distances. The inside diameters of the conventional circular shafts ranged from 3.7 to 7.0 m (12 to 23 ft). Most (72% ) of these conventional shafts were for production,

Jan 1, 1982

By Cathleen J. Webb, Arden D. Davis

The Homestake Gold Mine at Lead, South Dakota, has been proposed as the host site for the Deep Underground Science and Engineering Laboratory. The laboratory will house neutrino experiments in mine workings at the 7400-foot depth, as well as research in geomicrobiology, rock mechanics, and ground-water flow. Initial plans for the laboratory were developed in 2000 after Homestake Mining Company announced the closing of the underground gold mine. Homestake’s owner, Barrick Gold Corporation, had agreed to donate the mine for a laboratory if it could be protected from environmental liability. That initial agreement was delayed, and Barrick turned off the mine’s pumps in 2003, allowing lower levels of workings to begin to flood with water. In early 2004, the Governor of South Dakota signed an agreement with Barrick that would indemnify the company and eventually transfer ownership of the mine to a state laboratory authority. South Dakota’s governor also announced plans to ask the state legislature for funds to help in the initial construction of the laboratory. A consortium of scientists from several states is currently preparing a detailed laboratory proposal for the National Science Foundation.

Jan 1, 2005

By George S. Koch

Today, after about 30 years of development, computer-based analysis of geoscience data has reached a mature phase. From the tentative early beginnings recorded in the proceedings of the APCOM meetings, geoscientists are now able to emphasize the need for both pertinent mathematical/statistical models and computer hardware and software. From those models that are well understood in the disciplines of statistics and mathematics and for which effective computational methods are available, practitioners select and develop methodology for their particular purposes. Computer hardware is typically assembled from off-the- shelf components now readily available, with particular emphasis, whenever feasible, on microcomputers for reasons of economy and control by the scientific or engineering user rather than by a bureaucratic computer center. Computer software may be written by the user in high level languages such as Pascal, FORTRAN, or LISP. However, more often today geoscientists use routines available in spreadsheets, data bases, or statistical packages. In so doing, they save time and, programming costs and take advantage of routines written and maintained by large, well- established organizations, while losing the flexibility in specifying exact input/output afforded by writing in a high level language.

Jan 1, 1989

By Richard Gallagher, Russell K. McFarland

INTRODUCTION The Southern California Rapid Transit District has commenced Preliminary Engineering for an 18 mile Metro Rail Project. This initial line will consist of approximate 36 miles of single track tunnel and 16 subsurface stations. The estimated cost of $1.2 Billion in 1978 dollars, places it in the category of a major public works project. During the planning phase of this project, particular attention was paid to the National Academy of Science Reports, "Better Contracting for Underground Construction" (1974), "Better Management of Major Underground Construction Projects" (1978), and "Management of Urban Construction Programs" (1980). The improved transportation service that this project will furnish the Los Angeles Metropolitan Area will result in significant benefits that will add immensely to the economic well being of the community-which is one of Webster's definitions of improved productivity. RAPID TRANSIT PROJECT BACKGROUND Rapid Transit studies have been going c in the. Las Angeles area since 1925. In 1969 and 1974, sales tax ballot issues were not adopted by the electorate of the county mainly because the pre-ponderous of County voters are outside the City of Los Angeles.

Jan 1, 1981

By David G. Hammond

INTRODUCTION Previous papers and discussions at this conference have already covered the subjects of identification and nature of risks, allocation of risks and contractual arrangements. In this portion of the conference, in the light of topics already covered, we will consider how to minimize risks and how to mitigate losses. Webster defines mitigate as "to make less severe or painful", an apt definition for our purpose! RISK MANAGEMENT POLICY The first thing that must be said about risks, especially in construction, is that they exist and that they don't necessarily fall alike on the just and the unjust. Some risks, i.e., some kinds of risks, must be recognized as inevitable in engineering and construction and therefore must philosophically and realistically be accepted as part of situations to be dealt with. Dealing with means minimizing, covering, and sharing of risks and doesn't mean merely passing off the risks to someone else. While some risks can be avoided, for example, whether the structure will fall down or the excavation will cave in, risks management primarily deals with: A. minimizing risks---whomever risk it may be B. equitable sharing of those risks among the participants.

Jan 1, 1979

By Stanislaw Nawrat, Waclaw Trutwin, Waclaw Dziurznski, Janusz Roszkowski

In recent years attempts have been made to fight open and intensive mine fires by the use of special extinguishers, which are able to produce great volumes of inert gases directed into the fire zone. These extinguishers are derived from turbo-jet engines used in aircrafts and adopted for operations in mine conditions. The purpose of this paper is to draw the attention to a computer simulation method, enabling studies of dynamical behaviour of mine ventilation processes disturbed by open fires, which are also influenced by measures taken during fire fighting actions i.a. the mentioned operating extinguishers. The first part of this paper gives an account of the principles on which the computer simulation program, concerning the non- steady mine ventilation process, the fire as a heat source and the extinguisher as a source of inert gas and moisture has been based. The next part of this paper deals with simplifying assumptions and the subsequent limitations of the derived simulation pro- gram. Finally, from an example of a computer simulation, the results will be presented and relations shown between parameters characterising the ventilation process during the fire fighting action.

Jan 1, 1997

By A. J. Hendron, B. Mohraz, R. B. Peck

INTRODUCTION The state of the art of soft-ground tunneling was discussed in detail by the senior author at the 7th International Conference on Soil Mechanics and Foundation Engineering held in Mexico City in 1969. Little can be gained by repeating the information assembled at that time. Hence, in this report, only the briefest summary will be given of the overall state of the art and attention will be concentrated on trends and developments since 1969. A characteristic of recent developments is the continued trend toward use of shields and excavating machines. The implications of this trend with respect to design and construction, and particularly with respect to the treatment of unfavorable ground conditions, will be examined. Settlement associated with lost ground, a subject as old as tunneling itself, will be reviewed and methods will be considered for its reduction. Design of tunnel supports was discussed in detail in 1969 with respect to essentially rigid or essentially flexible types of linings. In this report, a definition of flexibility will be considered and design procedures suggested for linings of flexibility intermediate between the two extremes.

Jan 1, 1997

By David L. Bradfield

This paper covers the development of the Yeelirrie Uranium Project from the discovery of the Yeelirrie deposit in 1970 to the present time, with emphasis on the mining, processing, and environmental requirements of the project. The Yeelirrie Uranium Project is managed by the "Yeelirrie Uranium Joint Venture Partnership", which, when formed, consisted of Yeelirrie Development Company Pty., Ltd., Urangesellschaft, Australia Pty. Ltd. and Esso Exploration and Production Australia Inc. The Yeelirrie Uranium Joint Venture Partnership holds mineral claims over the Yeelirrie uranium ore deposit in Western Australia. This deposit encompasses some 35 million tonnes of ore containing in excess of 50,000 tonnes of uranium as U308. Agreement has been reached with the State of Western Australia to mine and process the ore to produce uranium ore concentrate. The Project scope provides for an open-cut mine, alkaline leach hydrometallurgy plant, power plant, township, airstrip, access roads, community services and utilities. The Yeelirrie Uranium Project described herein has progressed through the stages of exploration, mine evaluation, process testing, project scope definition, environmental approval, Pilot Plant operation, preliminary engineering and the publishing of a definitive Project Feasibility Study. This article summarizes the project development through the above stages.

Jan 1, 1984

By Peter W. Willcocks

The Cyanide Regeneration Process (CRP) was developed by Golconda Engineering and Mining Services and installed at Golconda's Beaconsfield Gold Tailings Retreatment Project situated in Tasmania, Australia. The Tailings Project is a 1000 ton per day carbon-in-pulp treatment plant, feed for which consists of tailings material which is dredged from the Tamar River. The pulp is screened to remove debris, then cycloned to form two products. Underflow pulp is stored in a 350 ton bin and cyclone overflow passes to a thickener. The coarse pulp material is fed to the grinding circuit then rejoins the thickened slimes in the cyanide leach circuit. Gold is extracted by carbon-in-pulp techniques. The plant is sited in rolling, hilly country approximately 200 meters from the Tamar River. The residue disposal area is quite small consisting of four dams, totalling 42 acres. The regional climate is cool and wet with little evaporation; therefore, we anticipated a net increase in contained liquor, and subsequent storage problems. Our plan was to remove cyanide from the liquor prior to returning the detoxified solution to the river system. Such treatment was not required until midway through the second year of the project. Initial testwork on sample material indicated that destruction of cyanide by chlorine was the simple solution. Subsequent follow-up on actual plant liquor indicated a huge chlorine requirement due, we believe, to the substantial degradation of vegetable matter plus organic content from the marine environment. The cost of cyanide destruction could not be justified.

Jan 1, 1998

By Glenn Melchert, Paul Eger, Jon Wagner, Dave Antonson, John Folman

Current approaches to reclaiming acid generating tailings include permanent water cover or encapsulation with various synthetic liners and/or clay. Although these methods can be effective, some ongoing maintenance will be required in perpetuity to ensure that water levels are adequately maintained or that the integrity of any capping system is protected. The successful creation of wetlands in tailings basins offers the possibility of creating a stable environment for the tailings with minimal maintenance. Acid-generating tailings from a massive zinc sulfide deposit in Winston Lake, Ontario, were placed in small cylindrical tanks to examine the feasibility and effectiveness of creating wetlands and mitigating acid and metal release. Two uncovered controls were established in addition to the five treatments, which were done in duplicate. Each wetland tank was 117 cm in diameter and contained 6 1 cm of tailings. Treatments included 61 cm cover of wetland soil, 61 cm of glacial till, 61 cm of tailings, and two tanks with 71 cm of water. One of the water covers included the aquatic macrophytes: Elodea canadensis, Potamegeton sp., and Ceratophyllum demersum. Cattails (Typha latifolia) were planted in the plots with substrate cover, and the initial water level was set at ten centimeters. The pH within the tailings in the treated tanks generally ranged between 6.0 and 6.5 and zinc concentration ranged from 0.02 to 0.1 mg/L. The drainage from the controls had an average pH of 3.3, and 7,700 mg/L of zinc.

Jan 1, 2000

By Kerry Lahti, Bryan Ulrich

On Feb. 11, 2005, more than 20 mining professionals gathered in Elko, NV for a day-long round-table discussion on heap leaching. Attendees included project managers, operators and environmental professionals. They represented 10 mining organizations. Knight Piésold sponsored the special event. Its seven representatives included three staff members from the company’s Elko Operation, and one each from its Denver, Cajamarca (Peru) and Vancouver offices. The roundtable format was chosen to allow people from the mining industry to share ideas and experiences in an open forum. Rather than presenting prepared talks, spontaneity was encouraged. This resulted in a lively and enjoyable discussion.

Jan 1, 2005

By Richard E. Gertsch

A century of experience with mechanical excavation machines is beginning to pay dividends to the mining industry. Mining is moving from mechanical excavators to mechanical miners. These mechanical mining systems are poised to make a significant impact on hard-rock mining, both underground and surface. Mechanical mining machines have had a long and successful career in coal and evaporites ("soft-rock") mining. Unlike most mechanical hard-rock mining, these systems actually mine ore. For example, the most productive underground method has been, arguably, longwall mining. Mechanical excavation machines are mostly used in civil tunneling or in driving mine openings such as vent shafts. Civil tunneling is a notable mechanical excavation success. Even with its high capital cost, a tunnel boring machine (TBM) can drive kilometers (miles) of tunnel at very low cost. In hard-rock mining, mechanical excavators bore tunnels, raises and shaft openings in the mine, but rarely mine ore. Like the soft-rock miners, their contribution to mining is important and their development must continue. Generally, they are used as excavators not miners. Current trends guarantee development of true general-purpose hard rock mechanical mining machines. Mechanical miners will become a complete mining system and will determine the design of the mine. Mechanical methods will reward the operator with lower costs and high productivity.

Jan 1, 1992

By Keiichi Fujita, Katsumoto Ueda, Hiroshi Nakauchi, Naohiko Okumura

INTRODUCTION This paper presents (1) modified slipform system which was employed for simultaneous concrete placement for permanent lining and Instruction of a partition wall in the execution of a ventilation shaft 620m deep, and (2) current shaft sinking techniques which have been applicable and efficient for the subsurface conditions in Japan. MODIFIED SLIPFORM SYSTEM FOR PERMANENT LINING OF VERTICAL SHAFT General Information This paragraph deals with rapid construction by using modified slipform system for the permanent concrete lining and a partition wall of ventilation shaft, which has inside diameter of 620m and depth of 620m, of Enasan Highway Tunnel. The general feature of the shaft is illustrated in Fig. 1 and standard section of the shaft is illustrated in Fig. 2. The geological condition surrounding the shaft is mainly of ryolite and surface is of talus, but as a whole, they are rather weak and weathered rocks with faults, fissures and clay seams. 220mm borehole for the geological investigation was used as a drainage hole, predicting the amount of water inflow into the shaft to be 10t/min. The shaft was executed mainly by means of the conventional short step sinking method of 1.2m lift, employing temporary headframe and hoists. For each lift, 40 to 50cm thick temporary concrete lining was used. About 28,600m3 of rocks were excavated and

Jan 1, 1979