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By Herman Gill, Dani Delaloye, Madelyn Rubin

The Foothill Tunnel is a remote 16-mile-long untreated drinking water tunnel in the San Francisco Public Utilities Commission’s (SFPUC) Hetch Hetchy Water and Power (HHWP) system. The 14-foot horseshoe shaped tunnel, constructed in the 1920s, is lined intermittently with concrete over approximately 53% of its length, with the balance being unlined rock. After detailed planning, in January of 2020 Mott MacDonald and HHWP staff completed a visual inspection and documented the condition of the tunnel with electronic data collection, photographs, and video with audio recording. The result was a comprehensive condition assessment that identified key areas of the tunnel to monitor.

Jun 13, 2021

By Hans W. Brodbeck

The Advisory Conference on Tunnelling of the OECD, held in Washington, D.C. in June 1970, has established the following definition: "Tunnelling refers to the construction by any method of a covered cavity of predesigned geometry whose final location and use are under the surface, whose cross-sectional area is greater than 2 square metres". (1) The definition makes clear that the term includes all types of underground construction, be it in hard rock, soft ground, under mixed conditions, underwater, etc. Small-sized tunnels in rock therefore constitute but one part of the tunnelling scene. With an ever-growing urbanisation taking place in industrialized as well as developing countries, the demand for small-sized tunnels is, however, rapidly increasing and requires a far-reaching mechanization of excavation and support functions. This trend is accentuated by the fact that small-sized tunnels are far more labor-intensive than large ones, and, with wages raising at a much faster rate than costs for plant and equipment, this will accelerate the introduction of new tunnelling systems. SMALL-SIZED ROCK TUNNELS The main field of application for a tunnelling system for small sized hardrock bores is thus defined. It is in fact the numerous relatively short tunnels required under cities and other populated

Jan 1, 1974

By E. Manev

Thin aqueous equilibrium film studies and surface tension measurements on a mixed surfactant system consisting of polyethylene oxide (a model frother) and potassium ethyl xanthate (a model collector) enable the interaction between the two surfactants at the air/solution interface to be elucidated. For the film containing the non-ionic frother, the interface was charged and addition of low concentrations of xanthate acted as a common electrolyte and reduced the thickness of the film inducing rupture. However, at high xanthate collector concentrations, the negative charge xanthate was found to interact with the non-ionic and caused a build-up of negative charge at the air/solution. Higher frother concentrations were necessary to produce non-rupturing thin films upon increasing the xanthate concentration.

Jan 1, 1992

By M. Akram

Stability assessment of entry roofs is an essential precursor to all underground design. Both multi-seam interaction and longwall mining can subject entries to radical changes in the surrounding stress field. Such loading changes frequently produce instability and failure in the roof, floor and pillars. Roofs are shown to be vulnerable to stress-induced failures, particularly when the load is unsymmetrical. To predict the effects of changes in stress field, roof failure conditions under increasing loads were studied using finite element analysis and body loaded photoelastic models. A large range of geologic conditions were evaluated and incorporated into the model using Monte Carlo methods. Entry analysis using the model showed the roof to be particularly vulnerable to shear with the location of the failure site changing to meet loading and geologic conditions. Results were correlated with field data to determine stress levels at which failure could be expected to occur. Based on this research a roof stability model SESAME was constructed for roof stability evaluation under specified loading conditions.

Jan 1, 1993

By Jürg Künzle

The use of the underground space has been a recurring issue in human history, whereas the reasons for building subsurface structures have changed over time. In the decades to come, the world will be marked by a variety of underground projects never before seen. This paper describes a series of characteristic challenges of designing and building underground freight transportation systems, with reference to the example of Cargo sous terrain, a privately funded underground logistics project in Switzerland. It provides an overview of contracting practices that allow these challenges to be addressed with success.

Jun 13, 2021

By Ron Derrick

SX operators have conducted extensive shut-downs and repairs over the years to mitigate solution leaks from failed stainless steel false floors and walls in rectangular mixersettler mix boxes. Hydrodynamic modeling using first principles and constitutive equations of fluid mechanics can inform an efficient structural redesign sufficient to eliminate the plate failures. Updated mix boxes have been performing without failure for over a decade. Given the extensive construction of the original Holmes and Narver mixer-settler design throughout the world that includes stainless steel lined rectangular primary and auxiliary mix boxes, SX operators may benefit from the approach, eliminating costly shutdowns, leaks to containment, and hazardous repairs.

Feb 1, 2024

By E. A. Sigworth

Our interest in metallurgical applications for activated carbon was thoroughly aroused when laboratory studies indicated that each dollars worth of carbon could retain as much as four dollars worth of tin. Since then other data was developed suggesting many Potential uses in the metallurgical field it is hoped that, the information presented in this paper may encourage studies by knowledgeable individuals in metallurgical operations. Activated Carbon accomplishes its results by adsorption which involves selective removal of materials from solution by holding the compounds on the carbon surface at the active areas. An example of adsorption is the dyeing of cloth where the dye is selectively held on the cloth surface and the concentration in the dye solution is thereby reduced. Many theories exist on, adsorption, but the predominant factors involved in metallic ion adsorption probably are that adsorption is indirectly proportional to solubility and is benefited by high concentrations acting to squeeze out molecules in smaller amounts.

Jan 1, 1962

By Alphonse C. Van Besien

It is doubtful if anyone knows precisely how many U.S. coal miners have been killed by roof falls. In 1931, 51 miners were killed by falls or rock in every 10-day period (Paul, 1). Roley (2) indicated that from 1882 to 1945, over 3,700 men were killed by roof falls in Illinois alone. During this 63-year period, roof falls accounted for 47.6 percent of the coal mine accident fatalities. Similarly, Price and Nolting (3) reported that during the 10-year period beginning in 1937, roof falls claimed over 50 percent of the lives lost in West Virginia coal mines. Over 150 miners died under fallen rock in West Virginia alone, in each of those years. Certainly, the statistics have improved over the years. The Theodore Barry Report of 1971 (4) indicated that during, the previous 4 years, fewer than 100 miners per year lost their lives to roof falls--in the entire United States. The improvement is less remarkable when it is realized that the accident rate has declined only as the number of miners employed underground has declined. The TRW Report (4) pointed out that although the number of fatalities in underground coal mining (from all causes) had been cut in half from 1956 to 1965, the fatality rate per thousand miners had remained virtually constant. The decreased accident rate was due not to a reduction in hazards but to a reduction in work force. Roof falls still claim approximately 50 percent of the lives lost in underground coal mines. Considering the increased underground production of coal which must result from our energy crisis, the environmentalists' pressure against strip mining, and our inevitably diminishing supply of strippable coal, it is apparent that some means must be found to reduce the number of lives claimed by coal mine roof falls.

Jan 1, 1973

By Tony Walsh

Australian Stock Exchange Limited (ASX) -ASX is ranked 9th in the Morgan Stanley Capital International (MSCI) Index – only 2.02% of that Index. -1520 companies – 400+ mining & mining exploration. -Over 50% of Australians own shares in ASX listed co.s -Disclosure standards play a vital part in providing investors with confidence, thereby building depth and liquidity in the market.

Jan 1, 2003

By H. Huang, R. N. Gow

"Previously, Gibbs’ phase rule was applied to mass-balanced EH-pH diagrams for the Cu-As-S-H2O system. Diagrams were generated using the stoichiometry of enargite as a basis. In this study, the calculations were expanded to cover the stoichiometries of three other Cu-As-S minerals (tennantite, sinnerite, and lautite) and compared to enargite. Stability regions within the resulting EH-pH diagrams were found to change with stoichiometry such that a particular mineral would predominate if its stoichiometry was used in the calculation. Solution speciation was also found to vary, with thioarsenate being the best example. This stoichiometric effect helps to explain results reported in the literature and would be difficult to realize if it were not for mass-balanced calculations. INTRODUCTION A comprehensive thermodynamic review has recently been conducted on the aqueous copper-arsenic-sulfur system (Gow et al., 2014a-d). The free energies of over 100 species were collected from various authors and thermodynamic databases to produce mass-balanced EH-pH diagrams, using the thermodynamic equilibrium calculation software, STABCAL (Huang, 2014). The full database was listed and discussed by Gow et al. (2014A). Resulting diagrams were generated for enargite and confirmed with Raman spectroscopy using bulk mineral electrodes in order to identify reactions spectroelectrochemically. Theoretical calculations agreed well with the experimental results under alkaline conditions (Gow et al., 2014a), acid conditions (Gow et al., 2014b), and alkaline sulfide leaching conditions (Gow et al., 2014c). In this study, additional mass-balanced EH-pH diagrams are generated by changing the copper-arsenic-sulfur stoichiometry from enargite (Cu3AsS4) to tennantite (Cu12As4S13), sinnerite (Cu6As4S9) and lautite (CuAsS). Regions for the thermodynamically stable species are shown to change with the four different mineral compositions. Potential leach conditions, both for co-dissolution and selective dissolution techniques, were examined for differences in predominant species according to changing copper-to-arsenic ratios, sulfur compositions, and sulfur oxidation states."

Jan 1, 2015

By A. P. Mehta

The role of microorganisms in the leaching of metal sulfides is well established (Torma, 1977; Murr, 1980). However, this established knowledge applies mostly to chemolithotropic microorganisms such as Thiobacillus ferrooxidans which function optimally in leaching catalysis between 25-35° C, and in a pH range of 2-2.5. Although leaching with thermophilic microorganisms capable of extending the range of catalytic viability beyond 35° C is also documented, there are few if any attempts to optimize or extend sulfide concentrate leaching with thermophilic microorganisms. When mixed metal sulfides or other materials having different rest potentials (referenced to the standard hydrogen electrode, SHE, in the electromotive series) make contact in a conducting, aqueous medium, the contacting members will act as an electrochemical cell, with the member having the higher rest potential assuming the role of an electrical cathode. In leaching reactions involving such galvanic couples, the cathode becomes passivated, while the anodic member reacts vigorously due to the electro- chemical reaction which occurs (Hiskey and Wads- worth, 1975). Serry, eta1 (1978) observed that when chalcopyrite and pyrite were in intimate contact in natural ores, the chalcopyrite reacted vigorously by galvanic conversion as a result of the higher rest potential (~ 0.63 V) as compared to the chalcopyrite (~ 0.53 V). In addition, it was postulated that because of the elemental sulfur which can form on the anodic chalcopyrite in this galvanic conversion process, reactions in acid-bacterial medium would be expected to have accelerated copper extraction because of the conversion of any sulfur product layer on the chalcopyrite anode to sulfuric acid according to the following general reactions: [MS?M2+ + S° + 2e- (1) and 2S° + 302 + 2H20 bacteria?-2H2SO 4 (2)] where M in reaction (1) designates the metal (or metals in the specific case of chalcopyrite) to be released to solution by galvanic conversion.

Jan 1, 1982

By H. Huang, R. N. Gow

"In Part I, Gibbs’ phase rule was applied to mass-balanced EH-pH diagrams for the Cu-As-S-H2O system. The diagrams were generated using the stoichiometry of enargite as a basis. In this study, the calculations were expanded to cover the stoichiometries of three other Cu-As-S minerals – tennantite, sinnerite and lautite – and compared with enargite. Stability regions within the resulting EH-pH diagrams were found to change with stoichiometry such that a particular mineral would predominate if its stoichiometry was used in the calculation. Solution speciation was also found to vary, with thioarsenate being the best example. This stoichiometric effect helps to explain results reported in the literature and would be difficult to realize if it were not for mass-balanced calculations. IntroductionA comprehensive thermodynamic review has been conducted on the aqueous copper-arsenic-sulfur (Cu- As-S) system (Gow et al., 2014, 2015a, 2016b; Gow, Huang and Young, 2016c). Data on the free energies of more than 100 species were collected from various authors, and thermodynamic databases collated to produce mass-balanced EH-pH diagrams using the thermodynamic equilibrium calculation software STABCAL (Huang, 2014). The full database is listed and discussed in Gow et al. (2015a). Diagrams were generated for enargite and confirmed with Raman spectroscopy using bulk mineral electrodes in order to identify reactions spectroelectrochemically. Theoretical calculations agreed well with the experimental results under alkaline conditions (Gow et al., 2015a), acid conditions (Gow et al., 2014) and alkaline sulfide leaching conditions (Gow et al., 2015b).In the present study, additional mass-balanced EH-pH diagrams were generated by changing the Cu-As-S stoichiometry from enargite (Cu3AsS4) to tennantite (Cu12As4S13), sinnerite (Cu6As4S9) and lautite (CuAsS). Regions for the thermodynamically stable species were shown to change with the four different mineral compositions. Potential leach conditions, both for co-dissolution and selective dissolution techniques, were examined for differences in predominant species according to changing copper-to-arsenic ratios, sulfur compositions and sulfur oxidation states."

Jan 1, 2016

By R. B. Hawkins

The discovery of the gold deposits of the Jerritt Canyon district and the construction of the E. R. Bell Mine is one of the significant mining developments in the United States during the past ten years. This mine will exploit one of the larger deposits of disseminated gold presently known, with proven, recoverable reserves in excess of 67.6 million grams of gold. Interest generated by the success of this project has contributed greatly to the tremendous resurgence in exploration for disseminated gold deposits in Nevada and throughout the west. The Jerritt Canyon project, including the Bell Mine, is a 70/30 joint venture between Freeport Gold Company and FMC Gold Incorporated, both of which are wholly owned affiliates of the respective parent companies, Freeport-McMoRan, Inc. and FMC Incorporated. Under the terms of the joint venture agreement, Freeport Exploration Company, another Freeport-McMoRan affiliate, manages the exploration and pre-mine development. Drilling, design, construction and management of the Bell Mine are provided by Freeport Gold Company.

Jan 1, 1982

By Matthew Burdick, Andrew Rule, Erica Bailey

The Second Narrows Water Supply Tunnel, Burrard Inlet Crossing project for the Greater Vancouver Water District entails deep shaft construction, subway sized pressurized face tunneling through highly variable ground conditions, installation of three permanent steel water mains and construction of elaborate valve chambers adjacent to either shaft. The paper discusses key elements of the planning and implementation of 6.69 m Ø slurry mixshield tunnel boring machine (TBM) assembly in a small diameter deep shaft including incorporation of a fully pressurized launch lock, preparations for saturation diving, surface support infrastructure and initial mining sequence.

Jun 13, 2021

By Bo Hyun Kim, Mark K. Larson

Although techniques and practices of mining are highly advanced, coal pillar bursts or bumps continue to occur. Many uncertainties remain because of the highly anisotropic characteristics of coal seams that are associated with geologic structure and the mining-induced spatial redistribution of stress in coal pillars. Thus, to prevent fatalities in underground coal mining, continuous efforts are required to better understand the catastrophic failure mechanisms in coal mines. In this study, 3DEC modeling in conjunction with the Discrete Fracture Networks (DFNs) technique was performed to better understand the true anisotropic behavior of the specimens acquired from a bump-prone underground coal mine. The spatial characteristics of the dis- continuities (i.e., cleats and bedding planes) as input data for the 3DEC model are estimated based on the results of the laboratory tests and field observations. The DFNs explicitly generated the coal seam that was poorly or well cleated, indicating the different spacing between cleat apertures using the probability distribution functions for fracture density (or frequency) and size. The heterogeneity of the engineering properties (i.e., cohesion and tensile strength) are also considered by Monte Carlo simulations. Simulation results of laboratory tests using the 3DEC model and DFNs technique agreed well with the results of the laboratory tests. These calibrated results can be used as we seek to evaluate bump risk by modeling at field scale.

Jun 25, 2024

By Dennis E. Peterson

Land subsidence had been observed in recent years throughout the Southwest. Particular examples of this phenomenon that have gained wide publicity axe in the Long Beach and Central Valley areas of California and, the Houston area of Texas. Less well known is the fact that the land surface Is subsiding in many parts of Arizona, including the Phoenix area. The causes of this problem vary from place to place, as do also the rates of subsidence. In Houston it has been related to pumping water from artesian aquifers; in Long Beach to the development of oil fields; and in the Central Valley to both the lowering of artesian pressures in deep aquifers and the wetting of poorly consolidated surficial deposits. The mechanism by which subsidence occurs in southern Arizona, even though it can be correlated with the continued lowering of ground water levels, is not as apparent as in these other cases. It is the purpose of this paper to examine both the causes and affects of land subsidence in southern and central Arizona.

Jan 1, 1965

By O. Porterfield, M. O’Kane, M. Endersby

BHP Iron Ore initiated research programs in January 1995 to develop long-term plans for decommissioning waste rock material at its Mt. Whaleback operation. More than 2 Gt (2.2 billion st) of waste rock were deposited during the past 30 years. Ultimately, a total of 4 Gt (4.4 billion st) will be deposited in waste rock dumps constructed near the open pit. The Mt. Whaleback operation is located in a semiarid climate adjacent to Newman, Western Australia. The primary research program includes the development of technology for the long-term performance of the waste rock dumps with respect to vegetation, slope stability, surface runoff, erosion and water infiltration. This paper focuses on the design and implementation of a cover system to prevent water infiltration to the underlying waste rock. Data obtained from a laboratory program and from soil-atmosphere modeling was used to design horizontal field test plots. The construction of the horizontal surface field test plots is discussed together with the field instruments installed to monitor performance. The cover system is designed to maximize infiltration during wet periods for subsequent evapotranspiration while minimizing surface runoff. The result is a near-zero net infiltration to the underlying waste material. An important feature of the design is the use of run-of-mine waste material as the cover material. Monitoring is in progress and will continue for at least two annual wet/dry cycles. The optimum cover system should minimize the net infiltration of water to the underlying waste rock while maintaining physical and ecological integrity for long-term performance.

Jan 1, 2000

By L. H. E. Weyher

In a previous paper presented at the 1966 Annual Meeting of AIME we reported our work, conducted at the Pennsylvania State University, on the hydrocyclone washing of fine coal.' The initial evaluation based on that work demonstrated the feasibility of hydrocyclones as fine-coal cleaning devices, and in that previous paper we presented selected test data that showed in principle how product yield and assay respond to variations of the major cyclone operating variables. The present paper reports in greater detail on the findings and presents a comprehensive evaluation of our data as follows: ? Hydrocyclone throughput rates were related to feed pressure and other variables by regression equations. These equations are compared with other capacity- versus-pressure drop expressions taken from the literature on classification cyclones.

Jan 1, 1968

By Christopher Nelsen, Daniel Dobbels, R. Zachary Hollenbeck

Recent major floods have inundated Historic Ellicott City, Maryland, resulting in loss of life and property damage. Howard County, Maryland, has developed the Ellicott City Safe and Sound Plan to mitigate the risk of flash flooding in the Historic District, including a proposed stormwater conveyance tunnel. Challenges to overcome include thick zones of saprolite along the alignment, multiple near-surface structures, and minimal rock cover under an active railroad, while minimizing impacts to the public and historic structures. The project will also pursue recognition through the ISI Envision verification process.

Dec 1, 2022

By Kef ton H. Teague

This paper will discuss bentonite deposits in Texas, Oklahoma, Louisiana, Mississippi and Alabama. The discussion will be re¬stricted to a review of the so-called calcium or non-swelling bentonites. In other words the exchangeable cation is calcium. The term "bentonite" is used to describe a clay material, composed essentially of the clay mineral montmorillonite. In addition, bentonites may contain various impurities such as glass shards, feldspar, quartz, muscovite and biotite mica, glauconite, pyrite, hydrated iron oxide, gypsum, organic material, etc, Most of the southern calcium bentonites contain at least 70% montmorillonite, Bentonite as mined may range in color from dark grayish greens through various shades of grays, reds, yellows and browns to nearly white. It is normally massive and breaks with a conchoidal fracture. When air dried, closely spaced shrinkage fractures occur. Moist bentonite has a soapy feel, with little or no obvious "grit". Bentonite deposits were first discovered in Mississippi about 1925, in southern Monroe County. During the thirties and early 1940's, deposits were identified in Alabama, Texas, Oklahoma, and Louisiana. Perhaps the earliest production of southern bentonite was from a deposit in the valley of the Tombigdee River, south of Jackson, Alabama in 1936. Production commenced in Mississippi during the latter part of 1938 at Pontotoc. The growth and development of the bentonite industry in the southern United States owes its beginning to three events. The first of these was the discovery by German researchers,

Jan 1, 1972