Search Documents

DEFENSE Materials Procurement Agency has been moving rapidly to encourage copper industry expansion programs. Although copper production is at a high level, a shortage exists on a world-wide basis as well as on the domestic scene. Projected expansion programs will not ease this current demand for most of them are 2 to 5 years off. Refining facilities are adequate but there is a shortage of ore and scrap, and it is for this reason that the expansion programs are directed at developing more sources of supply. The domestic expansion programmed thus far and understood to have been arranged with price escalation should the domestic price go to 271/20, were summarized by American Metal Markets as follows (dates of announcement are given in parenthesis: .1-Copper Cities Mining Co.'s, $15,000,000 expansion near Miami, Ariz., to be operating about 1954. DMPA will buy 22,500 tons of copper a year up to a given amount on an agreed price of 23¢ per pound, with some exceptions and depending upon salability at a higher price to other purchasers in the U. S. (September 25th). 2-An RFC loan of $60,000 to North Butte Mining Co. to be paid off on the basis of deliveries at a purchase price of 241/20 per pound (September 25th). 3-A $25,000,000 expansion program by Phelps Dodge to provide 38,000 tons per year by late 1954. DMPA would purchase it at a price of 22¢ per pound up to 112,500 tons providing other purchasers in the U. S. will not pay a higher price (September 26th). 4-Anaconda Copper Mining Co. $40,000,000 expansion in Nevada to provide more than 30,000 (might be increased to 45,000) tons per year. DMPA would purchase the copper at 250 per pound for a limited period of time if it is not salable to industrial users at above this price. Production would start around 1953 (November 14th).

Jan 1, 1952

By J. R. Cobble

Dissolution of chalcopyrite with acidified ferric sulfate produces a sulfur layer on the unreacted chalcopyrite surface that interferes with further dissolution. The U.S. Bureau of Mines has developed a process to improve the leaching kinetics of these types of diffusion-controlled systems. The system features the Bureau-developed turbomill, an attrition grinder that scrubs the reaction product coating away from the unreacted mineral grains during leaching. The system can be operated continuously at any temperature up to the boiling point of the leaching agent. This method is a hydrometallurgical alternative to chalcopyrite smelter technology and eliminates sulfur dioxide emission problems with its associated costs. Batch testing at 900 C with the chalcopyrite-ferric sulfate system resulted in copper extraction exceeding 99 pct. At an optimal energy consumption of 1,520 kW· hjst, 95 pct of the copper was extracted. The pregnant liquor was clarified and tested for typical solvent-extraction recovery of the copper. Two-stage extraction and two-stage stripping recovered 96 pct of the copper in an electrolyte suitable for copper electrowinning.

Jan 1, 1993

By Kalervo Rankama

UNTIL a few years ago, geological mapping, the study of ore boulders, and different geophysical methods were the principal means used in the systematic search for mineral deposits covered by a layer of disintegration products or soil. These methods have been developed to a high stage of perfection as far as the geometrical definition of the conductor is considered. Use of geophysical methods in prospecting is based on the fact that an ore body differs from the country rock not only geologically but also in its physical properties. The general drawbacks and complications included in the use of geophysical methods are well known to everyone who has been using them, so need not be entered into here in detail. One of the more important ones is the fact that geophysical methods are unable to furnish information concerning the chemical composition of the ore bodies responsible for the indications. Further, the ores of many metals, such as silver, gold, beryllium, zinc, mercury, tin, lead, vanadium, antimony, chromium. molybdenum, tungsten, manganese, cobalt, nickel, and the platinum metals cannot be directly located by known geophysical methods, owing to lack of physical characteristics suitable for distinguishing them from the country rock. Thus it is quite natural that efforts have been made to develop direct methods for prospecting and locating ore bodies of the elements named. Known as chemical, biogeo-chemical, and geobotanical methods of prospecting, these have been much improved during recent years. A brief review of these methods and of some results obtained with them will be presented in the following, on the basis of available information and my own experience.

Jan 1, 1947

By D. Harrington

We Americans pride ourselves that ours is the greatest, most advanced and most civilized nation in the world, yet statistics indicate that apparently we have little appreciation for the lives and limbs of the people whose efforts give us whatever greatness we possess. The latest available statistics indicate that the annual accident death rate per 100,000 of population is nearly 80 or far higher than that of any other country in the world except Chile; is more than double the rate in Hungary, Netherlands, Ireland, Belgium, Denmark, Italy, Germany, Norway, Sweden, and Finland; is nearly double that of England, Wales, the Union of South Africa, New Zealand, Japan, Australia, and Scotland; and is 25 to 40 percent greater than Switzerland, France and Canada. To make matters worse, from the viewpoint of mining; the latest available statistics give mining by all adds the worst accident rate of the major industrial occupations in the United States, the accident severity rate for mining in 1935 being listed by the National Safety Council as 10.14, the next highest rate being 4.52 for construction, and the average rate for 30 main industries being 1.58. IMPROVEMENT IN SAFETY RECORDS Offsetting to a slight extent this rather dark picture is the fact that starting about 1930 the mine-accident rate in both coal and metal mining began to fall, reaching an all-time "low" in metal mining in 1932 and in coal mining in 1933. It now appears probable that the year 1936 has again lowered the accident rate in coal mining and this, together with the fact that the years 1933, 1934, 193 5, and 1936 all set much lover accident rates in coal mining than ware achieved for any similar previous period, gives hope that the trend is definitely in the right direction, though from the above figures mine-accident severity has a long, tedious road to travel before it becomes as low as the severity rate of all other major industries in the United States.

Jan 1, 1937

By L. K. Eigenbrod

Throughout the mining industry, pneumoconiosis is one of the most severe occupational health problems being faced. The goal of completely eliminating pneumoconiosis as an occupational health hazard was underscored by the Federal Government with its enactment of Public Law 91-173 (Federal Coal Mine Health and Safety Act of 1969). Under this law, permissible dust level standards will be placed at 2 mg/m3 in mine atmospheres by December 30, 1972. The mining industry is thus faced with the tremendous technical challenge of achieving this level. Two basic questions can be raised with regard to this legislation. First, does a maximum dust concentration of 2 mg/m3 prevent the occurrence of pneumoconiosis? Secondly, can this dust standard be achieved using presently available methods and equipment? A precise answer to the first question has not yet been developed by the medical profession. Studies are continuing on the origin, prevention, and therapy of pneumoconiosis, and permissible dust levels could become even lower as medical evidence accumulates. The mining industry has addressed itself to the problems of dust con-tro1 for many years as related to personnel health, explosive mixtures, visibility, and machinery damage. Dust control methods being employed involve

Jan 1, 1971

By Kevin J. Ma, John Stankus

"In order to access remote reserve areas, some U.S. coal mines have to maintain aged underground entries for a great distance. However, high humidity, warm temperature, and time dependent deterioration can cause progressive roof deterioration and unexpected roof falls can, pose a great challenge to ground control engineers. With an active belt structure in place and limited space, re-bolting becomes very costly, less effective, and, sometimes, impractical and unfeasible. To gain long-term entry stability and serviceability, operators typically rehabilitate the aged belt entries by installing standing steel set supports. In the last several years, Keystone Mining Services, LLC, (KMS) has assisted many coal mines with their belt entry rehabilitation projects, evaluated the ground condition of various aged belt entries, and designed different standing steel set support systems. This paper presents a case study of a large-scale roof fall that occurred at an aged belt entry in a mine located in an eastern coalfield, analyzes root causes of excessive deformation of square sets that were installed in an adjacent entry, evaluates the adequacy of an existing rehabilitation square set, and develops remedial recommendations for future rehabilitation practice. Based on the case study, the paper outlines design guidelines for rehabilitation steel sets that include field evaluation, engineering considerations, design assumptions, steel structural analysis, and field installation quality control. INTRODUCTION With gradual depletion of shallow coal reserves, some underground coal mines have to maintain long-term entries (belt, track, return airway, etc.) for a great distance in order to access remote coal reserve areas. However, due to high humidity, warm temperature, and aging in the belt entry, roof strata weathering and pillar degradation become more and more severe. Progressive roof deterioration poses a great challenge to ground control engineers. Pillar rib sloughs at certain locations, entry width increases in some areas, immediate roof sags, immediate roof rock falls out between bolts, existing bolts lose functionality due to corrosion, cutters develop deeper in corners, and strata separation develops deeper up into the main roof. As a result, unexpected roof falls occur in a random manner resulting in loss of production, damage of belt structure, and even injuries to underground personnel."

Jan 1, 2017

By F K. R Klose

Malmberget is a sublevel caving mine owned and operated by Luossavaara-Kiirunavaara Aktiebolag (LKAB), a Swedish state-owned iron ore mining company, in northern Sweden. The mine has an annual iron ore production of approximately 15 Mtpa. The current strategy foresees an expansion which will increase the mine’s depth considerably. Ventilation and air conditioning modelling for the planned expansion is ongoing. One of the most influential parameters for ventilation planning anddesign for a deep mine is geothermal gradient, which is crucial for the design of the refrigeration system. It is determined through virgin rock temperature (VRT) measurements carried out at various depth below the surface. This paper details these measurements and the determination of geothermal gradient for Malmberget Mine for the expansion study, which were necessitated by thelack of information for the focus depth and area.

Oct 12, 2022

By A. W. Gauger

DESPITE many handicaps and in the face of many discouragements anthracite and bituminous coal producers continue to supply the needs of the nation now vastly multiplied by the demands of the greatest war of all time, total output being about 620,000,000 tons of bituminous and 64,445,000 of anthracite. The progress made by this industry during the national emergency reflects more credit on all connected therewith than will ever be given. Not only has the industry been called upon to produce more coal than ever before but it has also sent representatives to England to study and advise on methods for increasing production there, and has co-operated with other Allied Nations by welcoming engineers sent to this country to study American practice. One noteworthy development has been the growth of strip mining in the

Jan 1, 1945

By W. H. Class

The embrittling effects of oxygen, ozone, nitrogen, air, and surface residues, on NaCl has been investigated. The embrittlement by ozone and oxygen was found to be associated with the formation of a NaClO3 surface compound. In these cases the initial crack that was responsible for fracture (in a bend test) always nucleated at the corners between the tension and side faces. The behavior of air was very erratic and on certain days did not produce enzbrittlement. During these periods, crystals that had become embrittled by the ozone treatment completely recovered their ductility after a short exposure to the ambient atmosphere, It was established many years ago1 that considerable ductility could be obtained in NaCl single-crystal specimens if the crystal surfaces were dissolved in water either during or immediately prior to the test. The original interpretation of this effect by Joffe attributed the enhanced ductility to the removal of surface microcracks by dissolution. Later investigations2'3 have suggested that the exclusion of air from the specimen surface is the criterion for extensive plastic flow prior to fracture. The air em-brittlement in this later work was attributed to the diffusion of gaseous atoms into the surface layers of the crystal, thereby impeding the movement of dislocations. This model satisfactorily accounts for the reembrittlement observed after further air exposure subsequent to the water dissolution treatment. However, the situation has recently become more complex by the observations in several laboratories4-t that under certain conditions air exposure does not impair the ductility of NaC1. It has also been recognized5 that improper drying operations after water dissolution can leave surface precipitates that lead to embrittlement. Cleavage defects on as-cleaved crystals can often be another source of embrittlement. In the present work the effect of the gaseous atmospheres nitrogen, argon, air, oxygen, and ozone, on the ductility of rock salt was studied extensively. The embrittlement resulting from oxygen and ozone exposures was found to be associated with the formation of a NaC1O3 surface film. It is suggested that certain atmospheres, one of which often can be ambient air, which inhibit the formation or favor the decomposition of this compound, can promote ductility. Thus one aspect of the Joffe effect is certainly related to the removal of surface compounds or complexes by water dissolution. The effect of surface precipitates that remain after drying operations and of cleavage defects were also studied. In neither of the latter cases was the embrittlement as severe as that found with a NaClO3 surface layer. PROCEDURE AND SPECIMEN PREPARATION The nature of the embrittlement produced by the agents mentioned above was studied by means of microscopy, mechanical testing, and X-ray diffraction. Specimens were cleaved from large crystals of optical quality sodium chloride obtained from the Harshaw Chemical Co., and, except for those tested in the as-cleaved condition, were given a 15- to 20-sec immersion in distilled water followed by a rinse in absolute methyl alcohol. The specimens were then blotted on a soft, absorbent paper, and dried by a few seconds exposure to a stream of warm, dry air. Such a procedure was found to give a control surface which was microscopically free of residues. (A few crystals were intentionally painted with a concentrated NaCl solution in order to investigate the effect of surface residues). All specimens were of 0.140 sq in. cross-section. Crystals prepared in the above manner were immediately placed in a gas train where they could be exposed to the desired gases for preselected periods of time. For the oxygen and nitrogen exposures, pure reagent-grade gases were employed. The ozone was provided in the form of an ozone-oxygen mixture (approximately 10 pct ozone) prepared by passing commercial grade oxygen over a strong ultraviolet light source. All gases were dried prior to their introduction into the train. Since argon was found to be completely inert in its behavior (i.e., residue-free specimens that were exposed to argon were not embrittled), it was periodically utilized to check the control specimen surfaces as well as the condition of the gas train used for aging the specimens. After exposure to the gaseous media in question, the crystals to be used for the measurement of the strain to fracture were transferred from the gas train to a protective oil bath (without further exposure to the atmosphere) where the tests were conducted in three-point bending. The apparatus was so adjusted that the load could be applied at a constant, continuous rate. Other Snecimens from the gas train were deformed

Jan 1, 1962

By Steve W. Webb

The Bureau of Mines is researching a new technology for dewatering clay suspensions that consists of flocculation by high-molecular-weight poly-ethylene oxide (PEO) polymer and subsequent removal of water from the floes via a trommel. The minimum amount of PEO required to dewater the clays depends on the ions adsorbed on the surface of the elay particles. Infrared studies were performed on clays with Li+, NH4+, K+, Mg2+, Ca2+, Ba2+, or 8r2+ adsorbed, with and without adsorbed PEO, to develop data to aid in understanding the dewatering mechanism. Hydroxyl stretching modes between 3,400 and 3,250 em-I, associated with water adsorbed on the clay, showed changes in intensity proportional to the ionic eharge-to-radius ratio; that is, the ionic potential. In addition. a water-bending vibration of adsorbed water at 1,630 cm-1 showed variations associated with water desorption. The data are consistent with changes in adsorption of PEO resulting from variation of the acidity of water coordinated with the exchange ions, induced by the variation in field strength of the ions with the ionic potential.

Jan 1, 1986

By Nagarajkumar BV

Pavai-and TeampT JV started working on the project T49A, Sumbar J & K State as part of slope and earth stabilization for ongoing Banihal - Katra Railway Connection Project. This project has several tunnels and bridges with slopes that are protected with various types of protection system such rock bolting, rock anchors, and micro piles. For the main two bridges Bring number 2 and 3 at T49 A location Pavai - TeampT JV has to design and execute the circular group of micro piles (Fig.1) for deep excavation of earth for the purpose of construction of well foundations (CAISSON FOUNDATIONS) for both bridge 2 and 3 piers. In this paper we discuss about the purpose, basic design, detailed design approaches and actual work implementation of micro pile with composite rock bolt applications and permanent rock anchors for slope stabilization works in this project.

Nov 1, 2022

By R. P. Tavares, M. Isac, R. I. L. Guthrie

"The configuration of the metal delivery system used in twin-roll casting can play a significant role in determining both internal and surface quality of the strips produced by this process.In the present work, a mathematical model for coupled turbulent fluid flow, heat transfer and solidification was developed and used in the study of metal delivery systems for twin-roll casting of low-carbon steels. This study was applied to a pilot twin-roll caster being investigated in Canada, with a roll radius of 0.3 m, producing strips of thicknesses from 4 to 7 mm, at roll speeds ranging between 4 and 12 m/min. Various configurations of metal delivery systems were simulated and their effects on the advance of the interdendritic solidification front and levels of turbulence and temperature within the caster investigated. According to the predictions of the model, an extended nozzle with inlet flow towards the surface of the rolls seems to be the best alternative for feeding liquid steel into twin-roll casters.A full scale water model of a pilot twin-roll caster was also built and used to qualitatively validate the predictions of the mathematical model.Various techniques for fluid flowvisualization were applied. In general, the predictions of the mathematical model were in reasonable agreement with the experiments with the water model."

Jan 1, 1999

By C. Matthews, A. Vo

"Australia is one of the world’s leading exporters of bulk commodities and the extensive use of sampling equipment is key to the successful management of each mining operation. At the process plant, without a full understanding of the feed, product and tails, it is impossible to fully optimise the performance of the plant, such that the metallurgical balance is often open to error. At the port, a statistically correct, bias free and compliant sampling system is crucial to ensuring exported minerals are reflective of their true value and to avoid penalties. Over the last decade, as a result of the iron ore boom, there has been high demand for reliable, representative and standard compliant solids sample systems in Australia. This paper reviews several solids sampling applications at Australian mine sites, the challenges and experience gained and how the implementation of reliable representative sampling systems has provided better understanding of plant process performance, improved plant control and overall benefits to the operations.INTRODUCTION Mining is the primary contributor to the Australian economy with Australia ranking in the top 4 in economic resources for 21 primary industrial minerals in 2016 (Britt, et al., 2017). Australia is one of the world leaders in the export of the majority of its commodities including gold, copper and iron ore (Britt, et al., 2017). Therefore, a suitable and standard compliant sampling system is essential for evaluating plant performance and content verification. At the mine and at the port, the larger iron ore miners in Australia have developed stockpile models to predict the grade of their ore down to individual blocks of the stockpile. This allows the miner to create the right blend of material for sale to their customers and ensures they are not underselling their product or at risk of penalties for impurities or low grade. As an example, the average difference between the benchmark 62% Fe and low grade 58% Fe fines at the time of this report averaged US $30/tonne according to the Metal Bulletin Iron Ore Index. At a shipload of 180kt this would be a variation of US $5.4M. Whilst this is an extreme example, it highlights the economic importance of producing the correct grade product and a recognised representative sample of said product."

Jan 1, 2019

By Larman J. Heath

Liquid incendiaries were burned within the interstices of several different types of sandstone cores to determine the technical feasibility of increasing sandstone permeability by this method. Fuel-oxidant mixtures were tested in 186 cores; six cores exploded when ignited. In virtually all instances, the explosion completely pulverized the sandstone cores. In addition n those cores damaged by explosions, 24 cores were fractured so severely that permeability tests were impossible. Although combustion gener¬ally increased the permeability, specific mixtures at given pressures were inconsistent in their ignition and burning behavior. Tests indicated that the heat of burning incendiaries significantly increased sandstone permeability. The improved permeability ratios were usually less than 2, but one was 10.3. Permeability alteration by other in situ methods was not as effective as that by flame propagation.

Jan 1, 1971

By K. Biswas

So far, all pillar design methods or approaches consider the coal seam as a uniform structure From some mine visits in northern Appalachian Region. it is found that some coal seams have binder or parting material within the coal scan with varying thicknesses and numbers- And it has also been found that these kinds of hinder materials tire prone to weathering when exposed to ambient mine moisture In this paper an attempt has been made to study the weathering susceptibility of parting materials and coal when exposed to moisture and a two dimensional finite element analysis has been carried out to study the effect of the presence of partings on the structural integrity of the coal pillar in terms of short-term and long-term stability.

Jan 1, 1995

By Willard L. Cumings, Benjamin L. Miller

(Glen Summit Meeting, June, 1911.) I. THE CAMAGUEY DEPOSITS. 1. Location. THE Camaguey brown iron-ore deposit covers the top of San Felipe hill, the nearest point of which lies 14 miles NW. of the city of Camaguey. While there are several low flat-topped hills in the vicinity covered with a more or less continuous mantle of brown iron-ore, the deposit of San Felipe hill is the only one of any size and importance, and the name "San Felipe district " is proposed for the region. The deposit extends in a NW-SE. direction for a distance of about 10 miles, with an average width of 5 miles. The location is shown in Fig. 1, a sketch-map of the eastern part of Cuba. Fig. 2 is a map of the San Felipe district. 2. Description. The district is mentioned by Spencer,1 who says: "The Cubitas iron-ore fields are situated from 12 to 15 miles north of Camaguey City, in the province of Camaguey Within an area measuring roughly 10 miles east and west and 4 miles north and south, there are several flat-topped mesas rising 300 to 400 ft. above the level of an almost featureless plain which extends for many miles in all directions except toward the north." With the exception of the discrepancy in his statements as to the distance from Camaguey and the area of the hill, which is over 50 sq. miles, his description is a very good one. Kemp 2 has the following to say of ores in Carnaguey Province * Geologist, Bethlehem Steel Co. + Professor of Geology, Lehigh University. 1 Bulletin No. 540, U. S. Geological Survey, p. 324 (1908). 2 The Iron Ore Resources of the World, printed by the Eleventh International Geological Congress, vol. ii., p. 795 (1910).

Mar 1, 1911

By R. C. Fernandes, F. L. Santos

Aluminum alloys in particular, have certain limitations when subjected to welding process. This is mainly present because aluminum alloys have high thermal conductivity, high contraction in solidification and high hydrogen solubility. Taking this into account, the FSW process has great potential for this application, since it is autogenous, held without metal melting and without the use of slags or shielding gases. From this concept, the aim of this study is to evaluate the joining of thin sheets of aluminum alloy 3105 H26 with 0.7 mm of thickness. To performing of the tests, some parameters were analyzed, such as: tool penetration in the sheets, attack angle, the type of welding tool and penetration control mode (position or force). The results indicated that the force control mode is most suitable for thin sheets, and the transient state at the beginning of welding was the most critical part to control the welding quality.

Jan 1, 2015

By Constantine C. Popoff

"INTRODUCTION AND SUMMARYDuring 1946 several high-grade limestone deposits in western Washington were examined by the Bureau of Mines. This report presents the data obtained from investigation of the Sauk Mountain deposits in east-central Skagit County, Washington.The investigation consisted of transit and topcgraphic surveys and sampling. The areas selected for sampling were first cleaned by blasting; channel samples up to 40 pounds were cut where practical. Chip samples averaging 30 pounds were taken where channel samples could not be cut. A total of 21 samples in the Sauk Mountain area were taken and. analysed. The locations of the samples are shown in figures 2 and 4, and the analyses are listed in tables 1 and 2. This investigation is a part of a long-range program of general investigation of mineral resources for future industrial development of the Pacific Northwest. The Sauk Mountain deposits were investigated for the purpose of disclosing now sources of high-purity limestone, which could be mined and shipped at low cost to Seattle and other industrial cities in the Pacific Northwest."

Oct 1, 1948

By B. Peszko

There are many measuring methods of grain sizes. Taking into consideration the fine grained materials, one of the existing techniques is measurement of grain size by the Coulter Counter method. This method is based on the measuring the changes of electrolyte resistance during grains flow through the calibrated diaphragm. This method is relatively simple to apply, significantly precise and the results are given quickly. However, the problem is that the measurements are limited by the size of diaphragm. Because of this situation, measurement of grain sizes by this instrument is possible in range from 10% to 60% of diaphragm diameter. This limitation causes the necessity of re-placing diaphragm in case when the measured grain size distribution concerns the material of large size range. In purpose of determining the total grain size distribution, the synthesis of some partial distributions, given for individual grain fractions (with different diaphragm applied), is required. This is possible to do by calculating the mixture of distribution functions, created from the partial distribution functions. Two materials were selected to research: quartzite and glass, which were comminuted in cylindrical crusher, additionally grinded, screened and then analyzed by Coulter Counter for five grain fractions: 0~125 µm, 0~80 µm, 0~56 µm, 0~40 µm and 0~25 µm. For each fraction, five different partial distributions were given (in case of glass ? four), which are the basis for the creating the joined grain composition. To assure the adequacy of the given distribution function, it is necessary to obtain the possibly best approximation of partial distributions. In the work, both the parametric and non-parametric methods of density approximations of investigated random variable. For each grain fraction the approximations were done by three traditional distribution functions: RRB, GSA and log-norm distribution functions and three methods of non-parametric approximation: Gauss kernel, Epanechnikov kernel and orthogonal Fourier series method. As the criterion of the certain distribution function acceptance, the value of the residual deviation was assumed, given by the formulae:

Jan 1, 2014

By Alex Grenoble, Alex Reeb, George Filz, Farzad Abedzadeh

"This paper summarizes available information on the characteristics and properties of deep-mixed soilcement produced by the wet method. The topics covered in this paper include: unit weight, unconfined compressive strength, strength variability for field mixed materials, influence of curing time, influence of consolidation pressure, Young’s modulus, differences in strength and stiffness between small and large samples, creep deformations, Poisson’s ratio, and tensile strength. In addition, this paper discusses the development of design considerations and recommended property values for a project that uses soilcement to protect an existing dam penstock from loads applied by an overlying stability berm. Some of the key recommendations for the deep-mixed soil-cement to be used in this project are that (1) a curved strength envelope that includes tensile strength can be used in the analysis, (2) the stress-strain and strength properties can be characterized using Duncan and Chang's (1970) hyperbolic model, and (3) a specification based on the median unconfined compressive strength value is appropriate.INTRODUCTIONFor many projects, including foundation and embankment support, deep mixing can be designed based on simplified procedures and following standardized guidelines (e.g., FHWA 2013). However for unusually complex or critical projects, it is often necessary to perform numerical analyses, and in order to perform these numerical analyses well, a thorough understanding of the material properties is needed.This paper summarizes information on the characteristics and properties of deep-mixed soil-cement produced by the wet method, and it discusses the development of design considerations and recommended property values for a specific project, herein referred to as the penstock project, that requires numerical analyses. For the penstock project, a horseshoe-shaped enclosure of soil-cement is being considered beside and above an existing dam penstock to protect it from loads applied by an overlying stability berm that will be constructed for seismic remediation. The concept is to use soilcement created by the deep mixing method along the sides of the penstock and to use compacted soilcement above the deep mixing to create the crown of the protective soil-cement zone around the penstock. For this application, the soil-cement stiffness, rather than its strength, is the controlling design parameter. To achieve the necessary soil-cement stiffness, the strength will be high enough that the factor-of-safety values against instability along potential failure surfaces passing through the soil-cement are high. Following conventional practice, the soil-cement acceptance criteria will be based on the unconfined compressive strength, and the specified strength will be selected to produce the desired modulus value."

Jan 1, 2015