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New equipment for seabed sampling, presently at the prototype stage, operates on the principle of diamond core drilling with wire line core barrels and is designed to drill cores from the seabed at depths down to 200 m with a continuous recovery of cores from an attendant vessel. The machine operates on the seabed by remote control from a console on the vessel. Neither installation nor operation requires the use of divers. Principal Applications Principal areas of application for the drill which is dubbed Maricor include investigation drilling in the continental shelf, mapping geological conditions before large drilling platforms are installed and exploring proposed undersea tunnel routes.

Jan 11, 1973

By G. R. Purdy, J. G. Parr

The intermetallic compound Ti2Co was studied by X-ray diffraction and metallographic techniques. The phase occurs off stoickzometric composition, with its greatest variance at high temperature. The solubility limits of the phase have been cletermined, and an amendment to the titanium-cobalt phase diagram is suggested. THE first intermetnllic compound to appear at the titanium-rich side of the titanium-cobalt system was found by Laves and wallbauml to be Ti2Co. They described this compound as isomorphous with Ti2Ni and Ti2Fe, and demonstrated that it had a face-centered-cubic structure with 96 atoms per unit cell. This contention is supported by the work of Duwez and Taylor2 and Orrell and Fontana3 who also determined the lattice parameter to be about 11.30A. Rostoker4 believed that Ti2Co did not exist, and that the phase considered by the other workers to be Ti2Co was Ti,Co20. However, Orrell and Fontana determined oxygen and nitrogen contents and found that their alloys did not contain sufficient of these elements to produce significant quantities of a stoichiometric oxygen compound. The present investigation was initiated to determine the composition limits of the phase Ti,Co.

Jan 1, 1961

By Nelson Severinghaus

Consolidated Quarries Corp. must conduct operations for an average sales price of $1.25 per ton, about the same price at which stone was sold 25 years ago when the dollar was worth twice what it is now. To maintain success in a competitive business, the company must solve the usual production problems, which will be discussed here in the order they occur in the flowsheet. Most crushed stone quarries must first remove soil and decomposed rock. Although seasons of lower sales sometimes release regular quarry excavating and haulage equipment for this purpose, overburden is often too extensive for this method to be used. In such cases, special equipment must be assigned or the job may be contracted. As many earthmoving contractors have heavy duty specialized equipment well suited to overburden removal, they should be seriously considered before the job is undertaken. Pockets of clay beneath peaks of hard stone sometimes defy mechanized removal. Pick and shovel laborers at this point might be supplanted by more ingenious use of pumps and water or some other mechanical means. Where overburden is extremely heavy or difficult to remove, underground mining must be considered.

Mar 1, 1956

By A. E. Wheeler, H. Y. Eagle

The copper industry in the Province of Katanga, in the Belgian Congo, which is now controlled and operated by the Union Minére du Haut Katanga, had its inception many years ago in the vision of a Scotsman, Robert Williams, now Sir Robert Williams, Baronet. He it was who personally negotiated the mineral concession with King Leopold of Belgium, sent in the prospecting parties who located most of the present mines of the company, later arranged for the Belgian participation from which the present company was formed, and has been its active mentor ever since. The idea back of his efforts was the establishment of an industry on the Congo-Zambezi divide, of sufficient importance to draw up to it the head of the Cape to Cairo Railroad, the dream of Sir Cecil Rhodes, and the consummation of which he had left as a legacy to Mr. Williams, his successor. The reports of the prospecting expeditions showed that copper in profitable quantity was there, but many difficulties lay in the way of the establishment of the infant industry. The isolated location of the mines, various tribal wars, the Boer War, and many other factors contributed to making progress very slow. However, in spite of these difficulties the railroad was finally built and a blast-furnace plant erected at Lubumbashi, near Elisabethville, the capital of the Province. Operations of this plant were started in 1911, treating high-grade oxidized ores and producing pig copper by a reducing smelting. Production has been continuous since that time and the company has grown so that at present it ranks as the largest individual copper producer in the industry. It is a fitting monument to the foresight, optimism and driving force of its founder, and the progressive policies of his Belgian colleagues. In January, 1914, the Union Miniere du Haut Katanga engaged as its consulting engineer, Archer E. Wheeler, metallurgical engineer, at that time general superintendent of the Great Falls plant of the Anaconda Copper Mining Co. Mr. Wheeler was commissioned by the Board of Directors to proceed into Katanga, and make all necessary investigations to enable him to report on a comprehensive development program, and to recommend a scheme of treatment particularly for their low grade

Jan 1, 1934

By I. L. Barker

ALTHOUGH valuable information has been pub-lished on the important problems of slag losses with which every copper metallurgist has to contend, a great deal of money is still being wasted in copper smelters all over the world, through metal being irretrievably lost in reverberatory slags. When smelting a relatively low-grade pyritic concentrate together with a proportion of direct-smelting oxi- dized ore, as is done in Oroya, slag volumes are of necessity high, and even a relatively clean slag, say of 0.5 pct Cu, means a loss of almost 4 pct of all the copper charged, or over $1,000,000 annually at present output and prices. While it is known that such losses can often be reduced by allowing the slag time to settle, with or without addition of a reducing agent such as coal or pyrite, the facilities for such treatment are not always available in a plant of old design working to capacity under severe space limitations. Nor is it easy under such conditions to run large scale tests which may endanger the smooth flow of production for considerable periods without yielding

Jan 1, 1958

By H. L. Ames, P. H. Jennings, R. W. Stanley

A process has been developed for leaching copper, lead and calcium from molybdenite concentrate. The leachant is a solution containing an oxidizing chloride (e. g., CuC12, FeC13) and an alkaline earth metal chloride (e. g., CaC12). Cupric chloride and ferric chloride, in the presence of 20-30% calcium chloride, are effective oxidants for chalcopyrite and galena. Calcium chloride, in addition to promoting the rate of leaching, serves to lower the solution pH and raise the boiling point. Leaching for two hours at 110'~ with a 1 % CuC12-10% FeC13- 30% CaC12 solution results in the extraction of up to 98% of the copper in molybdenite, 98% of the lead, and 79% of the calcium. Less than 0. 5% of the molybdenum is dissolved. The leach solution can be rapidly and effectively regenerated with gaseous chlorine and recycled. Build-up of copper and lead in the leach solution is controlled by discarding about 30% of the leach solution each cycle.

Jan 1, 1973

By Robert B. Fulton

Staurolite, an iron aluminum silicate mineral, is used industrially as the source of aluminum in portland cement manufacture in areas where the aluminum constituent is not economically available from shale or argillaceous limestone. It is also used as a high value- in-use sand blasting agent and as a premium grade foundry sand. It is produced by E. I. du Pont de Nemours & CO. as a coproduct in titanium mineral production in Florida where it was first recovered on a commercial scale in June 1952 from the Pleistocene sand deposit known as Trail Ridge. In the Trail Ridge deposit it comprises about 36 of the heavy minerals, the principal other heavy mineral constituents being ilmenite, leucoxene, rutile, zircon, kyanite, sillimanite, and tourmaline. Staurolite and the other silicate nonconductive heavy minerals are separated from the conductive titanium minerals on high-tension separators. The silicates are then separated from one another magnetically, the staurolite being relatively magnetic. In the total processing, 200 tons of raw sand yield 7 tons of heavy mineral concentrate from which about one ton of staurolite is recovered. Staurolite production is approximately 100,000 net tpy. No other commercial production of staurolite is known. This process yields staurolite concentrates of the characteristics given in [Table 1]. These concentrates are sold as three products with the size distribution of subrounded particles shown in Table 2. All three grades are used in sand-blasting for cleaning metal, for paint removal, and for cleaning buildings. Staurolite compares favorably with lower unit cost abrasives, such as boiler slags and mineral aggregates, in applications where the abrasive is used only one time and is not recovered. Because it is hard, fine, clean, and dense it can reduce blasting time, with less material reportedly being required

Jan 1, 1975

By H. R. Peterson

The control of autogenous grinding circuits is very similar to the control of conventional grinding circuits. In both circuits the classifier must be operated to achieve the required degree of mineral liberation. Crude ore grade and grinding mill density are important in both circuits. The biggest difference between the control of the two circuits is the pronounced effect that crude ore changes have on autogenous circuits. The importance of crude grade, weight recovery, size and hardness is greatly magnified because the crude ore in the autogenous circuit is also supplying the grinding media. Crude ore sizing is a particularly critical factor in achieving efficient primary autogenous milling. Because of the above, computer control is advantageous for autogenous circuits. Changes in crude ore may necessitate rapid changes in the entire circuit control strategy, and only a computer can facilitate these changes. Also, the techniques of control are very different for conventional and for autogenous grinding. Set-point control is usually satisfactory in conventional circuits, but the multiplicity of varying conditions in an autogenous circuit usually require some type of computer optimizing search routine. Autogenous mills can be separated into two general types. In primary autogenous mills the media is obtained from the mill feed, and in pebble mills the sized pebble media is added separately from the material being ground. PRIMARY AUTOGENOUS MILL CIRCUIT CONTROL - FIGURE 1 Power Draw Primary autogenous mills are usually run at full motor loading so production will be at maximum. Therefore, power draw must be closely controlled; this is done by adjusting feed rate. The versatility of computer control is extremely valuable for power control, especially during starting and stopping. To bring the mill power up as fast as possible at

Jan 1, 1982

By R. H. Barham, G. W. Nabor

Linear aquifers, either limited or essentially infinite, may be encountered in reservoir engineering practice. In areas where faulting fixes reservoir boundaries, the fault block reservoir may have an aquifer of limited extent whose geometry is best approximated as linear. An infinite linear aquifer can occur as a regional feature whenever water movement through the aquifer member is constrained to one direction. Such constraints can arise from major faults, facies changes or pinchout of the member. Miller* pointed out that linear aquifers have received only meager attention in the past. He analyzed the performance of finite and infinite aquifers, developed working equations and curves, and presented examples. While Miller's curves may be used fairly easily, a separate one is required for each size of aquifer. In this paper, Miller's equations have been used as a starting point. By modifying them slightly, they can be reduced to a form which yields a single working curve, applicable to any size of aquifer. Thus. interpolation between curves is eliminated and accuracy is improved. Miller's results for finite aquifers covered only the boundary condition of no flow across the outer aquifer boundary. This paper also includes the case of constant pressure at the outer aquifer boundary.

Jan 1, 1965

By Archer Wheeler

THE copper industry in the Province of Katanga, in the Belgian Congo, which is now controlled and operated by the Union Minere du Haut Katanga, had its inception many years ago in the vision of a Scotsman, Robert Williams, now Sir Robert Williams, Baronet. He it was who personally negotiated the mineral concession with King Leopold of Belgium, sent in the prospecting parties who located most of the present mines of the company, later arranged for the Belgian participation from which the present company was formed, and has been its active mentor ever since. The idea back of his efforts was the establishment of an industry on the Congo-Zambezi divide, of sufficient importance to draw up to it the head of the Cape to Cairo Railroad, the dream of Sir Cecil Rhodes, and the consummation of which he had left as a legacy to Mr. Williams, his successor. The reports of the prospecting expeditions showed that copper in profitable quantity was there, but many difficulties lay in the way of the establishment of the infant industry. The isolated location of the mines, various tribal wars, the Boer War, and many other factors contributed to making progress very slow. However, in spite of these difficulties the railroad was finally built and a blast-furnace plant erected at Lubumbashi, near Elisabethville, the capital of the Province. Operations of this plant were started in 1911, treating high-grade oxidized ores and producing pig copper by a reducing smelting. Production has been continuous since that time and the company has grown so that at present it ranks as the largest individual copper producer in the industry. It is a fitting monument to the foresight, optimism and driving force of its founder, and the progressive policies of his Belgian colleagues. In January, 1914, the Union Miniere du Haut Katanga engaged as its consulting engineer, Archer E. Wheeler, metallurgical engineer, at that time general superintendent of the Great Falls plant of the Anaconda Copper Mining Co. Mr. Wheeler was commissioned by the Board of Directors to proceed into Katanga, and make all necessary investigations to enable him to report on a comprehensive development program, and to recommend a scheme of treatment particularly for their low grade

Jan 1, 1932

By Alexander Field

INTRODUCTION THE Bureau of Mines is investigating the problem of slag viscosity, its variation with the temperature and with the composition of the slag, and its effect upon the distribution of the sulphur between molten iron and slag, as introductory to a series of contributions to the theory of the metallurgical processes. The method of measurement, viscosity, apparatus, furnace and other accessories mentioned in this paper have been described fully in a Bureau of Mines report.1 THE LITERATURE ON SLAG VISCOSITY The viscosity of blast-furnace slag had not been measured previous to the investigation described in this report. A number of investigators have determined the "fusibility," or softening temperature, of slags by means of the cone method or, other deformation method, but these methods supply only limited information regarding the temperature-viscosity relations.-of the slag in question. Any deformation method that may be employed indicates only the temperature at which the slag attains a more or less definite viscosity, the magnitude of the value obtained depending on the method used. For details of the various methods used by different investigators, see, the Bureau of Mines paper already referred to. An isolated measurement by Doelter on a single mixture at 1,300° C. represents the highest temperature reached in the various viscosity investigations previous to those described in this report, in which results have been referred to absolute units. Arbitrary deformation tests have of course been made at much higher temperatures.

Jan 2, 1917

By L. Ibagos S., T. Balberyszski

The volumetric flow rate and the initial concentration of the copper sulfate solution influence the rate of reaction and, hence, the precipitation efficiency in a continuous launder cementation system. Using a model of such a system it was found that the precipitation efficiency is related to the two process parameters by the approximate expression [ log [1-n] = -[0.072 co 2.91 e – 0.511c o Q 1.15 ] N Q] where c is the initial concentration, Q, is the volumetric flow rate and N is the number of launders in the system. This expression agrees with an equation developed for the rate of the cementation process if it is assumed that the exponential factor represents the change in the surface area with concentration and the exponents 2.91-and 1.15 relate the hydrodynamic conditions and the surface concentration to co and Q. The experimental results are used to determine the values of a Precipitation Coefficient for any volumentric flow rate and initial concentration of solution. Knowing the Precipitation Coefficient, the total volume of launders that will result in a given precipitation efficiency can be calculated. It is established that maximum precipitation efficiencies are obtained for initial concentrations between 6.0 and 7.0 gpl and volumetric flow rates of approximately 350 m3 /hr Good agreement between calculated and actual launder volumes is obtained for a number of industrial operations for which a comparison is made.

Jan 1, 1973

By Homer Turner

COALS, other than anthracite, have been so thoroughly studied under the microscope during recent years, that we now know what kinds of plants and what parts of plants form the bulk of lower rank coals from peat to bituminous coal. The microscope has also shown the state of preservation of such vegetation as well as the nature and distribution of products of plant decay. These and further details have been ascertained mainly through the employment of two methods of attack, section cutting and maceration. Anthracite has failed to respond to these methods, so well adapted to the study of lower rank coals and, therefore, has been neglected by investigators to such an extent that there is much doubt as to its microscopical characteristics. The object of this paper is to lift anthracite from its realm of obscurity by demonstrating the wealth of microscopical detail that is revealed when reflected light is used on a properly polished and etched surface and, further, to show the relationship between anthracite and bituminous coal.

Jan 2, 1925

By Robert I. Kingman

SUFFICIENT testing has been performed with the Dutch State Mines Cyclone for thickening and desliming flotation feed at the concentrator of the National Lead Co., Tahawus, N. Y., to prove its application for this work. It is the purpose of this article to present some of the test results, operational details and advantages of cyclone thickening and classification. The metallurgy of the mill operation was described by Frank R. Milliken, assistant manager of the titanium division.l The present flowsheet for the recovery of ilmenite consists in grinding the crushing plant product in four open-end rod mills in closed circuit with mechanically vibrating screens to approximately -20 mesh. The screen undersize is treated in Crockett magnetic separators which produce three products: magnetic concentrate, nonmagnetic tailing containing ilmenite and gangue, and a Crockett slime overflow. The non- magnetic tailing is classified into eight sizer spigots products and a classifier overflow. The spigot sand products are tabled separately to produce a rough ilmenite concentrate, a middling product and a tailing. The table middlings are returned to Crockett feed. The table concentrate is dewatered and dried and further concentrated on Wetherill magnetic separators to produce the finished ilmenite concentrate.

Jan 8, 1950

The report of the Comittee on Nominations was received and ordered to take the statutory course. Thereupon the chairman was authorized to appoint a committee of three members to report at the next meeting of this Board regarding the suggestions made by the Nominating Committee. The following vote of thanks was then passed to the members of the Arizona Committees and others: "WHEREAS, the Board of Directors of the American Institute of Mining Engineers has a deep appreciation of the splendid success of the Arizona Meeting and WHEREAS, the Board is aware that this success was brought. about by the generous and efficient efforts of the members of the Local Committees, therefore it is

Jan 12, 1916

By J. L. Lytton, J. E. Dorn, L. A. Shepard

Single aluminum crystals were subjected to creep in simple shear on the (111) planes in the slip direction. The activation energies for creep were calculated from the effect of small abrupt changes in temperature on the creep rate just before and immediately following the temperature change. The results definitely establish the fact that creep of single aluminum crystals occurs by-three unique processes, characterized by thethree distinct and isolatable activation energies: The 35,-500-cal-per-mole activation energy obtained at the highest temperatures was ascribed to a dislocativationtion climb process; the 28,000-cal-per-mole activation-energy process, occurring over the intermediate-temperature range was attributed to a cross-slip mechanism; and it was suggested thot the 3400-cal-per-mole process observed below 400°K may be the Peierls energy. THE most pertinent question regarding the phenomenon of creep in crystalline materials is concerned with the identity of the crystallographic mechanisms of deformation that control the creep rate. For many years slight progress was made in uncovering the basic mechanisms for creep. Over the past 10 years, however, two parallel lines of investigations have contributed to a more definitive understanding of the processes involved in creep. The extensive development and maturing of dislocation theories for deformation of crystalline materials' proved to be of paramount importance for this progress. And second in importance was the replacement of the former prosaic methods of creep testing by new techniques'." which were especially

Jan 1, 1959

By Guy R. Johnson

In working brown iron-ore mines on the system employed at Longdale, namely, stoping from the top down, the usual procedure is to drive a succession of upraises from the lowest adit to the highest, or to the top of the deposit, as the case may be. These up-raises are usually driven 120 feet apart., along the strike of the vein,. As the work goes on, they are connected by levels, 10 feet spa* (vertically), and then serve as chutes. A transit is useless in surveying these chutes, and the writer has for several years made use of a hanging compass. The method of using this instrument, described in a former paper (Trans., xx.,.105), embracing as it does the use of a cord and several strips. of wood,

Jan 1, 1894

By Milan Matula

One of the main characteristics of the development of rock mechanics in some countries is a close cooperation between experts in rock mechanics and workers in related fields, including soil mechanics and engineering geology. The purpose of this chapter is to outline the contribution that engineering geology can make to rock mechanics and to present a few examples of engineering geology studies that have been used in solving some practical rock mechanics problems. Engineering geology investigations dealing with the influence of geological factors on the physical properties of rock materials and rock masses fall into three main categories : 1) Systematic study and correlation of the physical properties of the main rock types with the petrogenetic evolution that caused the differences in the properties of these various rock types. 2) Study of the heterogeneity and anisotropy of both rock materials and rock masses. 3) Delimitation of rock masses which are approximately uniform in physical properties (quasihomogeneous units). Delimiting of the quasihomogeneous rock masses is the main contribution that the engineering geologist can make to rock mechanics. This delimiting is based on the evaluation of many complex geologic factors, not on test results alone, and therefore is most effectively done by trained engineering geologists. The foregoing types of studies are being used in Czechoslovakia for several purposes, including : 1) the compilation of regional engineering petrologic data-that is, the systematic definition of the main rock types of the country in terms of their representative physical characteristics;

Jan 1, 1970

By Y. C. Liu, W. R. Hibbard

Based on pole figure data and microstructural observations, the re-crystallization orientation found in a copper strip previously cold-rolled 99.5 pct from a single crystal with an initial (110) [112] orientation may be described as: a 30° rotation, clockwise and counterclockwise, about octahedral poles of the cold-rolled texture such that all four poles function at a low annealing temperature (400°C) and only three of them function at high temperatures (500' to 1050°C). The relative intensity of deformation stresses on various slip planes can be correlated with the choice of poles affecting the rotations found in the recrystallized orientations. ROTATIONAL reorientation about the poles of densely packed crystallographic planes is an important characteristic of secondary recrystallization" in face-centered cubic metals. Some evidence has also been interpreted to show that such a rotational relationship also exists in the primary recrys-tallization process." In an investigation of the crystallographic relationships in the recrystallization process, several aspects of the experimental procedure should be considered. With cold-rolled poly-crystalline metal as the initial material, pole figure analysis leaves many ambiguities as to whether or not simple indices can be assigned to adequately represent its orientation. The rolling texture does not consist of a single texture. Minor deformation textures are usually present. In all cases, twin textures are present. The presence of both minor and twin deformation textures influences the recrystallization texture. In order to study the recrystallization mechanism, a more precise knowledge of the history of the material before recrystallization is necessary. Tensile deformation of a single crystal usually produces residual stresses which are concentrated at slip bands. Since the exact nature and orientation of these potential nuclei sites cannot be experimentally evaluated, the tensile deformation of a single crystal was not considered adequate. From the work done by Barrett and Steadman6 n copper, it appeared that cold rolling of a single-crystal specimen with an initial (110) [112] orientation would yield a specimen which fulfills the conditions required for the present investigation, namely a highly preferred single rolling texture with relatively homogeneous stress distribution. By investigating the recrystallization texture of this material, additional details of reorientation during recrystallization might be obtained. The purpose of this paper is to describe such an investigation. Experimental Procedure Copper used in the present investigation was cathode sheet with a purity of 99.94 to 99.97 pct. A copper single-crystal specimen, 1.15x0.8720x0.5322 in. (thickness) was cut from a cylindrical crystal which was grown in a Bridgman furnace.' The cutting was accomplished on a horizontal milling machine operated at a very slow speed to obtain a (110) plane in the rolling plane and a [112] direction in the rolling direction. The disturbed surface was removed by electrolytic polishing in dilute orthophos-phoric acid (H3PO4) with a specific gravity of 1.14, and a current density of about 1 to 2 amp per sq cm. A 3-min polishing was needed to eliminate the disturbed surface causing Debye-Scherrer rings and a 45-min polish produced a surface which yielded sharp rounded Laue spots. It was estimated that about 1/16 in. of metal was removed from the original cut surface. The final orientation of this specimen before rolling was about 2" from the (110) plane in the rolling plane with a [112] direction aligned in the rolling direction. It is possible that a small amount of strain was still present in the cube despite the fact that the Laue spots seemed very sharp. It is doubtful, however, that this would be an important factor after a subsequent rolling reduction of 99.5 pct. This copper specimen was rolled on a laboratory rolling mill with two highly polished rolls 37/8 in. in diam in the following manner: 0.010 in. per pass to 50 pct reduction, 0.005 in. to 70 pct, 0.002 in. to 85 pct and, finally, 0.001 in. per pass to a 99.5 pct reduction. Specimens, about 1 in. sq with the rolling edges intact, were cut from the rolled strip by the electrolytic method previously described, after the strip

Jan 1, 1954

ONE of the largest hard rock operations ever undertaken on the continent is part of the Aluminum Co. of Canada's gigantic British Columbia development in the mountainous wilderness back of the north coastal port of Prince Rupert. To provide electric power for the huge aluminum smelter under construction at Kitimat, 400 miles northwest of Vancouver, Alcan is reversing the flow of a 5000 sq mile drainage area by blocking the eastward-flowing Nechako River with the largest sloping clay core dam in the world. The backed-up waters of a 110-mile chain of lakes will be tapped at their eastern end by a 10-mile tunnel piercing a mile-high mountain range. From this tunnel water will pass through penstocks to a subterranean powerhouse after a drop of 2600 ft and empty into the Kemano River almost at tide water. A projected battery of eight turbine-driven generators will produce more than a million horsepower, although, initially, three generators of 140,000 hp each will be installed. Power will travel 50 miles across another mountain range, over a glacier, and across an arm of the ocean to what will ultimately be the world's largest aluminum smelter-a plant 2 ½ miles long. Ore smelted at Kitimat will come from Jamaica, but carving the tunnel, penstocks, and powerhouses cavern out of the heart of a mountain is so vast a job that most of the problems of a major mining operation are encountered. The powerhouse cavern alone is a big hard rock job. This chamber lies 1400 ft back from the mountain face and will eventually be 1100 ft long, 80 ft wide, and an average 118 ft high. Now under construction, the roof of this cavern will take the form of a parabolic arch. The prime contractors, Morrison-Knudsen Co. of Canada, are to excavate a length of 700 ft by May 1954. This section will provide a main control room, erection bay and space for eight generating units. The roof arch is to be lined with reinforced concrete and a plan now under study provides for concrete curtain walls separated from the rock sides of the cavern to prevent moisture accumulation. Cavern Excavation Excavation of the cavern began with the driving of an 8x8-ft exploratory drift 1500 ft long. Two horseshoe-shaped access and tailrace tunnels were bored to serve excavation work. These tunnels are approximately the same length as the exploratory drift and 25 ft high. The floors of both tunnels were graveled to permit the use of rubber-tired equipment. Eventually, the tailrace tunnel will be enlarged to 40 ft height to drain water from the turbine pits below the powerhouse floor. When the tunnels reached the cavern location, a mucking tunnel, approximately 25 ft square, was driven the projected length of the powerhouse at the floor level of the cavern. Another tunnel, 10 ft square, was carried in the same direction from the exploratory drift at the level of the arch spring line, 65 ft above the cavern floor. To connect these two tunnels, seven shafts 10 ft wide and approximately 80 ft long were driven through to the lower mucking tunnel, 65 ft below. These shafts were located on 120-ft centers, the length of the powerhouse cavern. Blasting is done from this upper tunnel to the final line of the roof arch. Two bulldozers, an International TD-24 and a TD-9, doze blasted material to the shafts where it drops to floor level. From here, the rock is loaded by Eimco loaders and power shovels into rubber-tired Koehring Dumptors and Euclid end-dump trucks. The arched roof section will be completely excavated and concreted before vertical blast holes are drilled down from the level of the arch spring line to the floor of the cavern. The arched roof section with its parabolic curve will have a width of 80 ft and a rise to the crown of 47 ft.

Jan 1, 1952