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By Roger J. Araujo

A photochromic material is one which undergoes a change of color when exposed to light and reverts to its original color when the light is removed. Review articles carrying extensive bibliographies have been written by Brown and Shaw (1) and by Schwab and Bertelson (2). Organics. Schwab and Bertelson divide the reactions in different organic photochromic materials into some half-dozen categories; Windsor (3) reduces these to the following three main classes of general interest, based on how they work. 1. Stereoisomers. Absorption of light breaks one of the chemical bonds in a. ring molecule, thus allowing the molecule to unwind and form a different geometrical arrangement. The reverse process is a reforming of the bond. Examples of this class are the spiropyrans and the anils. 2. Dyes. A triphenyl methane dye, for example, is oxidized by energetic light; the absorption characteristics of the positive ion so formed are different from those of the original electrically neutral benzene rings. 3. Triplet States. In the class of polynuclear aromatic hydrocarbons, ground-state molecules are excited first to a singlet state by irradiation, and then go, via the lowest triplet state, to an excited triplet state. Visible light is absorbed in the triplet-triplet transition.

Jan 1, 1970

By R. K. Agarwal

In this paper a simple three-layered medium is considered. A circular hole is centrally located in the intermediate layer. The layered sheet is loaded uniaxially perpendicular to the stratification. The Young's modulus of the intermediate layer is lower than that of the outer layers. The stress distribution around the circular hole in a stratified medium is significantly different when compared to the case of a continuous homogeneous medium. The distribution depends upon the ratio of the height of [the] intermediate layer and [the] hole diameter. A comparison of stress the distribution and procedures for preparation and testing of [the] model are given. The potential of the technique is outlined.

Jan 1, 1968

By Ivor Hawkes

A wide variety of borehole gages have been developed for measuring rock stress. They all operate on the principle that stress changes around a borehole result in deformation that can be measured by the gage and interpreted in terms of the stress change either by calculation or calibration. In general terms, gages that comply with the borehole deformations are referred to as “deformation meters” and those that restrain the deformations by reason of their rigidity are referred to as “stress meters.” The main advantages claimed for stress meters are: their “stress” sensitivity is much less dependent on the rock modulus than that of deformation meters, and they are clamped firmly in the borehole. The use of each of the borehole gages developed for stress determinations in rock in the main has been confined to the laboratory responsible for its development. To be generally accepted a gage must meet the following specifications : 1) Gages to be left in place to measure stress changes must be relatively cheap, and if possible recoverable, so that large numbers can be used to obtain an overall picture of the changing conditions. This, of course, is not necessarily the case for recoverable gages designed for absolute rock stress measurements where usually only one or two gages are involved. 2) For use in the adverse environmental conditions encountered underground, it is essential that gages be robust, stable, and unaffected by high humidity, corrosive water, or dust. 3) Highly qualified technicians are rarely employed specifically for rock mechanics studies in mines or on civil engineering sites and there- fore gages designed for measuring stress changes must be easy to set and

Jan 1, 1972

By David Sinclair

THE dimensions and shapes of mine structures may at present be determined by (1) field experience, (2) structural calculations, and (3) barodynamic tests.§ None of these, however, provide information as to the stresses, their direction and distribution in a mine structure. For the design of pillars, the placing of openings relative to working places such as gangways, haulage levels, etc., this information is desirable. Photoelastic methods provide this and, while relatively new, their appli-cation in all engineering fields is assuming increasing importance. This paper, therefore, will present the method with a few applications to mining, and with sufficient reference for further study by the reader. PART I THE PHOTOELASTIC METHOD The photoelastic method of stress measurement determines the stress distribution in a two-dimensional model by optical means. It makes use of the fact that when a piece of isotropic transparent material, such as glass, celluloid, or Bakelite, is stressed and viewed in polarized** light a picture is seen which indicates by its color bands of light, or fringes, the magnitude of the stresses, their direction and their distribution.

Jan 1, 1940

By David Sinclair, Philip B. Bucky

THE dimensions and shapes of mine structures may at present be determined by (1) field experience, (2) structural calculations, and (3) barodynamic tests.§ None of these, however, provide information as to the stresses, their direction and distribution in a mine structure. For the design of pillars, the placing of openings relative to working places such as gangways, haulage levels, etc., this information is desirable. Photoelastic methods provide this and, while relatively new, their application in all engineering fields is assuming increasing importance. This paper, therefore, will present the method with a few applications to mining, and with sufficient reference for further study by the reader. PART I THE PHOTOELASTIC METHOD The photoelastic method of stress measurement determines the stress distribution in a two-dimensional model by optical means. It makes use of the fact that when a piece of isotropic transparent material, such as glass, celluloid, or Bakelite, is stressed and viewed in polarized** light a picture is seen which indicates by its color bands of light, or fringes, the magnitude of the stresses, their direction and their distribution. GENERAL EXPLANATION The stress at any point 0 in a structure (Fig. 1), may be resolved into two components, P and Q, each a pure tension or compression, at right angles to each other, called principal stresses.1 To fully identify the stress, the values of P and Q and their directions or angle [0] must be known.

Jan 1, 1940

By AIME AIME

INSTITUTE members attending the Annual Meeting in New York who want to see one of the mining engineers' newest aids, photoelastic stress analysis, are due for an interesting afternoon on Thursday, Feb. 15, when open house: will be held at the Columbia University mining laboratory. Information as to the direction and distribution off stresses in mine structures, which has been developed by Professor Bucky, associate professor at the Columbia School of Mines, and David Sinclair, research assistant, is useful in the design of pillars and in the placing of openings relative to working places such as gangways and haulage levels.: This work has been sponsored during the last ten years by the Engineering Foundation.. It is fully reported in T. P. No. 1140.

Jan 1, 1940

By Charles E. Johnston

By substituting photoelectric automatic car loading for mechanically induced hydraulic automatic loading and by protecting the process against operational failures, the engineering staff at International Minerals & Chemical Corp.'s Carlsbad potash mine has developed a reliable loading process that operates without an attendant. The photoelectric control, developed primarily because of frequent failures in the hydraulic control system, has not changed the basic loading operation and physical layout. Mine-run ore ranging in size from minus 200 mesh to 30-in. lumps is dumped onto a conveyor belt which discharges into a so-called "flop gate chute" which in turn, feeds the ore into six-ton capacity mine cars. Each car is filled progressively by moving the entire trip forward. When a car is filled 12 in. above its rim, the direction of flow into the car is reversed 180º and filling of the next car back is begun while the entire trip is moved forward again. Once the next car is properly spotted under the front chute, the flow is again directed to the forward position.

Jan 9, 1962

By Y. J. F. Haven, G. H. J. Kitson, D. G. Beadle

I have read this paper with considerable interest. By using an automatic instrument to assess the dust samples taken in South African collieries, the authors are ahead of the gold mining industry, which still uses the laborious method of microscopic assessment, with its limited accuracy, of the half-a-million dust samples taken each year. As the authors state, the result obtained from the photoelectric assessment of the samples is approximately proportional to the surface area of the respirable dust. However, modern theory is that, in assessing coal dust, it is the respirable mass which is important in determining the danger to health. Thus Table II of their paper is of considerable value in showing the relationship between the P.E.R. value and the mass concentration measurement. Unfortunately this table only gives the mean relationship. The important point is to know the scatter around this mean. If the scatter is small, then this mean value (for different operations) would have considerable value in converting from respirable surface area to respirable mass, but if the scatter is large, then such a conversion, using a fixed factor, will have little value. In the text the authors mention the range of values as being between 3 to 24, but without a statement on the number of samples used to determine this range and their distribution, this is a rather nebulous statement. I hope, in their reply, that the authors will give, in statistical terms, some statement on the overall correlation between these two parameters. I might add that at present a member of my staff is working on similar relationships for dust samples taken in gold mines. Another factor which may well be most important in determining the danger of dust levels in coal mines is the composition of the dust, specifically its quartz content. I understand that the authors have some information on this point, and to make their results of greater value in International comparisons of dust levels and the concomitant development of pneumoconiosis, it will be extremely useful if they could place this information on record. Even though, as I have said above, modern theory postulates that respirable mass is a better parameter to use than respirable surface area, the problem remains of how to measure this parameter with short time sampling, which, as the authors point out, is their preferred strategy for dust sampling and dust control. I know of no easily portable instrument, independent of external power supplies, which can, in 5 to 10 minutes, collect sufficient dust to enable it to be weighed accurately. Thus the authors' implied intention of continuing to sample by their present techniques and using their present parameter to report the results is, in my opinion, an entirely valid decision.

Jan 10, 1968

By W. T. Turrall, D. Porter

THE crystal laboratory, Dept. of Physics, Massachusetts Institute of Technology, was confronted with the problem of obtaining a supply of optical grade calcium fluoride (CaF2) for use in growing synthetic CaFe2 crystals. A search of the known fluorspar deposits did not indicate that any quantity of optical spar could be obtained. Even the best material had to be sorted by hand to remove impurities. The process for growing CaF2 crystals developed by Professor D. C. Stockbarger of the Dept. of Physics, M.I.T., necessitates very pure feed materials. Exclusion of impurities is required, even in amounts detectable only spectrographically. The impurities occurred as minute inclusions of SiO2, BaSO4, CaCO3, FeS2, water or air. Crystals up to 4 in. in diam and weighing several pounds are made by the Harshaw Chemical Co. in Cleveland. Since the time required to grow a 4-in. crystal is about one week, and since the cost of manufacture is high, removal of impurities by any concentration method appeared practical. The mineral engineering section of the Dept. of Metallurgy undertook to investigate the possibility of concentrating clear optical fluorspar, -4 mesh +10 mesh, from a feed containing over 99 pct CaF2. Various innovations of the known methods of concentration were considered, but in each case the minute amount of impurities associated with the crystal produced such extremely small differences

Jan 1, 1952

By A. Tremari, Paul I. Eimon

Photogrammetrists are studying with new interest the problems of mine mapping and mining engineers are beginning to see what photogrammetry can do for them. Administrators in a number of European and U. S. mines have tried photogram- metric methods and are finding that better maps and data, needed for mine development, can be produced with savings of time, men, and money. In addition to wide use in small scale mapping projects, photogrammetric methods are now used for producing large scale plans and maps in German coal and lignite mines, in some U. S. open pit mines, to inventory TVA coal stock piles, and to compute highway excavation volumes. In each case surveying and map compilation has been made more efficient and accurate by photogrammetry and at significant savings over ground methods.

Jan 5, 1959

By Donovan J. Benton

Photogrammetric methods are advancing rapidly and show considerable promise as a ground control research tool. The ability to quickly capture three-dimensional geometry, especially changes in geometry, in underground and laboratory settings is a significant advance from point distance measurements. Photogrammetry is being applied in both of these settings as part of the NIOSH ground control research. This paper describes these applications and the equipment and software being employed. It also describes tests conducted to quantify the accuracy of these systems. Accuracy varied with system specifics and procedures. A factory-calibrated camera produced results within 1/32 of an inch, plus 0.04%. A user-calibrated camera was found to be less accurate, at 1/20 of an inch, plus 0.24%. These calibrations demonstrate that photo grammetry can produce research quality measurements in laboratory and mine settings.

Jan 1, 2014

By G. Poropat, A. R. Guest, H. P. Grobler

At the De Beers Consolidates Mines operations it is common practices to perform Geotechnical mapping of the newly exposed faces in the waste and ore rock. The purpose of Geotechnical mapping is to quantify the in-situ fracturing of a rockmass that in turn is required during the planning and application of a mining method. Whether it is to determine slope angles, caveability, impact of blasting or support requirements. This mapping involved a cumbersome and time consuming procedure that requires individual examination and description of the natural inherent fractures exposed by mining. During highwall mapping in an open pit this can be a safety concern due to the duration of time spent below a highwall. The advantages gained through the recent introduction and application of SiroVision® allows safer mapping, an increase in statistical fracture population, archiving of rock faces and the more accurate reflection of the true mapping. This paper aims to describe in detail the application of the recently developed SiroVision®, photogrammetry software, to replace conventional face mapping. A De Beers Consolidated Mines, il est pratique courante de faire une cartographie géotechnique des tailles récemment exposées dans le rocher stérile ou minerai. Le but de la cartographie géotechnique est de quantifier la fracturation in-situ d’une masse rocheuse, qui sera nécessaire lors de la planification et application d’une méthode minière, que ce soit pour déterminer les angles des galeries inclinées, les possibilités de foudroyage, l’impact du dynamitage, ou les besoins en supports. Cette cartographie nécessitait une procédure longue et compliquée qui demande l’examen individuel et la description des fractures naturelles propres exposées par l’opération de mine. Pendant la cartographie de parois dans une exploitation à ciel ouvert, cette opération peut être dangereuse à cause du temps passé sous la paroi. Récemment, le lancement et application de Siro Vision apportent l’avantage d’une cartographie plus sûre, une augmentation des statistiques de population de fracture, l’archivage des tailles de roches, et le reflet plus précis de la cartographie. Le but de l’étude présente est de décrire en détail l’application du développement récent de Siro Vision, logiciel de photogrammétrie, pour remplacer la cartographie de taille conventionnelle. Bei den De Beers Consolidates Mines Operationen ist es gängige Praxis geotechnische Aufzeichungen des Taub- und Erzgesteins neu geöffneter Abbaustellen zu erstellen. Zweck dieser geotechnischen Aufzeichnungen ist die vor-Ort-Quantifizierung des Bruches der Gesteinsmasse, welche im Gegenzug während der Planung und der Anwendung einer Abbaumethode erforderlich ist, sei es um einen Neigungswinkel festzustellen, Abbaubarkeit, Auswirkung von Sprengungen oder Anforderungen an Unterstützungen. Die Aufzeichnungen waren mit umständlichen und zeitaufwendigen Prozeduren verbunden, die eine individuelle Prüfung und Beschreibung der durch den Abbau freigelegten natürlichen inhärenten Brüche, verlangten. Dies kann auf Grund des Zeitraumes der unterhalb einer Flözoberschicht verbringt wird zu einer Frage der Sicherheit werden wenn die Aufzeichnung einer Flözoberschicht im Tagbau erfolgt. Die Vorteile auf Grund der jüngst erfolgten Einführung und Anwendung der SiroVision® gestatten sichereres Aufzeichen, eine Zunahme in der statistischen Menge an Gesteinsbrüchen und eine akkuratere Reflektion der tatsächlichen Aufzeichnungen. Diese Arbeit hat zum Ziel im Detail die Anwendung der kürzlich entwickelten SiroVision®, eine photogrammetrische Software, die die konventionelle Abbauortaufzeichnung ersetzen soll zu beschreiben.

Jan 1, 2003

By Yi Luo, Jian Yang, YUJIA LIAN

Scale physical models, constructed according to the principle of similarity theory, have been widely used to simulate the mining disturbances to surrounding strata and to evaluate the effectiveness of implemented ground control techniques. This technique has also been used for studying mining-induced surface and subsurface subsidence. The movements of the observation points installed on the physical model at different mining stages are currently measured using total station which is time-consuming and inaccurate especially on small scale models. A photogrammetry-based measurement system has been developed. During a physical modeling process, photos of the model can be taken during the simulation process reducing survey time from hours to a few seconds. A program, Photogrammetry Analysis for Physical Modeling of Mine Subsidence Process (PAPMMSP), developed based on photogrammetric principle is used to quickly identify the installed observation points and accurately determine their coordinates. The measurement accuracy is well under submillimeter level—an ultra-important advantage as any measurement errors in coordinates are magnified by the model dimension scale (commonly 20 to 400). A physical modeling case of subsurface strata movements and deformations associated with longwall mining operations is presented in the paper to demonstrate the functions and capabilities of the developed photogrammetry program.

Aug 11, 2020

By Yi Luo, Jian Yang, YUJIA LIAN

Scale physical models, constructed according to the principle of similarity theory, are widely used to simulate the mining disturbances to surrounding strata and to evaluate the effectiveness of implemented ground-control techniques. This technique has also been used for studying mining-induced surface and subsurface subsidence. The movements of the observation points installed on the physical model at different mining stages are currently measured using a total station, which is time consuming and inaccurate, especially on small-scale models.

By T Wang, D Wang

Photogrammetry-based techniques supported by traditional mapping tools are more frequently used for open pit geotechnical mapping. It fundamentally involves the collection of geological, structural and rock mass data from pit batters when safe to do so. These are essential components for refining and implementing continuous improvements to geotechnical models. The geotechnical model is used to review bench performance, optimise geotechnical design parameters, interpretation and analysis of pit slope stability. This paper is a case study of implementing different pit mapping methods at Mount Carlton gold mine, North Queensland. It critically reviews the tools required, including the Brunton compass, mobile application Clino, geotechnical data mapping software CloudCompare (2015) and Sirovision software. The review compares the image precision, structural measurements and data analysis. The review also underlines mine site management philosophy for safe geotechnical data collection to identify in-pit geotechnical hazards and the mitigation of potential slope instability. Sirovision is a remote sensing system for site geology mapping and interpreting geotechnical characteristics of exposed mining faces. The system utilises off-the-shelf digital SLR cameras to capture stereo photographs of the rock face and uses the latest image processing technology to generate accurate 3D models. These 3D models are digitally analysed using computational geometry to extract unbiased and accurate geological and geotechnical data. CloudCompare processes high accuracy 3D dense cloud rock surfaces reconstructed with photogrammetry software to extract the geological planes using the FACET or Compass plugins. The major discontinuity sets can be observed and the orientation (dip/dip direction) obtained from the algorithm is accurate and reliable for geotechnical assessment, including kinematic and rock slope stability analysis.

Nov 29, 2022

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