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By G. T. Lapidus, J. Trejo-Gallardo

A phenomenological model is presented for leaching silver from silver sulfide contained in mineral particles with ammoniacal thiosulfate solutions of copper in stirred reactors. Experimental results were used to adjust the kinetic parameters of the model, such as the reaction order and velocity. The incorporation of the cuprous sulfide-silver sulfide equilibrium at the reaction interface allowed the prediction of the conversion limits for different reagent concentrations. The information obtained from the reactor model was later integrated into a heap leaching simulation, whose results adequately describe tendencies observed in column tests, with respect to variations in copper and thiosulfate concentrations. Comp

Jan 1, 2005

By J. Shibata, N. Murayama, H. Yamamoto

As one of effective usages of wastes discharged in the non-ferrous metal industry, the syntheses of AlPO4-5 and hydrotalcite were carried out using aluminium dross as a raw material. AlPO4-5 is an aluminium phosphate condensate with properties of zeolitic materials and large pore size. Hydrotalcite is an inorganic anion exchanger and has a layered structure of complex hydroxide. They were synthesized in an autoclave at high temperature and pressure. Various physical properties such as crystal structure, surface texture, and specific surface area were measured. AlPO4-5 can be synthesized from aluminium dross under hydrothermal conditions at 180°C-200°C, and 3h. At the same time, AlPO4-34 and non-porous AlPO4 were also formed as by-products. The crystals of AlPO4-5 have a hexagonal structure. Lt is desirable to heat the reaction product at around 550 °C to remove tri-ethyl amine. The specific surface areas of the reaction product before and after heat treatment at 550°C were 17.9m2/g and 358m2/g, respectively. Hydrotalcite can be obtained by a co-precipitation method from the aluminium dross and waste MgCl2 solution discharged in the aluminium regeneration process. Small amounts of SiO2, Al2O3, and Fe2O3 remain in the reaction product as an impurity component. The interlayer distance of the obtained reaction product is about 0.3 nm. Hydrotalcite changes to Mg-Al oxide during calcination at 500 °C for 3h, and then hydrotalcite is formed again by a rehydration operation. The physical properties of the reaction products obtained from the wastes were very similar to those from fresh reagents.

Jan 1, 2004

By H. F. Winham

THE history, development, subsurface geology, production, economics and estimated reserves are discussed in this paper. The Magnolia structure is an anticline with a known maximum structural relief at 372 ft., and the areal extent of the producing acreage is 4494 acres. Production is obtained from the Smackover oölitic lime and 116 successful wells have been drilled. The field, which was developed on 4o-acre spacing, has been under strict control. It is believed to be producing with a strong water drive. To date it has produced more than eighteen million barrels and the estimate of ultimate recovery is 220 million barrels. EARLY HISTORY The Magnolia field is in Columbia County, Arkansas, T. 17 S., R. 19 and 20 W. Various geologists had long been interested in this general area, and as early as 1921, John F. Magale was able to define a surface structure. The first wildcat, one of the first in Columbia County, was drilled in 1923 by Mid-States Oil Co., in sec. 10, T. 17 S., R. 20 W. This well was about 1 ½ miles northwest of the Kerlyn Oil Company's discovery well and was based on surface geological work done by jewel and Dobie. Subsequently, several shallow wells that were not carried below the Upper Cretaceous beds were drilled in the immediate area of the discovery well, but none of them contained any commercial showings of oil or gas. In the latter part of 1935, Elam and Magale (or Southwood) Garrett No. I was located in sec. 13, T. 17 S., R. 20 W., ¾ mile east of the discovery well. It was drilled to a total depth of 4018 ft. in the lowermost Glen Rose beds but failed to obtain any showings of oil or gas. Interest had been stimulated in this general area, however, by the discovery of several oil fields, mainly Glen Rose oil production in the Rodessa field in Louisiana in 1935, Smackover lime production in Snow Hill in May 1936, production from the Cotton Valley formation in Schuler in 1037, and Smackover lime production from the Buckner field in November 1937. With this background and subsequent seismic work, which was carried on partly because the old shallow wells drilled in the township had shown evidence of closure in the Upper Cretaceous beds, the discovery well, Kerlyn Oil Company's Barnett No. I, sec. 14, T. 17 S., R. 20 W., was originally projected to a total depth of 6300 ft., to test the equivalents of the Morgan sands of the Cotton Valley series, then producing at Schuler. The well was carried to a total depth of 6325 ft. and tested the objective beds without finding commercial production. In the meantime, however, one well had found production in the Jones sand and another in the Smackover lime at Schuler. Kerlyn immediately made arrangements to deepen the Barnett well to the Smackover lime. The top of the Smackover lime was encountered at 7618 ft. and the well was cored and drilled to a depth of 7740 ft.

Jan 1, 1942

By HeeDong Lee, Owen Reedy, Lawrence Matson, Naidu Seetala, Thomas Key

Spark Plasma Sintering (SPS) consolidated ZrB2+SiC composites using nano-powders (around 40 nm) showed smaller grains compared to those using micron size powders and segregation of SiC into islands is minimal but with higher oxidation of ZrB2 to form ZrO2 in nano-composites. Argon-gas purging prior to SPS consolidation at around 2000 °C and 40 MPa of ZrB2+20vol.%SiC nano-powders was used to minimize the oxidation and obtain fine granules with high densification. The densification of the Argon-gas purged nano-composites is higher compared to those consolidated without Argon gas purging. The EDX analysis showed a strong reduction in the oxygen peak for the Argon gas purged composites. The XRD spectra also support this observation with less ZrO2 phase composition in Argon gas purged composites. The Vickers micro-hardness showed slightly lower values for Argon gas purged composites though they have higher densification.

Mar 1, 2017

The Gippsland Basin, southeastern Australia, has an Upper Cainozoic history of episodic change of hydrology and the related environment, reflected in the geomorphology and surficial deposits of the onshore basin and the hydrodynamically controlled accumulations of petroleum of the offshore basin. Succeeding this episodic pattern, man through a number of activities, has had a sudden and major impact on the hydrology and the related environment. Activities include those directly affecting the groundwater system, such as extraction of fossil fuels with the consequent threat of land subsidence; irrigation and clearing of vegetation and the consequent effect of salinisation; change of land use and installation of septic tanks with resulting nitrate pollution; damming of streams and the consequent reduction in the frequency of floods with degradation of the biological Environment; de-snagging streams and construction of cutoffs with increased stream erosion, modifying wetlands including drainage, with the consequent degradation of their ecosystems; and increase in phosphate and nitrate inputs to the coastal lakes with the risk of their eutrophication.

Jan 1, 1992

By James R. Finlay

SOMETIMES the American Institute of Mining and Metallurgical Engineers appears to be a strictly technical society, and if so my paper should deal with the technical operations of finding and producing gold. But I have not been engaged in practical gold mining since 1910. What I have been doing mainly for the last 25 years is to try to figure out what the income of a mine-gold, or any other-would be worth to an investor. So I have been in contact with gold mining, in one way or another, for some 42 years. I say that with a purpose. In that time the industry has been through one of its cycles. The value of gold mines is very dif¬ferent at different points in one of these cycles. For this reason the cycle of gold mining is a highly practical study. The cycle of gold is a more or less rhythmical change in its value or purchasing power measured in the grand average of other commodities, which is the same thing as its price. Taking the price of gold in 1897 as a stand¬ard, a dollar at that time declined to 55c. in 1913, to 26.8c. in 1920, and since then it has risen to 47.4c. in 1930 and to about 64c. in 1932. It is worth about 21/ times as much now as it was in 1920, but less than two¬thirds as much as in 1897. When this change is applied to the value of a gold mine still greater differences are evident. The cost of producing gold is of course measured in labor and other commodities, and as that cost goes down the margin of profit measured in the gold itself increases. Thus a mine which might make only 10 per cent profit in 1920 on its gross output may easily make 25 per cent now. The stockholder gets 2 ½ times more gold that is worth 2 1/2 times as much in purchasing power, therefore the real value of his holding has risen by the one factor multiplied by the other, giving him 61/4 times as much goods or services as he had in 1920.

Jan 1, 1933

A mobile vacuum sweeper to remove loose coal and coal dust from underground coal mine workings was designed, built, tested, and evaluated. The design was based on an extensive test program. Pick up and conveying rates vs. air volumes, velocities, and nozzle shapes were determined for coal rubble in a laboratory pneumatic handling system. A gas/solids separation system was developed and tested in the laboratory capable of separating the solids loading from the vacuum system air stream to the very high degree required to preclude degradation of the ambient (mine) air. Two designs were made, one for belt conveyor and one for general district cleanup. The belt cleanup machine was chosen for test and demonstrated in an underground coal mine performing cleanup work in belt haulageways and on ribs.

Jan 1, 1975

By H. G. Lucas

A feeder screw supplied at constant pressure by a hopper-orifice arrangement was developed for feeding solids in size ranges up to several hundred micrometers at constant flow rates. Performance of the feeder was evaluated by measuring the flow rates obtained with 3-to 7-micrometer coal ash, 70 percent through 200-mesh coal, and minus 325-plus 400-mesh coal ash. Constant feed rates within a few percent of set values were achieved for half-hour periods for the larger particles and for 5-minute periods for the finer particles. Suggestions are given for feedstock preparation and feeder operation for optimum performance.

Jan 1, 1974

By W. W. Odell

Once it was believed that anthracite or coke were the only fuels generally available and suitable for the generation of water gas, particularly so when this gas was made in the generators of standard carburetted water-gas sets such as are commonly used in the manufacture of city gas. During the past 8 years, practice has changed considerably and it is now common to find gas plants operating without anthracite or coke and using bituminous coal in the generator. This change in fuel has appreciably increased the marketability and sales of certain coal producers' products; accordingly it is of interest to coal operators and others to know the reason for this change, the present trend in practice and the adaptability of various coals for generation of water gas. This paper briefly discusses these conditions and some of the factors relating thereto. Bituminous Coal not Ideal but Cheaper than Coke In spite of many changes which have been made in both process and generating apparatus for using bituminous coal as generator fuel more efficiently, in general it is not an ideal fuel for this purpose. It is supplanting coke because it costs less; it is so much cheaper per ton delivered at the gas works that water gas made therefrom costs less per unit-volume than that made from coke, even though the quantity of generator fuel consumed per therm (100,000 B. t. u.) of gas made is greater with coal. This is the reason why so many city gas plants, as well as others, are using bituminous coal instead of coke. Conditions Favoring Change from Coke to Coal The conditions which have made it possible and feasible, as well as economical, to supplant coke with coal may be summarized as follows: (1) Changes in methods of operating and alteration in generating apparatus; (2) lowering of the calorific standards for city gas, and (3) availability

Jan 1, 1927

By James E. Parkes

The Silver Spring Transit Center is a new three-level transit center that will include bus loops for County, Metro and intercity buses, parking, and retail space. It replaces an existing bus station and connects to a busy metro rail station in downtown Silver Spring, Maryland. Significant site constraints in both plan and profile had to be dealt with in developing a design for support of the structure. Over 90 rock-socketed drilled shafts ranging in size from 3 to 7 foot in diameter were ultimately used to accommodate the limited space and large column loads, and to adapt to the variable rock surface at the site. Site access during design was limited due to the existing active bus station, so contract documents were adapted to include further explorations. Differences in anticipated and actual field conditions regarding the depth, quality, and variability of the rock had to be overcome in construction. Osterberg Load Cell testing during construction allowed for verification and optimization of the shaft design. Additional issues dealt with on this constrained site in an urban setting included construction staging issues, such as working around specialty contractors for tieback walls, blasting operations for rock excavation, productions issues for hard bedrock, as well as coordination issues with third parties, most notably the Washington Metro Area Transit Authority. Aspects of the foundation design and optimization, preparation of the contract documents to deal with the complicated nature of the project, and lessons learned from construction are also discussed.

Jan 1, 2011

The paper concerns an unconventional, yet promising, use of waste magnesite dust and fines. In India a significant amount of this dust is generated from some of the integrated iron and steel industries, refractory and cement plants, during calcination of raw magnesite. However. it is possible to utilize this dust, which is normally a waste, conveniently and economically for the production of magnesium. chemicals. A bench scale study was carried out to determine the rate of formation of sulfated com¬pounds of Mg.Ca,and Fe, inter alla, present in the dust system containing MeO constituents (in which Me=Mg.Ca,Fe,Si,Al etc.) Effects of various process parameters, which affect the reaction rate as also the purity of the product ,were also studied. Some work carried out to develop the process flow charts involving the salient steps to produce magnesium chemicals commercially is reported in the paper .

Jan 1, 1992

By J. S. Roberts

"Campbell mines has been in operation since 1948. Part of the process consists of roasting of a flotation concentrate which contains arsenopyrite.At present operation level the milling rate averages about 850 t.p.d. and about 48 t.p.d. of concentrate is roasted. The gas emissions at present contain between 3 and 3.5 t.p.d. of arsenic trioxide, about2 - 2.5 t.p.d. of particulate matter and between 19 - 25 t.p.d. of sulphur dioxide. The particulate is extremely fine calcine dust and it assays about 4 oz. Of gold per ton.Until 1974 the gas was discharged untreated through a 125' stack.UntreatedThe decision was made in 1972 to erect a gas treatment plant, construction ran through 1973 and operation began in 1974. The cost of the installation was about 1.3 million dollars.On investigation the process technology, it was apparent that the plant operated by giant Yellowknife for the same purpose was the model we should study. I would like to acknowledge the fine cooperation we had from giant, the plant that emerged is very similar to theirs and incorporates some improvements suggested by them and based on their operating experience.The plant is designed to remove arsenic and solid dust and it has no provisions to remove sulphur dioxide.We depend upon the 125' stack to assure adequate dilution. Because of the nearby airport the stack cannot exceed 125'. A stack burner is provided that can ""y used to heat the stack gas and carry it higher into the atmosphere when there is an inversion condition.The removal of arsenic from hot gas is fairly simple. The sublimation point is about 425°f, a few degrees above this point the arsenic is a gas and a few degrees below it condenses into a solid form. The arsenic could have been removed by simply dropping the temperature below the condensation point and collecting all the solids in a baghouse. This would have removed the possibility of recovering the gold in the calcine dust and would have produced an impure and more bulky arsenic material to be placed in safe storage. The decision was made to collect the solid dust in a hot electrostatic precipitator operating above the sublimation point and subsequently lower the temperature below the condensation point and collect the arsenic in a baghouse."

Jan 1, 1976

By M. A. EI Zeky, A. E. El-Nikbaily, M. A. Shahin

"Possible mechanisms of microsilica dust formation and factors affecting its quantity have been discussed. General mathematical models to predict the dust quantity based on electrical and coke consumptions, and flue gas temperature as functions of silicon recovery in the process and silicon content of the alloy have been established. It has also been shown that the flue gas temperature can be used as an additional process control parameter. Comments are made on the effect of the dust formation on the whole process economics and it is pointed out that the formed microsilica dust is a valuable by-product and not an industrial waste. INTRODUCTIONFerrosilicon is produced in electric arc furnaces with submerged electrodes. The charge mixture consist s mainly of quartzite, coke as the reducing agent and iron chips. The products are ferro silicon and carbon monoxide, various other volatile materials, water vapour and silicon monoxide gas. Carbon monoxide and silicon monoxide oxidize at the charge surface when mixed with air entering through the furnace hood openings. The off-gas contains a considerable amount of dust, which is mainly very fine particles of silica formed as a result of oxidation. The emission of dust containing gases to the atmosphere causes serious pollution problems to the environment. Therefore, the control of the formation of the dust, preventing it from escaping to the atmosphere, and dealing with this very fine dust collected from the flue gases represent important technological and economical parameters in the ferrosilicon production industry.This paper is concerned with the relations between the quantity of formed micro silica dust, as a function of both silicon recovery and silicon content in the alloy, and various other technological parameters; and their possible effects on the energy consumption and economics of the whole process."

Jan 1, 1989

By B. Xu

Keywords: Magnetic damping, g-jitter, Hot-film anemometry Results from an experimental study on natural convection induced by temperature gradient in molten gallium contained inside a rectangular container. The damping effect of the convective flow from an externally applied static magnetic field is investigated. Induced velocity and temperature fields are mapped using a standard constant temperature hot-film anemometry and a thermocouple with and without the applied magnetic field, respectively. Detailed experimental setup and procedure are depicted in the present paper. Obtained velocity and temperature profiles are examined against previous numerical simulations and reasonably good agreement has been achieved. Obvious damping effect can be observed in both the temperature and the velocity profiles when the external magnetic field presents.

Jan 1, 2005

By Carlos Del Castillo Whittembury

El presente texto señala el uso de la bioRemediación como principal técnica que permite la digestión de residuos orgánicos contaminantes de aguas, suelos y aires. En el caso del agua, su limitación está en el tiempo de mantenimiento (5 días) donde se necesita contar con tanques o pozas acordes con los flujos a tratar, así como el control periódico del sistema. sistema. En el caso de suelos contaminados, es una de las opciones más convenientes por la facilidad de aplicación y la capacidad del tratamiento para remediar. Finalmente, en el uso del aire, los sopladores con membranas porosas mejoran los niveles de oxígeno disuelto, empleando menor energía eléctrica, cuyo aspecto redunda en un menor costo de los tratamientos. En este sentido, se busca mostrar nuevas tendencias de tratamientos a fin de regresar a las condiciones originales las aguas, suelos y aires contaminados por residuos orgánicos, inorgánicos e incluso por hidrocarburos, las cuales están disponibles en el Perú.

Sep 12, 2005

By M W. N Buxton, M T. Bootsma, J Benndorf, C Alford

Research in the field of cut-off grade optimisation has shown a relationship between cut-off grade, project life and net present value (NPV). Lane’s theory demonstrates that cut-off grades can be optimised in order to maximise project profitability. Although the theory forms the basis for many open pit mining projects, application of the theory in underground mining remains limited to-date. The main reason for this is the complex interaction between all processes in underground mine planning, which makes it difficult to apply Lane’s mathematical optimisation approach.Recently a new stope optimiser product was released. The AMS Stope Optimiser automates the design of underground stopes at user-defined cut-off grades and allows for rapid evaluation of mine designs at different cut-off grades. Using this software, an optimisation approach was developed and validated on an underground gold deposit in northern Sweden. Potential project NPV increased by approximately 30 per cent when using this new approach.Spatial grade uncertainty in mineral resources was identified to be a major risk in underground stope design. The optimisation approach was further extended to account for grade risk using estimated and stochastic simulated resource models. The resulting optimisation process accounts for grade risk early in the design process and reduces the risk of a stope not meeting the cut-off grade with subsequent financial loss.CITATION:Bootsma, M T, Alford, C, Benndorf, J and Buxton, M W N, 2014. Cut-off grade-based sublevel stope mine optimisation – introduction and evaluation of an optimisation approach and method for grade risk quantification, in Proceedings Orebody Modelling and Strategic Mine Planning Symposium 2014 , pp 281–290 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Nov 24, 2014

By S. W. Jacobsz, E. P. Kearsley, N. K. Schoeman

A physical modelling approach was adopted to simulate the process of cave mining propagation at various horizontal to vertical stress state ratios, and image data was captured and used to characterize the resulting failure mechanisms. Image processing was integrated into the study to determine minor principal strains in models to identify where critical extensional strains had been exceeded relative to crack propagation. The study exhibited a scale factor magnitude of 119 using a calculated critical extensional strain value of 0.014% for the modelling material used. It was perceived that cave propagation occurred through successive parallel extensional ‘fracture bands’ in all cases, as noticed in models of prior studies, deviating from that described by the Duplancic model. Cracks tended to bisect regions of minor principal strain equal to the critical extensional strain, which suggests ‘fracture banding’ is an acceptable failure mode for brittle, rock-like materials. Moreover, it was found that models with lower horizontal to vertical stress ratios (K ratios) showed a greater degree of vertical development of the caving mechanism (at similar vertical stresses), while the vertical extent of the cave was suppressed in models with higher K ratios. Models subjected to larger vertical stresses experienced slower cave formation in latter time-steps. These models exhibited larger two-dimensional caved perimeters and areas, respectively.

Nov 30, 2022

By John Platt, Mark Stephens

"When blasting is required in critical areas and anticipated shot movement and quick cleanup areessential to the success of the project it is extremely important to use the best technology available to achieve the goals expected by the customer. Wampum Hardware was given such a challenge in 2014-2015 when the PA Turnpike and New Enterprise Stone and Lime hired the company to do presplit blasting along the PA Turnpike. The face height averaged 45 feet (13.72m) and the shots had to be controlled to stop within 60-75 feet (18.29-22.86m) of the face or in this situation before they entered the travel lanes on the PA turnpike. In many if not most blasting environments, it is essential in controlling the movement of a blast, to make certain that the face holes are drilled at exactly the right place, with the proper amount and type of burden in front of and to the sides of the borehole. Profiling is an important first step to insure that the holes are drilled at exactly the right place and showing us the correct amount of burden in front of each and every drill hole."

Jan 1, 2016

By AIME AIME

BECAUSE of its unequalled skill, your country in- creased its production until, in 1913, it produced 40 per cent. of the world's consumption of coal, iron ore, and cast iron; 45 per cent. of the steel; and 60 per cent. of the copper. Your industrial effort, in a general manner and your mining effort in particular, has been tremendous. In the general economy of the world, you occupy an incomparable position of power and action. All your curves of production, mineralogical, metallurgical, financial, commercial, have taken terrific trigonometrical tangents and you will easily under- stand the sorry position of your competitors. I must, therefore, pay a tribute of homage arid admiration to you all who, each in his sphere, have been the artisans of such prosperity and my earnest wish is that you continue in this way.

Jan 1, 1920

By Charles H. Grant

Some of the limiting factors relative to explosive crushing of rock and ways to overcome a few of these problems are presented. Relationships between borehole diameters, bench heights, and spacings, along with a review of the influence geometry has on energy as these are changed, are discussed. Efficiency in use of explosives and the decay of energy as it moves through rock and is absorbed and dissipated, is described, along with fragmentation as a function of spacings and energy zoning, etc. Communications are one of the major problems encountered. In an effort to provide a better understanding of the use of explosives, it is necessary to take a little different view of what explosives are, how to look at them as tools to fragment rock, and some of the problems encountered in doing so. First, take the explosive: although there are many factors involved, consider these as being reduced to only two — shock-strain imparted to the rock by the high early development of energy, and the gas effect which is a combination of heat, moles of gas formed, rate of formation of these gases which develop pressures, etc. First, consider shock energy by itself and assume there is no gas effect in the reaction. Fig. 1 illustrates a block or cube of rock, in the center of which is detonated an explosive charge which is 100% shock energy. Tensile slabbing would be seen on the surface and probably the cube of rock would generally hang together even though microcracks were formed. If the situation is reversed and an explosive whch has no shock energy and only gas effect (Fig. 2) is considered, the cube of rock would act as a pressure vessel and contain the pressure from the gas effect until it exceeded the rock-vessel strength; then the rock would break in a few large pieces. If these two kinds of energy are put together and the area of shock-strain around the explosive (Fig. 3) is considered, the two energies will be seen working together to furnish broken rock. The gas effect applies pressure to the microcracks formed from the shock energy to weaken the rock-pressure vessel and propagate these cracks to break the rock apart. It not only will be broken more finely, but will break apart at a lower pressure than the gaseffect case, since the shock energy has first weakened the rock vessel. Although tensile spalling from the shock-strain imparts momentum to the rock, the main source of displacement comes from the gas effect. The term "rock" is being used to mean any material to be blasted. These energies are absorbed by the rock in different ways. First, classify rock into two main categories: "elastic" and "plastic-acting." Elastic rock should be thought of as rock which can transmit a shock wave and is high in compressive strength, such as granite or quartzite. Since this elastic rock transmits a shock wave well, it makes good use of the shock energy from the explosive-forming cracks, etc., for the gas effect to work on. Plastic-acting rocks are rock masses which are relatively low in compressive strength and absorb shock energy at a much faster rate, thereby making poor use of the shock energy by not developing as extensive a cracked zone for the gas effect to work on. Rocks of this type are generally softer materials such as some limestones, sandstones, and porphyries. For the most part, the shockenergy part of the explosive reaction is wasted in plastic-acting rock, leaving most of the work to the gas effect. Since the ratio of gas effect to shock energy is different in different explosives, it is easy to understand why some explosives perform well in elastic rock and poorly in plastic-acting rock, and vice versa. Some of the most difficult blasting situations arise when mixtures of plastic-acting and elastic rock are encountered (Fig. 4). Fig. 4 shows an example of granite boulders cemented together with something like a decomposed quartz monzonite which is plastic-acting. The elastic granite boulders will transmit the shock-strain within itself, but when this shock tries to move through the monzonite to the next boulder, its intensity is absorbed by the monzonite and little shock-strain is placed on the adjoining boulder. In addition to this loss by absorbtion, shock reflection at the surface of the boulder will effect tensile spalling. The net effect is poor breakage of the boulders which do not have drillholes in them as they simply will be popped out with the muck. The same is true (Fig. 5) when layers and joints make

Jan 1, 1970