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By H. D. Van Veldhuizen

The Multilateral Investment Guarantee Agency(MIGA) is part of the World Bank Group, and has as its mission the facilitation of foreign direct investment by providing political risk insurance (guarantees) to foreign investors and lenders. As a development institution, MIGA is required to ensure that the projects that it insures will bring development benefits to the host country. Demonstration of this includes review and analysis of the environmental and social soundness of a prospective investment. Environmental guidelines and policies developed by the World Bank Group are important components both in analyzing the environmental and social soundness of a prospective investment and in risk management. MIGA has recently formalized and adopted environmental assessment and disclosure policies. The approach taken by MIGA to environmental review of investments and implementation of these policies is described in this paper.

Jan 1, 2000

By Marcel Haffen, Jean Janin

The purpose of grouting is to modify the permeability and strength characteristics of the subsoil in such a way that the planned structure can be efficiently constructed at a given location. This technique, which originally underwent considerable development in the field of dams construction is constantly evolving and it becomes more and more important in urban zones of intensive underground development for projects such as transport tunnels, stations, car parks, ect. Grouting becomes more and more indispensable whatever the natural characteristics of that subsoil ; such is the case particularly when the planned work runs through cohesionless granular soils, usually water-bearing such as alluvium, sands, disturbed ground, fill material, etc. The selection of the grouting method and the extent of treatment required at depends on two fundamental factors. 1º) nature and behaviour of subsoil to be treated. There is no need to stress the necessary of a good knowledge of geotechnical, hydrological and chemical characteristics of the ground to be treated. At the present time the specialists in these fields have available numerous methods of analysis, either laboratory or field tests, which enable to evolve a suitable treatment.

Jan 1, 1997

By J. F. Cuderman

In situ experiments at the Department of Energy's Nevada Test Site (NTS) have extended the technology of propellant-based fracturing to include liquid- filled, uncased boreholes. Previous work had developed the technology for liquid-free, uncased wellbores. Test results show that fracturing behavior is considerably more complex in liquid- filled boreholes than in the liquid-free case. Compared to liquid-free boreholes, liquid-filled boreholes have faster pressure risetimes and lower peak pressures, large hydraulic-type fractures propagating several meters beyond the end of the test zone, numerous oscillations in the pressure history, and variable types of fracturing within a single test region. Multiple fracturing is initiated in the wellbore of a fluid-filled borehole when the proper propellant mixture is used but, unlike fluid-free wellbores where up to eight fractures propagate, only one to three hydraulic- and/or shear-type fractures propagate. Hydrodynamic effects involving liquid compression during borehole pressurization appear to be responsible for the differing phenomena observed in fluid- filled boreholes.

Jan 1, 1986

By S. W. Nicholson, L. G. Woodruff, K. J. Schulz, W. E. Cannon

The 1.1 Ga Midcontinent rift of North America has many similarities to the geology of the Voisey's Bay region in Labrador and the geology of the Noril'sk region in Siberia. These similarities include the hosting of large volumes of sulfur- undersaturated and trace-element-enriched basalt, having igneous centers characterized by crustal contamination, being characterized by metal depletions in some mafic units (an indication of prior sulfide segregation) and having known occurrences of Ni-Cu sulfide mineralization. These similarities along with new geophysical data and refined models for Ni-Cu sulfide deposits suggest that the Midcontinent rift probably contains undiscovered Cu-Ni [±] PGE sulfide deposits, some of which could be the size and grade of a Voisey's Bay or Noril'sk deposit. In particular, intrusions and related feeder systems that occur in northern Michigan and Wisconsin, as well as to the southwest along the rift margin, deserve serious examination.

Jan 1, 1999

St. Peter sandstone is very different from the minerals and rocks that have been studied extensively in mining. On the one hand, it is brittle as characterized by an unusually high friction angle and steeply curved failure envelopes. On the other hand, it is friable, possessing extremely low, and in most cases zero cohesion. The scarcity of the ground control techniques for this particular mining environment has created many difficulties for the mine operators. In order to resolve these problems, the geotechnical properties of the St. Peter sandstones were investigated through a comprehensive research program, which included uniaxial test, triaxial test, porosity test, thin section, X-ray diffraction (XRD), and scanning electron microscope (SEM). The specimens used for the uniaxial and triaxial tests were specially prepared because of the highly friable nature of the St. Peter sandstone. Thin section, XRD and SEM were utilized to examine the effect of the microstructure of the St. Peter sandstones on its strength characteristics.

Feb 27, 2013

By Siegmund Babendererde

1. Introduction In Sayreville, New Jersey, the Middlesex County Utilities Authority put the construction of a 1041 m long sewer outlet to tender in June 1989. It had an internal diameter of 3,36 m and was part of a sewage treatment works project for county Middlesex. The contract was awarded to the Lodigiani Company, USA, who employed Hochtief Incorporated as subcontractor to drive the sewer outfall. 2. Ground Conditions According to the preliminary geological site investigation, carried out by the consultants Metcalf & Eddy, the tunnel passed through marine deposits.

Jan 1, 1991

By Carlos Henrique Turolla Maia, Ulrich Maidl, Marc Comulada, Julio Claudio Di Dio Pierri

"Pure sands are typically the domain of slurry shields due to their high permeability and their granular characteristics. However, the Earth Pressure Balanced (EPB) shield machine technology has advanced in recent years with improved conditioning agents and shield machines that are equipped with slurry injection facilities and alternative mucking methods. These new so-called hybrid EPB machines have steadily increased the range of application of the EPB technology. The contribution discusses the capacities and operational features of hybrid EPB vs. slurry shield technology in pure sands. At the example of the Metro Line 4 in Rio de Janeiro (Brazil), the contribution shows that hybrid EPB tunneling in pure sands is possible and it is compared with a state-of-the-art slurry shield project as the KASIG project in Karlsruhe (Germany). Furthermore, the control of the support pressure by means of foam conditioning and slurry injection in conjunction with a close, real-time monitoring of machine parameters is discussed. INTRODUCTION Slurry shield and EPB technologies have both undergone significant developments in recent years, leading to the use of parts of one technology in the other and even to completely hybrid systems. Also the ranges of application (see recommendations by DAUB (DAUB 2010)) of both technologies have been shifted far beyond their original limits and are largely overlapping by now. Nevertheless, the basic principles of face support remain unchanged. Exploiting the possibilities of process data analysis (Maidl 2014), the interactions between the ground and the shield machine are a matter of research and have been intensely investigated. PRINCIPLES AND CALCULATION OF FACE SUPPORT PRESSURE Figure 1 shows the principles of two approaches for the determination of required support pressures: kinematic methods and numerical methods. Kinematic methods that are employed for the assessment of face stability only consider the situation in front of the TBM. The required face support force is determined by means of an assumed failure wedge that would form in ultimate limit state. Based on the ground properties, the vertical surcharge and the self-weight is transformed into a horizontal force along a virtual sliding surface. This horizontal force is to be balanced by the face support. The calculation results are amended by respective partial safety factors for water and earth pressure and the method-specific support pressure fluctuations are added."

Jan 1, 2016

By Peter K. Weissenborn, Robert J. Pugh

The contrasting behaviour of electrolytes in inhibiting coalescence of bubbles was explained by the positive and negative distribution of anions and cations at the gadwater interface. Further, the efficiency of electrolytes which do inhibit coalescence of gas bubbles can be linked to a counter ion hydration mechanism and the effect of electrolyte concentration on gas solubility. A correlation was found between the transition concentration of electrolyte needed to prevent the coalescence of bubbles and the reduction in gas solubility. Hence, the inhibition of bubble coalescence in electrolyte solutions appears to be linked with the utilization of water molecules in the hydration of cations and a consequent reduction of water available for gas solubility.

Jan 1, 1995

By T. F. Torries

Market data commonly perceived as being useful to industry for decision making include prices, production and trade quantities, production and transportation costs, stocks, customer's needs, and competitor's qualifications. Costs and factors affecting costs are particularly important in determining competitive positions and possible future prices. These costs include relative cost of production as well as cost experienced by the buyer in making the final product. Care must be taken to calculate costs in a consistent manner to achieve meaningful analyses.

Jan 1, 1987

By J. A. Herbst, Z. Rogovin

In order to develop more accurate procedures for scale-up and design of semi-autogenous grinding mills through detailed mathematical models, a better understanding of the charge motion and rocklball segregation is needed. To achieve this a 0.61 m (2.0 ft) diam by 0.305m (1 .0ft) length plexiglas mill was constructed as a scale model of a commercial SAG mill. Rock motion in the rotating mill was simulated using various sizes of ceramic balls. Quantitative measurements of dynamic angle of repose, water and slurry motion, holdup and size segregation of the charge were taken. In addition, a video presentation (available to the public) was prepared to elucidate charge and water motion at various mill speeds, charge volumes, rocksize distribution, and flow rates.

Jan 1, 1990

By Isobel Clark

Geostatistical methods of estimating ore reserves and other spatial phenomena are becoming increasingly wide spread in their use. Properly applied, Geostatistical estimation falls into two stages -- the "modelling" of the spatial variability within the study area; and the use of this spatial model to provide an appropriate estimation technique. The first stage usually consists of construction and interpretation of semi-variogram graphs, and the second is the development of the corresponding Kriging method. Because of the apparent subjectivity inherent to the first stage of a geostatistical analysis, attempts have been made to provide methods of "testing' whether a particular semi-variogram model (say) adequately represents the study area. Increasingly, the choice of model is being justified by a process known as "Cross Validation'. With this approach, the analyst uses a partial data set to estimate values at actual sampled positions. "Real" and "estimated" values are then compared in such a way that the model can be accepted or rejected. This paper discusses the process of cross validation in some detail, using case studies as examples. Some problems with the technique are illustrated and discussed.

Jan 1, 1986

By S. N. Mukherjee

Maintenance of equipment in Longwall faces plays a vital role in face performance. This is more prominent when shortage of spare parts and trained personnel occurs. A study was made in an operating Indian Longwall face for identifying the types and meantime between failures. Though the duration was not enough and study was not very elaborate, it revealed certain interesting facts. The machine availability was found to be poor, though a maintenance schedule was followed. Failure of simple parts like AFC chain connectors even resulted in loss of production of 10 times the complete chain cost. This pinpoints that a proper maintenance schedule is to be developed considering the human factors and local conditions existing in the particular country. Operations research techniques could be used in the process.

Jan 1, 1989

By H. K. Lin

Cyclic voltammetric and potential step chronoamperometric techniques were used to study gold dissolution in cyanide solution. Three distinct anodic peaks and one cathodic peak appear on the voltammogram between -0.50 and 0.80 V vs. SCE. The corresponding reactions were proposed to explain the peaks and the passivations. The proposed reactions were in agreement with the effect of pH and cyanide on the magnitude of the peak currents. Cyclic voltammetric tests, with various vertex potentials, were also conducted to examine the proposed reactions. Steady-state currents at various potentials were obtained by potential step chronoamperometric technique and were compared with transient currents obtained by the cyclic voltammetric technique.

Jan 1, 2002

By A. Perelli Cippo, R. Granata, D. A. Bruce

During the last few years, significant advances continue to have been made in aspects of grouting technologies used for ground treatment in advance of tunnelling. In permeation grouting, fundamental researches have continued into improving the penetrability characteristics of cement-based grouts. The twin advantages of field regrinding normal grouts to reduce cement particle sizes, and incorporating special additives into stable grouts, are now being systematically exploited in major soft ground tunnelling projects in Europe. The methodologies of jet grouting continue to be developed with special attention being paid to qa/qc issues, reducing unit production costs, and improving predictive capabilities for subsequent settlements.

Jan 1, 1993

By Donald A. Dahlstrom

If you have ever driven on the Autobahns of Western Germany, you are well acquainted with the "fast lane." There is no speed limit; there are only two lanes in the direction you are going, and if you choose to drive in the fast lane, you had better be prepared to drive faster than anyone or someone will tailgate you with a constant screeching horn until you move to the "slow lane." The prize for this mastery of the fast lane is some kind of a "macho" feeling and getting to your destination sooner than your competitor. This has some comparisons with today Is liquid-sol id separation. We've certainly had our moments in the fast lane but we've also had other countries forcing us into the slow lane at times. It can be very embarassing when someone almost runs over your back and then shakes a fist at you as you shakily scatter to the much slower and overcrowded lane. Because of necessity, there will be many new improvements and added requirements in the next decades into the 21st century and beyond. Those countries and industries that can maintain the pace in the fast lane will be successful while the others may well be relegated to the non-competitive lane. Before considering what will be the challenges in the future for competitive liquid-sol id separation performance, it would be wise to review progress over the past forty years in this area. The author has to admit his ancient age and believes he can act as an evaluator of these many advances. To place the beginning of the 40 years (the author predates his initiation into liquid-sol id separation by one more year), the United States was still building smelters and operating them with little or no sulphur dioxide removal , practically

Jan 1, 1989

By Gunnar Sparrman, Börje Ahlgren, Sten Rosenström

Starting in 1967 two major hydroelectric power projects have been implemented in East Africa viz. Kafue Gorge in Zambia and Great Ruaha in Tanzania. The two projects have similar characteristics and each consists of an underground power plant, a dam in connection with the power plant and a reservoir dam. The power plants are both designed and constructed according to principles applied in Scandinavia for a long time. Each consists of a headrace of a horizontal unlined rock tunnel with a length of about 10 km, vertical penstock shafts, machinery and transformer halls in large rock caverns and a tailrace of an unlined rock tunnel with a length of about 1 km. The head of the power plant of Kafue Gorge is 400 m, Great Ruaha 175 m, the capacity is 900 MW and 200 MW respectively. Both plants were executed in one stage, but building and erection works were made in two stages. However, the power plants show some interesting differences in design. The power plants are briefly described in the following, special regard being paid to the excavation works. GEOLOGY General The foundation of Eastern and Central Africa is made up of ancient crystalline rocks, consisting of sediments, lavas and intrusives, mostly intensively altered by repeated metamorphism. This repeated metamorphism - dynamic, ther-

Jan 1, 1979

By P. Venkatsubramanian, D. R. Maneval

An insufficient hydrologic data base exists for most large and small coal basins in Alaska owing to the lack of need in the past to collect data. The runoff process is insufficiently understood which is complicated by specifically northern phenomenon, and the lack of understanding of hydrologic relationships in permafrost environment. This paper presents an understanding of the hydrologic effects of frozen ground and presents methods by which the influence of surface mining upon the hydrologic balance can be analyzed.

Jan 1, 1987

By C. Tsiouvaras

Restoration of bauxite mining areas constitutes a difficult issue to address due to the destruction of the vegetation and soil decay of the excavated area. In this study woody species growth, in relation to altitude, heavy metal concentrations and mechanical texture of the underlying mining waste, were investigated. The research was implemented on restored sites of a bauxite mine in the Fokida Prefecture of Greece. These sites were located in three different elevations and the restoration took place in two phases, in 2001 and 1996. Heavy metals measurements showed some correlation among the different metals, whereas their concentration was also associated with plant growth parameters.

Jan 1, 2007

By J. W. Sweeney

The .Florida land-pebble mining industry of central Florida was examined to identify trends in land use; conflicts in land use; and the effect of the conflicts on mineral resources. Many conflicts exist in the study area, such as conflicts with other users of land resources and land surface; conflicts with high revenue land users; conflicts for land surface in urban and suburban areas; and conflicting restrictions concerning utilization. Projections are made showing that lands in phosphate company ownership are expected to be made available to help meet the need for future urban expansion in the study area. Some phosphate resources have been lost due to land use conflicts, however, most of the resource loss has been small. Land use conflicts and phosphate mining are reconcilable and considerable progress toward their maximum and multiple use of land and mineral resources can be resolved through farsighted planning based on factual data.

Jan 1, 1972

By Wilson I. L. Lim, Jonathan J. Campbell, Luis A. Tondo

An important issue in the use of high pressure grinding rolls when grinding ores is wear of the rolls. Due to the abrasive nature of the ores, significant wear rates have typically occurred. Attempts to address the wear problem require a better understanding of the wear mechanisms. A probable wear mechanism is the abrasion of the rolls surface due to extrusion of the compacted material as it leaves the rolls. This paper presents the results of a study on a number of ores to examine the extent of extrusion that occurs. The study involved laboratory, pilot and full-scale high pressure grinding rolls. The effect of variations in parameters such as grinding pressure, rolls speed, initial gap settings, feed topsize and moisture was investigated. The results indicate that extrusion increases with increasing grinding pressure and rolls diameter, while the use of studded or profiled rolls significantly reduces the extrusion effect compared to smooth rolls. It was also found that rolls speed and feed moisture can have significant effect on extrusion, depending on the material.

Jan 1, 1998