Search Documents

By Dong-mei Zhang, Feng Zhang, Hong-Wei Huang, Qiang Huang, Bin Ye

"1. INTRODUCTION Nowadays, many cities around the world have constructed metro tunnels to alleviate transportation pressure from rapid urbanization. In soft soil areas, metro tunnels are usually constructed by shield-tunneling method due to its high efficiency and little disturbance to environment. However, the tunnels may show significant post-construction settlement after several years of operation. Take Shanghai Metro line 2 for example, the maximum longitudinal settlement reached 160mm after ten years of operation, shown in Figure 1. When analyzing varying factors that contribute to the long-term settlement of tunnels, the effect of cyclic loading from train vibration is rarely taken into consideration for most researches only focus on the influence of leakage problems in the tunnel while neglecting train vibration induced leakage and resulting settlement. It’s true that metro tunnels from shield-tunneling method are prone to have leakage problems due to the special structural configuration. Furthermore, trains move hundreds of times inside the tunnel every day, which inevitably will cause accumulation and dissipation of excess pore pressure. When the excess pore pressure dissipates, tunnel settlement induced by train vibration occurs(Deng F H, 2007). Although researchers (Zheng et al., 2005; Wongsaroj et al., 2007; Mair, 2008; Shin et al., 2012; Zhang et al., 2012, 2015) conducted extensive numerical analysis on the relationship between tunnel settlement and relative permeability of tunnel to surrounding soil by treating tunnels as permeable media, their attention was only paid to the tunnel settlement from reduction of hydrostatic pressure in the ground, rather than from the dissipation of excess pore pressure generated by train vibration. Therefore, the influence of train vibration on the long-term settlements of metro tunnels is still not clear."

Jan 1, 2016

By Edward J. Zeigler, John T. Miller

INTRODUCTION Construction of Phase I, Section A, of the Baltimore Region Rapid Transit System required that six underground stations be built using a cut and cover excavation technique. For five of these stations, soldier piles, used as support of excavation, were installed with tip elevations well below the bottom of the excavation. However, in the case of the sixth subway station, the Mondawmin Station, soldier piles were installed only through soil and decomposed rock, with the tips of the piles being stopped well above the bottom of the excavation in partially decomposed rock. Below the tips of the soldier piles, and below a cut slope where piles were not installed, the sides of the excavation consisted of partially weathered and fresh rock and were supported by a combination of rock bolts, wire mesh and shotcrete. An extensive installation of geotechnical instrumentation permitted detailed monitoring of horizontal and vertical movements of the soldier piles and the walls of the excavation. Preliminary studies indicated that the excavation support system selected for the Mondawmin Station would have several advantages over a conventional system consisting of soldier piles extending to the bottom of the excavation, braced with prestressed struts. These advantages included lower cost of installation, a decreased time required for installation, and a more open excavation for the contractor during construction of the station. The Mondawmin Station is situated in the northwestern quadrant of Baltimore City, approximately 6.4 km (4 miles) from the center of the City. The station lies midway in a project 12.9 km (8 miles) long identified as Phase I, Section A, of the Baltimore Region Rapid Transit

Jan 1, 1981

By John T. McDonough

The Climax Mine of AMAX's Climax Molybdenum Division is currently producing approximately 34,000 tons of molybdenum ore per day from two underground levels (see Figure I), and initial design is underway for the next deeper (1200) level. The aim of this report is to present the methods of site evaluation used at Climax for cavability determinations and underground support design. Climax succeeds with its panel caving system of mining (Julin, 1973) (Figure 2) largely because of the presence of pervasive geologic structural discontinuities. The stockwork ore body at Climax was formed by the multiple intrusion of mid-Tertiary rhyolitic magmas into Precambrian granite, schist and gneiss, and the hydrothermal emplacement of molybdenite into the network of fractures that were generated during the forceful upward intrusion of magma. Subsequently, intrusive events that were more deeply seated refractured the overlying, ore- bearing stock and propagated a complex system of axial and radial fractures. Post-ore movement along the Mosquito Fault (Wallace, 1968) and its associated stranded shear zones further fractured the ore body and disordered the existent geologic structure. The result of these structural events is a brittle, crystalline ore body that is transected by a complex pattern of faults, shear zones, and joints that augment cave initiation and enhance comminution of the ore blocks. Generalizations can be made about the structural trends within the ore deposit (King, 1946; Kendorski, 1973), however, the intensity and orientation of geologic structure is by no means uniform throughout the ore body. The relative intensities of silicic and argillic alteration are also highly variable (Vanderwilt and King, 1955). As a consequence, no single rock-mass model suffices as a standard for mine design, and site characterization for cavability and support design is a continuous process.

Jan 1, 1977

By I. Shah, L. G. Austin

A method for quantitative investigation of the phenomena involved in fine grinding of materials that follows the changes in the breakage rates of fine particles has been presented. For relatively hard, brittle, non-coating material like quartz, the slowing down effect of breakage rates starts to be significant at relatively coarse sizes, which goes often undetected in closed circuit grinding systems, producing relatively coarse product, say P80=75µm However, for fine grinding systems, as the -10µm fractions begin to build-up, and classification becomes more difficult, the build-up of fine sizes causes a slowing down effect Compounding this problem is the difficulty of obtaining accurate cumulative weight size distributions in the fine size region.

Jan 1, 1983

By Marie-Antoinette Dziurla, Barrie Johnson, Åsa Kolmert

Acidophilic bacteria are well known for their role in accelerating the oxidative dissolution of sulfide minds, such as pyrite. Other acidophiles, however, are able to catalyze dissimilatory reductive reactions. Bacteria that reduce ferric iron to ferrous, and sulfate to sulfide, were isolated from ARD-impacted environments and immobilised onto porous beads made of recycled glass. Column bioreactors containing colonized beads were constructed and peacolated with synthetic and actual ARD, and evaluated for their capacities to promote iron or sulfate reduction, and pH amelioration. Iron reduction did not require strictly anoxic conditions in bioreactors, and rates of up to 800 mg Fe3+ reduced/(l*day) were achieved, with a conversion efficiency of up to 98%. Using mixed populations of acidophilic fungi and iron-reducing bacteria, the bioreactors were capable of promoting iron reduction using paper pulp as sole carbon and energy source. Reduction of sulfate in pack bed bioreactors was observed with acidic wastewaters of pH 3 and above, though average rates of 300 mg sulfate reduced/(l*/day) were less than those recorded for circum-neutral pH systems. Bioremediation of ferric iron-rich ARD was assessed using coupled iron-reducing and sulfate reducing bioreactors.

Jan 1, 2000

By R. S. Conti

The US Bureau of Mines (USBM) has developed an inflatable feed-tube seal (IFTS) for high-expansion foam generators. The IFTS is a lightweight, portable, rectangular inflatable bag that can be used by firefighters to rapidly seal large openings, such as those in underground mines, and to simultaneously provide a feed-tube for a high-expansion foam generator. Thus allows fire fighting foam to freely flow to the fire site and control or extinguish the fire. Studies indicated that a high-expansion foam plug will travel 183 m (600 ft) down an entry with a 4.5% rise in elevation, before leakage of foam from around the inflatable partition.

Jan 1, 1996

By Barry R. Doyle, Ilsley Roger C., John Ramage

It was anticipated that settlement would occur when tunnels were excavated in weak organic soils with high groundwater levels in downtown Milwaukee. Because of the potential for damage to adjacent buildings, an approach was devised during the design to address this issue. In order to do so effectively, estimates of settlement trough geometry were made; buildings identified which were potentially at risk; the means of settlement measurement designed; and threshold limits of settlement and courses of action specified. Bid items were provided for underpinning the critical structures. The approach addresses the design issues and delineates the sharing of risk between the owner and contractor. The predicted and actual performance experienced are also discussed.

Jan 1, 1989

By Kalliat T. Valsaraj, Louis J. Thibodeaux

A mathematical model is described for the transfer of hydrophobic compounds from aqueous to an immiscible organic phase using fine bubble aeration; the process otherwise known as "solvent sublation" an adsorptive bubble separation process. The limitations of the model are explored by simulating experimental results both for a batch scale process and a continuous process. The qualitative predictions of the model with respect to the influence of the organic layer (mineral oil) are tested by performing experiments using chloroform and 2,3,6-trichloroanisole as hydrophobic compounds in the aqueous phase. The continuous process is seen to be limited by the requirements of fine bubble generation and the ratio of influent feed rate to air flow rate.

Jan 1, 1989

By C. H. Rawlins

Deep bed media filtration is used as a tertiary treatment step (after hydrocyclones and flotation cells) to remove fine oil droplets and solids from oilfield water before reinjection disposal or to remove particulate material from surface waters used for waterflood injection. Oil and solids injection requirements are typically <5 ppm concentration at <2 micron diameter. The preferred media for produced water filtration is walnut or pecan shell, however the use of this media has evolved by trial & error and the fundamental mechanisms that occur during separation and media cleaning have not been investigated. A project was initiated to fill in this knowledge gap by analyzing the physical, mechanical, chemical, and hydrodynamic properties of six types of granular filtration media (12/20 mesh size): garnet, silica, anthracite, pecan shell, English walnut shell, and black walnut shell. Comparison of bed packing, oil wetting, attrition resistance, particle strength, and fluidization has led to an understanding of the preferred filtration media for separation of fine oil droplets and solids.

Jan 1, 2010

By Anthony D. Hammond, Charles A. Kliche

A slope stability study for the Annie Creek and Foley Ridge Mines was undertaken to provide Wharf Resources, Inc. with a technical assessment of the stability of the slope for an overall pit slope angle of 60°. A rock analysis of the most critical and persistent combination of discontinuities was carried out using probabilistic methods. A detailed discontinuity mapping and assessment of the rock mass provided the orientation data used in this study. The orientation data were reduced and analyzed to identify the discontinuity sets. A statistical analysis provided information about the distribution of the data. A deterministic wedge stability analysis identified the critical combination of discontinuities; those with a low factor of safety were further studied using probabilistic kinematic and kinetic stability analyses. The results from this approach were used to obtain the reliability or probability of failure of the slopes.

Jan 1, 1988

By E. Topuz, M. J. McPherson, I. M. Konduri

This paper describes experiments conducted to evaluate the effectiveness of jet fans for ventilating blind headings in under- ground mines. A laboratory model of a mine heading was built by using dynamic similarity criteria, and water as the fluid medium. In order to verify laboratory test results, field experiments were designed and carried out in a full scale mine model and in a coal mine in West Virginia. Using CO, as the tracer gas and in combination with a computerized gas monitoring system, tests were conducted to evaluate jet fan performance. The results highlight the flexibility and versatility of jet fans for ventilating blind headings. Numerical modeling of a jet fan in a typical coal mine heading was carried out to evaluate the potential of computational fluid dynamics.

Jan 1, 1997

By B. Govindarajan, L. S. Rao, T. C. Rao, B. R. Rao

Laboratory leaching experiments were conducted to extract potassium from glauconitic sandstone, and the effects of important variables were studied. The reduced time plot (RTP) for all of the variables obtained from the experimental data has been quantified by this simple equation: R = 100 (1 - exp (-0.693 *(T/T50)0.605) The time required for 50% extraction (T50) has been correlated by a regression equation to variables such as acid strength, temperature, fluorite: glauconite ratio and % solids. Both of these equations were used to predict the extraction percentage at different process-variable levels. In addition, several other experiments were conducted at arbitrary levels of the variables to verify the equations developed.

Jan 1, 1994

By P. L. Webster, S. D. Thompson

The Coal Mine Belt Capacity Simulator (CMBCS) was originally developed to provide an improved belt capacity simulation through more detailed, flexible and realistic modeling of belt loading. While this model offered improved capacity design for conveyor belts and surge bins, it lacked the capability to simulate some key protection and segregation applications for bunkers. Recently, CMBCS was extended so that these latter bunker applications could be considered. In addition, a fear minor extensions were made to improve the model&apos;s flexibility and of efficiency. These various extensions and the steps taken to verify and validate them are described. The associated modifications in the model&apos;s input and output as well as the model&apos;s current requirements and availability are also discussed.

Jan 1, 1992

By T. Simpson

European industrial policy seeks to provide the right framework conditions to allow companies to develop and innovate and to make the EU an attractive place for job creation. This includes providing the basis for a competitive manufacturing industry which provides around 20% of EU economic output and employment for about 34 million people. The EU non-energy extractive industry with an annual turnover of around ?40 billion and a direct workforce of about 270,000 people is considerably smaller, but it plays a vital role in providing much of the manufacturing sector with raw materials. It also supplies very large quantities of minerals such as aggregates and natural stone to the construction industry, facilitating the development of modern infrastructure such as roads, railways, houses, schools and hospitals. However, despite an active extractive industry, Europe is increasingly dependent on imports of raw materials and particularly metallic ores and concentrates. In 2005, the trade deficit for minerals was in excess of ?11 billion, of which ?10 billion related to metallic minerals. Such import dependency is not a new phenomenon, but the rapid industrialisation of developing countries such as China and India has significantly increased global demand, resulting in large price increases for downstream industries and at times, bottlenecks in supply. The impact of this and other competitive pressures on some sectors of the European manufacturing industry, including the possibility of them being lost to lower cost countries outside Europe, has moved the issue of industrial policy and access to raw materials up the political agenda. A number of measures have already been announced by the European Commission to address these issues including: - The analysis of the competitiveness of individual industrial sectors, in order to understand their specific needs and take account of the particular opportunities and challenges they face.

Jan 1, 2006

By Sizhe Tan

An open pit mining operation can be considered as a production system with at least two products: ore and overburden (waste). A primary mine planning task is to schedule the production of ore and waste over its life span subject to several technical and economic constraints to maximize some objective such as the overall profit from the operation. Two major constraints are (i) the feasible combinations of ore and waste productions and (ii) the limiting function for ore production as a function of mine life. The task in scheduling production and stripping ratio (ratio of waste to ore production) is to find an ore production curve below the upper bound function of ore production, and a stripping ratio curve within the feasible domain of ore production and overburden removal while maximizing the defined objective. Zn this paper, feasibility of developing computerized optimization models to perform such a scheduling process is explored. Two optimization models are proposed for the task. In the first approach, a linear programming (LP) model is employed and in the second, a dynamic programming procedure (DP) is outlined. In these models, in addition to the consideration of the two major constraints mentioned earlier, various other contributing factors such as interest rate, equipment purchase cost and installation schedule, operating cost, and equipment idle cost are incorporated. An example is provided to illustrate the LP model application.

Jan 1, 1992

By Thomas Fenner

Surface and underground mining operations are often hindered by unknown tunnels and slopes and the precise locations of adjacent workings. Mine safety and planning are adversely affected especially in previously undermined areas where historical records are incomplete or nonexistent. The results of several ground penetrating radar (GPR) studies for the detection of known mine tunnels in underground coal, salt and gold mines are presented. A case study to locate unknown, abandoned mine workings at a surface gold mine successfully located all workings to a depth of 11 m (36 ft).

Jan 1, 1996

By D. E. Ranta, Ora H. Rostad

Ore reserve estimation, from the earliest "quick and dirty" estimates made at the first consideration of a possible project down to periodic revisions of detailed estimates made during the life of a mine, should take into account many geologic and allied factors in order to obtain results that will provide proper guidance for necessary economic decisions. Factors include: sample collection and analysis, character of the vein and associated wall- rock, mineralogy, pre and post mine oxidation effects, core loss, sample correlation, internal vein structure, wallrock controls, geologic factors affecting dilution in mining and interrelated mining and milling problems.

Jan 1, 1992

By O. Fernandez, M. Vesely

Abrasive grinding, leading to ultrafine product and "critical size" material buildup inside the mill, is proposed as the cause of high power consumption and low capacity in many fully autogenous grinding processes. Addition of steel balls (hence, semiautogenous grinding) or pebble removal and separate crushing have been used, with different efficiencies, to overcome the problem. Information and data for the conceptual analysis, basic design, and operation of a pebble crusher at the Los Bronces semiautogenous grinding plant is presented along with data showing a production increase of 1000 t/d (1100 stpd) and significant operating costs savings.

Jan 1, 1987

By B. K. Parekh, W. M. Goldberger

Sludge obtained during the production of magnesium (Mg) from molten MgCl2 by electrolysis contains entrapped magnesium particles. The sludge containing the magnesium particles is a friable, continuous matrix of frozen salts that may also contain some oxides and impurities. Due to the high reactivity of magnesium metal with water, a dry process was developed to recover magnesium metal from the sludge. The process utilizes mineral-processing unit operations. The steps include selective comminution, screening, attritioning and tabling. Recovery of the high-grade (>90%) metal was in the 70% range. The novel process was also successfully applied to a magnesium-alloy for the recovery of metal from the sludges.

Jan 1, 1997

By Clay Haynes, Tim Pearia, Robert Robinson, Judy Cochran

A 1.89 km-long, 4.5 m-I.D. tunnel was successfully constructed through saturated hard clay, and highly abrasive dense sand and gravel, with groundwater heads ranging from 10 to 20 m. In order to address these conditions, a Lovat earth pressure balance TBM was used, with soil conditioning by foam, water and various polymers. Support was provided by a single-pass segmented concrete lining. Groundwater inflows of 400to 1,600 lpm at times created challenges for changing cutting tools. Surface settlements were generally less than measurement thresholds, except under very low cover at startup. This project provides a pivotal case study of the successful application of EPBM technology in saturated, abrasive glacial soils and the successful application of soil conditioners.

Jan 1, 2003