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By Y. Luo

Based on the concept of slope stability analysis, a formula for determining an important parameter required in the mathematical model for the prediction of mining subsidence in hilly terrain has been proposed. The slope geometry and soil physical and mechanical properties of the surface natural slope can all be considered in the formula. Incorporation of this new formula into an existing mathematical model provides an integrated approach in studying ground movement in hilly regions.

Jan 1, 1998

By T. Knuutinen, M. Klemetti, P. Mörsky

This paper presents a comparison study done at VTT's new pilot plant facilities in Outokumpu, Finland, for chromite ore. The ore was ground in a rod mill -, a ball mill - and high pressure roller mill - ball mill circuit in the capacity range of 0.5 - 3.0 t / h. The main grinding characteristics are discussed and the quality of the products are compared from the mineralogical point of view. The benefits of high pressure roller mill comminution for further mineral processing of chromite is also discussed.

Jan 1, 1995

By David Conover

The El Boleo Copper Project is currently in the final design stages for development of a 3-MM-tonne/yr underground copper mine located in Baja California, Mexico. The nearly horizontal mineralized zones are amenable to exploitation by conventional mechanized coal mining technology using continuous miners, shuttle cars, and belt haulage. The mine design resembles a typical full-extraction coal mining operation utilizing a sequence of mains, sub-mains and production panels. Due to numerous faults, mining will be conducted as several small adjacent mines accessed through adits from large arroyos cutting through the mine area. Up to four seams may be mined in some areas with a maximum overburden depth of about 250 m. The ore zone is relatively weak and plastic, subject to extensive creep over time. The mine workings will pass through areas of historical shortwall mining panels where the ground has flowed into old entries and gob areas, and then reconsolidated. A small test mine was developed to evaluate mechanical cutting performance, roof-bolt anchorage capacities, roof and pillar stability and caving behavior. In-mine measurements were combined with two- and three-dimensional FLAC models to evaluate alternative development and production pillar designs. The paper will discuss the various factors influencing ground stability at the El Boleo project and the strategies employed in developing a suitable ground control design.

Jan 1, 2009

By C. Sampaio, C. Petter, M. Veras

"INTRODUCTION Use of sensor technology applied to the gravimetric beneficiation is intended for the selective preconcentration or separation of various minerals. Sensor Based Sorting (SBS) uses sensors to identify the particles and separate them by a mechanical process (flap) or pneumatic ejection valves (Wotruba et al. 2014). The principle of the SBS technology to separate mineral particles consists of three phases which cover feed,detection and separation. (killmann, 2009 Apud nienhaus et al. 2014). The applicability of the technique in an early stage of beneficiation enables free particles and poor grade to be a part of the process. The mass of tailings to be processed can be removed at the initial stage to save energy, water and equipment maintenance (Wotruba et al. 2014). Lindner (2010) suggested that the use of SBS technology would only will be possible if there exsists an electromagnetic interaction in all the wave spectra interacting with the solid ore. The interaction of electromagnetic waves depends directly on the characteristics of the material. The material receives a spectrum of electromagnetic waves by irradiation and this results in a reduced wavelength with differing types radiation such as fluorescence, reflection, remission, absorption, transmission and transmission. The frequency of the wave spectrum varies between 1000 and 1020Hz, illustrated by the data in Figure 1, which shows that each type of sensor emits a wavelength inversely proportional to the frequency ranging from 10-11pm to 104km, and the frequency that varies between EHz 103 and 1020kHz. The difference between the electromagnetic spectrum variations can only be visible to the human eye at wavelengths with intervals between 380nm and 780nm (Wotruba et al. 2014). One of the main advantages of operating with imaging sensors is the versatility of the images which can take on zero, one, two or three dimensions shown below as a point, a line, an area or a spatial image, as illustrated in Figure 2. According to Schubert (1988), to separate a mineral particle it is necessary to follow the characteristics of mineralogy, physics and chemistry with or without use of water. The use of new technologies can help reduce operating costs and improve utilization of mineral resources."

Jan 1, 2016

By K. Getsos

Western Greece is a favorable site for exploration and discovery of oil fields. The most important potential source rocks seem to be all the rocks deposited before middle Jurassic under special circumstances, such as reducing conditions, which allowed preservation and maturation of the organic material. In general all the rocks of middle Jurassic to Paleogene are not favorite source rocks. The porosity type was studied on fifty samples using scanning electron microscopy (SEM). Potential reservoir rocks are the porous Paleogene wackestones-packstones with boring, channel and vuggy porosity type. Finally seal rocks are the impermeable mud-stones and wackestones of Jurassic, Cretaceous and Paleogene age. These rocks consist of micrite and whole sells of foraminiferas and the porosity type is mainly intercrystal/interparticle. A Total Organic Carbon (TOC) analysis, conducted on seventy samples using a wet oxidation method, has revealed an extremely low TOC content (less than 0.05 %). This amount is by far less than the minimum organic content amount, required for source rock characterization and characterizes all the rocks of middle Jurassic to Paleogene age. Additionally, 18O and 13C stable isotope analysis was contacted and the results are given in d values. All the rocks within the studied time interval have much lower d values than petroleum source rocks. Clay mineral content was studied in almost seventy samples. As is indicated by the clay mineral content the studied rocks have reached up to the Middle Diagenesis and the temperature during diagenesis was rather low.

Jan 1, 2006

By Hee-Young Chung, In-Mo Lee, Jeongjun Park, Hangseok Choi, Seok-Won Lee

"When using a Tunnel Boring Machine (TBM) during tunneling work, unexpected ground conditions can be encountered that are not predicted in the design stage. These reduce the stability of tunnels, and can result in considerable economic losses. This paper analyzes the potential risk events that may occur due to risky ground conditions. A resistivity survey is utilized to predict the risky ground conditions ahead of the tunnel face during construction. The potential risk events are evaluated considering both the occurrence probability and the impact. A TBM risk management system that can suggest proper solution methods for potential risk events is also developed. Multi-Criterion Decision Making (MCDM) is utilized to determine the optimal solution method to handle risk events. Lastly, an actual construction site, at which a risk event occurred during tunnel construction, is analyzed utilizing the Earth Pressure Balance (EPB) Shield TBM, to verify the efficacy of the proposed system.INTRODUCTION The Tunnel Boring Machine (TBM) method has been widely adopted in numerous tunneling projects because, as a mechanized tunneling method, it is also environmentally friendly, exhibiting minimal noise and vibration when compared with conventional tunneling method. In addition, it provides considerable economic benefits that allow for a high advance rate for long drives during construction. However, the TBM method has a limitation, as it is unable to deal with unexpected situations during construction, as the system is not capable of moving backwards. This leads to delays or even stoppages, and a corresponding increase in construction costs due to the need to arrange for alternative equipment and solutions. It is essential to retain systematic management in order to prevent or deal with unforeseen consequences such as the collapse of a tunnel face, ground surface upheaval or settlement, and construction delay due to water leakage during construction. Therefore, a systematic risk management system that is applicable during the construction stage of the TBM tunnel should be developed, taking into account the predicted risky ground conditions ahead of the tunnel face in advance."

Jan 1, 2016

By Takashi Sasaoka

About 200 M tons of coal were imported into Japan in 2007 and Indonesia was its second largest exporter, accounting for about 30 M tons (12% of the total imported coal). Indonesia produced about 200 M tons of coal, about 75% of which was exported in 2007. As the Indonesian government has decided on an energy policy wherein 33% of the country?s primary energy demand will be met by coal by the year 2025, the domestic demand for coal has increased dramatically in recent years. Over 99% of the coal produced in Indonesia comes from surface mines. However, the conditions of surface mines are worsening each year: the stripping ratio is increasing, approaching the economic ratio, and the infrastructure for coal from inland mining areas is insufficient for such intense mining operations. To meet the demand for coal in Indonesia and the rest of the world, underground mines have to be developed. However, mining engineers and/or miners in Indonesia do not have a lot of experiences, expertise and know-how concerning the plans and operations of an underground coal mine. In addition, the industry faces a lot of problems which include poor conditions such as a steep coal seam, groundwater problem, stability of highwall, etc. Under these situations, a mine targeted in this research attempts to develop a new underground mine from an open-cut highwall because the stripping ratio in the surface mining area has almost reached the limitation of economic value. This paper discusses the possible development of a new underground coal mine from an open-cut highwall by means of field observation and numerical analysis.

Jan 1, 2009

Flooded-bed scrubbers on continuous miners have been shown to be an effective respirable dust control technology, traditionally used during the extraction of extended cuts of up to 12.2 m (40 ft). To effectively use scrubbers in faces that employ exhaust ventilation, the return ventilation curtain or tubing should be located outby the scrubber discharge on the continuous miner, which results in a setback distance from the face of approximately 12.2 m (40 ft). The goal of this research was to compare respirable dust levels generated in 6.1 m (20 ft) cuts when using extended curtain setbacks with a scrubber operating to dust levels in 6.1 m (20 ft) cuts when using traditional exhaust face ventilation without a scrubber operating. Dust surveys were completed at three mines with area and personal sampling conducted to quantify respirable dust concentrations on a cut-by-cut basis. Sampling results did not show a statistically significant difference in respirable dust at the continuous miner or shuttle car locations with and without the scrubber operating. However, with the scrubber operating, respirable dust concentrations in the return airstream downwind of the miner showed reductions of 91%, 86%, and 40% at Mines A, B, and C, respectively. The reductions at Mines A and B were statistically significant. Likewise, reductions in respirable quartz dust levels in the miner return were observed at all three mines, with statistically significant reductions of over 80% observed at Mines A and B. Consequently, operation of the flooded-bed scrubber did not impact respirable dust levels in the face area but did significantly reduce respirable and quartz dust levels downwind of the continuous miner. These results were obtained with the mines operating at or above the minimum operating levels specified in their ventilation plans.

Feb 23, 2014

By B. Petri, N. Rouse

"Air overpressure monitoring procedures and instrumentation guidelines which apply to production blasting in underground limestone mining are not readily available. The industry also lacks an applicable source for air overpressure levels that are produced by blasting operations in underground limestone mines. As such, there was no available background data from which the expected overpressure levels from production blasting in a new underground limestone mine could be predicted. During the development phase of the mine, it was imperative that newly constructed underground structures be capable of withstanding the overpressure produced by blasting in nearby production headings. To ensure the structures could withstand the blast-induced overpressure, a study was conducted to record empirical overpressure data and develop a model which could be used to control air overpressure levels by the production crews. This document describes the procedures used to develop the model, the development of the model, and the applicability of the model for predicting underground blast overpressures. INTRODUCTION A developing underground limestone mining operation required that a ventilation wall be built to house the permanent mine fans. At the time of the study, the mine was a single-level room and pillar operation with a 7.9 meter (26 ft) high roof, 13.7 meter (45 ft) wide entries, and 13.7 meter by 13.7 meter (45 ft by 45 ft) pillar dimensions. The mine is accessed via a 396 meter (1300 ft) long decline and 100 meter (330 ft) deep ventilation shaft. The ventilation wall was to be partially constructed of autoclaved aerated concrete blocks, for which dynamic strength data from explosives loading were unavailable. The company ownership feared that airblast may affect the wall due to the close proximity of the working faces. Therefore, the company management asked that the overpressure levels be estimated and compared with the designed wall strength. Few studies that apply to explosively-driven air overpressure levels in underground production blasting were found through a literature review. Therefore, the logical approach to assess the overpressure levels was to monitor the blast pressures at the site and conduct a thorough evaluation of the data. As a result of this study, the equipment setup and monitoring procedure used to record the airblast data is described. Finally, the experimental data gathered during the monitoring program is presented, trends and findings from the data are discussed, and recommendations for further study are presented."

Jan 1, 2015

By H. V. Fairbanks

It is estimated that millions of tons of coal fines are unsaleable each year due to difficulty of drying them economically with conventional mechanical dewatering and thermal drying equipment. The difficulty is due to the fact that coal of small particle size presents a large surface area with polar groups which have a great affinity for water. In order to remove this water thermally, a high temperature is necessary which oxidizes the surface of the coal. This substantially reduces the heating value of the coal. If drying could be satisfactorily carried out at a lower temperature, much more of the heating value of the coal fines could be retained. It was conjectured that acoustic energy applied during the drying process might prove to be of value since acoustic energy has the property of producing cavitation at a liquid-solid interface when the intensity is sufficiently great. This cavitation process produces water at room temperature which can be carried away from the solid surface by a flow of relatively cool air. Hence, moisture removal is made possible at a lower temperature.

Jan 1, 1966

By H. Lawrence

In 1977, the Bureau of Mines awarded a grant to the State of South Carolina to explore the possibility of using Landsat multispectral scanner (MSS) data as an aid in monitoring surface mining activities in selected counties of the State. Work had been done in Aiken County prior to the grant by Bureau of Mines and State personnel at the EROS Data Center using both the GE Image 100 and ESL IDIMS systems. The initial work on the 1-100 consisted of locating and measuring the areas of various kaolin mines. The results were excellent on location, identification, and accurate area measurements of several mines as compared with aerial photos of each mine. The effort also included locating and measuring the size of all mines (including sand and gravel) within two U.S. Geological Survey (USGS) 7 ½ min quadrangle maps. Line printer overlays using the IDIMS equipment and software resulted in the location of all known mines within an estimated error less than ±91.4m (5300 feet). Mine acreage was calculated by counting each symbol (which represented one pixel) and multiplying by 1.1 (the number of acres per pixel). Figure 1 shows a portion of one quadrangle overlay. Table I gives a comparison of acreage measured for sever- al mines from the 1-100 and IDIMS systems vs. aerial photo measurements.

Jan 1, 1979

By B. Li

"The spontaneous combustion of coal storage pile(Gangue Hill) is one of the seriously threat encountered in coal mining and storage. The dynamic accumulation of internal heat in coal storage pile(Gangue Hill) provides continuous heat-source for coal spontaneous combustion. Combined with the features and characteristics of coal pile storage, a technology of heat pipe(HP) is applied to enhance heat transfer. In order to prevent spontaneous combustion of coal storage piles (hillock) due to regeneration, a method using heat pipes to destroy the heat preservation conditions of coal storage pile(Gangue Hill) is proposed, which reduces the risk of coal spontaneous combustion and prevents coal fire. A theoretical model of Coal-Thermosyphon has set up to analysis the radius of cooling effect area quantitatively. An experimental equipment of the heat transferring in a set of heat pipe, which used to study the influence on coal pile temperature distribution, has been designed. Results show, the heat pipe has a significant effect on inhibiting the coal spontaneous combustion process by destroy the heat preservation conditions of the coal. Under the experimental conditions, the most obvious coal temperature decline appears at radius 20.0mm around the pipe, dropped from 45.8? to 32.5?, a decline of 29%; the coal pile temperature at radius 420mm from 12.9? to 12.4?, a decline of 3.87%. And the research offers an effective and new approach in its application and promotion for preventing and controlling in coal spontaneous combustion.INTRODUCTION China is one of a few countries which utilize coal as the major source of energy in the world, and is the one whose characteristic of energy structure is rich coal, deficient oil and lean gas. Relatively speaking, China is abundance in mineral resources. The coal, which is the fundamental resource in the process of industrialization, is the main energy in china. Thus China cannot alter the situation of coal consumption dominated a leading role in its energy structure in near term.A massive of coal gangue would be produced every year in China with the mining activities. And it’s estimated that almost 360 million tons gangue were dumped in 2003, accounting for 10 percent of the whole coal production. Huge numbers of coal waste piles have more than 2,600 seats, which cover an area of over 12,000 hectares. Worse more, the coal gangue still has an annual growth rate of 100 million tons. Toxic smokes and greenhouse gases are discharged directly and prolongly into the atmosphere due to coal gangue spontaneous combustion. Even worse, waste dump explosion cause massive losses and are able to endanger the safety of workers. For example, one waste dump of the NO.4 Mine of Pingdingshan Coal Group Co., Ltd. occurred twice of explosions in 2005, and about 3.13 million tons of waste rocks were thrown within the range from 100 to 300 meters, eight people were killed and 122 rescuers and miners were burned, and economic losses were estimated more than 3,000 million."

Jan 1, 2015

By R. Mishra

The validity of the concept of mine resistance in ventilation systems is examined. Mine resistance is the proportionality constant relating the head generated by a fan and the quantity flowing through it when the fan is connected to a mine circuit. It is the total effect of all branches in the mine ventilation circuit. Its importance lies in the fact that for new mine projections, and in the extensions of existing mines, ventilation calculations are usually based upon adjustments of the mine resistance. In ventilation circuits with regulation, and/or with multi-fans, simple adjustments of the mine resistance curve do not lead to correct solutions. A ventilation system consists of several interconnected subsystems where one subsystem behavior affects that of the others, and the total system. Through a series of simple but realistic examples, the authors will demonstrate the importance of the systems concept in mine ventilation, and its practical application to coal mine ventilation planning.

Jan 1, 1977

By Jenny Alsén, Hans Hogard

"Construction of large facilities underground in urban areas has many advantages. In order to show the advantages, a case study of the Norsborg metro depot in Stockholm Sweden has been made. The Norsborg metro depot will be the largest and most modern underground metro depot in northern Europe. The depot has been built in hard rock in an urban area with small impact on the environment and local residents. The paper describes how it is possible to build underground facilities in a cost efficient way and take care of the challenges regarding working environment that comes with locating a permanent working place underground. INTRODUCTION The Stockholm area is one of the five fastest growing regions in Europe and home to more than a fifth of Sweden's population on just two percent of Sweden's surface. The population is growing rapidly, with about 35,000 people per year and is expected to reach 2.6 million in 2030. In order to meet the development and enable continued growth, housing projects and expansion of infrastructure need to keep the same pace; this is an easy conclusion to make but much more difficult to realize in practice. The main challenge is to accomplish development in a sustainable and efficient manner, minimizing the use of resources and land. By constructing facilities underground more urban space will be made available for development and/or for greening of city centers. Considering sustainability factors such as land value in decision making for placing of structures or facilities, underground locations could become a first choice alternative. During 2015 and 2016, several major underground infrastructure projects in the city of Stockholm will start, including a 14 km sewage tunnel and an 18 km by-pass highway tunnel. Furthermore the Stockholm metro system is currently undergoing the largest expansion since the 1970’s, a 19 kilometers extension of the metro system including new trains and new stations is planned. During 2013 - 2015 Skanska Sweden took part in the construction of a new metro depot placed underground in the southern part of Stockholm; the Norsborg metro depot. This is a top modern urban underground facility that in 2017 will serve as depot for 17 new metro trains. The project was selected for “Outstanding Project of The Year” at the ITA Tunneling Awards 2015."

Jan 1, 2016

By D. T. Jr. Tarr

History of Development The hydrocyclone, probably because of its basic simplicity, has been used for various classification applications since before 1890. A patent was granted in the United States in 1891 to Bretney on a device for separating sand from water, collecting the sand in a closed chamber for intermittent discharge, practically identical to some present-day water desanding cyclones. Between 1900 and 1937 there were 30 or more additional patents issued on liquid cyclone configurations or their use. About 1937 liquid cyclones began to be used commercially in the treatment of cellulose fiber in the pulp and paper industry separating contaminating particles from the fiber in water suspension used for making high grade paper products. Nichols Engineering & Research Corp. of New York was marketing a liquid cyclone for cleaning sand and din particles from fiber suspensions in the pulp and paper industry by 1937. The designs during this period were such that the cyclones discharged a small amount of relatively high density material into a chamber connected to the cyclone apex which in turn discharged the collected dirt material intermittently. By the early 1940s hydrocyclones as we know them today began to appear both in the pulp and paper industry and in coal prorzssing.18 Considerable experimental work was done on small, mostly 3-in.- diam, cyclones operating at relatively high pressure drops, in the range of 50 psi, to remove very small contaminating particles from cellulose fiber in the production of high-grade writing papers in the paper industry.18

Jan 1, 1985

By G. Ofori-Sarpong, A. -S. Adam, R. K. Amankwah

"In the application of the BIOX® technology, high tailings grade (2-16 g/t) may be generated with a decrease in overall gold recovery, which sometimes make it economically unattractive. This paper investigated the causes of the high tailings grade by using samples from the Bogoso BIOX plant. Partial chemical analysis, diagnostic tests and cyanidation optimisation studies were conducted to invoke understanding into the high tailings grades. Diagnostic study on the tailings showed 48.34% of gold in carbonaceous matter, 17.12% in quartz, 13.40% as liberated gold, 11.51% imbedded in sulphides and the remaining 9.65% in carbonates. Optimum cyanidation recovery of 90.4% was established for the BIOX concentrate at 7 kg/t NaCN, 40-50 g/L activated carbon and residence time of 40 hours. The recovery was sensitive to carbon and cyanide concentrations but additional cyanide was not economical. High preg-robbing indices of 72.7% and 64.4% were recorded for the BIOX product and the flotation concentrate respectively. This confirms the inability of the BIOX process to deactivate carbonaceous matter, which remains a serious precursor for low overall gold recoveries and high CIL tailings. INTRODUCTION Gold ores may be broadly classified as refractory and non-refractory. Non-refractory ores are easy to treat but refractory materials require complicated flowsheets for metal extraction (Hausen and Bucknam, 1985; Schmitz et al, 2001; Marsden and House, 2006). As near surface non-refractory gold deposits are getting depleted, the increasing price of gold and increasing demand for gold, have encouraged many gold producing companies to treat refractory ores for gold recovery. The refractory behaviour of these ores may be due to the presence of sulphides, tellurides, cyanicides and/or carbonaceous matter. Refractory ores do not respond well to conventional cyanidation as the gold is either occluded by or in solid solution in sulphides, or is in association with cyanicides (Marsden and House, 2006). Further, carbonaceous matter preg-robs gold during leaching (Osseo-Asare et al, 1984; Hausen and Bucknam, 1985; Schmitz et al, 2001). The two major causes of refractoriness are the presence of sulphides and carbonaceous matter, and these render the ore double refractory (Nyavor and Egiebor, 1992). Oxidative pre-treatment processes such as high pressure leaching/oxidation; biological oxidation, ultra-fine grinding and roasting are required to render refractory ores amenable to conventional cyanidation (Marsden and House, 2006). Biological oxidation, however, has become the preferred pre-treatment route because it is more environmentally friendly and convenient even where only partial oxidation is required. Comparative tests have demonstrated that bioleaching can achieve the same or better results than roasting or pressure leaching in terms of gold recovery (Yannopoulos, 1991; Brierley, 1997). Further, biological treatment processes are more cost-effective, environmentally friendly and safer."

Jan 1, 2017

By Martin B. Hudson, John Yao, Matthew R. Crow, Yiming Sun, John T. Waggoner, Roozbeh Geraili Mikola

"The Wilshire Grand redevelopment project in downtown Los Angeles includes construction of a new 73-story tower. Construction required excavation up to 93 feet deep (28 m). The south side of the excavation, up to 57 feet deep (17 m), required placement of shoring within about 6 to 10 feet (1.8 to 3.0 m) horizontally away from a 400-foot-long (122 m) section of one of the existing Los Angeles Metro Red Line twin subway tunnels. These tunnels were constructed using a 22-foot-diameter (6.7 m) digger shield, and were initially supported with expanded, precast concrete segments, with final cast-in-place reinforced concrete lining. The temporary shoring system for the deep excavation consisted of soldier piles generally spaced at 8 feet (2.4 m) on center with multiple levels of tieback anchors extending above the subway tunnels. The lowest level of bracing consisted of rakers supporting walers attached to the soldier beams because installation of tieback anchors at that level would conflict with the tunnels. Numerical analyses were performed to predict tunnel movement caused by the excavation and its effects on the train operations. This paper describes the numerical modeling, tunnel and geotechnical instrumentation and monitoring program, and comparison of the computed and observed tunnel responses to the deep excavation and tower construction. With increasing urban redevelopment in major cities, the project is a valuable case history for excavation adjacent to existing tunnels. INTRODUCTION The Wilshire Grand redevelopment project includes the demolition of a 16-story hotel built in the early 1950s and the construction of a new 73-story tower in downtown Los Angeles (LA) that will be the tallest building in the western United States. The project site is situated on approximately 2.7 acres (1.1 Ha) of land bounded by Figueroa Street to the east, Wilshire Boulevard to the north, Francisco Street to the west, and 7th Street to the south (see Figure 1a). The new tower is being constructed by Turner Construction for Hanjin International Corporation. Construction of the basement and foundation of the new tower required excavation up to 93 feet (28 m) deep. Shoring was designed by Cefali & Associates and installed by Malcolm Drilling Company. Along 7th Street, an excavation up to 57 feet (17 m) deep required shoring to be installed within about 6 to 10 feet (1.8 to 3.0 m) horizontally from an existing 400-foot long (122 m) section of one of the LA Metro Red Line subway tunnels (see Figure 1b). The tunnels, extending from the 7th/Metro Station to the Westlake-MacArthur Station, were constructed in the late 1980s and early 1990s with an excavated diameter of approximately 22 feet (6.7 m). They were initially supported with expanded, precast concrete segments with a final cast-in-place reinforced concrete lining. The existing hotel was demolished in 2012 and 2013, with shoring installation and excavation for the new basement occurring as the demolition occurred. At the time of writing, January 2016, the structure of the building adjacent to the tunnels is largely complete."

Jan 1, 2016

A comprehensive understanding of the effects of autoclave configuration (batch, semi-batch, continuous) on the residence time necessary to achieve a target conversion is a prerequisite for design of commercial scale autoclaves. Particle size distribution, mineral and reagent concentrations, temperature and mixing also influence the conversion. This paper outlines the bases of using test data to predict performance of commercial scale autoclaves. Recommendations for coordinating test program design with selection of scale-up method are provided. Examples are given to illustrate the different levels of engineering effort needed to meet corresponding levels of design optimization and accuracy.

Jan 1, 1998

By Jack A. Simon

Coal is defined as a combustible rock that originated in the accumulation and physical and chemical alteration of vegetation. Coal can be ignited and burned like the wood that was man's earliest fuel, but coal gives more heat than the same amount of wood and has many industrial uses. Unlike wood, coal is not generally found on the surface of the ground but is mined from the solid rock of the earth. Before taking up the occurrence, formation, and the unique character of coal in the rock sequence, let us briefly consider the general character of all rocks in the crust of the earth. Relatively little is known about the very earliest history of the earth, although a number of logical theories have been developed. Manned exploration of the moon and the rocks returned to earth continue to provide some answers to questions concerning the earth's origin and history. The period of earth history with which we concern ourselves here begins after great areas of water had evolved on earth and substantial land areas of once molten (igneous) rock existed. Weathering and other processes that attacked the surface of the rocks reduced them to small particles. Water provided by rainfall transported this material, ultimately, to large bodies of water where it was deposited. Thus was initiated the geologic sequence of sedimentary rocks that lie above the once molten igneous rocks. The crust and upper mantle of the earth are made up of several large plates along which difEerentia1 movement (primarily horizontal) takes place. Such movements, although small, are occurring today. These horizontal movements are accompanied by vertical movements causing important changes in the relative position of the continents and oceans. Low-lying coastal swamps with favorable climates are ideal locations for coal accumulation and burial by river-borne sediments, and large areas are affected by relatively minor vertical movements of the shoreline. The large plates have continually or intermittently moved throughout the geologic past, resulting in various configurations of the continents and oceans, and coal-forming conditions have occurred at numerous times and places. Vast areas of our continents have been repeatedly inundated by shallow oceans and only relatively small parts of the present continents appear to have been above sea level throughout geologic time. Great forces acting principally along plate margins have folded and broken the crustal rocks, forming large belts of mountains.

Jan 1, 1981

By Magnus Ericsson

The unexpectedly quick recovery in world crude steel production in the second half of 2009 was due almost entirely to increased production in China that began in late 2008. Previous peaks in monthly production in China were matched by April 2009. The rest of the world had still not reached pre-crisis production rates by May 2010. Chinese production drives growth, but there has been some growth in most other larger crude steel producing countries as well, compared to production in 2009. If the production rate of the first four months of 2010 continues, the total output of crude steel in 2010 will be somewhere around 1,410 Mt (1.5 billion st), the same as in the record year of 2007.

Jan 1, 2010