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By A. D. Garman

This paper presents one of a series of digests of foreign mining legislation and court decisions which is being prepared in advance of a general report relative to the right of American citizens to explore for minerals and to own and operate mines in various foreign countries . This interpretation of the laws of El Salvador has been prepared from the best available information in Washington , but is released subject to correction and amplification , if necessary , by the proper American diplomatic and consular officers to whom it is being referred through the courtesy of the Department of State . Under the terms of the Code of Commerce ( arts . 12ff . ) , foreigners living in El Salvador can engage in business on the same terms as nationals . This involves ( = $434.00 ) - except for those with a working capital , of less than a thousand pesos inscription in the merchants ' register , which can be refused only in case of manifest disability of a permanent nature .

Sep 1, 1930

By L. Henry Smith, David C. Arthur

"The Williams Mine is Canada’s largest gold producer, with annual production of 450 000ounces from 2 300 000 tonnes of ore. Highly mechanized and automated underground mining practices are employed in order to achieve and maintain high levels of productivity and minimize costs.The mine ventilation system is modified to include a new vent raise and variable pitchvane-axial fan. This addition allows several fan installations underground to be decommissioned. A substantial net savings in installed horse power is achieved.Heating costs associated with under-ground ventilation air are a significant portion of mine operating costs. Air heating costs are substantially reduced by recovering heat from upcast exhaust air, minewater and compressor cooling circuits. This waste heat is used to supplement propane fired air heating systems for underground ventilation air. An additional benefit is the availability of a heat sink for summer cooling of the compressors.System design, energy savings data and payback calculations are presented."

Jan 1, 1996

By A. Anani

The goal of hot mix asphalt (HMA) design is optimal material blending to meet Superpave specifications. HMA cost minimization has being modeled as linear programing (LP) (Awuah-Offei et al 2011) and mixed integer LP problems (Brown et al, 2012) and solved with commercial software such as LINDO and CPLEX. Often these software, which are designed to solve general optimization problems, have licenses that cost thousands of dollars. The objective of this study is to develop a novel solution algorithm to the HMA optimization problem presented by Brown et al. (2012), which will negate the need for expensive commercial packages and is specific to this problem. This novel algorithm is based on the branch and bound algorithm for solving mixed integer problems. The algorithm is incorporated into a software package with an easy-to-use graphical user interface. The developed algorithm is validated using a real-life HMA problem. Using this solution algorithm will save companies thousands of dollars, otherwise used to purchase software licenses.

Feb 23, 2014

By Colin Connors

Cemented rockfill is a key component in the success of underground mining at the Jerritt Canyon Joint Venture. The Murray and SSX mines are characterized by relatively poor rock mass quality, and the goal of complete mining recovery makes maintaining a high quality backfill product vital to the safety and efficiency of the mining operations. A large portion of the ore production from the Murray mine originates from drifting under backfill. Modelling studies performed to investigate induced loading of the backfill were used to develop engineering specifications for the backfill material. Operations history has shown an almost 100 percent stability of the backfill when mining is carried out beneath it. The volume of backfill required each year (approximately 300,000 tons) and the required cement content have a significant impact on the total mining costs. The potential for cost savings associated with higher replacement of cement with Type "C" fly ash and the implementation of a backfill strength management strategy were therefore evaluated.

Jan 1, 2001

By David Pentz, Paul Hodges

GENERAL INTRODUCTION The object of this paper is to discuss those aspects of open pit mine design which are affected by geotechnical factors. The temptation exists for some practitioners of geotechnical engineering to believe that this relatively new engineering discipline is the ‘be all and end all of mining.’ In the opinion of the authors, this is fallacious but, as our ability to put numbers to the behaviour of rocks and soils improves, it is clear that geotechnical engineering will become an integral and important part of designing and operationg mines success- fully. Open pit mines in the context of this paper also includes open cast mines, where the 'ore" is extracted and the waste material is immediately replaced or ' backfilled in the mined portion of the pit. Open pit mines operating today move from very small tonnages a day to in excess of 400,000 tons per day. Several mines are operating and are being designed to capital expenditure for such projects in some cases exceeds five hundred million dollars and in a few cases will exceed one billion dollars. The size of this investment means that financing will have to be provided from banks or joint partnerships. This financial environment means that planning will be carefully scrutinized by experienced representatives of financial institutions or other mining companies. All too often a project has been put in jeopardy because the personal desire of one or two men to make a project proceed has caused incomplete planning or perhaps in some instances deliberately leading observers 'down the garden path.’ In our opinion the day is rapidly arriving when the quality, logic, practicability and completeness of the planning will make the difference between securing financing or not and, in the cases of existing open pit mines, of the difference between survival and closure.

Jan 1, 1977

By Philip Drinker, R. M. Thomson

In the mining and metallurgical industries, numerous problems arise requiring determinations of solid and of liquid particles suspended in air. Frequently, these problems are of local interest and involve purely economic or operating difficulties; on the other hand, toxic effects from the inhalation or the ingestion of substances suspended in air may be a matter of concern. For checking up process improvements or for determining ventilation efficiencies in problems of this general nature, various methods have been proposed. .Although simpler methods are often satisfactory, precipitation combines several desirable features that other methods lack. This paper is, therefore, devoted to a discussion of portable alternating-current precipitators applicable to the quantitat,ive determination and microscopy of dusts, fumes, and smokes in air. Small particles suspended in gases, such as air, are referred to in the literature as aerosols or suspensoids. Of these terms, suspensoids appears to be preferable as being more nearly in keeping with words in everyday use. In problems involving air pollution by small particles—by suspensoids—it is convenient to distinguish three broad classes based on the size, the degree of dispersion, and the method by which the particles become suspended in the air. Dusts.—Particles or aggregates of particles, 150 to 1 micron in diameter, that are thrown into the air by mechanical agencies are termed dusts. Examples are silica; talc; cement; organic dusts such as hard rubber, starch, and cocoa; flocculated fume, and smoke products. Fumes.—Particles, 0.2 to 1 micron in diameter, formed from chemical or physicochemical reactions are known as fumes. Examples are ammonium chloride, lead and mercury, zinc and magnesium oxides, fogs, and acid mists. Smokes.—Particles, less than 0.3 micron in diameter, formed by incomplete combustion of carbonaceous and other substances are called smokes. Examples are the particles formed from burning tobacco, oil, tar, and gas.

Jan 1, 1925

By B. Stewart, R. Li

Coal waste materials inhibit the direct establishment of vegetation due to adverse physical and chemical properties, particularly low water retention and high potential acidity. The Moss #1 coal refuse pile is located in Dickenson County, Virginia, and was idled in the late 1980s with little topsoil resources available for final closure. The refuse was acidic (Total S = 0.38%; pH = 3.6), black in color and high (70%) in coarse fragments. The refuse also had a low water-holding capacity (4.5% in < 2.0-mm fraction). A small plot experiment was established on the refuse pile to evaluate the effects of liming rates (50% and 100% of lime requirements) and topsoil thickness (15, 30 and 60 cm) on vegetative growth and leachate quality. Liming and topsoil amendment increased the surface soil pH from <4.0 to >6.0 over a two-year period, which resulted in greater vegetative cover and biomass than the control plots. All topsoil treatments resulted in greater vegetative cover and biomass than plots treated with lime only. This was due to improved surface soil physical and chemical properties. A topsoil treatment of 60 cm gave the thickest vegetative cover and biomass yield. Such a treatment, however, would be cost-prohibitive at this location. Applica¬tion of 27Mg ha`1 of lime to the refuse surface along with 15 cm of topsoil produced acceptable two-year vegetative cover and biomass, and this appeared to be the optimal treatment for this particular situation. Both liming and topsoil had no affect on leachate pH and the electrical conductivity of leachates collected below the plots. This suggests that surface revegetation will have little effect on the quality of water draining through the pile. Therefore, long-term water-treatment requirements may not be reduced by successfully revegetating the pile surface.

Jan 1, 2000

By David R. Mitchell, R. B. Hewes

MANY processes for cleaning coal that are in use depend primarily on physical properties of coal and refuse other than specific gravity and surface conditions relating to froth flotation. These properties are shape, coefficient of sliding friction, resilience, friability, magnetic susceptibility, and electrical conductivity. In many of these processes specific gravity does have some effect and many separators are designed to utilize more than one of the physical properties cited. Although the processes described herein do not have a widespread application, yet for specific coals and specific conditions, they are economically important. A problem confronting many coal-mining districts is the marketing of the slacks or screenings and dust passing the final sizing screens. Processes in commercial use installed primarily to increase the form value, and hence the market value, of these slacks and dusts include briquetting, packaging, and low-temperature carborization. MECHANICAL PICKERS Machines utilizing shape, fictional resistance, and differences in resilience of coal and impurities are usually called mechanical pickers. They require a closely sized feed, therefore their use is confined to the pea, nut, and egg sizes. Various types of these devices are described by Berrisford, 1, 2 Taggart, 3 and Peele. 4 Shape In general, coal differs in shape from its accompanying dirt throughout the range of commercial sizes. Coal, breaking into roughly, cubical particles, contains a greater number of axes that are approximately the same length than does the dirt. The latter, consisting of pieces of slate and shale and lenses of pyrite, is flatter in nature. Further, flat coal often has a dirty, slaty appearance, even though of high quality. Mechanical pickers known as flat pickers, or "flatters," are widely used in the Pennsylvania anthracite region to remove flat coal from the final clean coal. This practice greatly improves the appearance of the final market product.

Jan 1, 1943

By M. R. L. Blackwell

Over the period 1964 to 1969 Conzinc Riotinto of Australia undertook and completed an evaluation of a large low-grade copper orebody on Bougainville Island in the Territory of Papua and New Guinea. From the outset it was clear that the geographic, climatic and topographic characteristics of the area would necessitate a heavy capital outlay on production and support facilities. Both the physical problems and the magnitude of the investment amplified the need for a thorough and rigorous evaluation of the various strategies for exploiting the orebody. In view of the number of independent and inter-related variables and the flow of new data, a computer-based evaluation process extended the scope and depth of the analysis considerably. The system used permitted an iterative assessment and re-assessment of the various strategies with the results becoming increasingly refined with time. This process encompassed the modelling of the orebody, the simulation of alternative operating strategies and the determination of the financial profitability of the project,

Jan 1, 2014

By Carolina Vaghetti

Aliar qualidade do produto final e otimização dos custos de produção é o que toda indústria de componentes mecânicos almeja. Um dos problemas enfrentado na produção de eixos automotivos é o surgimento das distorções de formas, e saber as causas dessas distorções vem se tornando cada vez mais imprescindíveis. Dentre os processos de fabricação, o tratamento térmico é conhecido como uma etapa da produção que potencializa os efeitos dos potenciais de distorção acumulados ao longo da cadeia. As tensões residuais são consideradas um dos principais potenciais de distorção e, por isso, é de grande importância o seu entendimento. Sendo assim, o presente artigo, inserido no âmbito do projeto "Investigation and improvement of a manufacturing process chain from cold drawing processes to induction hardening", realiza uma análise das distorções e da distribuição das tensões residuais após a têmpera por indução e uma análise das tensões residuais após o processo de retífica durante a fabricação de eixos automotivos de aço ABNT 1045. Foram variados parâmetros nos processos de trefilação e têmpera por indução. A partir dos resultados obtidos, foi possível verificar a influência da profundidade de camada temperada, onde a maior camada apresentou, em média, maiores distorções.

Aug 16, 2017

By Nozomu Hasegawa

The phase diagrams and microstructures of the slags in the Mitsubishi Continuous Copper Smelting and Converting Process were studied for the prevention of the magnetite troubles such as accretion build-up on furnace hearths and launders, blockages at the melt outlet, slag viscosity increases and so on. According to the results of those studies, the silica and lime contents in the silicate slag at the smelting furnace, and the lime content in the lime-ferrite slag at the converting furnace were changed, resulting in lower and more consistent copper levels in the discard slag, with much less need for operators to clean melt outlets and launders. However, these changes may decrease the desirable amount of accretion-coating inside the furnaces and thereby reduce furnace campaign lives. Therefore, a method of estimating the magnetite level in the melts was developed, and slag compositions and temperatures have been controlled within the appropriate ranges to prolong furnace lives and also prevent magnetite troubles.

Jan 1, 2003

By Bruce Conard

For many years, Bruce Conard has been engaged in reading about and discussing the desired sustainability of the mining and metals resource industry. He has, however, become concerned that there is a greater issue that requires our urgent attention: what challenges do we face as a global society? His Distinguished Lecturer presentation traces the idea of environmentally sustainable economic development but concludes that a business’ interest in its sustainability is predicated on the sustainability of our global society. Conard reviews some of the most serious challenges, including population growth, clean energy supplies, freshwater availability and climate change, and calls on scientists and engineers not only to apply their skills in helping solve these challenges, but most urgently, to speak with intelligence and passion about the need to act now.

Jan 1, 2014

By J. Van Kleunen

In the Spring of 1959 the Riverside Cement Company, a Division of American Cement Corporation, placed into operation at their Oro Grande California plant a new crushing-blending-reclaiming facility. This new facility, in conjunction with other modernization in the plant, has established a degree of automation and reliability on a-plant-wide basis which heretofore had not been attained in the industry. The blending and reclaiming facilities for raw stone and cement clinker at this plant represent not only the first computer programmed materials handling system of its type in the industry, but also the first installation of specialized equipment which was designed for high capacity, fully automated operations.

Jan 1, 1963

By A. S. Atkins

The interest in the use of micro- organisms in the leaching of sulphide minerals has been traditionally exploited as a scavenger process for the recovery of valuable metal by- products from waste ore dumps. Environmental concern on sulphur emission from conventional pyrometallurgical plants together with the cost of stack cleaning systems to comply with legislative control also indicate baccerial leaching to offer a low cost treatment for the processing of sulphide minerals. The paper describes the effect and limits of relatively coarse particles on the complete leaching of pyrite and its importance to the practical application in dump leaching operations of sulphide minerals. It has also been demonstrated that static leaching techniques have encouraging economic potential for process plant operations compared with agitated leaching systems.

Jan 1, 1984

The link between exploration success and new ideas from research and development (R&D), although often assumed, is rarely well explained or well illustrated. One issue is understanding the role of innovative ideas in the exploration process, and another is determining the relative contributing factors to an exploration success. A useful measure of gold exploration success over an extended time period and geographic area is discovery rate (&#952;): Discovery rate &#952; = gold discovered/exploration expenditure (usefully expressed as tonnes of gold per $1 million). The total gold discovered is strongly leveraged to discovery rate, as any increase in &#952; typically has a positive effect on exploration expenditure. Hence, improving the discovery rate is a key driver for a sustainable mineral industry, especially for gold. There are very few ways to influence &#952; beyond innovative R&D ideas and breakthroughs, and well-motivated and trained staff. The Australian gold industry has experienced exceptional exploration success with 9956 tonnes of gold discovered from 1979 to 2003, inclusive. This equates to: Discovery rate &#952; = 0.9 t/A$1 M Two-thirds of this gold has been found in the Yilgarn craton of Western Australia (6265 tonnes Au). Without this exploration success, there would have been no platform on which to build the current gold industry and to take advantage of elevated gold prices and advances in mining and processing. Several causes of the Western Australian gold success have been proposed, and more than one may be correct. Gold price, and mining and processing advances have all had influence; but exploration success and discovery of gold were essential to add to the miniscule resource base of 1979. A comparison of the exploration methods used to search for gold in the Yilgarn craton in 1979, and 1990, highlights a small number of breakthrough ideas introduced to the industry during the 1980s, and in most cases emanating directly from local R&D. By the 1990s, these ideas were being used in most gold exploration programs in the Yilgarn craton, and are still used today. These six breakthroughs are: epigenetic timing of gold deposit formation (ie after formation of rock sequence), chemical and mechanical role of host rocks, relevance of carbonate alteration haloes, gold dispersion in the regolith, optimal sampling media, and appreciation of landforms in exploration program design. Interestingly, gold exploration science in Western Australia entered the 1980s period without rigid paradigms in place regarding gold deposit formation; there was a balance between descriptive and genetic models, there was scope to research gold deposits from microscopic to global scales and there were highly effective industry research uptake processes in place: it is suggested here that these favourable conditions contributed to the exploration success and industry growth.

Jan 1, 2007

By Thomas Fraser, H. F. Yancey

Prior to the war just ended, Germany was the greatest coal producer in continental Europe. In 1943 the production of coal, bituminous and higher in rank, together with brown coal calculated to the equivalent amount of bituminous coal, is estimated to have been about 240 million metric tons, according to the War Department. Before the war production in Germany exceeded consumption. No other country in continental Europe except Poland had a large surplus. However, England&apos;s surplus was the largest in Europe as a whole. Before World War II the Ruhr Basin normally supplied about 70 pet of the total production of high-rank coal, the Saar and Aachen about 6 pet each, Upper Silesia about 14 pet, and Silesia and Saxony the remainder. Nearly one third of the brown coal was produced in the Rhineland, a little less than one half in central Germany nest of the Elbe River, and about one fourth east of the Elbe. Bituminous coal and brown coal together constituted by far the most important energy resources of the old German Reich. Bituminous coal furnished nearly 70 pet of the total energy requirement, brown coal supplied about 25 pet, and water power, wood, petroleum and alcohol together aggregated only 7 pet. Because it was the most important single mineral resource of Germany, an excess of coal enabled the Reich to import nearly all the other mineral products that she lacked, such as iron ore from Lorraine. The area adjacent to the coal fields was supplied with gas from an interconnected grid. Similar electric grids are based on brown coal with the power stations at the mines. Coal tar provided the foundation for the development of the extensive German chemical industries as exemplified by the I. G. Farbenindustrie. For almost a century, German scientists have been adequately supported both by the State and by industry in studying improved methods of utilizing coal. In Germany the mineral rights were reserved by the State and ordered eatraction of coal was enforced. Each lease comprised a relatively extensive area. which accounts for the generally large size of the mines and mining companies In 1938 there were 160 mines in the Ruhr, with a total output of 125 million tons but 90 pet of the production was controlled by 20 companies. By far the largest single coal-mining company in Germany was the Gelsen-kirchener Bergwerke A. G., which produced nearly 27 million tons in the Ruhr in 1937. Second was Saargruben A. G. a State-owned company operating in the Saar, which produced &apos;lore than &apos;3 million tons. Third was Bergwerksgesellschaft Hibernia A. G., with 10 million tons, also in the Ruhr. Briquettes are made from both bitumillous coal and brown coal, but in 1938 some 44 million toils of brown-coal bri-

Jan 1, 1947

By Thomas Fraser, H. F. Yancey

Prior to the war just ended, Germany was the greatest coal producer in continental Europe. In 1943 the production of coal, bituminous and higher in rank, together with brown coal calculated to the equivalent amount of bituminous coal, is estimated to have been about 240 million metric tons, according to the War Department. Before the war production in Germany exceeded consumption. No other country in continental Europe except Poland had a large surplus. However, England&apos;s surplus was the largest in Europe as a whole. Before World War II the Ruhr Basin normally supplied about 70 pet of the total production of high-rank coal, the Saar and Aachen about 6 pet each, Upper Silesia about 14 pet, and Silesia and Saxony the remainder. Nearly one third of the brown coal was produced in the Rhineland, a little less than one half in central Germany nest of the Elbe River, and about one fourth east of the Elbe. Bituminous coal and brown coal together constituted by far the most important energy resources of the old German Reich. Bituminous coal furnished nearly 70 pet of the total energy requirement, brown coal supplied about 25 pet, and water power, wood, petroleum and alcohol together aggregated only 7 pet. Because it was the most important single mineral resource of Germany, an excess of coal enabled the Reich to import nearly all the other mineral products that she lacked, such as iron ore from Lorraine. The area adjacent to the coal fields was supplied with gas from an interconnected grid. Similar electric grids are based on brown coal with the power stations at the mines. Coal tar provided the foundation for the development of the extensive German chemical industries as exemplified by the I. G. Farbenindustrie. For almost a century, German scientists have been adequately supported both by the State and by industry in studying improved methods of utilizing coal. In Germany the mineral rights were reserved by the State and ordered eatraction of coal was enforced. Each lease comprised a relatively extensive area. which accounts for the generally large size of the mines and mining companies In 1938 there were 160 mines in the Ruhr, with a total output of 125 million tons but 90 pet of the production was controlled by 20 companies. By far the largest single coal-mining company in Germany was the Gelsen-kirchener Bergwerke A. G., which produced nearly 27 million tons in the Ruhr in 1937. Second was Saargruben A. G. a State-owned company operating in the Saar, which produced &apos;lore than &apos;3 million tons. Third was Bergwerksgesellschaft Hibernia A. G., with 10 million tons, also in the Ruhr. Briquettes are made from both bitumillous coal and brown coal, but in 1938 some 44 million toils of brown-coal bri-

Jan 1, 1947

By Peter T. Luckie, Joseph W. III Leonard

INTRODUCTION In a bed of fine coal, water can be found in the interstices created by the particle surfaces and in the pores within the coal particles. The extent of the interstices voidage is obviously a function of the particle sizes and morphologies, as shown by the fact that the bulk density of coarse coal is greater than that of fine coal. After drainage, the voids can be completely or partially filled. By increasing the suction pressure across the bed, as is done in vacuum filtering, the quantity of water in the voids can be reduced. But eventually the increased suction pressure has little influence on the moisture reduction. In addition, the moisture in the pore structure of the coal is unaffected by the mechanical removal of the moisture in the interstices. When this condition is reached, the total moisture content of the coal can only be reduced further by evaporating the water. Evaporative drying is done for one or more of the following reasons: 1. To avoid freezing difficulties and to facilitate handling during shipment, storage, and transfer to the points of utilization. 2. To reduce the heat loss due to evaporation of the moisture from the coal during the combustion process, thus increasing heating efficiency. 3. To decrease transportation costs. The heating value of coal is equally improved for each percentage point reduction in the noncombustibles in coal. It is estimated that a reduction of 1%22 in the total moisture in the coal increases the thermal efficiency of the heat-raising process by about 0. Some coal buyers consider 1 % moisture content to be the equivalent of a 4% ash content.23 It is important to avoid drying the coal to too low a moisture level, since the complete removal of surface moisture to produce a bone dry product can result in a serious dust, wind lost, and safety problem. Surface moisture con- tents of 3% or less for shipped coal are not uncommon. However, the evaporatively dried coal may be lower, Y, to 1%, since the mechanically dewatered coal may be higher. Evaporatively dried coal can be treated (sprayed) with chemicals in order to control the dustiness and any freezing difficulties, thereby providing the producer with more operational flexibility. The evaporative drying of coal is essentially a process of simultaneous transfer of energy, usually in the form of heat, and water, in the form of vapor, from the coal. In order to remove the undesired moisture, it is necessary to raise the temperature of the water from the entering temperature of the feed stream, TF, to the boiling point of the water (usually taken as 212"F), vaporize

Jan 1, 1991

By George H. Hope, Steve Ciccone

"The Red Dog Mine is both the largest known zinc reserve and the largest zinc producer in the world. The mine started in 1989, and by 1999 had increased production from approximately 300,000 tonnes per year (t/yr) of zinc concentrate to in excess of 900,000 t/yr. The VIP Mill Optimization Project further increased zinc concentrate production to 1.1M t/yr while improving both product quality and zinc recovery. The Mill Optimization project also addressed a number of issues related to risk reduction: power generation capacity, water treatment capacity and concentrate thickening. The project was faced with numerous challenges, the most daunting of which was the schedule. This US$105M project was executed, from conception to completion, inside of two years. Less than nine months elapsed from concept to delivery of materials and equipment to site. The project also faced a 100-day ice-free shipping window, the challenges of construction in an Arctic environment, and an extremely tight labour market for qualified craft personnel. These challenges were successfully addressed with several innovative approaches to project execution, including an Alliance contracting arrangement between the owner, engineer and contractor; full integration of the team; construction of modules in Anchorage; and fast-track engineering, procurement and construction.INTRODUCTIONThe Red Dog Mine, which began operations in 1989, is located above the Arctic Circle in Northwest Alaska, approximately 145 km north of Kotzebue (Figure 1). An 80-km road connects the mine site to the DeLong Mountain Transportation System (DMTS) port site. Red Dog is the largest known zinc deposit in the world, with known reserves totalling 94.5M tonnes, and is the largest zinc producer with a concentrate production rate of more than 1.1M t/yr.Open-pit mining is by typical drill, blast and load operation using moderately sized mining equipment. Ore is processed through conventional crushing, grinding, and flotation to produce separate lead and zinc concentrates. Filtered zinc and lead concentrates are trucked year-round to the DMTS port site, where they are stored in two A-frame buildings, 330 and 440 m long. A lightering barge system is used to transfer concentrate from the shallow water load-out to deep-sea vessels anchored approximately two miles offshore. Shipping is limited to a 100-day, ice-free window beginning in early July."

Jan 1, 2003

By Olivia Perkins, Shawn Sismondi, Adrian St. John, Vicky Potts

"INTRODUCTION An inherent aspect of any tunnelling project is ground risk: how it is identified, quantified and managed throughout the various stages of a project. Early identification of these risks, such as adverse ground conditions or potential obstructions is crucial; however specific identification of all risks will inevitably be limited by the extent of the desk study, ground investigation and accuracy of as-built information available, particularly in a densely populated urban environment such as London with a long and varied history of development. It is therefore crucial to have suitable plans and procedures in place for dealing with potential ground risk scenarios if they occur during construction work to ensure the safety of the workforce and to protect nearby critical assets. A number of experiences of potential ground risk were encountered during the Sprayed Concrete Lining (SCL) works on Crossrail contract C300/410 which was constructed by a joint venture of BAM Ferrovial Kier (BFK). The C300/410 works, undertaken in the heart of London, comprised of over 2.5km of SCL tunnels for Bond Street and Tottenham Court Road Stations and the Fisher Street crossover, as well as two 6.2km TBM tunnel drives between Royal Oak and Farringdon. BFK appointed Donaldson Associates as their SCL designers for the works; together they were responsible for excavation stability up to the point of ring closure. Despite the majority of SCL tunnelling works at Bond Street and Tottenham Court Road being through the favourable medium of London clay, there remained areas of local geotechnical challenges. Some of these were expected from the outset, some became apparent as works progressed from records of other nearby excavation works, and some were only encountered during tunnel excavation. Being located in the centre of London meant that there always remained a possibility of meeting some form of obstruction from previous structures. However, identification of all potential issues prior to the commencement of the works was challenging and proved to not be entirely possible. Through a series of case studies, this paper documents incidents where obstructions or adverse ground conditions arose. These scenarios all had the potential to cause safety risks, impact the tunnel design and/or construction methods and ultimately add time and cost to the works. The paper discusses how these challenges were overcome which utilised in part, a progressive risk reduction cycle, feeding back knowledge gained at all stages of construction into the approach for undertaking the works. It also examines what could be done in future to further reduce the ground risk through early identification, communication, education and appropriate contingency measures."

Jan 1, 2016