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By T. McNulty

The author was privileged to find employment as a uranium mill chemist for The Anaconda Company while working his way through school in the mid-1950s. He then served Anaconda in various technical and management positions until 1980. This paper describes the prevalent technologies employed by uranium producers, briefly describes various mines and mills in the U. S., and memorializes a few of the thousands of men and women who contributed to the U. S. Uranium Boom. Following isolation of uranium as an element by M. H. Klaproth in 1789, uses of uranium were confined primarily to pigments, glass coloring agents, and ceramic glazes. In 1896, Antoine Becquerel found that uranium is radioactive, releasing particles and energy as it decays. In 1898, Pierre and Marie Curie isolated radium from uranium and learned that it can be an effective treatment for some types of cancer. In 1939, it was discovered that the isotope U235 is fissionable1 . Up to this point, nearly all uranium production was from pitchblende concentrates made in Bohemia, Canada, and the Belgian Congo. In 1938, only about 5 percent (23.85 short tons) of global output was produced from ores of the carnotite mineral that were being mined in the U.S. By the early-1950s, physicists in many countries had begun to recognize the potential for nuclear chain reactions. Ernest Rutherford (UK), Frederick Soddy (UK), and Leo Szilard (US) explained transmutation of elements and formulated the principle of “atom splitting”. In 1934, Marie Curie’s daughter, Irène, and her husband, Frédéric Joliot, identified uranium as the most viable source for this new form of energy. The basic fission process was unraveled by German scientists in December 1938. After Hitler’s army seized the uranium deposits in Czechoslovakia, many feared that Germany would build the first nuclear weapon.

Mar 2, 2022

By Gilmore R. Tostengard

The advent of inexpensive computers has opened vast opportunities for improved planning and control of capital projects. The mining and mineral processing industries have welcomed the opportunity, and new and improved quantitative management techniques have abounded. This chapter will discuss commonly used computer applications for economic justification of the project, preparation of the cost estimate, planning the work schedule, monitoring work progress, and control of costs and productivity. Finally, there is a review of the degree to which the industry uses these applications. Our experience suggests that while we in the industry have been quick to adopt the new techniques, the quality of our input data has not always kept pace. During the next decade, our push should be toward improving the quality of the basic data and assumptions so that we can fully benefit from the sophisticated techniques. The GIGO (garbage in, garbage out) principle is a wellworn cliche, but it is especially valid here. One of the keys to getting good input is commitment. Unless the managers who are to use or benefit from the system are committed to it, the effort will fail. They must be com- mitted to the underlying principles of planning and control sufficiently to expend their time and resources on them; planning should be especially given emphasis. They can't be too busy to plan.

Jan 1, 1979

As noted by D.W. Fuerstenau in his Plenary Lecture at the Conference on Extractive Metallurgy of Gold and Base Metals, Kalgoorlie, Australia, "Com¬minution of solids is surely one of the oldest technologies that, even in this day and age of DNAs, chips and space exploration, continues to challenge our scientific acumen and engineering ingenuity." Thus, the fundamentals of comminution continue to receive a great deal of attention in the literature. This was particularly true in 1992 with the publication of the proceedings from the SME-sponsored symposium, Comminution Theory and Practice. Papers covering topics ranging from liberation to comminution fundamentals to novel size reduction techniques are included in this review. Liberation Liberation continued to be a prime area of research interest, not only in terms of liberation modeling, but also in understanding the basic mechanisms involved in mineral liberation. King (Comminution - Theory and Practice, pp. 3-15) described a method for determining the interphase area between mineral grains. He showed how the mea¬surement of interphase area before and after comminution could be used to determine the presence or absence of intergranular fracture. Lin, Miller and Cortes (Kona, Vol. 7) discussed the use of computed tomography (CT) as a nondestructive means of investigating three-dimensional particle composition. The use of this technique in constructing coal washability curves from CT data was presented.

Jan 1, 1993

By Patti J. Best

The Southern Powder River Basin (SPRB) now commands 30% of the US utility, coal market due to the region's low mine production costs, competitive rail rates and low sulfur content. In 1997, production exceeded 240 Mt (265 million st). This was an in¬crease of 104 Mt (115 million st) since 1989 and 4.5 Mt (5 million st) above 1996. Continued growth is expected as the second phase of the Clean Air Act Amendments (CAAA) approaches. This growth will be the greatest in the southern part of the Basin where coal quality is higher. Coal characteristics SPRB coal is classified as subbituminous due to its low heating value and high moisture content. The coal is characterized by low sulfur and ash contents, low ash fusion temperatures and high reactivities. In 1997, the average heating content was 8,593 Btu/lb, with an average sulfur and ash content of 0.79 lbs S02/million [ ] Btu and 5.13%, respectively. The distinguishing characteristic of SPRB coal is its low sulfur content. Most SPRB coal contains less than 1.2 lbs S02/million Btu. This is the approximate definition of "compliance" coal for Phase II of the CA AA. Much of the coal, particularly in the southern part of the Basin, is referred to as "super-compliance" coal due to SO2 contents of between 0.4 and 0.7 lbs SO2/million Btu. The SPRB is divided into three geographic clusters based on coal quality. Mines located in the southern part produce coal with the lowest average sulfur content and highest heating content, almost 400

Jan 1, 1998

By Erik S. Bernard

"INTRODUCTION Conventional steel bar reinforcement is used in many tunnel linings to provide high flexural and tensile load resistance. These Reinforced Concrete (RC) tunnel linings may suffer flexural cracking during service or, in the case of precast concrete segments, during production, handling, or installation. Cracks can lead to corrosion of steel reinforcement, so limits are placed on maximum acceptable crack widths to reduce the likelihood of corrosion during the intended design life (AFTES, 2013; MC2010, 2012). However, the relatively light level of reinforcement used in many applications can result in quite wide in-service crack widths, so either additional steel bar reinforcement is required to limit maximum crack widths, or fibers can be included to control crack widths. Numerous investigations have been undertaken into the efficacy of including steel fibers to reduce crack widths in conventionally reinforced members (Stang and Aarre, 1992; Abrishami and Mitchell, 1997; Bischoff, 2003; Dupont and Vandevalle, 2003; and Jansson et al, 2010), but steel fibers suffer the problem that they are at least as sensitive to corrosion at cracks as steel bars and therefore have similarly tight limits placed on acceptable crack widths (AFTES, 2013). An alternative means of maintaining narrow crack limits in RC members has therefore been sought. The current investigation was instigated following an observation that theories promoted as an explanation for the ability of steel fibers to reduce crack widths in reinforced concrete flexural members (Deluce et al, 2014) do not depend on the material composition of the fibers used but instead depend primarily on the tensile stress generated by the fibers across cracks. Since it is known that macro-synthetic fibers are capable of equaling the post-crack tensile capacity of steel fibers, it has been hypothesized that macro-synthetic fibers are also capable of reducing crack widths in reinforced concrete flexural members but with the added advantage that macro-synthetic fibers are completely immune to the effects of corrosion. Use of macro-synthetic fibers to reduce maximum crack widths in reinforced concrete flexural members subject to aggressive environmental exposure is more rational than use of steel fibers because steel fibers are very sensitive to the corrosive effects of environmental exposure at cracks. The current investigation was therefore undertaken to explore the potential use of macro-synthetic fibers to reduce maximum crack widths in reinforced concrete members subject to flexure. Barchip BC54 fibers were selected as they are one of the most widely used and competitive high performance macro-synthetic fibers currently available."

Jan 1, 2016

By S. E. Phillipson, S. Romberger

The Late Miocene San Cristobal Ag-Zn-Pb deposit represents syngenetic and epigenetic mineralization with low- and high-sulfidation characteristics. The geology of the deposit is characterized by barren dacitic ring fracture domes, mineralized resurgent rhyodacite domes, strongly altered and mineralized tuffaceous lacustrine sedimentary rocks and an extensive crystal-lithic tuff debris apron. The orebody is hosted by intracauldron sedimentary rocks and breccias. Fluid inclusion data suggest that silver, lead and zinc were transported as chloride complexes and precipitated by cooling in veins from <5% (by weight) NaCl eq. fluids at 170° to 215°C. Silver spatially and perhaps temporally associated with resurgent rhyodacite was transported as a chloride complex and precipitated by increased H2S activity or increased fluid pH.

Jan 1, 2002

By Hans G. Machel

In low-temperature diagenetic environments (0 c T c 60 - 80°C), elemental sulfur forms by six common processes: via (1) inorganic oxidation of H2S by molecular oxygen, (2) inorganic oxidation of H2S by ferric iron compounds, (3) polysulfide disproportion- ation; and via the microbial metabolic actions of (4) colorless sulfur bacteria, (5) colored sulfur bacteria, and (6) some types of thiobacilli. Economically viable deposits of native sulfur usually are formed by only one process: inorganic oxidation of H2S by molecular oxygen. The amount of elemental sulfur is also limited by three common processes that destroy it in low- temperature diagenetic environments: bacterial reduction, bacterial oxidation, and inorganic oxidation. In high-temperature diagenetic environments (80 - 10o°C c T c 150 - 200°C), particularly in sour gas reservoirs, there are seven common processes forming elemental sulfur: (1) SOdH2S reaction, (2) H2S- hydrocarbon reaction, (3) polysulfide disproportionation, (4) catalytic H2S decomposition, (5) C02-H2S reaction, (6) chlorinification, and (7) exsolution of physically dissolved elemental sulfur. Natural processes that destroy or remove elemental sulfur in such settings are hydrocarbon sulfurization, polysulfide formation, and advection. In most sour gas reservoirs, relatively small quantities of elemental sulfur occur as a free phase (solid or liquid). However, elemental sulfur often precipitates in copious amounts from the reservoir fluids via exsolution and polysulfide disproportionation during production of sour gas reservoirs. By extension, elemental sulfur may precipitate from reservoir fluids in relatively large quantities upon uplift and erosion of deep sour gas reservoirs, or from advection of sulfurous fluids into shallower settings via faults or other high-permeability pathways.

Jan 1, 1992

By Tan Zhenxiang

INTRODUCTION Koolyanobbing is an open cut iron ore mine, which is located in Yilgarn region of Western Australia. To prevent the operators from suffering silicosis diseases and protect the air from being polluted, a series of dust control measures have been taken. These measures include ventilation and dust control system for sample preparation shed, dust collecting system for drill rig, dust suppression system for ore processing plant, dust control for haul road. The details related to individual dust control measure are dealt as follows. SAMPLE PREPARATION SHED DUST CONTROL The sample preparation is one of the major dust sources at Koolyanobbing. The activity is being carried out at the sample preparation shed. It typically needs to go through the following stages, that is, crushing, splitting, drying and pulverising. The amount of dust generated from crushing and splitting is mainly determined by the moisture content contained in the pre- pared sample. A significant amount of dust is generated at the sample pulverising stage due to cleaning sample bowl with com- pressed air. To protect the sample preparing personnel&apos;s health and make the dust level in the air meet the requirement from the health and safety authority, a central ventilation and dust control system has been installed at the sample preparation shed. As shown in Fig. l, the system consists of suction heads, suction lines, dust collector and vacuum fan. The fan creates vacuum environment in the system, therefore the dust is drawn into the dust collector through the suction heads and suction lines. The dust collector is of fabric filter. When the dusty air comes to the filter, the dust in the air is collected and retained on the surface of the filter while the clean air passes through and enters the atmosphere. The retained dust is blowed out by the pressured air pulses and deposits into the dust bin underneath the filter. A time relay device is used to control the cleaning time and the cleaning interval. DRILL RIG DUST CONTROL A hydraulic percussion drill is used to drill blast holes. To carry out the drilling operation properly and efficiently, the cut- tings are being flushed out of the hole by the compressed air. In order to prevent from the fine particles in the cuttings escaping to the air, a dust collector is attached to the drill. The collector mainly consists of suction head, cyclone and bag filter. Refer to Fig. 2. The suction head is installed at the lower end of the feed beams and is movable. The moving range is up to 250 mm. It is not only used to restrict the cuttings, but also used to prevent water from entering the filters when drilling wet hole. A 406 mm diameter primary cyclone is used to separate the heaviest particles in the cuttings. It is also used as blast holes sampling equipment. One part of the dust particles are collected by a sample bag through a splitter attached to the end of the cy- clone. The rest of the particles fall down to the ground through the closing rubber. The bag filter is driven by a hydraulic motor (1). It is used to collect the lighter particles in the cuttings. The filtering area is 16 m2 and the dust separation efficiency is up to 99.9%. The working principle of the filter is demonstrated in Fig. 3. When the rock drill (9) flushing is turned on, the pressurised air from the compressor is directed to the rock drill and to the pres- sure switch (10). The pressured air will open the pressure switch to de-energise and close the solenoid valve (4) The pressure affecting the cut-off cylinder (5) keeps the exhaust port flap open. When the flushing valve (8) is closed, the pressure affecting the cut-off cylinder disappears and the internal intake opening flap is closed by a spring. The pressure also ceases to affect the pressure switch and the spring switches the contact to the point 2. The time relay (11) is now activated and gives a 0.5 second current impulse to the solenoid valve and keeps the current cut off for approx 8 seconds. When the solenoid valve is live, it opens and lets an impulse of pressured air to the filters (2). These impulses will clean the filters.

Jan 1, 1997

By R. L. Brown

The Buchans mining district is located roughly at the center of the island of Newfoundland and contains some 18 separate mineral deposits. The first of these deposits was discovered in 1905, the latest discovery having been made in 1979. To the present (1983), some 16 Mt (17.7 million st) grading 1.33% Cu, 7.5% Pb, 14.5% Zn, 115 g/ t (3.7 oz per ton) Ag, and 1.4 g/t (0.04 oz per ton) Au have been mined. Mining operations are now largely terminated, but a few hundred thousand tons of economically marginal reserves may be mined in a salvage operation. The Geological Association of Canada Special Paper No. 22, "The Buchans Orebodies, 50 years of Mining and Exploration," contains papers which describe the history, geology, and the application of evolving geological concepts in exploration. Papers by Neary, Swanson, and Thurlow and Swanson in that volume are topical to the present discussion. Successful exploration techniques at Buchans included physical prospecting, utilization of the state-of-the-art geophysical techniques, saturation diamond drilling which was made possible by the high gross value of the existing ore, and, since 1955, diamond drilling directed by fairly well understood geological parameters. The record of discovery started in 1905 when the Buchans River deposit was found by Matty Mitchell, a prospector employed by the Anglo- Newfoundland Development Co., a British company which owned mineral rights over a very large area in the Red Indian Lake-Exploits River drainage system.

Jan 1, 1991

By Kevin Sharman, Peri Mehling

A detailed assessment of acid rock drainage (ARD) potential was conducted at the Quintette Coal Mine site in northeastern British Columbia The site is unusual in that the coal seams contain low sulphur levels as compared to eastern coals (typically less than 0.5%), and the non-coal wastes generally do not to have the potential to generate acid on the basis of static ABA tests. The presence of small iron-stained seeps on the pit walls indicate localized sulphide oxidation, while the overall mine site drainage has remained of excellent quality with extremely low levels of metals after approximately 15 years of mining. Thus the site provides an excellent comparison to more problematic coal mine sites. For the Quintette assessment, static acid-base accounting (ABA) analyses of individual samples were compared to criteria for potentially acid generating materials developed for the U.S. Appalachian coal, as well as criteria developed in British Columbia for hard rock mines. Geologic units were characterized by the percentage of samples, or weighted thickness, that was deemed potentially acid generating (PAG). Links were then made to actual seepage and water quality emanating from geologic units around the site. Seeps at the site demonstrate a large range in pH (2.32 to 8.18). The few acidic seeps (pH < 4.0) were found to contain elevated levels of sulphates, dissolved iron, manganese and aluminum, consistent with the metals typically of concern in Appalachian coal mines. Other heavy metals that were detected in acidic seeps at Quintette included copper, zinc, nickel and cadmium. The use of simple ABA tests, and comparison of individual sample results with the Appalachian and British Columbia criteria, was found to be useful in predicting the probable sources of the small localized acidic seeps.

Jan 1, 2000

By O. Tsuge, G. Hoffman

ITmk3®(Iron Technology Mark III) is an innovative new ironmaking technology whereby high quality iron nuggets are produced directly from iron ore fines and coal in a rotary hearthfurnace1). The reaction mechanism has been investigated in detail through fundamental laboratory research2)3), and the ITmk3 process has progressed from the laboratory to commercialization by the success of the pilot plant tests initiated at Midrex’ Technical Center and at the Kakogawa Bench Plant (KBP) located at Kobe Steel Ltd. Kakogawa Steel Works4)5). Pilot operations have demonstrated rapid production of the iron nuggets with complete metal/slag separation at a relatively low operating temperature. The Kakogawa Bench Plant (KBP) in Japan has logged 21 days continuous operation during which high quality iron nuggets were produced directly from fine ore and coal. The operation technology and the engineering data obtained from these pilot tests were instrumental for the scale-up of the ITmk3 process for the Mesabi Nugget Corp. pilot demonstration plant, which is located at Cleveland Cliffs Inc. Northshore Mining iron ore pellet plant in Silver Bay, MN. The ITmk3 process is an ideally suited technology for siting at the iron ore mine, as it allows the economical production of a value-added merchant iron product.

Jan 1, 2003

By Frank F. Aplan, G. Rinelli

INTRODUCTION Coal is a solid, combustible mineral substance resulting from the degradation and alteration of vegetable matter largely in the absence of air. In this natural process of coalification, some non-combustible mineral matter is always associated with the combustible material. Coal preparation or cleaning is the process of removing this inert mineral matter from the coal. Preparation is highly successful in removing the large fragments of inert material, but is not very effective in removing the fine inorganic mineral matter intimately associated with the coal. Of the 600 million tons of coal produced in the United States every year, approximately one-half is produced by coal cleaning methods (1). The bulk of this tonnage is cleaned by coarse or intermediate gravity preparation methods (5 inches to 28 mesh, Tyler). Fine cleaning, say, -28 mesh, is done by shaking tables, washing cyclones, and flotation, or, until recently, the fines were either incorporated into the clean coal or simply discarded--not infrequently, the latter. In 1972, only 13 million tons of raw coal were cleaned by flotation in the United States, and from this 8.4 million tons of clean coal were produced (1). The percentage of clean coal produced by flotation in Europe (England, West Germany, Poland, U.S.S.R., etc.) is substantially higher. However, coal flotation has grown rapidly in the United States from only a few plants in 1950 to 31 in 1960 (2) and 66 in 1970 (1). Virtually all new preparation plants incorporate flotation into their basic flowsheet. The essential difference between ore and coal flotation is that for ores the entire tonnage is ground to flotation size, whereas for coal

Jan 1, 1976

By Sakir Selcuk, Brian Hamilton, Paul Zick

The 1.8 mi (2.9 km) Minneapolis-St. Paul International Airport Light Rail Transit Tunnels and Station project is comprised of the underground segments of the 11.8 mi(18.8 km) Hiawatha Light Rail Transit route in Minneapolis, Minnesota. The 21 ft 2 in(6.5 m) diameter twin tunnels were mined 65 ft beneath one of the busiest airports in the United States using an earth pressure balanced tunnel-boring machine. This paper will provide a project overview, review the major equipment selected, tunnel segment casting, and describe excavation and lining operations for the tunnels and station.

Jan 1, 2003

By Kalyan Saikia

An integrated statistical-geostatistical modelling of gold exploration data of Gurahar Pahar prospect of Mahakoshal greenstone belt in Central India has been attempted. Statistical modelling of gold accumulation and width reveal a positively skewed 2-parameter lognormal distribution fit with an estimate of mean gold as 0.84 gram/tonne. Geostatistical modelling provided a spherical semi-variogram function fit with mean kriged estimate and mean kriging variance of gold as 0.76 gram/tonne and 0.23 (gram/tonne)2 -respectively. Ore inventory and grade-tonnage relationships for a selected part provided an estimate of 3,36,000 tomes of ore with an average gold of 0.76 gram/tonne at 0.5 gram/tonne cutoff grade.

Jan 1, 2002

By Mark Cadzow, Rodney Lamb

CARBAD is a recently developed Australian process for the recovery of gold and platinum group metals (PGM). The process relies on the selective agglomeration phenomena of the gold and PGM to capture the mineral in a carbon-hydrocarbon media. The precious minerals are then extracted from the loaded media by a solvent gold room process producing a relatively pure concentrate. The media is then reformed and recycled. The process development from batch test work to a 5 t/h commercial scale CARBAD plant is discussed. The operation and results of processing a variety of ore types at several alluvial and hardrock gold mines is examined. The operating and capital costs for the CARBAD process shows that it is significantly less than that the conventional CIP/CIL. The environmental safety of the process is a major feature where precious metal deposits are located within urban environments or within wilderness areas.

Jan 1, 1989

By R. V. Ramani

Control is a vital management function by which operations are brought into compliance with predetermined standards to achieve the goals of an enterprise. Events that are characterized by a low degree of expectation, avoidability, and intent necessarily have a low degree of control. Such events are difficult not only to predict but to control as well. Fortunately, very few industrial situations fall into that category of events. It is an axiom of control technology that in order to control, one must first measure; further to measure, one must know the characteristics of the subject (or environment) upon which the measurement must be made. Finally, if measurements are to be made reliably, the influences that affect the measurement must be known and, if possible, understood. The complete control cycle therefore consists of the following: (1) defining the objective, (2) planning to achieve the objective, (3) putting the plan into practice with appropriate instructions, (4) measuring variables or parameters of interest, (5) transmitting and transforming the measurements to analyze the system&apos;s status and to predict the future outcome, (6) comparing these with the defined objective, and (7) determining and taking corrective actions to bring the actual results closer to the objective. The management principle underlying the control cycle is the principle of management by exception. The application of the principle and the frequency with which corrective actions are taken vary according to the purposes of the review and control. For example, the control of a machine operation (e.g., truck on a haul road) may require adjustments and therefore data, analysis, and decisions, in intervals of seconds whereas the review for ore-grade control may take several hours. Reviews, on the other hand, for cost control may be done in intervals of weeks or months. In any case, three specific purposes of the control cycle are: (1) to correct the operation so that it follows the accepted plan closely, (2) to evaluate the operation and predict future outcomes in light of changes in the environment or of more experience, and (3) to review the objectives and modify these to be reasonable and realistic.

Jan 1, 1979

By C. H. Bucknam

Acid neutralization titrations were applied to the characterization of soil and overburden for the control and prediction of acid rock drainage in the coal fields of the eastern United States in the 1970?s (1). These became known as the Sobek methods as a result of the early United States Environmental Protection Agency publication and the methods have been modified (2) to be adapted to many applications in the metal mining sector (3,4,5,6,), and, as a result, there are a large number of acid neutralization potential methods being used that are referred to as Modified Sobek methods. Standardization of neutralization potential methods for metal bearing ores and related materials based on carbonate carbon, rather than titration, commenced in the 1990?s through the American Society of Methods and Materials (ASTM) Committee E01 on Analytical Chemistry for Metal Ores and Related Materials Subcommittee E01.02 on Ores, Concentrates and Related Metallurgical Materials (7). A subcommittee section, E01.02.05 on Environmental Methods, was organized to coordinate the method and material standardization efforts of ASTM and the Acid Drainage Technology Initiative Metal Mining Sector (ADTI-MMS) Prediction Committee (8), which took on the project of standardization of the acid neutralization potential acidity titration method (ANPA) to supplement the carbonate carbon method in E1915 (9) for application to samples which have metal carbonates (10), in particular, which result in overestimation of the neutralization potential using the carbonate carbon methods (11).

Jan 1, 2010

By J. Moreno, P. Sinton, R. Vogwill

Groundwater models are often used to estimate and optimize dewatering volumes, locations, and rates, as well as water supply production for mines. Projections of future dewatering rates are highly dependent on the conceptual model used as a basis for the numerical model. This paper presents an audit of modeled dewatering rates versus actual data and an examination of the reasons for discrepancies. The setting is a gold mine, in a collapsed volcanic crater breached by the ocean. Mining will occur to about 200m below sea level within a remnant geothermal system. A detailed hydrogeologic investigation was conducted to support dewatering and geothermal depressurization design for future mining operations. These studies included development of a three-dimensional model to simulate heat and density-coupled groundwater flow, using software developed by URS/Dames & Moore. In this paper, the groundwater modeling results prepared 5 years previously by others was audited using operational dewatering data. This model was then extended using the new mine schedule and actual locations for dewatering wells to predict future dewatering requirements. In addition, a comparison between “hot” and “cold” model results was used to assess the need to use a heat-coupled versus a standard groundwater model for dewatering predictions.

Jan 1, 2003

By Eugene F. Casey, William H. Hansmire, J. Ghaboussi, Randall L. Lentell, Harvey W. Parker

INTRODUCTION Construction of a major intercepting sewer in Brooklyn, New York involved tunneling in soil over several subway lines. In two instances the clearance between the subway and sewer was sufficiently close that concern was raised about the influence of the new construction. Prior to each critical crossing, analytical studies were performed which characterized the tunneling influence. It was demonstrated that with adjustments in construction procedures the crossings could be made without affecting the integrity of the subway linings. A comprehensive program of instrumentation and full-time monitoring was undertaken to ensure that any unforeseen adverse developments during crossing would be recognized. The successful crossings were subsequently made with minimal influence. Reported herein are the special construction conditions for the two crossings, the analytical simulation of behavior, and the results of monitoring on the subway linings. SEWER TUNNEL CONSTRUCTION AND EXISTING SUBWAYS The Red Hook Intercepting Sewer is a 2600 m (8600 ft) long tunnel which is part of a major water pollution control project in New York City. For clarity of nomenclature, the sewer is termed a &apos;tunnel&apos; while the rapid transit structures are termed &apos;subways&apos;. For routine construction, the tunnel was mined by hand with a 3.2 m (10 ft-5 in.)

Jan 1, 1981

By George S. Austin

Perlite is rhyolitic glass with 2 to 5 percent by weight (wt.%) bound water held within the silicic-glass structure. It is often distinguished by vitreous, pearly luster and concentric perlitic fractures ("onionskin"). Occurrences worldwide are associated with Tertiary to middle Quaternary volcanic rocks. Perlite is in silicic domes, plugs, laccoliths, flows, vitric tephra, chill margins of dikes and sills, and welded ash-flow tuffs. It is a hydrated volcanic glass formed through secondary alteration of obsidian by the incorporation of water into the glass/silica structure. Post-emplacement hydration (weathering) of cooled glasses by meteoric water is the principal alteration process, but some hydration by magmatic or meteoric water during or shortly after emplacement, or hydration by water exsolved during cooling may occur. Commercial "perlite" is any volcanic glass that expands or "pops" when heated quickly to plasticity while evolving steam and thus forming a lightweight, frothy material. The expansion temperature typically ranges from 1,100 to 1,500°F. An expanded volume increase of 10 to 40 times the original volume yields expanded densities of 1.5 to 11 pounds per cubic foot (lbs/ft3). Perlite is mined by eight companies at 10 operations in six western states. New Mexico accounts for more than 80% of the total tonnage mined. The rest comes from Arizona, California, Colorado, Idaho, and Nevada. In 1992, domestic production was 571,000 short tons (st), domestic apparent consumption was 591,000 st, and the value of crude perlite was $15.3 million. In 1991, with about the same production and price of crude perlite, the gross value for expanded perlite was $101.7 million. Perlite exports in 1992, primarily to Canada, are estimated an 30,000 st; and imports, from Greece, are an estimated 50,000 st. In 1992, 70 plants in 33 states expanded crude perlite. Construction uses of expanded perlite accounted for 66% of total domestic sales. Expanded perlite used as filter aid accounted for 15%. All other markets, including use as a filler and in agriculture, accounted for 19%. Leading states for expanding perlite, ranked by order of sales, were Mississippi, Pennsylvania, California, Illinois, and Georgia. Domestic perlite encounters transportation disadvantages in some areas of the eastern United States compared to perlite imported from Greece. However, western U.S. perlite exports to Canada offset this in large part, and net import reliance for perlite is about 3% of domestic consumption. Perlite grab samples were tested at the New Mexico Bureau of Mines and Minerals Resources (NMBMMR) for their basic suitability in horticulture, construction, filter aids, and fillers/extenders using Perlite Institute techniques modified by the NMBMMR. Most commercial perlite ranged from 2.5 to 3.0 wt.% bound water for all major types (classical, granular, and pumiceous). Expanded density varied widely, but the lowest density of 1.9 lbs/ft3 was for granular. Average brightness of expanded perlite was 47.6 to 69.3%. Nonexpansibles, commonly obsidian or "dead" perlite, ranged from 18 wt.% to less than 1 wt.%, with granular perlte generally the lowest. Compacted density was not related to either perlite type or nonexpansibles present. Sieve analyses of the -50+100 mesh product showed that, in general, pumiceous perlite produces more fines and classical and granular perlite average 60 to 80% -30+100 mesh after expansion. Samples were tested for crystalline silica that ranged from below the detection limit of 0.5 wt.% to nearly 0.2 wt.%, but most tested below 0.5 wt.%. Although quartz content can be lowered in the expanded product by the expansion process, producers can further lower crystalline silica in the product by mixing low-quartz crude with high-quartz perlite before expansion. Chemical analysis by x-ray fluorescence confirms the rhyolitic composition of perlite, but indicates that surface weathering may increase the concentration of some elements, such as potassium and calcium, by infilling cracks or fissures developed during or after perlite emplacement.

Jan 1, 1995