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By Steve Cole

"The economic and strategic importance of PGE bearing deposits is fuelling renewed exploration and development efforts in the precious metals mining sector.This paper presents a review of the various techniques used in the processing of PGE bearing ores, from primary benificiation to processing routes for the different flowsheets that have been developed amongst current producers. Recent innovations such as preconcentration of ore using gravity separation, recent trends in flotation circuit design and the development of hydrometallurgical routes for the direct treatment of flotation concentrates without the need for smelting will be discussed. Data from recent projects will be presented to illustrate common characteristics of PGE ores and concentrates.INTRODUCTIONThe six platinum-group elements (PGE): ruthenium, rhodium, palladium, osmium, iridium and platinum, together with gold and silver, are considered to be ""precious"" metals. The recent spike in platinum and palladium prices coupled with the projected increase in demand for the metals has fuelled a spate of exploration and new projects in the PGE sector. Historically primary producers of PGE metals have controlled the flow of information relating to the mining and processing of these ores into the public domain. Very little published information relating to individual operations and processes is available in comparison to the abundant literature relating to other metals.The purpose of this paper is to provide a general overview of the issues relating to the processing of PGE ores. Each topic discussed could easily be the topic of a paper or book and so in many cases only the surface of the topic will be scratched. An attempt has therefore been made to provide as many references as possible.This paper discusses the classification and location of PGE ores, the mineralogical factors that affect recovery of PGE's, methods currently used for recovering PGE's and process trends in PGE metallurgy."

Jan 1, 2002

By John Addison

Experimental animal studies comparing asbestos and non-asbestos varieties of tremolite indicate tremolite asbestos is markedly more carcinogenic. By direct analogy, the differences in carcinogenicity between tremolite asbestos and non-asbestos prismatic tremolite should be the same for the other types of amphibole that also crystallize in the asbestos and non-asbestos habits. The earliest of the experiment animal studies, done more than 25 years ago, have design limitations by modern standards including the use of injection or surgical implantation as the route of administration rather than the more relevant route of inhalation. However, the differences in the carcinogenicity of amphibole asbestos and non-asbestos amphiboles are sufficiently large to be clearly discernable even with the study limitations. Together with later studies on these and related minerals, there is strong evidence of a much lower hazard associated with the shorter, thicker fibers of the non-asbestos amphiboles, than is found for the asbestos analogues of the same mineral. It is possible that the non-asbestos amphiboles are no more hazardous than other silicate minerals widely considered nuisance dusts. © 2007 Elsevier Inc. All rights reserved. Keywords: Amphibole; Asbestos; Tremolite; Carcinogenic

Jan 1, 2007

THE object of this paper is to review certain features in connection with the mining of narrow lodes, say up to 20 ft. or so wide. The types of ore-body to which it is intended to refer are those which occur. chiefly as fissure or shear-Iodes-that is, those lodes which are to be found in belts of country which have been subjected to dynamic stresses, resulting in the formation of cracks and fissures, into some of which has been concentrated sufficient metal-bearing material to form ores. Very frequently one of the walls of such a lode is found to be a fault, or plane of differential movement.The first point which comes up for consideration is the shaft and its position. From the information afforded by the prospecting which has been done on a lode relative to the dip, nature of country, &c., the position of the main hauling shaft can be determined. For purposes of general utility the hangingwall is generally chosen, if a vertical shaft, though, on account of freedom from creeps, the foot-wall would be safer. Vertical shafts are preferable to underlie shafts in many ways; but wherethe lode maintains a flat dip the cost of cross-cutting at the various levels becomes very heavy'. This difficulty may to some extent be modified· by sinking a vertical shaft in the hanging-wall...

Jan 1, 1912

By Takefumi Takuma, Masashi Nagano, Christopher DellAringa

Multiple agencies in Southern California are retrofitting and upgrading their levees to catch up with ever-advancing urbanization affecting the requirements for existing channels and levees in this seismically active zone. Pressed-in sheet piles have been specified on some of these projects to minimize noise and vibration problems associated with sheet pile installation. This paper will study three Southern California levee and sewer pipeline retrofit projects that utilized pressed-in sheet piles in hard soil conditions with N-values higher than 50. BACKGROUND Southern California is home to numerous drainage channels fortified with earthen levees. In spite of the region’s semi-arid climate with varying annual precipitation from year to year, winter storms can bring in heavy and continuous rainfall to the area which overwhelms the levees’ capacities at times. Some levees are running through densely populated areas with homes and other sensitive structures such as underground utilities and bridge piers. Conventional sheet pile driving utilizes either percussive or vibratory pile driving methods, both of which generate high levels of noise and vibration, causing nuisance and potential damage to nearby structures. On the other hand, the press-in piling method utilizes a hydraulic force to push piles into the ground, thus practically eliminating the noise and vibration issue. Although there are types of press-in piling systems mounted on tall leaders on large crawler-base machines, they are less frequently used due to its much larger size and more limited drivability than the type discussed hereunder. The other type of press-in machine sits on top of already installed piles and is anchored with its own weight and additional counter weight when starting off as shown in Figure 1. Once the first few piles are pressed in, the equipment grips on top of the installed piles and moves forward on its own as the pile installation progresses. See Figure 2. This method does not use a vibratory or percussive force to install piles.

Jan 1, 2018

The proper selection of a coal for a particular use depends on knowledge of fundamental data concerning the coals that offer, particularly their type and rank. Type of coal depends on the nature of the original plants and the environment in which they accumulated.Rank reflects the subsequent metamorphism of the coal, and is of two kinds-physical rank and chemical rank.INTRODUCTIONIn the different coalfields of the Commonwealth of Australia there occur many different kinds of coal which provide the coal-research worker with a wide range of material, but to the fuel technologist they represent complex problems in utilization.In the past it has been common practice to instal coal-using equipment of a design based on plant used in large industrial centres of other countries and then search for supplies of suitable coal. This has led to the transportation of coal mainly from New South Wales to other States, which have inadequate supplies of coal suitable for use in the equipment they have installed. However, modern economy and industrial practice demand local resources of coal for the development of industry, transport and domestic services, and a change in the old order is rapidly taking place. Technologists and engineers are now faced with the problem of designing and installing equipment to use whatever kind of coal is available in local coalfields.Much has been accomplished in this direction and important investigations are at present being carried out, but there still remains a wide field of problems for research.In planning and carrying out investigations into coal utilization it is essential that fundamental data and knowledge should be available and that its significance should be appreciated.

Jan 1, 1955

By Scott Rosenthal, Kyle Murphy

This paper discusses the trials and tribulations of obtaining Velocity of Detonation (VOD) readings in small diameter blast holes in an underground mine. Montana Technological University (Montana Tech) obtained a time-domain reflectometer (TDR) type VOD monitoring unit. Purchase of the VOD monitor was justified on verifying explosives performance used in Montana Tech’s practical underground mining class and provide a teaching aid for the school’s rock fragmentation class. Before demonstrating the unit to students, we figured we better learn how to use it first so we give the students an appropriate experience. Our first learning was in obtaining the correct coaxial cable for the VOD monitor and how to properly terminate the cable. Once the cable was on-site and terminated, VOD testing could commence. Use of the VOD monitor was tested underground in small diameter holes (1.5-inch, 38 millimeter) pneumatically loaded with ANFO. After a few failed trials, and follow-up discussions with the supplier, VOD readings were obtained for the ANFO loaded holes. Additional readings were obtained for a pre-split product and detonating cord to satisfy our curiosity that the unit was performing as specified by the manufacturer. This paper will share our learnings in the hopes that others can benefit.

By S. Ersayin

In 1998, the Concentrator Modeling Center was established within the Coleraine Minerals Research Lab to develop models for simulation of iron ore processing plants, and to assist plant operators in improving performance of their aging plants. The short-term objective was to develop necessary models for reliable simulation using conventional techniques, while the long-term objective was set as liberation-based modeling and simulation of these plants. The short-term objective was achieved in 2002, after the development of models for magnetic separators, hydroseparators and fine screens. A project funded the US Department of Energy was carried out to demonstrate the capability in improving iron ore processing at the Mittal plant. As a result of this study, a 10% improvement in throughput at the plant was obtained, and simulation became a desired tool for plant operators. A significant step in the long-term objective was reached in 2005 with the development of a liberation model. This was followed by incorporation of models capable of processing liberation data into the software. By early 2007, the Center had the capability of performing liberation-based simulation of entire plants.

Jan 1, 2008

By N. C. Matheson

The West's Shell Pile has been used on sites with very soft ground conditions for over 60 years. Fibre reinforced precast concrete shells 900mm long are threadled onto an internal mandrel which can be extended according to the depth driven to attain the load bearing resistance. On completion of driving the mandrel is removed leaving the precast shells to form a permanent lining to the cast insitu concrete core. To give resistance to high contamination, a tar based epoxy coat is sprayed on the outside of the shells or a flexible PVC liner is installed inside the shells to protect the core. Fundamental to the resistance to contamination is the quality of the precast fibre reinforced concrete shell, the mix design and method of manufacture. A series of detailed laboratory experiments were carried out using samples immersed in concentrated acid and sulphate solution. The long term effects of exposure to contamination is recorded in the case studies of existing piles at two gasworks sites.

Jan 1, 1989

By Jamal Rostami, Ataollah Rahbar

"Uma Oya Multipurpose Development Project is under construction in Sri Lanka. This project involves 2 Rolled Concrete Core (RCC) Dams connected through a tunnel currently under construction by Drill and Blast method. The water is transferred from first diversion dam to the 2nd regulatory dam and from which, it will be transferred through a 14 km headrace tunnel to the top of a 650 m deep drop shaft that feeds the high pressure water to an underground powerhouse and turbine chamber for generation of 120 MW of electricity. The Headrace and Tailrace tunnels are being excavated by two 4.4 m diameter double shield TBMs. The headrace tunnel has already passed 5km milestone and is mined in hard rock, while the tailrace tunnel has been completed in rather weak and fractured ground. This paper will review the history of the project along with the geology of the site. The operation of TBM in headrace tunnel will be discussed in more detail, focusing on the challenges of excavating through very strong and abrasive quartzite and gneiss on this site, as well as reaches of tunnel in high inflow of water reaching 400 L/Sec. INTRODUCTION This paper aims to introduce the Uma Oya Multipurpose Development Project (UOMDP) as a hydro mechanical project in Sri Lanka, targeted generating hydro-electric power, transferring water for irrigation purposes and controlling seasonal devastating flood. This project lies in the south-eastern part of the central highland region of Sri Lanka (Figure 1). The main part of the project is located in the south-western part of the Badulla district in the province of Uva. The south-eastern end of the project site is in the central west of the Moneragala district (province of Uva). Bandarawela is the largest urban setting within the project area, located halfway between the upstream and the downstream ends of the planned hydropower plant and combination of dams, tunnels, and downstream facilities. The Multi-Purpose Project Of Uma Oya is planned to convey water from Uma Oya to Kirindi Oya Basin for hydroelectric energy generation includes Puhulpola RCC Dam on the Uma Oya river, Dyraaba RCC Dam on the Mahatotilla Oya river, a conveyance tunnel from Uma Oya to Mahatotilla Oya (L=3750m), a long feeder tunnel from Mahatotilla Oya to Kirindi Oya. The feeder (power) tunnel Lot consists of a headrace tunnel (L=15554m), the surge shaft (L=200m) and tank on the upstream of the vertical shaft, a vertical shaft with steel lining (L=650m), an underground powerhouse and a tailrace tunnel (L=3650m)."

Jan 1, 2016

By D. Imeson, T. Grammatikopoulos, M. Aghamirian, M. Oliazadeh

"More than 70% of potash is produced worldwide by froth flotation. Flotation of potash was developed in the early 1930s. Amines are widely used for flotation of sylvite (KCl) from halite (NaCl) and insoluble materials such as clays. Amine collector is also absorbed by clays. Therefore, clays are usually separated by scrubbing and de-sliming prior to flotation. Alternatively, slimes can be floated ahead of potash flotation. Flotation recoveries of sylvite are commonly in the range of 85%, while losses can occur in slimes, flotation tailings and make-up of process brine. Ores containing free coarse-grained sylvite are generally screened, whereas both fine and coarse fractions are conditioned and floated separately. The unique features of potash flotation include solubility of sylvite in water, the size of particles floated and fast kinetics. Particles up to 2.3 mm can be floated and about 50% of flotation feed can be removed in the rougher stage in few minutes. The main challenges in potash flotation are the recovery of potash from slimes, flotation efficiency in the presence of carnallite and recovery of coarse potash grains. A review of potash flotation shows that there is still room for improvement in both coarse and fine potash flotation. The present paper reviews the most significant flotation parameters including reagent type and dosage, flotation circuits, flotation equipment size and new developments in potash flotation. The latter include new reagents, flotation technologies (Hydrofloat, Jameson and column cells) larger flotation cells and slimes flotation.INTRODUCTION Potash is the common industrial term for potassium in various chemical combinations and minerals soluble in water. About 90% of potash produced worldwide is used as agricultural fertilizers. Flotation is the main treatment process of sylvinite (KCl-NaCl) ores for recovery of sylvite (KCl). Potash concentrate should contain a minimum of 95% KCl and be relatively free from 0.2 mm KCl fines. The flotation process for beneficiation of potash ores was developed in United States and Russia concurrently in the early 1930s. In 1934, Potash Corporation of America applied flotation process in a commercial scale (Tippin R.B. and Huiatt J.L). In the initial application, halite (NaCl) was selectively floated by employing lead chloride as an activator and soap as collector. The sylvite concentrate was reported in the cell underflow."

Jan 1, 2012

By David C. Kraft

Helical piles and ground anchors were used to meet critical design and constructability requirements for an urban forest Canopy Walk at the Atlanta Botanical Garden, Atlanta, GA. The 12-foot wide pedestrian walkway path was to be nestled among the treetops of a forest, extending to 600 ft. in length, and soaring 40 ft. high above the forest floor. Of particular concern during construction was that the foundation system for the temporary steel shoring system had to be non-invasive to the subsoil, could not damage the forest floor, trees, root systems, or foliage, and upon completion of the concrete walkway pour, could be removed, again without disturbing the subsoil. Accubrace, Inc. designed and installed all the helical foundation types, as well as provided steel braces, typically used in Tilt-Up building construction, for the walkway project. The braces, some extending to 43 ft. in length, were used to provide lateral support against wind loads for the walkway form. In addition, the braces acted as secondary support for lateral loads during the placement of wet concrete along the 600 ft. length of the walkway. Helical foundation products installed included vertical compression piles, ground anchors for tension rods, and ground anchors for the braces. The installation of the piles and anchors was particularly challenging since the forest floor elevation varied as much as 50 ft. due to the presence of a ravine. Information is provided on the subsoil conditions, required loads, design, installation, and acceptance criteria for each helical product type installed for the project. The results of vertical and lateral load tests on the helical piles in the pre-construction phase, conducted in conformance to project specifications are presented. Photographs to illustrate the nature and complexity of the project are included. The concrete pour for the walkway was successfully completed on December 12, 2009, and the walkway was opened for visitors in May, 2010.

Jan 1, 2011

By Khaled Morsy

Cementitious seals are made of foamed cements with strength ranging from 100 to 600 psi. These cementitious seals are usually used at locations where the seal will be subjected to some convergence, assuming that this material can absorb entry closure without compromising the structural integrity of the seal. Prior to 2006, Lake Lynn Experimental Mine (LLEM) conducted full-scale tests on various cementitious seals designed to meet or exceed the 20-psi horizontal static load requirements of the old 30 CFR1 75.335. Both hydrostatic and dynamic loading tests were conducted. The structural response (pressure and displacement readings) obtained from these tests were recorded. The stability of the cementitious seal is based on balancing the load applied to the face of the seal from the explosion against the shearing resistance at the seal/rock interface. Therefore, the properties of the seal/rock interface, such as stiffness, cohesion, friction, etc. are critical to determine the stability of a cementitious seal. These properties are usually assumed by the researchers in their models. This paper emphasizes the importance of having the correct properties of seal/rock interface in the numerical modeling. FLAC 3D models were developed to simulate Celuseal2 cementitious seals subjected to both hydrostatic and dynamic loadings. Using the hydrostatic and dynamic loading test data conducted at LLEM, the static and dynamic properties of the seal/rock interface were back calculated. The FLAC 3D models showed good agreement with the test results.

Jan 1, 2009

By L. J. Kane

Conventional methods for determining the size of dust suspended in a gas require that agglomerates (clusters of particles) first be broken into particles, but in evaluating industrial dust-removing equipment the size of the agglomerates as they actually exist in the gas stream is far more important. This paper presents results of an investigation by the Federal Bureau of Mines to develop methods for determining the size of dust agglomerates suspended in a gas stream. The studies are part of the Bureau's continuing research on synthetic liquid fuels. The size and size-distribution of agglomerates as they exist when the gas reaches the filter was determined by using a membrane filter in conjunction with a dust count under a microscope. A membrane filter is a cellulosic sheet about 150 microns thick containing millions of holes per square centimeter--holes of uniform diameter that run directly through the sheet without interconnection.

Jan 1, 1960

By J. Dean Warner

Alaska contains many critical and strategic minerals that are scarce in the conterminous United States. Among these are tin, tantalum, and columbium. This Bureau of Mines report summarizes available data on the production, reserves, and occurrences of these minerals in Alaska. Alaska produces about 200,000 lb of tin per year, with historical production since 1901 estimated to have totaled 5,830,600 lb. Measured, indicated, and inferred tin reserves total over 140,000,000 Ib. Much of the tin production has been from the placer mines of the western Seward Peninsula; however, most of the reserves are in that area's lode deposits. Alaskan tin occurrences are part of a belt of tin mineralization that extends along the western coast of North and South America. The Alaskan portion of this "tin belt" comprises placer occurrences and lode occurrences of five major types: greisen, vein, skarn, pegmatite, and volcanogenic massive sulfide. Greisen and vein occurrences are the most abundant, but skarn deposits have historically been the most economically important. Columbium and tantalum have not been produced in Alaska; however, they may be recoverable as byproducts of tin, tungsten, gold, or uranium mining. Approximately 135,000 Ib of columbium oxide (Cb205) are inferred within the Tofty placer deposits in the Manley Hot Springs district.

Jan 1, 1985

By Yuanwci Shi

This paper discusses the results of research on the interaction between roof strata and shield supports including the active and passive supporting functions of the shield supports which prevents roof strata separation; pressure distribution on the canopy and under the base plate as measured in the laboratory and underground; comparison between various shield structures regarding their effectiveness on roof and floor control; and determination of optimum support capacity under given geological and mining conditions including hard-tocave roof

Jan 1, 1997

By Peter Chou

A total of 117 slope stabilization drilled piers were installed as part of a major hillside revitalization project. The 110-million dollar development, known as Stratford at Kenwood, included an 18-story upscale senior residential tower, a 3-story healthcare building, and 4-story condominium buildings, offering approximately 580,000 square feet of living space with panoramic views of Downtown Cincinnati, Ohio. In an effort to establish a flatter hillside plateau for the new 4-story condominium and to create a cut and fill balanced jobsite environment, an 800-foot long row of drilled piers and a 600-foot long multi-tiered shear key system was used to terrace existing 1.5H to 3H: 1V steep slopes and support the new fill. These slope stabilization features reduced the amount of spoils needed to be wasted off-site and mitigated the risk of slope instability. An ODOT/FHWA research indicated that spacing of stabilization piers and necessity of top-connecting elements are highly dependent on pier diameter, spacing, soil type, depth to potential failure surface, surcharge loads, and pier deflection. Due to pre-existing deep buried swales, various load combinations, and the complex mechanism of soil arching effects between adjacent piers, both analytical and numerical computer modeling was performed to estimate the loading on each pier. New generation multiplexed, 3-Dimensional, Micro-Electro-Mechanical-System based inclinometers were installed between selected piers to confirm the pier design, and monitor the fill placement, as well as long-term slope stability.

Jan 1, 2009

During recent years there has been a marked increase in the use of explosives in Queensland coal mines. Delay detonators have been introduced and their use has extended with the wider application of mechanised methods of mining.The need for careful study of the characteristics of delay detonators is stressed so that the advantages of simultaneous firing, from the points of view of safety and efficiency, may be obtained. With their use new potential hazards are introduced. These hazardsare considered and means whereby the overall safety may be improved are discussed.The increase in the number of misfires since the introduction of delay detonators is shown and the examination of misfired detonators is described. Lessons to be learned! from these misfires are noted and details are given of the essential requirements for safe and efficient blasting using delay detonators.INTRonUCTIONOne of the aims of mechanization in coal mines is to reduce the physical effort applied to the winning of coal. Explosives play an important part in achieving this and, following the introduction of power borers for the drilling of shot-holes in Queensland coal mines, much of the arduous work associated with coal getting has been eased. During recent years there has been a marked increase in the consumption of explosives, as shown in Table 1, and it must be the aim of all to use these explosives safely and efficiently. That there are dangers associated with the use Of explosives cannot be denied. The shotfiring operation is fully covered by legislation and, being under the control of one man, shQuld be capable of being carried out with a high degree of safety. The main source of accident appears to be the failure to take proper cover and this has resulted in...

Jan 1, 1958

By Vaughan J. P

The Pegmont deposit is a stratiform Pb-Zn sulphide body occurring in a thin, iron-rich metasedimentary unit situated near the top of the Kuridala Formation, a part of the Mary Kathleen Group of the Middle Proterozoic"Eastern Geosyncline" succession of the Mount Isa-Cloncurry district. The deposit appears to have developed in a shallow basin or depression on a sea or lake floor.Detailed chemical and mineralogical study of seven diamond drill cores through the ore horizon shows that in addition to galena and sphalerite the orebody contains a large range of iron-rich silicates and aluminosilicates.Further, five drill cores selected to represent a section from basin centre to basin edge exhibit clear and systematic chemical and mineralogical changes in the ore horizon in both a vertical and, most importantly, ill a lateral sense.Reconstruction of the sedimentary environment of the ore horizon as a whole shows this to be a silicate facies of a phosphatic, manganiferous iron formation or, more accurately, of "ironstone" in the sense of James (1966, U.S. Geol. Surv. Prof. Paper 440, chapter W).On the basis of both mineralogy and chemistry this silicate facies may be subdivided into three microfacies according to the dominant iron silicates characteristic of each: a fayalite microfacies, a hornblende-clinopyroxenemicrofacies, and a garnet microfacies. Significant Pb-Zn sulphide concentrations are confined almost entirely to the fayalite microfacies.

Jan 1, 1979

The object of this talk is to bring before members the importance of the prospector and the' State Battery system to the wealth and prosperity of the mining industry in particular and the State of Western Australia in general, and to touch on the more important features.Customs plants of any sort are usually subject to a good deal of critioism, usually on the large profits made at the expense of the customer, etc., and this often clouds the real value of the work being done.Prospectors, on the whole, are a good class of men; they work under conditions and difficulties which would deter those less spirited. Food, water and mining supplies are often difficult to obtain and frequently have to be transported great distances. Their mining tools are usually of the most primitive type, yet during last year over 109,000 tons of prospectors' ore were handled by the State Battery system for 73,250 fine oz. valued in Australian currency at over £587,000, the value being 57/- per long ton at par.This production brings the State Battery system into fourth position amongst the producers of the State, the yield being exceeded by the Lake View and Star, Wiluna and the Great Boulder.In passing I might mention that these notes were written at the end of the year 1940, and the above figures were for the previous period. The figures for last year, 1940, were not quite so good, being 101,000 tons for approximately 60,000 fine oz., valued in Australian currency at £572,000.In spite of this drop the State Battery system maintained its position as fourth in order of gold output for the State.The extractions, as a whole, throughout the system, were 92·54%, made up of 68·86% by amalgamation and 23·68% by cyanidation. These figures, for a group of 20 plants treating widely different classes of ore, must be considered satisfactory. The total production since inception is over £11,000,000 in Australian currency.State Batteries are usually more or less of a standard design. Ore is reduced to about 2i in. maximum size before being sent to the bins. Challenge automatic feeeders control the feed to each mill unit, amalgamated copper plates collect the free gold. Corduroy strakes are used with some ores after amalgamation, but in only a few cases has this been found of any advantage to the customer.The pulp from the battery is sampled, after leaving the tables, with a "Tazewell" sampler and pumped to dams for subsequent cyanide treatment.The "Tazewell" sampler is a machine driven by the moving pulp; and takes about fifteen dips per .minute from such pulp through a slotted...

Jan 1, 1941

By Clair Murdock, David Heath

The 1,280 MW Sir Adam Beck II Hydroelectric Project was constructed in the1950s, at Niagara Falls, Ontario, Canada. The twin intake tunnels total over 17 kilometers in length and pass deep below the City of Niagara Falls. The tunnels were excavated using drill and blast methods, with a top heading and bench approach. The shot rock was loaded with electric shovels and transported to the five shafts with off-highway trucks. The tunnel muck was hoisted to the surface by skip and transported by truck to disposal areas. The volume of underground excavation for the 15.55 meter diameter tunnels and the shafts exceeds 3,500,000 cubic meters, then and now the largest underground civil works excavation by drill and blast in the Western Hemisphere. The lining required over 900,000 cubic meters of concrete. All of this work was completed in three years, remarkable progress, considering the technology of the day, comparing very well with the rapid excavation and tunneling methods of the twenty-first century. Big, fast, and deadly—at least 20 lives were lost in construction accidents.

Jan 1, 2007