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By V. Sheikhzadeh, M. Saghaeian, R. Hejazi, P. Ghobadi

Design and selection of equipment for a grinding circuit strongly depends on the mill function, ore properties and requirements of the down-stream circuit. Primary mills usually work in open circuit and size distribution of product would be controlled in the final steps using a classifier like cyclone. Although HPGRs are mostly utilized as pre-grinding mills, it is preferred to utilize them in a closed circuit due to their specific mechanism of comminution. Unique mechanical design of HPGR and its completely different crushing process than tumbling mills needs precise consideration on its circuit design. In this paper, we investigate the impact of different parameters on design of pre-grinding HPGR circuit and selection of the proper classifier. Our study focuses on iron ore properties (e.g. moisture, particle size distribution of feed and product, compatibility and de-agglomerability). We also investigated various options of HPGR circuit according the classifier efficiency and influences on down-stream processes. The optimum operating parameters of HPGR (working pressure, speed and level of hopper) for the selected circuit were also determined based on pilot and industrial data. Our pilot and industrial tests and observations revealed that HPGR should be arranged in closed circuit because of the edge effect, as a negative factor of non-uniform distribution of pressure force along the roller width and presence of non-crushed particles in the mill product. Wet vibratory screen could be the optimum option for screening of its discharge. Fine part of the wet screen discharge could be delivered to the concentration stage without over-grinding in ball mill using a hydrocyclone working in a reverse closed circuit mode. Moreover, our pilot and industrial tests during design and operation of ten HPGRs in various iron ore processing plants proved that higher pressure and lower roller speed in a fixed level of material inside the hopper could give the desired product size distribution.

Jan 1, 2016

By David R. Burkhard

"Comparative roof beam performance, as measured by delamination within the bolted horizon, was used to evaluate two types of roof bolt drill hole geometries in a development setting. Short encapsulation pull tests had demonstrated a higher grip factor in drill holes featuring helical grooves in the side walls in comparison to drill holes featuring continuous smooth to slightly rough walls. The study incorporated the two geometries during development mining in which fully grouted mechanically anchored bolts were installed as primary roof support.bolts were installed as primary roof support.The study site, in an entry adjacent to a longwall panel, was instrumented with extensometers and data collected during longwall retreat. Statistical analysis was conducted to validate null and alternative hypotheses used to compare drill hole geometries. Analysis yielded no statistically significant difference between drill hole geometries. Inspection of the data does reveal less delamination within the smooth walled site in comparison to the site containing grooved hole geometry.INTRODUCTIONFrom their introduction as a means of ground control over sixty years ago, roof bolts today are the primary mechanism of roof support utilized throughout mining. Whether through suspension, keying, or beam building, roof bolts are employed to reinforce the inherent strength of the strata comprising the immediate roof with the goal of creating a competent bolted horizon of sufficient load bearing capacity to be self-supporting for a given mine's design life, stress regime, and geomechanical properties.For grouted bolts in sedimentary strata, axial loading due to vertical rock movement and bending due to horizontal rock movement are the principal means of loading (Signer, 2000). Regardless of the type of bolt and extent of grouting employed, the success of any roof bolting design is determined, to a large extent, by the effectiveness of load transfer between the rock, grout, and bolt.At San Juan Mine, an underground longwall mine located in the northwestern corner of New Mexico, a number of different roof bolt types, grades, and lengths have been used over the years in an effort to optimize primary roof support. One common denominator shared throughout has been the use of full length grout. Load transfer for full length grout is achieved primarily through mechanical bonding between the grout and rock. It is this interaction that is the focus of the study described in this paper. The study assessed and compared two types of bolt hole geometries employed during gate road development at San Juan. Underground instrumentation and evaluation of the bolted roof provided the means of assessment and comparison."

Jan 1, 2016

By Moussa Wone, William Levy, Christopher Caruso, Zachary Spera, Thomas Hennings, Richard Stacy Kinchen, PE Joel Kantola

"Owners constructing new combined sewer overflow (CSO) systems increasingly seek to have project design lives of 100 or more years in response to the growing size, complexity, and cost to construct and operate these systems. However, a codified and universally accepted approach to achieving this goal in the United States does not currently exist since service life prediction is a relatively new technical field. This paper discusses how the 100-year design life requirement was met for the design of tunnels, drop shafts, and diversion structures in the DC Clean Rivers Program (DCCRP). The authors identify some commonly referenced publications, present the testing framework used by the program manager to characterize the CSOs, review the design criteria used to guide the 100-year design life development, and establish guidelines to be considered by program managers and designers when implementing similar extended design life requirements in other CSO control programs.INTRODUCTIONLike many older cities in the United States, the sewer system in the District of Columbia consists of both combined sewers and separate sanitary sewers. When the capacity of a combined sewer is exceeded during storm events, the excess flow, which is a mixture of sewage and storm water runoff, is discharged to the District’s receiving water bodies (Anacostia River, Potomac River, and Rock Creek) and tributaries through outfall structures. This excess discharge during storm events is called a combined sewer overflow or CSO. A total of 53 CSO outfalls for the combined sewer system are listed in DC Water’s National Pollutant Discharge Elimination System (NPDES) Permit issued by the U.S. Environmental Protection Agency (EPA). The DC Clean Rivers Program (DCCRP) will reduce the number of CSO outfalls into the Potomac and Anacostia Rivers and decrease flooding in DC neighborhoods during extreme rain events by capturing, storing, and conveying diverted CSOs to the Blue Plains Advanced Wastewater Treatment Plant."

Jan 1, 2016

By K. Lim, J. Sobil, L. Galarza Castillo, F. Tozlu

"For mining operations globally, the scale and criticality of the grinding mill drive has meant that selection of the correct mill drive technology is paramount. With so much depending on the successful implementation of the electrical drive system— safety operation, timely installation, availability, energy efficiency, minimum maintenance and extend its use as tool to assist during mill liner exchange—customers are justified in their scrutiny and slow adoption of new drive technology. From the first installation of low, fixed speed synchronous motors to the introduction of the current source and further voltage source variable frequency drive, innovations require long periods of time and mining customers willing to push the industry forward. In recent years, the variable frequency drive has been the stepping stone for a new generation of mill drive technology. In use for decades in other heavy industrial applications, the drives allow for system optimization in a myriad of ways. The most dramatic of changes is in the design of the motor. Where in the past motor design was bound by line frequency, today the designer can optimize machine size and, more importantly, eliminate the need entirely for the synchronous motor. Induction motor design has now progressed to the point where low speed operation is possible at efficiency levels nearing those of the synchronous design. Moreover, the simplicity of the squirrel cage design means that availability, reliability and spare part requirements are greatly improved. As the next step in the evolution of large pinion driven grinding mills, the low speed induction drive offers a new reliable and robust system to the market.IntroductionAs deposit grades continue to decline, new ways of processing ever greater concentrator throughputs have been required to maintain throughput efficient and profitable operations. Furthermore, the high risk nature of mining developments requires a constant search for safer, higher availability and more efficient equipment design. Limitation of downtime is a key factor in ensuring mining operations can be sustained through volatile market conditions. Often processing the entire mine throughput through just 1 or 2 lines, the crushing and grinding circuits are of particular criticality to the uptime and, thus, profitability of any mining operation."

Jan 1, 2016

By A. Y. Senchenko, S. G. Rybkin, A. V. Aksenov

In gravity processing of gold-containing ore the target produced concentrate which is high gold grade primary concentrate contains a significant amount of cassiterite (SnO2). The plant attempts aiming at concentrate processing using a standard pyrometallurgical technology did not provide any positive results. The present paper is dedicated to development and testing of improved technology for pyrometallurgical processing of rich gold primary concentrate with high cassiterite content. According to material composition study primary concentrates produced at the plant contained 1.5–2.0% Au, 0.1–0.3% Ag, 55–65% SnO2, 20–25% Fe2O3, and 10–15% Fe3O4. The developed technology included alkaline nodulizing of primary concentrate mixed with sodium hydroxide and carbonate at 350–650°? with cake production. In blend nodulizing stannum and iron passed into sodium stannate (Na2SnO3) and sodium ferrate (NaFeO2) respectively. The blend of cake and fluxing agents was smelted at 1,150–1,200°? resulting in dore gold and slag production. Sodium stannate with 360°? melting point is well dissolved in slag system Na2OSiO2- B2O3-CaO. During plant tests 18.5 kg of high gold grade primary concentrate were processed, 1350 g of dore gold and 75 kg of slag were produced. Dore gold contained 16.5% Au, 0.95% Ag, 78.0% Sn, 3.1% Fe. Slag contained 12.4 g/t Au, 6.7 g/t Ag, 9.8% Sn, and 5.6% Fe. Gold recovery to target alloy was equal to 99.58 %, 87.8% of Sn passed into slag. This new technology was accepted for application at the plant.

Jan 1, 2016

By Gilles Cachia, Foteini Vasilikou, Seth Pollak, Hannes Lagger

"INTRODUCTION The Shatin to Central Link (SCL) is a new rail line being constructed by the MTR Corporation for the Government of Hong Kong to cater for the growing passenger demand between the North-East New Territories and the urban areas of the city. Contract 1103, which will provide the 4 km of running tunnels between the new Hin Keng and Diamond Hill Stations, was tendered in a design-build framework and awarded to Vinci Construction Grands Projets (VCGP) in October 2012, with Arup as Vinci’s lead designer. One of the most challenging pieces of work on the contract involved the construction of 133m of SEM mined tunnel on the northern end of the project. The Northern Mined Section (NMS) is an undrained, twin-track, single bore profile, broken out through the southern pipe pile wall of the Hin Keng Station cut-and-cover box, Figure 1. The tunnel has maximum excavated dimensions of 14.5m span x 12m height, with track spacing of 6.175m. The general excavation sequence consisted of 3 stages; a 6m high top heading (73.1m2), followed by bench (27.3m2), and invert (26.7m2). A risk-based approach to the design was taken given the large variation in rock level, cover, and an active stream course above tunnel crown. Ultimately, six different temporary support types were utilized in order to optimize the construction process through continually changing ground while maintaining a safe and stable excavation. Three main support types were developed during the initial design phase, along with a “contingency” case, which utilized a partial heading excavation sequence and enhanced face support. The purpose of the contingency support type was to have a robust, engineered design available for immediate implementation should unexpected ground behavior develop, leading to the breaching of instrumentation trigger levels. This support type was never implemented on site. Drill- and-blast tunneling commenced once 6m of rock cover was verified through forward probing. A robust instrumentation and monitoring scheme provided valuable data throughout excavation and the means to carry out a geotechnical back-analysis of the ground behavior and support performance."

Jan 1, 2016

By William A. Prosser, Kyle R. Ott, Philip Rice

"INTRODUCTION The existing Baltimore and Potomac (B&P) Tunnel accommodates Amtrak (National Railroad Passenger Corporation) and MARC (Maryland Rail Corporation) service between Baltimore, MD and Washington, DC and occasional local freight service. The Baltimore and Potomac Tunnel Replacement Project proposes new tunnel construction through Baltimore, Maryland along the Northeast Corridor (NEC) that maintains connections to Baltimore Pennsylvania Station. After the Replacement Project is constructed and operational, the disposition of the existing tunnel must be determined. The tunnel could be abandoned; however, considering its location in a congested downtown, alternative uses have been considered to take advantage of this unique piece of infrastructure by repurposing it. Alternative uses for the existing 140-year-old B&P Tunnel may end up being cost effective and should be considered, as the tunnel can be made accessible to construction crews for extended periods of time that will allow for efficient work activities unlike when it is fully operational. Possible alternatives include conversion for non-rail use, rehabilitation, or complete modernization for continued rail traffic. The following paper describes the four potential fates of the conceptual designs for the existing B&P Tunnel. The four concepts include: • No Build – rehabilitate to keep the tunnel operational. • Abandonment – complete or partial sealing of the tunnel. • Adaptive Re-Use –repurpose the tunnel with sustainable building practice. • Full Rehabilitation and Modernization – bring to current fire-life safety aspects. Of the four concepts, only the no build addresses maintaining the tunnel while it is under traffic. The remaining fates address the existing tunnel after the new tunnel is operational and railroad traffic has been diverted to it. Development of these conceptual designs were provided in a concept design study (Parsons Brinckerhoff/Parsons, 2015) that supports the National Environmental Policy Act (NEPA) review process for the Project, which includes evaluation of possible alternative uses of the existing B&P Tunnel."

Jan 1, 2016

By T. Bednarski, T. McCallum

"Physical impurity transfer in solvent extraction (SX) has a significant impact on operating costs, electrowinning (EW) performance, and cathode quality. Some operations use a wash stage to limit impurity transfer by diluting the entrained pregnant leach solution (PLS) to prevent direct transfer to EW. Wash stage operating conditions vary impacting impurity transfer. A number of factors impact dilution efficiency including mixer continuity, wash aqueous acidity, and organic quality. The impact of these variables on dilution efficiency was studied and compared to current industry practice. INTRODUCTION With the exception of iron, impurity transfer in copper SX is due to PLS carryover in the loaded organic via aqueous entrainment and crud movement. The quantity of impurity transfer is influenced by many variables including operating set points, organic quality, and settler housekeeping. Crud management and treatment is a common practice aimed at minimizing transfer of impurities to EW. Crud is a complex solid-stabilized emulsion of aqueous and organic[9]. As such, it contains a large aqueous component and the associated impurities (from the PLS). A common practice is to remove interfacial crud to prevent movement. Additionally, mixer continuity can be altered to enable compaction and improve the efficiency of interfacial pumping[10]. Understanding the factors impacting aqueous entrainment and optimizing the available controls should be a key focus for any operation. Aqueous entrainment in the loaded organic can be impacted by: • Mixer continuity • Mixer organic/aqueous (O/A) ratio • Mixer speed and impeller type • Organic and aqueous depths • Specific settler flow • Use of settler internals (picket fences, coalescing packs) • Organic quality • Design and operation of loaded organic tanks Conventional thought is to run the E1 mixer in aqueous continuity to reduce aqueous entrainment. Generally, O/A ratios close to 1:1 result in improved metallurgical and physical performance. Mixer speeds should be chosen to achieve acceptable stage efficiencies while minimizing over-mixing. Organic depths can be increased in the E1 stage to increase retention time and minimize aqueous entrainment. Settler internals can also be used, but require maintenance to maintain effectiveness. The quality of the plant organic inventory will impact physical performance. Poor organic quality can lead to higher phase disengagement times increasing impurity transfer to the electrolyte. Additionally, the design and operation of the loaded organic tank can impact impurity transfer[8]. Despite the variables that can be used to reduce aqueous entrainment and crud movement, impurity transfer is still an issue in some operations. For these operations with high PLS impurity concentrations, a wash stage may be beneficial to manage impurity transfer. Understanding factors impacting wash stage performance is important to optimize performance and limit impurity transfer."

Jan 1, 2016

By S. R. Xie, S. Gong, E. P. Li, S. S. He, Y. J. Sun, S. J. Li

"Based on the complicated geological production conditions and abnormal strata behavior of the fully mechanized caving face No. 102 in the Xinyang Coal Mine, we analyze the breaking and forming process of distinguishing key block structures in close spaced coal seams. This analysis establishes an integrated mechanical model of these distinguishing structures. Furthermore, the horizontal force TAB generated by downward key blocks A and B is quantified, as is the Pressure PG exerted by key block B on caved gangue. Finally, the interaction mechanism is revealed. Analysis of the results using Mathematica reveal the following: 1. Both TAB and PG exhibit approximately inverse relationships to coal pillar width b; 2. TAB exhibits an approximately exponential relationship with mining height M of which the base is greater than 1; 3. PG exhibits an approximately arctangent relationship with mining height M. Combining these results with field observations, we conclude that the area in the vicinity of supports 100#–120# in the upper area of working face No. 102 is the likely zone of abnormal strata behavior. Thus, this area was classified as a key control area. Based on these results, the graded support control technique is proposed. Application of this technique in the field resulted in a reduction in the rate of hydraulic support system malfunction from 47% to 7% in the key control area. In addition, during times of periodic mining pressure, the roof caving height value never exceeded 0.3 m and the maximum spalling depth never exceeded 0.2 m. Overall, the results indicate that this new technique has markedly increased the stability of surrounding support rock material. IntroductionClose-spaced coal seams are widely distributed in China, and mining proceeds from the uppermost to the lowermost seam (Zhang et al., 2008). In the case of coal seams in close proximity, a particular set of risk factors becomes pertinent. These include disturbance of lower seams during the mining of overlying ones and the decrease in mechanical stability of lower coal seams following repeated movement of key blocks in main coal seam roofs. This inevitably results in behaviour such as heavy wall spalling and support damage to fully mechanized caving faces in lower-lying coal seams, which necessitates a significantly increase in the measures to support surrounding rock material (Zhang et al., 2010; Huang et al., 2013; Xie et al., 2013)."

Jan 1, 2016

By Mauro Torres, Gabriel Zarate

"AngloAmerican used the extractant M5640 at Mantos Blancos and Mantoverde and uses PT5050MD at Los Bronces Division, which are aldoxime and modifier blends. In the first case, the modifier is the esther TXIB, while in the second case is the tridecanol TDA. It is a well-known fact that the extractant degrades while the modifier does not and with time the oxime/modifier ratio can change significantly, depending on the operating conditions of each plant.In order to evaluate the effect of this varying modifier content in the plant organic, especially in the organic losses, a complete metallurgical test work program was conducted at laboratory and pilot plant scale by Flomin SNF, a new extractant supplier. Results showed that the addition of an aldoxime without the modifier did not affect the chemical performance of the extractant, but there was a significant decrease in the viscosity and density of the organic.Based on the results obtained in the metallurgical program, it was decided to run plant scale tests at the SX plants of Mantos Blancos and Mantoverde. In these tests, instead of adding extractant to maintain the organic inventory, CuPROMEX 3406 which is an unmodified aldoxime was added until the original oxime/modifier ratio was reached. This was obtained after 6 months of operation and since then both plants are running with the extractant CuPROMEX 3302 both supplied by Flomin SNF.In the case of Los Bronces, the pilot plant work was completed and it is programmed to run similar plant scale tests. In this case, the oxime/modifier ratio increased and TDA will be added until reaching the original ratio.The plant results obtained at Mantoverde and Mantos Blancos, together with the pilot plant test results obtained at Los Bronces, are discussed in this paper."

Jan 1, 2016

By J. G. Stevens, S. W. Colley

"Selective separations of metals and ions in mineral extraction and refining are becoming more challenging as ore bodies become more complex and environmental pressures increase. The separation and containment of mercury produced in gold mining are a factor in the profitability and operability of mines. This paper will discuss the development and implementation of the Johnson Matthey HgFree selective mercury removal process. The process is designed to selectively recover co-leached mercury from either heap leach pregnant solutions at ambient temperature and low mercury concentrations, or electrowinning pregnant solutions at elevated temperature and high mercury concentration, without affecting gold or silver recovery. The process utilizes a highly selective adsorption-desorption step in which mercury is removed quantitatively by the HgFree adsorbent without adsorption of gold, silver or other metals present. Development of the original HgFree adsorbent has resulted in a process whereby mercury can be recovered as an inert salt and is never present as the free metal. The HgFree adsorbent can be regenerated and recycled in situ, and is capable of being reused multiple times. The overall process is compatible with existing gold mining and recovery practices and offers significant environmental and sustainability benefits, including reduction or elimination of the need to retort mercury with a subsequent reduction in potential mercury air emissions. Development of the HgFree adsorbent and process will be discussed along with a pilot operation at two operating mines.INTRODUCTIONMany gold ore bodies contain high concentrations of mercury which when extracted with cyanide, co-extract with the gold and other metals. This mercury is carried through the process with the gold, posing environmental and technical issues when it is separated from the doré. This paper describes a method to selectively adsorb mercury from the gold recovery circuit while it is in a soluble form, leaving gold to be processed as normal. The removal of mercury from the circuit eliminates the need for mercury retorting of doré and so reduces the potential environmental impact of fugitive emissions of elemental mercury."

Jan 1, 2016

By A. G. Doll

"This paper expands the SAG mill survey database published by the Author at Procemin 2013. The new database includes 49 published SAG/AG mill surveys and includes mills from all over the world. The paper will compare the survey database to SAG mill models by Austin, Morrell and Hogg & Fuerstenau with the purpose of demonstrating the degree of fit of the models to surveys and validating any empirical “fitting factors” used in the models.SAG mill power draw models are used in mill design and grinding circuit modelling to predict how much power will be consumed by a particular mill geometry and operating configuration. The importance of conducting surveys suited to model calibration will be highlighted because the review of literature shows that survey information important to modelling is often missing or omitted. A recommendation for the collection of data during a mill survey is presented, along with some assumptions used by the Author in the absence of certain data. The benefit to mining companies of publishing their survey data, and thereby allowing modellers to improve their model calibration, is discussed.The comparison of models requires a discussion of the measurement of power in a mill drive system as the models use slightly different position in the electrical network for ""where power is measured"". The benchmarking of models against plant operations requires a similar discussion of power measurement."

Jan 1, 2016

By Benno Ring

"When designing segmental lining at a cross passage, modern solutions try to bear the loads transferred around the opening within the rings by using shear elements in the ring joints. Commonly used shear systems providing coupling are cam & pocket, shear keys, bicones and steel dowels. These solutions have advantages and disadvantages, but most importantly they have limits in their capacity to stabilize the lining at cross passages. With the help of 3D-FE-analyses for an opening of one segmental ring these different solutions are compared taking various ground conditions into account. As a result the capacity of the individual system is determined. Notice is made regarding the applicability of the system as well as the consequences for the design and the verification. INTRODUCTION The design of the lining at a cross passage is among the most difficult tasks when designing TBM-tunnels. At one time the bedding of the lining disappears due to the excavation behind the lining, at another the ring-structure is interrupted when parts of the lining are removed for the opening. The trick is to transfer the loads around the opening into other segments and to areas of the lining which are still supported by the ground. In the rings immediately at the cross passage this creates a distribution of forces within the segments that strongly deviates from that of the regular lining. The design needs to consider the boundary conditions of the respectively chosen solution for stiffening of the opening and its peculiarities in the modeling as well as in the verifications. In the past segments of steel or an internal strutting of steel (DAUB 2013) placed around the later openings were commonly used, see Figure 1. The application of a strutting from the outside to the rings is restricted to such circumstances when for example a connection from a shaft to the tunnel can be made in suitable ground conditions (Ring and Glomp 2012). Though steel segments provide a robust solution, they are expensive due to their laborious manufacture, the high proportion of construction steel required and the time consuming installation in the tunnel (Häfliger 2013). A strutting of steel requires extensive design and verification. The resulting structure usually weighs several tons and must be erected as well as demounted within the confined space of the tunnel, requiring suitable transport and assembly equipment. The cross section remains restricted, thus causing a bottleneck for TBM operations and hindering the works and installations for the cross passage works."

Jan 1, 2016

By William G. Pariseau, Michael K. McCarter

"The challenge of estimating mine-wide subsidence and linkages to seismicity over tabular deposits is addressed by a special finite element technique (dual node - dual mesh). Subsidence and mine-induced seismicity begins near the face when caving occurs and propagates to the surface as extraction reaches a critical extent. Thus, the challenge is to obtain details at the face at the meter scale and also at the surface over the whole mine at the kilometer scale. Interactions between old and new sections of a mine are automatically taken into account with this technique. The finite element method is well established technology based on fundamentals of physical laws, kinematics and material laws. With this technique, no empirical ""scaling"" or fitting computer output by input data ""adjustment"" to mine measurements is necessary. Capability is demonstrated for doing practical whole-mine subsidence analysis from first principles. Mine-induced seismicity is shown to correlate well with face advance and element failure.INTRODUCTIONSeismicity associated with coal mining has been under study for several years by a team at the University of Utah. Team members include mining faculty, research geophysicists and students from the Departments of Mining Engineering and Geology & Geophysics. Mines in central Utah that have been studied include the Trail Mountain Mine (Pariseau, 2015; Pariseau and McCarter, 2015), the Beehive Mine, also known as the Des-BeeDove (Pariseau, 2014), and the Crandall Canyon Mine (Pariseau, 2015). These mines were developed from outcrops in the Wasatch Plateau coal field west of Price, Utah, where the topography is characterized by . steeply incised canyon drainages and high plateaus with relief of a thousand meters or so.Seismicity associated with coal mining in central Utah has been of interest for many years and includes studies in the Book Cliffs to the east of Price, Utah, where mining is still active (Smith et al, 1974; Agapito, Goodrich and Moon, 1997; Arabasz et al, 2001; Arabasz et al, 2002; Fletcher and McGarr, 2005; McGarr and Fletcher 2005; Maleki, 2005) and to the northwest (Ellenberger et al, 2001). Results of many micro-seismic studies are summarized perhaps best by lannacchione, et al (2005) in stating, ""Deviations from normal strata response can provide useful stability information.""This study concerns a fourth underground coal mine in the southern portion of the Wasatch Plateau coalfield, hereafter referred to as the MINE. Focus is on mining from 2004-2008 with the objective of examining mining in relation to seismicity."

Jan 1, 2016

By Georgios Kalamaras, Sebastiano Pelizza, Carlo Alessio

"This article describes, through the presentation of five cases-history, technological advances that the Authors together with Tunneling Contractors devised for coping with adverse geotechnical conditions. It is believed that by introducing these new elements in a method that has proven its value in Italy and abroad for the last 40 years, the umbrella arch method, due to its versatility and simplicity, can become a universal method for conventional tunneling in very poor ground conditions. After a description of common faults and mistakes in applying the method, 5 projects are presented which demonstrate that self-drilling pipes give excellent results in terms of performance a zero volume loss, while, function of the ground conditions the various grouting mixtures used, such as expansive jet-injected cement-base grouts and bi-component resins, extend the use of the umbrella-arch in variety of grounds even in presence of water-bearing lenses. The case-histories provide successful applications in different conditions.BASIC FEATURES OF UMBRELLA ARCH METHODThe umbrella arch method provides a short support of the tunnel vault just ahead of the excavation face. The method foresees the drilling and installation of peripheral, sub-horizontal steel pipes in the ground, followed by their grouting. The umbrella arch method is also known as forepoling, steel pipe umbrella, reinforced protective umbrella or simply “umbrella”. The umbrella arch method does not have a static function because the immediate stabilization of tunnel section is entrusted to the internal shell of steel ribs and shotcrete. The “umbrella” provides a pre-support of the excavation which has to be stable for an adequate length and duration permitting the installation of the next steel rib and shotcrete under conditions of safety (Figure 1).The umbrella-arch provides pre-reinforcement of poor ground around the tunnel perimeter in a simple and flexible manner that is adaptable to different ground conditions. In fact, it is possible to vary the number and length of pipes, the distance between them, their diameter and thickness as well as the overlapping length of two succeeding umbrella arches. The versatility of the umbrella arch technique allows its application to: clay deposits, granular alluvial deposits, moraine and debris materials even when containing large blocks, heavily jointed, foliated and tectonically disturbed rock masses."

Jan 1, 2016

By Ingo Ossenbühl, Wolfgang Dolsak, Vojtech Gall, Axel G. Nitschke

"Yielding support systems for application in underground construction have a long history, primarily in mining. Typical examples are tunnels subject to loading conditions that lead to overstressing of the newly installed support or existing tunnel structures in active fault zones. Recent applications for tunnel rehabilitation projects unveiled the capabilities and flexibility of combined yielding support systems presented in this paper. Frequently, the main requirements for tunnel rehabilitation applications are a fast, safe, and simple installation along with the need for flexibility with regards to existing tunnel geometries. A combined support system consisting of steel sets with yielding connections and special groutable hoses has proven to be an efficient support measure providing a multitude of advantages compared to conventional rehabilitation approaches. The presented yielding support system provides an immediate and active support, while it allows for controlled yielding upon experiencing loads beyond its support capacity. INTRODUCTION The excavation of underground spaces leads to redistribution in the existing stress regime. This load redistribution goes along with deformations in the surrounding rock mass. Magnitude and duration of these deformations depend on the tunnel’s depth and geological conditions, but also on the installed support system. Modern civil tunneling infrastructure has generally an envisioned service life of about 120 years. Conventional tunneling provides typically a dual support system, split into the initial (or primary) and final (or secondary) lining. A typical design principle in civil tunneling is to let the vast majority of deformations acting on the initial lining cease, before the final lining is installed. Based on this approach, the loading on the final lining is significantly reduced and signs of overstressing, such as cracking of the lining, are typically limited to the initial lining. However, special cases in swelling and squeezing ground require different approaches, including yielding support systems."

Jan 1, 2016

By J. F. Brune

"Re-occurring face ignitions in U.S. coal mines are concerning and require a closer look at air quality monitoring systems and practices employed in these mines. The explosion disaster at the Upper Big Branch mine in West Virginia in 2010 caused 29 fatal injuries and was largely caused by inadequate water sprays and inadequate ventilation monitoring. In this comparison, the author compares ventilation system monitoring in Australian, German and U.S. underground coal mines and makes recommendations for improvements and best practices. Mines in Germany and Australia are adhering to more stringent requirements for monitoring air quality and quantity and for monitoring water spray systems on cutters to prevent frictional ignitions. Air quality should to be monitored for sufficient oxygen, toxic gases, explosibility and for fire gases indicating a potential fire. Ventilation monitors must also confirm that sufficient quantities of air are available. Fully automated, continuously recording atmospheric monitoring and alarm systems are established practices in Germany and Australia and should be mandated for U.S. mines as well, in addition to the current, regular spot inspections of the ventilation system by certified mine examiners. BACKGROUND: METHANE EXPLOSIONS, FACE IGNITIONS AND NEED FOR AIR QUALITY MONITORING Accumulations of methane in face areas of underground coal mines frequently lead to ignitions that can cause burns, traumatic injuries and, in the case of the 2010 Upper Big Branch disaster, cause major explosions with multiple fatalities. Table 1 shows the number of reported face ignitions in U.S. coal mines between 2010 and 2014, based on statistical data published by MSHA (MSHA 2010 – 2014). Although there appears to be a downward trend in such ignition incidents over time, ignitions continue to occur with some regularity; and each ignition may cause a potentially catastrophic mine explosion.Per regulation, all U.S. coal mining machinery, continuous miners and longwall equipment, is outfitted with continuously monitoring methane sensors wired to cut power to the equipment as the methane level exceeds 1%. Face ignitions keep occurring because these sensors are usually not positioned in sufficiently close proximity to the coal cutting drums or to the freshly exposed coal face where the methane is most likely released. Therefore, methane may accumulate in explosive concentrations near the coal face and the cutting drums long before the gas concentration reaches the 1% level near the monitor and creates an alarm."

Jan 1, 2016

By Emanuele Catelli, Paolo Vicentini, Manuel Petitat, Paolo Lanfranchi

"More than 800 million tons of material will be excavated during large underground projects such as tunnels, undergrounds and power plants by 2030 in Europe only. The raw material excavated is often classified as waste, which involves environmental impact and transport issues: landfill areas, CO2 emissions and noise. But how can such massive amounts of material be transported, processed and deposited? Using the example of the AlpTransit Ceneri Base Tunnel (15.4 km), we show that suitable excavated materials can be used sustainably as a primary resource for tunnel concrete. This requires careful planning of the installations and storage areas by the client, timely building of the processing plants and other handling facilities outside the tunnel and a continuous evaluation of the raw material quality. 1. INTRODUCTION Spoil management is a central element of large construction projects. The systematic reuse of suitable excavated material not only saves natural resources, reduces transport distances and landfill volume, but can also decrease overall construction costs. Ideally, all of the concrete needed for tunnel lining can be produced with this on-site material. Such a natural resource management concept was applied for the construction of the new Gotthard Base Tunnel (L = 57 km). Spoil management concepts are, how-ever, difficult to implement and call for innovative techniques, sophisticated logistics and organization. In the context of large projects, environmentally friendly transport, processing and storage of millions of tons of excavated loose material represent another logistics challenge (Simmen & Lieb, 2010). This paper shows key factors that led to the successful completion of spoil management at the Ceneri Base Tunnel, which constitutes a part of the AlpTransit Gotthard Project (Figure 1)."

Jan 1, 2016

By S. G. Britton

"INTRODUCTION Strategies to improve performance in mining production, maintenance and mineral processing operations has evolved over time from straightforward time studies of individual machine performance in the 1960’s-1970’s to more sophisticated and better focused statistical and financial tools that have emerged in the 1980’s-1990’s . These newer strategies fall under the broad descriptive category of “Operational Excellence”. Operational Excellence is the term that embodies a number of performance evaluating strategies, the most popular and relevant to mining includes the following: • Six sigma for addressing errors within mining or milling process and work standards • Lean manufacturing to optimize organizational and operational performance through continuous improvement. There are other strategies that can be applied as well and this paper is not focused on a review of the pros and cons of any one strategy. However, the common threads in these strategies embody the expectation that expected results from these efforts can be quantified and that value will positively benefit the targeted work process, organizational unit, equipment deployment or time schedule when applied to it as part of continuous improvement efforts. The priority for proceeding with any one or more of these efforts is based on the calculated net value of the required resources to affect the change versus the estimated value gained. The practice is identified as the value mapping process. This discussion summarizes the value mapping process methodology used at a mature uranium mine and mill in northern Canada to work through the myriad of potential improvement efforts available through the operational excellence process for continuous improvement.THE RABBIT LAKE MINE AND MILL The Rabbit Lake Mine and Mill are located in northern Saskatchewan, Canada on the shores of Wollaston Lake (Figure 1).The mine was discovered in the mid-1960s and was built by Gulf Minerals, Ltd. The mill began processing uranium ore into yellowcake in 1975 from an adjacent open pit mine. A whole ore acid leaching followed by solvent extraction and precipitation forms the basic milling processes. The operation continued to produce yellowcake through a succession of open pits and finally opened an underground mine in the early 1990s. Since beginning production, over 200 million pounds of yellowcake has been packaged from the site, making it the sixth highest producing uranium mine of all time."

Jan 1, 2016

By J. F. Brune, A. Verma

"Face ignitions in underground coal mines are a major risk for underground mining operations, as they can lead to methane or coal dust explosions. The 2010 disaster at the Upper Big Branch Mine resulted in 29 fatalities due to a methane and coal dust explosion initiated from a face ignition. Much research has been conducted to mitigate face ignition hazards, from water sprays to installing passive and active explosion barriers. Despite the increased use of water sprays in U.S. coal mines, there have been more than 50 documented face ignitions in the U.S. underground coal mines since 2010, indicating that this hazard still prevails. This paper will examine the statistics of face ignitions and gas explosion in U.S. coal mines based on MSHA data. It will study factors contributing to these face ignitions and outline best practices for their prevention based on experience and practices worldwide. INTRODUCTION Methane and coal dust explosions are one of the major causes of coal mine disasters in the U.S. and around the world. Such disasters have resulted in the large number of fatalities and loss of mine infrastructure. The recent explosion at the Soma coal mine in Turkey has caused the death of 301 miners (Mining Turkey, 2014). As documented by U.S. Mine Safety and Health Administration (MSHA, 2015a), the U.S. coal mining industry has also experienced several catastrophic mine explosions with accidents at Upper Big Branch mine, Darby mine, Sago mine and Jim Walter Resources No. 5 mine in the last decade, causing the deaths of almost 60 miners. Every explosion requires a source of ignition, the right amount of fuel and oxygen. In underground coal mines, methane acts as a fuel while ventilation air acts as a source of oxygen. The source of ignition may vary from spontaneous combustion, electrical equipment and switchgear, mechanical heat sources, face ignitions due to friction rock-on-rock or from cutter bits and lightning strikes. Under the right conditions, energy of less than 0.3 mJ is sufficient to ignite methane-air mixtures (James, 2007) that can result in a catastrophic explosion. Much research has been done to mitigate the methane explosion hazard by proper dilution, continuous monitoring of methane and elimination of ignition sources. Historical studies indicate that face ignitions are the major cause of explosion in underground coal mining operations worldwide (Belle, Carey, and Robertson, 2012). Statistics shows that most mine disasters were started from a small face ignition, which turned into a major explosion fueled by additional methane and coal dust (Belle et al., 2012). To investigate face ignition hazards, researchers must study potential ignition sources as well as potential explosive atmospheres near mechanical coal cutting operations. Statistical analysis of U.S. coal mine face ignitions reported by the U.S. Mine Safety and Health Administration (MSHA, 2015b) shows that several factors are responsible for face ignitions."

Jan 1, 2016