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By A. David Miller, Douglas M. Barber

"The Rocky Mountain Arsenal was used by the military to produce chemical warfare agents and incendiary munitions for use during World War II and later by private companies for the production of industrial and agricultural chemicals. After an investigation performed in accordance with CERCLA confirmed significant levels of contamination due to the common industrial and waste disposal practices of the era and the discovery of over 300 species of wildlife inhabiting the land the Rocky Mountain Arsenal became a wildlife refuge and contamination cleanup efforts began. Three lime basins originally used to treat wastewater from the chemical production were decided to be contained in place, requiring a seepage barrier installed around the perimeter of the site to further prevent groundwater/contaminant migration. This case study will discuss the successful installation of a soil-bentonite cutoff wall around the area using deep soil mixing. Highlights of this case study will also include a discussion of the challenges faced due to construction activities performed with Level B Hazmat PPE requirements as well as added challenges brought on by the Winter season, after the project was delayed due to a positive air monitor detection for the chemical weapon Lewisite during construction of the work pad.INTRODUCTIONThe Rocky Mountain Arsenal (RMA), located just outside of Denver, Colorado, was established by the United States Army in 1942 to produce chemical warfare agents and incendiary munitions for use during World War II. Following the war, and as weapons production decreased, portions of the site were leased to private companies for the production of industrial and agricultural chemicals. The principal lessee, Shell Oil Company, manufactured mostly pesticides at RMA facilities from the early 1950s to the early 1980s.In 1984 an investigation began in accordance with the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) and confirmed significant levels of contamination due, in large part, to the common industrial and waste disposal practices of the era. It was also discovered that over 300 species of wildlife inhabited the land in the absence of regular human activity, including a group of bald eagles, leading to the passing of the Rocky Mountain Arsenal National Wildlife Refuge Act in 1992."

Jan 1, 2015

By S. Heusermann, S. Fahland, J. Behlau, A. Schäfers, J. Hammer

In the course of the deep subsurface use, the Federal Institute for Geosciences and Natural Resources has been carrying out extensive geological and geomechanical research and practical project work on domal salt structures, to prove their suitability e.g. for the disposal of radioactive wastes. Recent work on disposal sites has been taking into account the 3-D geological and geomechanical modelling of the underground structures. The geological models are generated using the special-construction openGEOTM code to improve the visualisation and interpretation of the geological data basis, e.g. borehole, mine, and geophysical data. For the geomechanical analysis of underground structures the JIFE finite-element tool has being developed to analyze large 3-D structures and to consider coupled THMC processes. The results of finite-element calculations, i.e. stresses, strains, displacements, and dilatant zones, are basic values for the evaluation of the stability of the structures and the long-term integrity of the geological barrier. As an example, the results of geological and geomechanical investigations of the Morsleben repository are presented including three-dimensional modelling of the entire geological structure of the central part of the mine as well as three-dimensional geomechanical model calculations to provide the necessary results for a long-term safety prediction.

Jan 1, 2015

By Randy Settgast, Daniel Moos, Hyunil Jo, Ghazal Izadi, Christine Baba

"Analyses of production logs of multiply fractured horizontal wells in unconventional plays show that only a small percent (~30%) of perforation clusters contribute to production. We present in this paper one possible approach to mitigating this problem, based on use of a fully 3-D numerical model of fracture propagation through a heterogeneous medium, by studying the influence both of spacing and of perforation friction on the initiation and propagation of simultaneous hydraulic fractures from a horizontal wellbore. The results indicate that while limited-entry perforating can help to equalize the lengths of fractures simultaneously growing from multiple clusters, it cannot equalize their widths. Both fracture width and fracture length can be equilibrated by combining non-even cluster spacing with limited-entry perforating. This has obvious benefits as it allows equalized placement of proppant across the entire series of perforation clusters, resulting in similar fracture widths and conductivities which enhances the likelihood that all clusters will contribute equally to production.INTRODUCTIONThere is substantial evidence from production logs and other information that during the hydraulic stimulation of horizontal wells, not all perforation clusters within a given stage will produce. One possible cause is the interaction between the hydraulic fractures emanating from each perforation cluster. Typically fractures created at the outer perforation clusters create “stress shadows”, i.e. increases in compressive stress in the minimum principal stress direction, which limit the growth of fractures growing from interior clusters; this is confirmed by modelling [1, 2, 3]. An example of this can be seen in Figure 1 which shows the final configuration of simultaneously propagating fractures from multiple, evenly spaced clusters when there is no perforation friction. The inner fractures are substantially shorter, reproducing the results by Bunger and Peirce [3]. The inner fractures also have substantially smaller widths.One approach to equalize the growth of simultaneously propagating fractures from a horizontal wellbore is by using limited-entry perforating as a method to equilibrate the flow rates into each of the different perforation clusters. Perforation friction is caused by the finite diameter of the entry points into the formation, and leads to a pressure drop across each perforation which is proportional to the flow rate squared. Fractures that take more fluid have a higher fluid velocity through the perforations than fractures receiving less fluid. This causes a larger pressure drop between the wellbore and more rapidly growing fractures, compared to the same pressure drop between the wellbore and the fractures that grow more slowly. Because pressure within the wellbore is approximately the same at each entry point, the larger pressure drop leads to less pressure being delivered to rapidly growing fractures, thereby decreasing their ability to propagate and reducing the amount of fluid they are able to receive. Because the mass rate of injection into the wellbore is constant, this forces more fluid into the fractures that were propagating more slowly, increasing their growth rate. It also increases the pressure required to drive fluid injection. The balance of these effects makes the system largely self-regulating and delivers more balanced fracture growth. While this effect is well known, it is often neglected in current numerical models."

Jan 1, 2015

By M. J. Makhula, R. M. S. Falcon, S. O. Bada, L. M. Falcon

"SynopsisThe combustion and co-combustion behaviour of macadamia nut shell, high-ash coal, and anthracite, along with their blends was studied using thermogravimetry. The reactivities of all samples were analysed in air, oxygen, and CO2 atmospheres and at different heating rates from 10 to 40°C/min. Macadamia shell was found to have a lower ash content, 0.36%, than coal with 27.49% ash. The calorific values were similar, 19.64 MJ/kg and 19.44 MJ/kg respectively. The differential thermogravimetric results indicate that as the heating rates increase the ignition, peak, and burnout temperatures increase significantly, leading to high combustion rates. The interaction between the fuels was evaluated using the weighted average model, and the results indicated that there is more synergetic interaction between 20% macadamia plus 80% coal under oxygen than in air and CO2 atmospheres. The results of the investigation provide the combustion and co-combustion characteristics of various samples and their blends and indicate their combustion compatibilities. IntroductionThe global macadamia nut industry is developing at a very rapid rate. South Africa is currently the world’s third largest producer, with a production of about 35 000 t as of 2012 (Department of Agriculture, Forestry and Fisheries, 2013), compared to 840 t produced in 1996. The greatest numbers of the macadamia nut farms in South Africa can be found in Mpumalanga, Limpopo, and KwaZulu-Natal provinces, with Mpumalanga as the largest producing area. There are many factors influencing the increased demand for macadamia nuts, the most important factor perhaps being their nutritional value (California Dried Fruit and Nuts, 2011; MPC, 2014) and their suitability as a feedstock for manufacturing cosmetics, bakery products, nut paste, chocolates, sauces, and ice-cream. As a fuel, macadamia shell has a high heating value ‘as-fired’ of about 20.71 MJ/kg (Vhathvarothai et al., 2013), which could in turn be used in drying the nust, and the shell could also be milled and applied as a fertilizer."

Jan 1, 2015

By Luis Rudolphy, Pekka Tähkiö

"Flotation plant design, construction and start-up can be challenging tasks, because multiple factors and disciplines have to be combined in an efficient manner, in order to execute a project that meets the technical, financial and timeframe expectations. Key considerations that need to be addressed when designing a flotation plant are process requirements, equipment integrability, automation, and up- and downstream processes/designs. Furthermore, several other lifecycle factors need to be considered, such as servicing and maintainability, operational costs, future expansions and decommissioning, among others. To address these challenges, Outotec has developed a new approach to designing flotation plants that targets eliminating most of the inherent risks that can be found in these types of projects. The new Outotec® plant is a fully modular approach in which the above-mentioned challenges have been taken into consideration in the design phase. As a result, the cPlant concept can give several benefits for new and experienced companies involved in the minerals processing business, such as lower risk investments, fast and cost-efficient flotation plant delivery, faster ramp-up period, easy plant expansions, fully automated processes and operation and maintenance ease. As well, dismantling and transportation of the cPlant to a new location is easy and fast, hence the new cPlant concept makes possible to exploit small, short-lifespan ore deposits and also retreat old tailings ponds that might contain valuable minerals and where the ore quantities are limited. Furthermore, cPlant is easily implemented for brownfields and temporary expansions during bigger expansions."

Jan 1, 2015

By V. S. Gischig, G. Preisig

Hydraulic stimulation of deep reservoirs is an essential procedure for developing engineered/enhanced geothermal systems (EGS), but also in other Geo-energy contexts. The goal is enhancing permeability to such a degree that fluid flow rates within the reservoir are sufficiently high for an economically productive reservoir. Two fracture stimulation mechanisms are distinguished that may occur concurrently during the hydraulic treatment: 1) During hydro-fracturing (HF) new tensile fractures are propagated from the borehole by means of a fluid pressure overcoming the minimal principle stress d3 plus the tensile strength T0 of intact rock. In case of a pre-existing fracture oriented normal to d 3 , the fracture can be opened by exceeding d 3 only. Fluid injection is performed via small packed intervals for creating a stack of hydraulic fractures. 2) During hydro-shearing (HS), over-pressure induces slip along pre-existing fractures that are favourably oriented in the stress field for reactivation in shear. Such stimulation is usually performed in a large packed interval or in an open borehole. Which mechanism occurs predominantly during stimulation depends on the rock mass structure and in-situ stress field, but also on the orientation of discontinuities intersecting the open-hole section and thus being pressurized. Both mechanisms also differ in how they affect fracture permeability. While permeability gained by HS is mostly irreversible due to rearrangement of asperity contacts accompanied with shear dilation, permeability enhanced during HF reduces nearly reversible after pressurization unless proppant is used to ensure permanent apertures. In this contribution, we critically discuss the pros and cons of both mechanisms regarding efficiency of enhancing permeability and the associated hazard of induced earthquakes based on literature review and numerical modelling. We review literature that reports on how much permeability required for productive EGS reservoirs and how much permanent permeability can be gained by stimulation. We also compile information regarding the degree of seismicity induced during HFor HS-dominated stimulation procedures, together with conceptual studies that reveal characteristics of seismicity associated with the two mechanisms. Many observations and models indicate that HF may have a higher tendency of being aseismic, while felt seismic events are usually associated with HS. Further, we present a hydro-mechanically coupled fracture flow model that investigates, if and to what degree the stimulation strategy can be designed such that one of the two mechanisms is evoked and dominates over the other. It shows that HS may dominate in presence of larger persistent fractures nearly optimallyoriented in the stress field, even if HF is attempted in short packed intervals. The model further demonstrates that stress transfer during HS promotes the development of permeability across an anisotropic layer of the stimulated rock instead of a large volume. Hence, the study sheds light onto the feasibility of creating productive EGS reservoirs in crystalline rock at several kilometres depths.

Jan 1, 2015

By Andrea Lisjak Bradley

Clay shales are currently being assessed as possible host rock formations for the deep geological disposal of radioactive waste. However, one main concern is that the favourable long-term isolation properties of the intact rock mass could be negatively affected by the formation of an excavation damaged zone (EDZ) around the underground openings. The goal of this thesis was to develop and validate a mechanically-based model of the deformation and failure process of a clay shale, namely Opalinus Clay (OPA), with particular focus on the influence of anisotropy on the short-term response of circular tunnels. To achieve this goal, a hybrid continuum-discontinuum numerical approach was developed in combination with new field measurements from the Mont Terri underground research laboratory. The response of OPA during the excavation of a full-scale emplacement (FE) test tunnel was characterized by geodetic monitoring of wall displacements, radial extensometers and longitudinal inclinometers. The deformation measurements indicated strong directionality induced by the combined effect of in-situ stress field and bedding planes striking parallel to the tunnel axis, with the most severe deformation occurring in the direction approximately perpendicular to the material layering. Computer simulations were conducted using a newly-extended combined finite-discrete element method (FEM/DEM), a numerical technique which allows the explicit simulation of brittle fracturing and associated seismicity. The numerical experimentation firstly focused on the laboratory-scale analysis of failure processes (e.g., acoustic activity) in brittle rocks, and on the role of strength and modulus anisotropy in the failure behaviour of OPA in tension and compression. The fracturing behaviour of unsupported circular excavations in laminated rock masses was then analyzed under different in-situ stress conditions. Lastly, the proposed modelling methodology was applied to the aforementioned FE tunnel to obtain unique insights into the EDZ formation process around emplacement tunnels for nuclear waste. The calibrated numerical model suggested delamination along bedding planes and subsequent extensional fracturing as key mechanisms of the damage process potentially leading to buckling and spalling phenomena. Overall, the research findings are already having a direct impact on the preliminary design process of an underground repository for nuclear waste in Switzerland.

Jan 1, 2015

By R. E. Vivas, J. Garcia

"INTRODUCTION Freeport-McMoRan is a leading international natural resources company that operates large, long-lived, geographically diverse assets with significant proven and probable reserves of copper, gold, molybdenum, cobalt, oil and natural gas. Freeport-McMoRan is the world’s largest publicly traded copper producer and largest producer of molybdenum. The Sierrita mine is an open pit truck and shovel operation from which copper and molybdenum are produced. An important key to Sierrita’s success lies in their ability to realize their plans in the field. In certain circumstances, the mine plans are not achieved, and the operation fails to meet its targets which is an issue revealed in reconciliation reports. This technical session discusses the methodologies and procedures used at Sierrita to monitor the implementation of the mine plans, measure the performance of the operation and reduce the variance between plan and actual. Ensuring the operation stays on target is vital so mine productivity and profitability can attain its maximum potential. PROJECT OVERVIEW The Sierrita mining complex is located in Pima County, approximately 20 miles southwest of Tucson, Arizona as shown in Figure 1. The first mining claims at Sierrita date back to the late 1800s while underground mining activities started in the early 1900s. However, open pit development of Sierrita began more than 50 years ago to become the modern mining complex it is today. In 2009, Freeport-McMoRan purchased the adjacent Twin Buttes copper mine, providing significant synergies in the Sierrita minerals district. This venture included the potential for expanded mining activities, operations growth for mining copper and molybdenum, and reclamation activity. It should be noted that in addition to copper and molybdenum, the Sierrita mine produces rhenium which is a rare and highly value metal. The ore deposit contains oxide and sulfide mineralization. The oxide ore is delivered to the leach process while the sulfide ore is routed to the crusher and mill circuit 4,700 jobs on Arizona’s economy Freeport-McMoRan partners with the communities near Sierrita to provide programs that contribute to their sustainability"

Jan 1, 2015

By O. Leuangthong, M. Nowak

"The impact of high-grade data on resource estimation has been a longstanding topic of interest in the mining industry. Concerns related to possible over-estimation of resources in such cases have led many investigators to develop possible solutions to limit the influence of highgrade data. It is interesting to note that the risk associated with including high-grade data in estimation appears to be one of the most broadly appreciated concepts understood by the general public, and not only professionals in the resource modelling sector. Many consider grade capping or cutting as the primary approach to dealing with high-grade data; however, other methods and potentially better solutions have been proposed for different stages throughout the resource modelling workflow.This paper reviews the various methods that geomodellers have used to mitigate the impact of high-grade data on resource estimation. In particular, the methods are organized into three categories depending on the stage of the estimation workflow when they may be invoked: (1) domain determination; (2) grade capping; and (3) estimation methods and implementation. It will be emphasized in this paper that any treatment of high-grade data should not lead to undue lowering of the estimated grades, and that limiting the influence of high grades by grade capping should be considered as a last resort. A much better approach is related to domain design or invoking a proper estimation methodology. An example data-set from a gold deposit in Ontario, Canada is used to illustrate the impact of controlling high-grade data in each phase of a study. We note that the case study is by no means comprehensive; it is used to illustrate the place of each method and the manner in which it is possible to mitigate the impact of high-grade data at various stages in resource estimation."

Jan 1, 2015

By Panagiotis (Takis) Katsabanis, Lyall Workman, Jack Eloranta

The reduction of metallic ores to concentrate consumes a great deal of electrical energy. In the past two decades, a number of case studies have demonstrated a beneficial relationship between powder factor and grindability. However, changes in mill performance cannot be attributed to changes in feed size alone. Blasting energy and the distribution of that energy appears to affect subsequent comminution beyond crushing. This experience has prompted researchers to attempt to duplicate and quantify the mechanisms involved. To date, published reports indicate a measure of success. However, the blast engineer and the mill engineer still lack the tools and basic understanding necessary for full drill to mill optimization.

Jan 1, 2015

By S. Perez

Core drilling is a fundamental process in the mineral exploration industry. As deep exploration in hard rocks is accelerated due to the depletion of near ground mineral resources, deep-drilling operations need to reduce their reliance in operators experience and begin to implement new technologies in order to increase efficiency and cost-effectiveness of the overall process. Currently, lack of real-time information on the bit/rock interaction is a major problem. Therefore the mechanism behind the acoustic emission, which is a proven technique for remote monitoring, generation in mechanical rock cutting must be understood in order to provide real time information about the rock. This paper aims to identify the influence of mineral composition of granitic rocks on the acoustic emission (AE) during rock abrasivity test with a single contact tool and to evaluate the feasibility of AE as a means to infer Cerchar Abrasivity Index (CAI). Single contact tool will provide precise and accurate description of the source of AE. To provide constant grooving speed Cerchar apparatus was modified to monitor AE during rock/tool interaction. Tests on the modified Cerchar apparatus are carried out under the static load of 70N and cutting speed of 1 mm/s. A Scanning Electron Microscope (SEM) is utilized to visualize the groove in the rock and to identify the mineral composition through Back-Scattered Electrons (BSE) reflected from the rock sample. Based on the microscope images, it was found that biotite shows a larger groove area and plate-like fractures accompanied with burst-type AE signal, whereas plagioclase and quartz, which are characterized by similar hardness and BSE brightness, possess shattered-like fractures and more continuous-type AE signals. In addition, a-value of the Gutenberg-Richter scale has been found to well correlate with Cerchar Abrasivity Index (CAI).

Jan 1, 2015

By Peter Cali, David Yang, Rakshya Shrestha, Ralph Griffin, Sushil Kafle, Motoji Watanabe

"As a part of the ‘US Army Corps of Engineers - New Orleans to Venice, Louisiana Hurricane Protection Project’, deep mixing ground improvement was designed to reinforce the soft ground for the emergency repair of a 7297-foot (2,224 m) long section of the Mississippi River West Bank levee in Buras Levee District under the contract ‘Emergency Levee Repairs – Contract P-17A, Plaquemines Parish, Louisiana’. The ground improvement utilizes a series of soil-cement panels oriented in the transverse direction of the levee. Each soil-cement panel consists of overlapped columns installed by the deep mixing method (DMM). DMM is performed from the existing top of levee and extended to competent stratum at depths varying from 26 feet (7.9 m) to 47 feet (14.3 m) below the working platform. The main purpose of the DMM panels is to provide shear resistance to the levee against lateral loads at high flood water condition. The DMM panels support the additional vertical load created by the increased height of the levee for hurricane protection and control the long-term settlement of the remediated levee, which might otherwise occur due to the compression of soft foundation soils. The total amount of DMM treatment is approximately 54,000 cubic yards (41,500 cubic meters). This paper reviews the project background, subsurface soil conditions and presents the design, construction and quality control of the deep mixing work for this levee repair project.INTRODUCTIONIn August 2005, Hurricane Katrina caused major damage to the federal and non-federal flood control projects in southeast Louisiana. In September 2005, Hurricane Rita caused further damage to this flood protection system. In an effort to minimize further damage and to enhance the protection level, certain non-federal levees located on the west bank of the Mississippi river in Plaquemines Parish, Louisiana were incorporated into the New Orleans to Venice Hurricane Protection project by the US Army Corps of Engineers (USACE). DMM techniques were then utilized by the USACE in several of these emergency projects and in many medium sized projects between 2006 and 2010 (Bruce et al. 2012). This project (called P-17A hereafter) which forms a part of this protection system is executed under the contract Emergency Levee Repairs, Contract P-17A. This is one of the largest projects of the USACE after LPV- 111. The huge LPV-111 project (5.5 miles (8.9 km) of levee) treated by DMM), the largest DMM project ever conducted outside Japan, began in 2010 and was completed in 2012 (Cali et al. 2012, Bruce et al. 2012).DMM is utilized at P-17A to construct a series of soil-cement panels oriented in the transverse direction of the existing levee to provide shear resistance to the levee against the lateral load during high flood water condition. The project extends 7297-foot (2,224 m) along the West Bank Levee of the Mississippi River in the Buras district of Louisiana, parallel to Louisiana Highway 23 (LA-23) as shown in Figure 1. It is located approximately 60 miles (96 km) south-east of downtown New Orleans."

Jan 1, 2015

By Bob Drew, Goran Vukovic, Bojan Zivanovic, Klaus Gamweger

Reaction bath temperature is a major factor in processing liquid metals and in many applications where a balance between process duration and temperature has to be found to run a procedure efficiently. Also extremes of temperature can decrease the output of a process if too cold or even make it impossible, conversely overheating can be detrimental to both the product and furnace integrity. With the help of the new online temperature measurement system very accurate monitoring of the process is possible in contrast to the current routine practice where the temperature is measured periodically with dip thermocouples. The system works with a digital, fiber optic pyrometer, which is embedded in a refractory housing. Installation in the lining is possible below liquid level as nitrogen is blown to keep the system open and to ensure continuous sight from the optical head of the pyrometer to the molten metal through the tuyere. This permanent temperature measurement gives optimal process control with the potential of taking appropriate actions at an early stage enabling proactive process control. Therefore energy savings and even process endpoint detections can be realized.

Jan 1, 2015

By Michael Gauna, Christopher Mark

"Coal bursts involve the sudden, violent ejection of coal or rock into the mine workings. They are almost always accompanied by a loud noise, like an explosion, and ground vibration. Bursts are a particular hazard for miners because they typically occur without warning. Despite decades of research, the sources and mechanics of these events are not well understood, and therefore they are difficult to predict and control. Experience has shown, however, that certain geologic and mining factors are associated with an increased likelihood of a coal burst. A coal burst risk assessment consists of evaluating the degree to which these risk factors are present, and then identifying appropriate control measures to mitigate the hazard. This paper summarizes the U.S. and international experience with coal bursts, and describes the known risk factors in detail. It includes a framework that can be used to guide the risk assessment process.BACKGROUNDCoal bursts involve the sudden, violent ejection of coal or rock into the mine workings. They are almost always accompanied by a loud noise, like an explosion, and ground vibration. Bursts are a particular hazard for miners because they typically occur without warning. During the years 2012-2014, serious coal bursts occurred at three different U.S. room and pillar mines. These events resulted in three fatalities and two permanently disabling injuries (MSHA, 2014; MSHA, 2013). In all three instances, the events occurred during pillar recovery at depths exceeding 1,000 feet (300 m). None of these three mines had previously reported a burst to MSHA. Coal bursts also occurred at three longwall mines during this same time period.Despite decades of research, the sources and mechanics of bursts are not well understood, and therefore these events are difficult to predict and control. Experience has shown, however, that certain risk factors are associated with an increased likelihood of a coal burst. A coal burst risk assessment consists of evaluating the degree to which these risk factors are present. In addition, some control techniques are effective in reducing the likelihood of an event or protecting miners from their effects."

Jan 1, 2015

By B. Barry, M. S. Klima

"Testing was conducted to evaluate the effects of hydroacoustic cavitation (HAC) treatment on two bituminous coal slurries and the subsequent separation of each slurry in a classifying hydrocyclone. HAC treatment was performed using a pilot-scale circuit fabricated by Furness-Newburge Inc. The circuit was designed to induce cavitation by means of flow through an ultrasonic resonator chamber or enhanced cavitation by initial flow through a cavitation chamber followed by flow through the ultrasonic chamber. The test materials were nominal -1,500-micron and -150-micron Illinois-basin bituminous coal slurries, which were obtained from an operating coal preparation facility. After 5 sec of HAC treatment, the median size of the -1,500-micron material was reduced, with ash values for certain size fractions decreasing more than 5 percent compared with untreated samples. Extending treatment time led to greater degradation of the +1,180-micron material and an increase in the -25-micron material, with ash reductions occurring for material in the -850+150-micron size range. Size degradation was less for the -150-micron material. Subsequent separation of the treated slurries was carried out in a hydrocyclone with diameter of 102 mm. HAC treatment led to a decrease in the ash value and an increase in the heating value of the underflow stream compared with the feed material. For example, the ash value was reduced by about 16 percent for the -1,500-micron material and 25 percent for the -150-micron material with heating value increases of 7 and 33 percent, respectively, after HAC treatment. Overall, HAC treatment appeared to have a slight effect on the size selectivity curves.IntroductionUltrasound in the range of 20 to 1,000 kHz, referred to as power ultrasound, consists of high energy waves that can create zones of compression and expansion when used to irradiate liquids (Frederick, 1965; Leighton, 1994; Mason and Lorimer, 1988). This action generates varying pressure regions leading to cavitation or the formation, growth and near-immediate collapse of microscopic voids or bubbles (Frederick 1965; Leighton 1994; Mason and Lorimer 1988). Collapse occurs when the bubble reaches critical size and cannot absorb additional sound field energy, and the critical size is governed by the ultrasound frequency (Shchukin et al., 2011)."

Jan 1, 2015

By Q. Li, X. -L. Lei

Accompanying global energy shortage and high energy prices, shale gas has been the focus of exploration and it has attracted great attention from both academia and industry. The combination of horizontal drilling and hydraulic fracturing enables the extraction of huge quantities of shale gas from impermeable shale formations. During the process of hydraulic fracturing, great amounts of water, sand and chemicals must be injected into the shale formation at a high pressure, which may trigger seismicity. Such events could occur due to the presence of faults or the reactivation of these potential faults. Shale is the main component of source rock in the Sichuan Basin, China, and has the greatest contribution to the natural gas of the basin. In order to investigate the fracturing mechanism of shale in the Sichuan Basin, China, a series of rock fracture tests under triaxial compression were carried out in the laboratory in order to investigate the hydraulic fracturing behavior in relation to the seismicity. Based on the high multichannel waveform recording system, the detailed spatio-temporal distribution of acoustic emission due to micro-cracking was used to examine the deformation and fracture behavior of shale. In addition, the effects of confining pressure on the deformation and fracture in shale under triaxial compression by acoustic emission monitoring and X-ray computed tomography were discussed in the paper. The experimental results indicate that the shale samples demonstrate brittle fracture behavior. The confining pressure has a great effect on the complexity of the fracture planes and the spatial distribution of acoustic emissions, but few contributions to the location of the major hydraulic fracturing plane. The foliation of shale plays a dominant role in the rupture process and the geometry of the major hydraulic fracturing plane. The high confining pressure increases the strength and restrains the deformation of shale during compression process. These results shed some light on the understanding of onset of hydraulic fracture initiation not only for shale gas exploration and production, but also for CO2 geological storage and underground energy storage.

Jan 1, 2015

By Jhon J. Silva Castro

Blast vibration records used in mining contain unwanted information in the form of noise due to long-period drifts, background noise, and noise due to the conversion of the analogue signal to a digital signal. When recorded signals from blasting are used to find other physical variables, such as going from particle velocity to acceleration or displacement, the additional information in the vibration signal can result in inaccuracies in the estimation of the peak values and more dramatically, the results in displacement or acceleration can be nonzero near the end of the record. There are different proposed methods to clean or filter the unwanted information from the signal. All of the methods are based on finding the best fit of the record average value (baseline) and then subtracting from the record under analysis to produce the desirable adjustment. Different criteria and functions are used to define the best fit. The function to use will depend on the shape of the record average values. The main characteristic of the baseline function is that it represents a low frequency wave. Such a low frequency wave can be a periodic function or a polynomial expression of nth order. According to the order of the polynomial expression, the baseline correction can be linear, parabolic or high order. In this document the detailed procedure and the results for the baseline correction of a blast vibration record using a periodic function and a polynomial expression of different order is presented. The results show that the drift problem when displacement is calculate using velocity records increases with the increase of the distance from the blast.

Jan 1, 2015

By R. Simon, A. Khosravi

"Tensile strength of rock samples is measured by direct and indirect tensile tests in accordance with standard guidelines. Due to the difficulties in performing direct tensile test, the indirect tensile (Brazilian) test is conventionally carried out to obtain the ultimate tensile strength. A limited number of studies have been conducted to investigate the role of sample size (length to diameter ratio = L/D) in the stress distribution of the Brazilian test using numerical and analytical methods. These investigations showed that the tensile stress distribution along the loading diameter is not uniform. They also indicated that the difference between the tensile stress at the middle part and at the sides of the sample with higher L/D ratio is greater than that in the other samples.The objective of this study is to show the effect of tensile stress distribution on the fracture surface created by the Brazilian test from a morphological point of view on the samples with different L/D ratio. Hence, a series of fracture surfaces created using the Brazilian tests on the rock samples with L/D of 0.5, 0.75, 1, 1.25 and 1.5 were investigated.In this study, all fracture surfaces were scanned by a 3D laser profilommeter. A number of roughness profiles parallel and perpendicular to loading axis have been selected from the samples with different L/D ratio and spacing of 1 mm. The results show that the roughness of the profiles perpendicular to the loading axis increases with an increase of L/D ratio, while the roughness of the profiles parallel to the loading axis decreases. Furthermore, some roughness profiles parallel to the loading axis were chosen and divided into three segments. The results revealed that the segment in adjacent to the upper loading platen possesses higher roughness than the other segments."

Jan 1, 2015

By K. K. Panthi, P. K. Shrestha

"Displacement of rock mass around a tunnel opening varies according to the rock mass properties, insitu stress conditions and applied support in the tunnel. Such displacement is also altered by presence of bands of rock mass that differ in properties. This paper focuses on the deformation behavior of rock mass around tunnel openings at four tunnel sections in Kaligandaki headrace tunnel where extensive instrumentation was done. Based on the actually measured tunnel displacement records and actually measured support pressure; back analysis has been done to estimate rock mass properties and insitu stresses. Numerical analysis has been done to analyze and assess the deformation behavior of the rock mass around the tunnel sections.INTRODUCTION Instrumentation and monitoring of tunnel convergences have significant importance in evaluation of tunnel stability. One of the key aspects of monitored data is that early convergences can be used in estimation of long term convergence. In addition, these data can also be used in evaluation of rock mass parameters and in-situ stresses around the tunnel. Convergence around a tunnel periphery may vary according to rock mass quality. Presence of bands of different rock mass may hinder the displacement pattern in the tunnel. Particularly, displacement characteristic of tunnel periphery in schistose, foliated and deformed rock mass is altered by presence of bands of comparatively stronger rock mass, e.g., quartz veins or presence of shear seams or faults. Similar observations were also recorded in monitored tunnel sections in Kaligandaki headrace tunnel, located in the Nepal Himalayas. Extensive monitoring was done by installing multiple point borehole extensometers (MPBX) at three different locations of the tunnel periphery at four different tunnel sections. In addition, convergence measurements by tape extensometers and installation of pressure cells to record support pressures were also carried out at each of the tunnel sections. Observations showed that the tunnel convergences varied according to rock mass quality, in-situ stress and effective support pressure.Rock mass parameters and stresses have significant role in the extent of tunnel deformation, but these parameters are often unknown or difficult to predict. Back analysis based on actual tunnel displacement records and known support pressure is believed to be an important method in such endeavor. This paper performs back analysis to evaluate rock mass parameters and discusses correlation of rock mass behavior with tunnel deformation and applied support. For this purpose, the rock mass parameters are estimated from actual tunnel displacement records, mapped rock mass quality records and laboratory tested data. Then, numerical modelling is conducted to correlate post peak behavior of the rock mass with actual tunnel displacement."

Jan 1, 2015

By Stefan Larsson, Sadek Baker, Razvan Ignat

"This paper describes the execution of two full-scale field tests where a braced steel sheet pile wall interacting with rows of overlapping dry deep mixing columns was first excavated and then loaded to failure. The aim of the tests is to provide insight of the performance of dry deep mixing column rows located in passive zone and interacting with a retaining structure. The column rows were installed perpendicular to the sheet pile walls with two different area ratios, i.e. different distanced between the column rows. Both tests were extensively instrumented with inclinometers, pore pressure transducers, bellow-hoses, earth pressure gauges and strain gauges mounted on the struts. Results of the performedtests will serve as development of design methods for excavation support with columns.INTRODUCTIONDry deep mixing has been used with good results to strengthen the soil when excavations are to be performed in locations with thick soft clay deposits. An application that has increased in recent years is to install columns on the passive side of the retaining structure. Columns can be installed in different patterns but rows, grids or blocks are the most common arrangement. The use of column type ground improvement installed on the passive side of a retaining structure has been documented for a few field cases, Tanaka (1993), O’Rourke et al. (1997b), O’Rourke and McGinn (2006), Ou et al. (2008). By improving the soil on the passive zone, the passive earth pressure in front of the retaining structure is increased. This has proven to reduce the excavation induced deflections behind the retaining structure, reduce the structural forces (bending moment in the retaining structure, strut and anchor forces) and improve the safety against basal heave failure. The main focus of the conducted measurements within these cases has been on recording deflections and structural forces on the retaining structure and there is very little documentation available of the stress-strain behavior of the improved soil acting on the passive side of the retaining structure.Two full-scale tests of braced steel sheet pile walls interacting with rows of overlapping dry deep mixing columns were first excavated and then loaded to failure was conducted during the spring-summer of 2014. This paper briefly describes the test set up, instrumentation, test procedure and some selected results from one of the conducted tests."

Jan 1, 2015