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By Harold L. Lovell

Problems associated with fines (minus 6 mm, 1/4-inch) production, preparation, and utilization have long plagued the coal industry and are now more acute than ever. Continuous deep mining systems create more fines which have moisture; content greater than natural levels from dust control spraying and often add substantial levels of mineral matter due to mining selectivity constraints. Frequently, during preparation, more -fines are developed to achieve improved component liberation. Coal consumers often specify small sizes whether for carbonization, combustion, or conversion. Wet beneficiation systems process fines by several' types of unit operations, but usually must also incorporate costly and complex dewatering systems to reduce the moisture content of the products. Existing pneumatic preparation systems are constrained between product equality and yield by the sharpness of separation. These limitations become more severe with decreasing particle size and increasing feed moisture content. Control of particulate emissions, both process and fugitive, during pneumatic preparation, can be forbidding. A pneumatic preparation-process which would overcome these constraints, could be most enticing. The DryFlo system is being evaluated to quantify performance characteristics as regards these constraints.

Jan 1, 1976

By Anthony Edey

It is a generally accepted and widely discussed fact that the world in general, and the United States in particular, face a shortage of energy at the present time which will become worse in the future. There is, however, no sign of a similar concensus as to the actions which would prevent or overcome this expected shortage. An immense variety of solutions has, however, been put forward, ranging from the purely political to the outer fringes of sophisticated technology. One resource which surprisingly is often only cursorily included in this discussion is the immense known petroleum reserve lying within the United States. When this subject is discussed, indeed, it is usually in the context of the improvements in production or new discovery rate that could be expected to result from possible politico-economic actions that would raise the real price obtained for domestic crude. This interest in the potential for improved domestic production is undoubtedly justified, but very little attention is normally drawn to the fact that even under the most favorable policy framework the majority of the oil that has been, or will be, discovered will remain in the ground due to the inherent limitations of production through surface wells.

Jan 1, 1979

By G. P. Hand

The purpose of this paper is to bring to your attention the various kinds of high performance graphites available today, their characteristics and possible applications. These materials are products of a proprietary high temperature technology developed by Superior Graphite Company. We feel we have only begun to tap the potential of this technology and the utilization of the resulting products. During the course of the paper, we shall investigate high purity, high performance graphites made from raw materials such as mined natural graphites, synthetic graphites and petroleum derivatives. We shall define their characteristics and resulting benefits to current applications, along with applications currently under development. It is our desire to stimulate speculation and development of current high performance graphites and their applications as well as ideas for new high performance products and applications. First, a little background about the process. The technology was developed through a concentrated R&D effort which culminated in 1976 in the construction of a unique furnace capable of continuously processing tonnage quantities of granular carbons at temperatures in excess of 2,500 degrees C. This process is capable of refining various carbonaceous raw materials, including natural graphites, to levels of purity and consistency that were previously unattainable in commercial quantities. Carbon contents in excess of 99.9% are currently being produced on a continuous flow-through basis. Since beginning operation in 1977, this plant, located in Hopkinsville, KY, has been expanded in stages to its present capacity of producing over 45,000 tons of purified graphites and graphitic carbons per year. In addition to the purification process, the technology used allows the introduction of selected elements into the carbon/graphite structure to provide additional benefits. Elements of interest include boron, silicon, copper, iron and rare earths. The characteristics of and applications for some of these products will be discussed later.

Jan 1, 1990

By G. C. Tipper, A. P. Deane, A. G. Myers

SCHEME DESIGN London’s Heathrow Airport, as the world’s busiest international airport, is missing one vital aspect - a dedicated rail link which connects directly to the city. All this is about to change with the construction of Heathrow Express - a fast, high quality rail service between the airport and the centre of London. It was recognised in the mid 1980s that if Heathrow was to accommodate the forecast growth in passenger numbers and the resulting increase in road traffic, a dedicated airport rail service would be vital. The main access into the centre of Heathrow is via a road tunnel with a direct link to the M4 motorway. The airport has introduced a number of traffic management schemes, but these can only achieve so much benefit. Growth in air passenger traffic is predicted to continue at an average of 4% per annum well into the next century and it was clear that significant investment was needed. Heathrow Express at a cost of over £350 million will provide this when it starts its service in June 1998. The business case for the scheme is based on a rider ship of around 15% of air passenger traffic. The initial Heathrow Express service will be based on four trains per hour, up to 8 car train lengths, providing a high speed non-stop service between the airport and central London in just 16 minutes. Initially a joint venture between the British Railways Board and Heathrow Airport, by mutual consent of the two parties, Heathrow Airport recently purchased the British Railways Board share making this one of the largest private sector rail projects currently under construction in the UK. Leaving Paddington, the main rail terminus in West London, Heathrow Express trains will travel 12 miles on the newly electrified line to airport junction, north of the airport. At this point they will leave the mainline to enter a 5 mile tunnel section that runs underneath the heart of the airport. The railway companies are responsible for track work, signalling and electrification of the 12 mile main line section including a grade separated junction over the main tracks for the Great Western Railway which links London and South Wales. Heathrow Airport is re-

Jan 1, 1997

By V. de Ruiter

In the northwestern part of the Netherlands lies the deepest solution salt mine in the world. The company operating the mine is Frisia Zout bv (part of the K+S group). Extracting the NaCl from caverns at a depth of nearly 3000 m has a lot of challenges. Continuously monitoring, among others, the flows, pressures and salt concentrations is necessary to safely and economically mine the salt. A system has been set up at Frisia to be able to monitor the data from a distance. Data has been put in graphs to monitor the trends daily. All gauges are also continuously monitored to maintain accuracy. With this system a better understanding of the mining process has been made and has led to many optimizations.

Jan 1, 2008

By Robert Hochscheid

When the original water-only cyclone patents were established in the 1950?s, the supplies of low cost oil and natural gas were abundant and low selling prices for metallurgical and steam coal provided little incentive for developing more sophisticated coal cleaning systems. Bituminous coal sold for less than $5.00 per ton, and in this period many domestic coal producers discarded to the slurry pond the coal finer than 0.5-mm. For many producers, the selling price would not permit the recovery of the capital and operating costs required for dewatering and drying the fine coal. Water-only Cyclones Clean Fine Metallurgical Coal The first broad interest in the water-only cyclone became evident in the mid- 19601s, and though some work was done on coarser coals, investigators were particularly interested in cleaning coal finer than 0.5-mm. Flotation was the only fine coal cleaning method that was broadly accepted, but short-comings were recognized and investigators were looking for an effective fine coal cleaning device or system. Because of the greater market value and the need for reducing pyritic sulfur in metallurgical coals, much of the development work of the 1960's was done on coking coals.

Jan 1, 1981

By Harold V. Fairbanks

This investigation included a study of three different methods for the acoustic drying of ultrafine coals. Ultrafine coal being defined as coal which passes through a 100 mesh sieve. The first method employed stationary drying of small coal samples in sound fields having frequencies of 12,000 cps and 20,000 cps. Sound intensities up to 150 db were used. The second method employed the use of rotary drying kilns. The effect of such variables as temperature, sound intensity, coal feed rate, air flow rate, and initial moisture content were studied. The third method employed the use of a multi-tiered, vibrating screen dryer. The effect of initial moisture content and residence time were studied.

Jan 1, 1970

By Terry Owen

Business development process. Throughout Cyprus Amax's early months in Russia, the company stayed focused on what was needed from a deposit for economic success. Cyprus Amax's reason for success in Russia is that all involved - its Russian partners, the workforce and expatriates - provided a focused effort that served the project as it worked through the tender process and the Russian regulations. The company developed an understanding of the regulatory process by working with solid, ethical partners. Infused into the Kubaka management structure were Russians with the knowledge to facilitate the process and a professional group of expatriates. Developing credibility and a solid rapport with the Russian mining authority was critical to the success of this venture. Identifying and gaining the trust of key Russian individuals was also critical during the early stages. Gaining their trust and building credibility was part of the process. These key Russians were brought to the United States to visit existing Cyprus Amax mines. These efforts proved valuable in building an understanding with the Russians about the kind of company Cyprus Amax is and the kind of efficient operations that it can run. This was a learning process for all parties. Fortunately, the company was dealing with intelligent and educated people.

Jan 1, 1997

By P. Zhang, W. D. Xiao

"A process mineralogy study was conducted to guide the development of a process for the extraction of vanadic oxide (V2O5) and aluminum compounds from bone coal and its ash as well as the production of byproducts. Results show that to extract the targeted metals at higher recovery rates, one must find a suitable agent capable of destroying the structure of the mica and breaking down the lattices in which these metal-bearing minerals occur. For such minerals, metal extraction efficiency is usually low if the approach is simply adding an oxidant that cannot destroy the structure. In this research, a byproduct fluosilicic acid (H2SiF6) at 20 percent concentration from an operating phosphate fertilizer plant was found to be powerful and effective for the leaching of vanadium-bearing minerals such as mica. This environmentally friendly process improved the leachability of valuable constituents in the bone coal significantly, with the leaching rate of V2O5 increased to 94 percent, from 83 percent, and that of aluminum oxide (Al2O3) increased to 75 percent, from 40 percent. X-ray diffraction and chemical analyses showed that the structure of mica can be destroyed using fluosilicic acid either alone or in combination with sulfuric acid. Based on the process mineralogy study, a processing flowsheet was tested, which resulted in a final V2O5 powder product with purity of 99.2 percent and an overall recovery rate of higher than 85 percent. The flowsheet consists of leaching, ion exchange and ammonium precipitation. With this process, various byproducts could also be generated, including aluminum fluoride, cryolite, aluminum sulfate, calcium sulfate, ammonium chloride, sodium chloride and cement admixtures.IntroductionVanadium is an important rare metal broadly used in the production of steel alloys and nonferrous alloys as well as in the chemical field as a catalyst. Vanadium-bearing bone coal and clays are abundant in China, and they contain other valuable metals such as aluminum. Bone coal is a type of carbonaceous shale. The vanadium-bearing minerals mainly exist in mica, kaolin, iron oxides, tourmaline and garnet. According to previous studies (Xiao, 2007; Xu, 1989; Xu and Chen, 1991; Ji and Xu, 1991; Chen and Xu, 1992; Xu and Heng, 1992), vanadium occurs from the isomorphous substitution of V3+ for Al3+ or Fe3 + in the crystal lattices of mica, tourmaline, garnet, dolomite and aluminosilicate minerals. In iron oxide and kaolin minerals, vanadium appears as an adsorption form. The isomorphous substitution of vanadium is more stable in tourmaline, garnet and silicate minerals. Therefore, vanadium in bone coal may exist in three phases: vanadium-containing kaolin and oxides, vanadium-containing mica, and tourmaline and garnet (Xu and Chen, 1993; Xu and Zhang, 1993; Xu and Wang, 1994; Feng, et al., 2005; Lin and Fan, 2001)."

Jan 1, 2015

By S. Dereski, G. Chancellor

"INTRODUCTION Barrick Goldstrike underground mine is located in Northern Nevada on the Carlin trend. The underground mine produces approximately 1.5 to 1.8 million tons a year and approximately 400,000 ounces of gold a year. The mine is comprised of two main mining methods, underhand drift and fill and long hole stopeing. The mass blast project stated in 2012 as Value in Use project between Barrick, Southwest Energy and Orica, the goal of this project is to be able to blast an entire drilled stope in one blasting event instead of taking multiple blasts. This will improve productivity by eliminating intermediate blasts, reducing additional blast time, eliminate drill hole cleaning due to the previous blast. Project implantation started in the fourth quarter of 2013 and mass blasting has been common practice throughout all of 2014. STOPPING PRACTICE AT GOLDSTRIKE BEFORE MASS BLAST PROJECT The production from the Goldstrike mine is approximately 70% from stopes. The timely completion of all stoping blocks is imperative to maintaining the plan, delays in the execution of any particular block can have detrimental ripple down effects as neighbouring stoping blocks become delayed. Before the implementation of this project the standard practice for Goldstrike was to: 1. Drill the entire stope 2. Blast a bottom shot, normally between 10 feet and 20 feet off the bottom of the slot rings. This would be mucked out before the next shot 3. Blast a pull through shot, this included the raise and one or two production rings. Again mucking this out before the next shot 4. Blast production rings, one or two more blasts depending on stope size. In most cases between each of these blasts the holes in the other rings of the stope would have to be cleaned. This meant either cleaning manually using air and water, or mechanically cleaning with a bench drill. In many cases this resulted in delays in completing the stoping block."

Jan 1, 2015

By S. B. Bhagwat

The United States has abundant coal resources that could last at least another century. and probably longer at present consumption rates. Geographically, the coal resources are distributed over the entire nation including Alaska, although there are no coal deposits in the highly populated areas on the two coasts. This allows free access to the coal, but makes transportation more expensive. Not all coals can be utilized equally because they differ vastly in quality. The sulfur content of coals, considered as the most detrimental acid rain-causing element, varies from as low as 0.3 percent in some areas of the western U.S. to 5 percent or more in parts of the Midwest. The chlorine content, which causes corrosion of plant hardware, also varies regionally. The 1990 amendments of the Clean Air Act of 1963 (CAA) require that emissions of sulfur be restricted and rolled back in two stages by the year 2000. There have been a number of reports expressing concern about the future of the industry in the states where high sulfur coal is produced. The remedies devised by the federal government and many coal-producing states in the past to "se-cure" the future of the regional coal industries have focused on the physical task of removing sulfur rather than the economic challenge of doing so at a cost that will enable high-sulfur coals to survive and compete. The past remedies, generally, were not specific enough to account for the characteristics of regional coal deposits and did not look at the coal market as an integrated national and international entity. The State of Illinois has, in recent years, taken a more comprehensive approach to the solution of the problem.

Jan 1, 1992

By Roger S. Dewey

1.1. INTRODUCTION Despite indications of a general economic recovery in the U.S. during the mid-19801s, mine operators have not generally shared in the benefits of these reported better times. Budgets have not rebounded, borrowing is tougher, parent companies' pockets are not as deep as in previous years, and margins are not any better -- if there is any left over at all. Managing capital equipment budgets is always a challenge, and the last five years of stretched equipment lives make these decisions more tenuous. Delays and avoidance of replacements due to tough times inevitably makes those decisions increasingly difficult and usually more expensive The purposes of this paper are to present. a brief refresher outline of the fundamentals of equipment replacement analysis, to suggest a number of papers where analysis methods are explained in greater detail. and to recommend the use of a widespread microcomputer software capability (1-2-3) as the easiest path to a much-needed solution for a very difficult, and usually under-supported management decision problem 2. REPLACEMENT DECISION POLICY Investments in equipment replacements must compete for capital with all other investment alternatives. Capital for replacements of ten represents a greater commitment than do the new projects which a company might handle in a given year. But. sadly, formal policies for standardized analysis of replacements rarely exist, even in major companies. Yet this policy can be very significant in determining the competitiveness of a firm. Whereas many replacement decisions are based on cost minimization, economists and financial analysts agree that wealth maximization or return on investment is the superior criterion. Though the difference may seem slight, agreement on a firm's financial objective is vital. Replacement policy should be straight- forward. have a logical basis, and a proper level of sophistication. There are several reasons to develop a policy for replacement decision-making: [I] 1 - equipment's optimal economic life is nearly always shorter than its physical life; 2 - mine life often exceeds equipment life, so management must face these decisions routinly 3 - replacement capital costs, on an undiscounted basis, can run 25 to 75% of original capital 4 - technological changes may result in a newer machine or system which can operate more efficiently, more safely. or less expensively 5 - estimates should be made consistently in the fundamental areas of life expectancy, availability, utilization. price escalation, taxes 6 - long-term and short-term budgeting without decent data and analytical capability is nearly impossible, or at least ineffective Policy development assumptions which must be considered include: the planning horizon, cost patterns, interest rates, availability of capital, replacement vs. expansion, technology advances.

Jan 1, 1987

By D. H. Horswill

The Red Dog Mine is the world’s largest zinc mine. It is located 145 km (90 miles) north of the Arctic Circle in northwest Alaska on lands owned by the Inupiat Eskimo organization called the Northwest Alaskan Native Association (NANA) Development Corp. NANA acquired surface and subsurface title to this resource as part of its settlement lands under the Alaska Native Claims Settlement Act. In 1982, NANA entered into a lease agreement with Cominco. Cominco is an international mining company focused on zinc. It built and operates the Red Dog Mine. NANA’s principle objective in the development of the mine was to have it contribute to the development of sustainable communities within their traditional region. This meant creating job opportunities in a modern economy while preserving the traditional subsistence lifestyles. Preservation of their culture, language and traditions are as important to the NANA people today as they were in the past.

Jan 1, 2000

By C. L. Wilsey, K. M. Oakes, W. J. Reich, M. J. Protani

The time frame required to complete the National Environmental Policy Act (NEPA) process for a new mine, or for the expansion of an existing mine, can range between 9 months to 24 months, or more. The time frame will vary depending on whether an Environmental Assessment (EA) or an Environmental Impact Statement (EIS) will be completed. Completing properly designed baseline studies to collect natural resource data to support the EA or EIS prior to the start of the NEPA process can shorten this time frame. The two year natural resource baseline study completed by Homestake Mining Company for the Ruby Hill Mine, located in Eureka County, Nevada will be used as the case study to describe how properly designed and executed natural resource baseline studies streamlined the NEPA process.

Jan 1, 2001

By Hugh Boyd

Jet pulverization is a relatively new tool for fine grinding. It is not yet in general use in the mining and ore dressing fields, since most of the requirements in these areas have been for relatively coarse particle sizes. As the need for finer grinding increases - because of different ores, new products, and new values being sought - jet pulverization will, increasingly, be properly used.

Jan 1, 1969

By Stéphane Servant, Jacques Ouellet, Ferri Hassani

This paper presents essentially the logistic and practical aspects involved for in situ testing of mine paste backfill with a self-boring pressuremeter. The investigation discussed in this paper is part of an extensive and ongoing research project to identify and validate an in situ testing technique for cemented mine backfill such as hydraulic or paste backfill as well as Insitu behavior of backfilled stopes. After a literature review on field testing of soils and past experiments on mine backfill in situ testing, the self-boring pressuremeter was selected as the most appropriate instrument for this task. The authors presents in this paper the technical aspect involved in a field trials that was conducted in a Canadian underground mine using paste backfill. The results of this first successful trials show that self-boring pressuremeter test can provide high quality and reliable backfill characteristics results, using analytical techniques developed for soils (Ouellet et al., 1998). The parameters obtained were: estimation of the lateral stress in the ground, the soil stress-strain response and the soil strength. The logistic and equipment required to conduct such testing underground is fully described. Performance achieved in the field and technical difficulties encountered are highlighted. Recommendations for future experiments with such instruments are given. Some potential technical improvements to better adapt this in situ testing technique to mine backfill are proposed.

Jan 1, 2001

By Tassos Grammatikopoulos, Mike Johnson, Niels Verbaan

Seabed polymetallic nodules, which contain significant quantities of metals key to electrification (nickel, cobalt, copper, and manganese) can be processed using several different metallurgical processing options, including direct smelting and subsequent hydrometallurgical refining of the copper/nickel matte, ammoniacal leaching (gas reduction or Cuprion), and acid leaching (often reductive). Many of these approaches suffer from reduced cobalt extraction, difficult physical performance, or overall circuit complexity in general, leading to increased risk to the overall project. SGS has considered pressure acid leaching of nodules for further investigation, as publicly shared data on this processing route stems from the 1970s and 1980s and is not always easily accessible. This paper will detail the series of tests conducted and provide updated results obtained (high Ni/Co/Cu recovery with limited Mn/Fe), as well as comment on the potential treatment options on the product solution and residue.

Feb 1, 2025

By Wolfgang R. Wawersik, Charles M. Stone

INTRODUCTION Hydraulic fracturing was applied in horizontal drill- holes in the Salado salt formation near Carlsbad, New Mexico. Tests were performed approximately 650 m be- low surface to validate the design of a Waste Isolation Pilot Plant (WIPP) for the disposal of radioactive waste from defense activities of the United States. Hydraulic fracturing was performed primarily to determine whether the virgin in situ stress state at the WIPP site is isotropic and whether the magnitude of the virgin in situ stresses corresponds to the weight of the overburden. Beyond these limited objectives, however, measurements are now being reviewed to evaluate the usefulness of hydraulic fracturing in salt formations in general. Such measurements are desirable to determine stresses induced by mining and to monitor time-dependent stress changes around underground excavations in salt masses. Hydraulic fracturing was chosen because it is the only technique that can be readily applied in virgin ground far from existing mine openings. The method also appeared to yield directly the magnitude of the least compressive principal stress, regardless of the mechanical properties of the rock mass. A knowledge of the least principal compression was deemed sufficient to establish the isotropic character of the virgin in situ stress field under two conditions: (1) the Salado formation was mechanically isotropic, i.e., the fracture toughness did not vary normal and parallel to bedding so as to permit preferred fracture paths, and (2) pressure measurements were combined with determinations of the orientations of hydraulic fractures and, more generally, with observations of the characteristic hydraulic fracture patterns. The latter was possible by locating the drillholes for hydraulic fracturing along the axes of drifts that were mined several months later. The success of general stress measurements by hy- draulic fracturing of salt subjected to anisotropic stress conditions was and remains less certain. While the smallest in situ compressive stresses should still be equal to instantaneous shut-in pressures, there may not exist any unique relationships between the greatest and intermediate in situ principal stresses on one hand and the primary breakdown and fracture reopening pressures on the other. This problem would be a consequence of stress relaxation due to salt creep around any drillhole in which hydraulic fracturing tests are conducted. Moreover, lab- oratory measurements suggest that creep and stress relaxation could be so rapid that it might not be possible to interpret the measurements for anisotropic stress conditions even if hydraulic fracturing were performed as soon after drilling as possible. The primary objectives of the stress measurements in the WIPP were met by combining hydraulic fracturing tests with finite element analyses of the effects of salt creep, observations of hydraulically induced fracture pat- terns, and laboratory hydraulic fracturing tests on oriented core. In situ hydraulic fracturing tests in long drillholes were preceded by several trial tests to establish the best test methods and to demonstrate that salt could be fractured. The resolution of anisotropic stresses and special problems, e.g., in the identification of instantaneous shut-in pressures, are currently being addressed in hydraulic fracturing tests in a mine pillar, in tests following different delays between drilling and fracturing, and in tests with different frac fluids. This paper will review the main results of the analyses above and of one group of hydraulic fracturing tests at different distances from existing excavations. The paper will conclude with a brief description of the geometry of the hydraulically induced fracture patterns. Because of space limitations, it will be assumed that the reader is familiar with hydraulic fracturing or will first consult other sources (e.g., Cleary, 1980; Gronseth and Detournay, 1979; Zoback and Haimson, 1983; Nemat-Nasser et al., 1983; Kim et al., 1984)

Jan 1, 1986

By Peter Kowalczyk

Magnetic surveying and map production is well established in land based mineral exploration. Magnetic data are routinely used to map geology in covered terrains, to estimate the depth to basement in overburden covered areas, and to identify altered zones, mineralization, bedding attitudes, and fault networks both regionally in map view, and through interpretation to depth in 3D. Best practices for magnetic survey methods and magnetic interpretation exist in all areas of land based geophysical survey methodology - mineral exploration, hydrocarbon exploration, geological mapping, archeological mapping, and in military applications. At sea, and particularly under the sea, sophisticated magnetic surveys are being done, but it can be argued that these are primarily in niche applications, for example in naval mine-hunting and UXO applications. Magnetic data is not normally collected on AUVs and ROVs conducting mapping and hydrographic survey operations. OFG has developed physical and mathematical calibration routines so that magnetometers can be mounted directly onto AUV and ROV bodies where significant heading errors and magnetic gradients exist. This simplifies the routine deployment of magnetometers on AUVs and ROVs for mineral exploration and other magnetic survey applications without the need for towed bodies, ungainly mounting frames, or degaussing of the survey equipment. Our experience shows that magnetometers can be operated routinely on AUVs and ROVs and that with careful processing useful maps can be produced routinely at low cost.

Sep 1, 2014

By P. Asadollahi, M. Invernizzi

"This paper describes the innovative full-face conventional tunnel excavation technology, with its advantages in terms of savings and safety. The full-face approach has been developed throughout the experiences gained in tunnel construction. The innovative design approach is focused primarily on the deformation response of the ground acting first and foremost ahead of the face, which is analyzed, predicted and controlled by pre-confinement of the core. The advantage of this method is particularly evident in difficult grounds. This paper will present the outstanding benefits given by the adoption of the full-face approach in two projects, the “Sochi” and the “Visnove” tunnels. THEORY AND DESIGN ASPECTS OF THE FULL-FACE EXCAVATION The main challenges in tunnel and underground construction industry are gathering the design data from the ground that is being excavated and foreseeing the critical stage during construction, where the materials are in its most critical configuration. These challenges shall be addressed during excavation when the lining and the excavation disturbance have not yet reach the equilibrium. The in situ stresses in the ground are redistributed (forming an “arch-effect”) around the opening, with zones of increased stresses around the walls of the excavation (Figure 1). The distribution of the stresses can be close or far from the excavation profile, depending upon having a ground capable of withstanding the deviated stresses well or unable to withstand them, respectively. In the latter case, the ground will plasticize and deform in proportion to the volume of ground involved in the plasticization phenomenon. When the ground completely cannot withstand the stresses redistribution, it will cause the collapse of the excavation. While in the first case, the arch effect occurs naturally, in the second case, it does occur naturally only when the ground is stabilized properly. In the case of collapse, the arch-effect must be produced artificially operating on the ground prior excavation. The design should be based on the understanding of if and how the arch-effect can be mobilized during tunnel excavation and ensure that is formed by calibrating excavation and stabilization operations appropriately. The arch-effect is function of the medium that is being excavated, the action taken to excavate and the reaction expected following the excavation."

Jan 1, 2018