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By Gerald Zink

The object of underground excavation--apart from mining-- is to create an opening to serve as a part of some useful structure. The value of the opening lies in its conformity to the design configuration and its stability during the planned life of the structure. The wire saw could be used to excavate openings of high value at a cost competitive with present methods. First, a discussion of present methods will be used to explain where wire sawing fits in and how it should be applied. PRESENT EXCAVATION METHODS Tunnel Boring A recent advance in tunneling technology is the use of mechanical boring machines. There are many ways that a boring machine can reduce the cost of a tunnel or increase its value. I will mention a few of the advantages that have been demonstrated in tunneling projects. A tunnel can be bored without overbreak, allowing concrete lining to be poured to the design thickness without waste. Boring creates a minimum of disturbance to the tunnel wall, preserving the natural strength of the rock and reducing the amount of support which must be installed to maintain stability. A boring machine maintains the tunnel at its full dimensions and proper shape, and it leaves no rock projecting from the wall which must be trimmed off. The use of boring machines is presently limited to openings of uniform cross section and great length. If the previously mentioned attributes of mechanical boring could be applied to excavation of a wide variety of chambers and passages, then a corresponding decrease in cost and gain in value would be possible for chambers.

Jan 1, 1974

By Gary F. Rajala, Bruce R. Greenwood

INTRODUCTION The Empire Mine is an iron ore mining, concentrating and pelletizing facility operated by The Cleveland-Cliffs Iron Company in the Upper Peninsula of Michigan. Owners of the mine are Inland Steel, LTV Steel, Wheeling-Pittsburgh Steel and Cleveland-Cliff s. The orebody is a fine-grained, low grade iron formation with magnetite as the primary constituent. Also present are iron carbonates, iron silicates, chert, hematite, goethite and quartz. The original six concentrating lines were started in late 1963. Successive expansions of ten lines in 1967, five lines in 1974 and 3 lines in 1979 have resulted in Empire reaching a present annual capacity of 8.0 million long tons of pellets. The Empire flowsheet was developed over several years of laboratory bench testing, pilot plant testing and testing of a full-scale primary autogenous grinding circuit. Since the original flowsheet was established, modifications have been made based on pilot plant and full-scale plant tests. The present flowsheet for three sections of the concentrator consists of one stage of crushing, two stages of closed circuit autogenous grinding, two stages of magnetic separation, one stage of hydraulic concentration and two stages of flotation (rougher and scavenger). The flowsheet for the fourth section of the concentrator (Empire 4) is the same as the first three sections, except a crusher has been added to crush excess pebbles. The Empire 4 flowsheet appears in the at- tached figure. PRIMARY GRINDING CIRCUIT FLOWSHEET Empire has a total of 24 individual grinding lines. However, at the present time, Line 1 is not being used for processing crude ore. The primary mill on Line 1 is now grinding flux stone for fluxed pellet production and the secondary mill is being used as a ball mill to grind rougher flotation tailings prior to a scavenger flotation circuit.

Jan 1, 1992

By Keith G. Wallace, Daniel J. Brunner

The traditional approach to mine ventilation planning involved making estimates of airflows, including leakage routes, and summing the corresponding pressure drops along consecutive paths in order to determine the fan pressures required. This methodology changed completely with the availability of computers. Mainframe digital computers began to be used for mine ventilation network analysis in the mid-1960's. Their use spread rapidly throughout the world in the 1970's. Mainframe machines were employed owing to the need for high speed numerical procedures and substantial storage requirements. However, during the past decade, the growing availability of low cost but powerful microcomputers has allowed the development of net- work analysis programs that can handle ventilation systems of hundreds of branches, and which can produce results within a few minutes. This paper discusses recent advances in software and hardware development specific to mine ventilation planning. Software developments include interactive data and output manipulation, graphical representation of output, internal checks on input parameters to preset ranges and subroutines which calculate the gas distribution throughout the network from known gas sources. Hardware advances have led to significant increases in memory to facilitate the analysis of large ventilation models, math co-processor chips which greatly shorten run times, and plotter hardware for graphical output displays. Recent software developments make it possible to graphically display output on printers faster than on standard plotters.

Jan 1, 1989

By P. M. Fozzard

The Chaucha porphyry copper/molybdenum deposit was discovered by a United Nations team of geologists working with a ?counter- part" team of staff of the Ecuadorian government's General Directorate of Geology and Mines (DDGM) in July 1968. The exploration program formed the latter part of phase I work plan of a two-phased exploration project financed by the United Nations Development Programme and initiated in late 1964. The author was a team geologist during the period 1965-1967 and subsequently project manager for the period 1968-1972. The Chaucha property lies some 10 km (6 miles) east of the north- south-running western boundary of what was known as Operation Area No. 5. This area of some 10 500 km2(4050 sq miles) is a square truncated to the southeast and centered on the city of Cuenca, the major provincial capital (Azuay Province) of southern Ecuador. The eastern half of the exploration area is dominated by the Cretaceous- Tertiary sedimentary valley (basin) of Cuenca (Caar-Azuay) and its related drainage area. The western half, in which Chaucha lies, is dominated by the high Cordillera Occidental volcanic plateau and the western erosional valleys of the Andes draining to the Pacific. The valley that dominates the eastern part of the area [I500 m (4920 ft) above sea level] is transected by the Pan-American Highway. Because of increased agricultural activity associated with the Cuenca Valley, the area is reasonably well covered by a road network of varying quality. The high western area up to 4000 m (13,120 ft) in altitude is largely barren and completely inaccessible by vehicle. The geological reconnaissance map of the region is shown in Fig. 1.

Jan 1, 1991

By Janusz S. Laskowski

The most important type of potash ores, sylvinite, contains sylvite, halite and a small percentage of insoluble gangue [sulfates (anhydrite), carbonates (dolomite), and clay minerals]. Primary normal long-chain amines are exlusively utilized to float sylvite from halite, but since mines are also adsorbed by insoluble slimes, the process requires prior desliming. This is carried out either by mechanical means, or by flotation of slimes and blocking off the adsorption centers on clays with the use of polyelectrolytes. Fractional crystallization is employed to produce fertilizer grade KC1 from disseminated ores with a high content of slimes. An extender oil is needed in addition to mine to float coarse sylvite fractions. The process is carried out in a saturated brine at mine concentrations exceeding the solubility limit and is strongly affected by temperature fluctuations. All these important features, which make this process differ from a conventional flotation, result from a high electrolyte concentration.

Jan 1, 1994

By F. L. Wilke

A model is presented to minimize the winning costs per shift within the different sections of a potassium mine by liner programming and to simulate the other areas to get all costs in order to comp re different production strategies. he model is based on a a given total layout of the underground mining which is considered to be fix during the planning period. Room-and-pillar mining is assumed to be used. Potassium extraction is done by drilling and blasting. Transportation of the raw material to sectional crushers is done by scoop-trams where it is crushed to coarse-grains which allow further transportation by conveyor belts to the hoisting shaft or to a bunker. When production is stopped, the continuously working factory is supplied by means of this bunker. Starting from a desired composition of the raw material the model has to keep the given total. demand of raw material per shift, to minimize the winning costs, to keep the capacity constraints of the equipment and to determine the planned output of production of the sections per shift. Costs of the areas which follow the extractions are added to extraction costs in order to allow a comparision of costs of several alternatives of production. Optimization in extraction and assignment of scoop-trams to sections is done by linear programming. The other areas of the mine are treated by simulation. The model output is a schedule of the calculated costs broken down into costs of processes, equipment, and kinds of costs. This proceeding enables to compare different ways of production.

Jan 1, 1979

By Z. M. Zavodni, M. K. McCarter

This paper identifies physical conditions responsible for past instability of the Main Hill area in Kennecott Copper Corporation's Bingham Canyon Mine, Bingham Canyon, Utah, and describes successful stabilization techniques employed in this slide zone. Geotechnical highlights of recent slides are presented, including monitoring, geological engineering data collection, hydrology, physical rock properties, and stability analyses. Local conditions responsible for slope movement in the Main Hill zone are: (1) high pore water pressure that causes a substantial decrease in real and effective material strengths; (2) continuous structural systems that allow sliding in the more competent rock zones; and (3) broad areas containing fractured, altered , and incompetent rock and soil- like materials. The failure mode is structurally controlled and involves a circular-type soil failure in the toe region initiated by excessive pore water pressure. A surface mapping method is presented which assigns rock mass quality on the basis of block size and rock substance strength. This site characterization technique has successfully predicted slide boundaries and failure modes; used in conjunction with laboratory determined shear strengths, it has provided basic input for calculating slope safety factors in the Main Hill slide zone.

Jan 1, 1977

By R. Hiebert, M. Canty, S. Beckman

An innovative biological process is described for the treatment of cyanide-, metals- and nitrate-contaminated mine process water. The technology was tested for its ability to detoxify cyanide and nitrate and to immobilize metals in wastewater from agitation cyanide leaching. A pilot-scale demonstration is described in which a pilot plant was constructed to demonstrate the technology on a mine process-waste stream at a mine in Nevada. The demonstration was performed jointly under the Mine Waste Technology Program (MWTP), funded by the US Environmental Protection Agency (EPA) and jointly administered by the US De¬partment of Energy's (DOE) Western Environmental Technology Office (WETO) under Interagency Agree¬ment Number DW89938513-01-0. The Superfund Innovative Technology Evaluation (SITE) demonstration program was also involved in the project. MSE Technology Applications Inc. (MSE), Butte, MT, was the contractor responsible for conducting the project, and Pintail Systems Inc., Aurora, CO, was the technology provider. The pilot-scale unit was field-tested at Echo Bay's McCoy/Cove Mine southwest of Battle Mountain, NV. The biotreatment process was considered successful in destroying cyanide in the mine process water. The process was also determined to be effective in removing metals. The pH was consistently neutralized and nitrates were successfully removed from the mine process water. From the results of these pilot-scale tests, it was concluded that the biotreatment process potentially of¬fers an innovative, cost-effective alternative for the treatment of mining wastewaters.

Jan 1, 2000

By Joseph M. Keane

Introduction The English word "sedimentation" is derived from the Latin verb "sedere" meaning to sink down. As a mineral processing unit operation, sedimenta¬tion has been defined as the separation of a suspension into a supernatant clear fluid and rather dense slurry containing a higher concentration of solid (Brown, G.G. 1960). Sedimen¬tation has been historically subdivided into thickening, which has the primary purpose of increasing the solids content of one of the thickener prod¬ucts relative to the feed stream, and clarification, which has the primary purpose of removing solids from the feed stream to produce a product essentially free from particu¬late matter. There is no absolutely precise distinction between these subdivisions and in certain applica¬tions, both objectives can be accom¬plished. Major Design Factors The capacity of conventional metal¬lurgical sedimentation devices is a function of slurry throughput and its attendant settling rate. Important factors, recognized by early investigators (Taggart, 1972), which influence the settling rate of a given metallur¬gical slurry include: Feed dilution or solids-liquid weight ratio Size and shape of the particulate solids Specific gravity differential between the solids and liquid phases Presence of electrolytes and/or flocculants Pulp viscosity Slurry temperature In addition to the foregoing histor¬ical factors, recent investigators have noted (Pearse, M.J., 1977) that other parameters which may have an influence upon settling rate and, thereby, thickener performance include: Method of flocculant application Particle size distribution Particulate wetting characteristics Feeding arrangements Rake speed and type Existence of convection currents Wind disturbance Evaporation All of the above factors should be examined and the effect upon thick¬ener performance brought about by manipulating the factor over the expected operating range should be determined if performance optimization is desired.

Jan 1, 1986

By Howard L. Hartman

To concede that I am the most surprised - not to mention the least likely - recipient of the Daniel C. Jackling Award is a true confession I must share with you. Quite honestly, I've asked myself, "Why me?" The Jackling Award has a well-deserved reputation of being a practitioner's, a doer's, a CEO's award - not kudos for a retired school teacher! While at least five of the previous recipients have taught in universities, to my knowledge I am the first to earn the award for "alleged" academic accomplishments. It is humbling enough to keep me livable for a long time. If you glance over the roster of Jackling Award lecture topics, you will spot another anomaly: The lectures last year and this deal with the subject of education - the only two in the 37-year history of the award. The two complement one another rather well, too, C. Allen Bom of Amax addressing critical needs of public education, while I am going to look at the post-high-school years. But I want to focus on more than engineering education. The training role of industry - the principal consumer of our product-also warrants examination. As I hope to establish, there is something unique about mining engineering - education and practice - that is both strength and weakness. We need to recognize that, if we are to cope with the weaknesses in order to capitalize on the strengths. We look at five premises that relate to the uniqueness of the mining engineer and his or her preparation for a professional career.

Jan 1, 1991

By G. Bryant, P. Ziemkiewicz

Acid mine drainage (AMD) from both abandoned surface and underground mines is a serious problem. The flow of water and changes in quality over time from abandoned mines is important in determining remediation strategies. Acid mine drainage from surface mines is estimated to last for 10-20 years, while estimates of acid drainage from underground mines vary from 10- 100s of years. Fifteen underground mine discharges in West Virginia were studied to compare water quality changes between 1968 and 1999 to see if our data are consistent with other studies. Each of the discharges were categorized into one of three groups: undisturbed since 1968, affected by surface mining since 1968, and reclaimed. Comparing water quality between 1968 and 1999, the discharges in the undisturbed category showed a 35 to 95% improvement in acid concentration and a 40 to 99% reduction in iron concentration. The discharges affected by surface mining showed the most dramatic improvement. For acidity, iron, and aluminum, the percent improvements were all above 44%, and in most cases in the 70 to 99% range. In the reclaimed category, one of the four discharges declined in water quality. Discharge 82 showed a 76% increase in acidity, and iron and aluminum concentrations worsened by 58 and 96%. However, discharges 15 and 74 improved in water quality with a 94% acid load improvement and a 95% iron load improvement at both sites.

Jan 1, 2000

By P. Hambach

Murer Company, Andermatt, Switzerland, can claim to have done pioneer work in the construction of inclined shafts. This happened in 1968/69, when we decided to bore with a Wirth tunnel borer an inclined shaft, 1100 m in length, 3.0 m in diameter, and with a grade of 65%, in the 2400 kilo pascall per sq. cm granite of the Montblanc Massive. The whole excavation was accomplished in ten months which, at least for European conditions, can be claimed as a record. It was, at least to our knowledge, the first inclined shaft to be bored full-face (Fig. 1). Encouraged by the experiences and performances attained at Châtelard, we approached other projects of the same kind. We were awarded, together with Hochtief Ltd., Essen, a contract from Schluchseewerke, Freiburg, Germany, in December 1969, for the construction of a penstock for the Hornbergstufe at Wehr, Germany, with a diameter of 6.3 m. This inclined shaft with a grade of 55% is located in Schwarzwalder granite with a compressive strength of up to 2000 kilo pascall per sq. cm, about 31,000 psi. As no exact geological data were available about the rock to be worked, and a fault zone from 80 to 150 m long had to be faced, as well as a few individual fissures of varying thickness, it was decided to use the multi-stage method. The 3-m diam tunnelling machine which had driven the oblique shaft at Châtelard had now finished work, and an immediate beginning was made with driving the pilot staft. This was very welcome to the contractor, since exact information about the type of rock present and the inflows of water was required immediately and before the final borehole diameter was fixed, for the purpose of dimensioning the supports to be subsequently installed.

Jan 1, 1974

By Terry P. McNulty

During the last 30 years, at least ten authors have dealt with startup ("ramp-up') times for minerals beneficiation, hydrometallurgical, and/or pyrometallurgical plants. Most have attempted to identity the reasons for delays and some have suggested attributes common to successful startups, as well as those shared by unsuccessful ones. The most recent has advanced a project characterization matrix as a predictive tool for qualified users. This paper will summarize past work, will review cause and effect, will outline an approach for refining our ability to avoid costly delays, and will seek guidance from professionals most likely to use such a tool. INTRODUCTION During the last few decades, many billions of dollars have been lost by investors in mineral industry projects that did not perform as well as their developers had hoped. The most common form of failure has been the inability to generate a profit quickly, and delayed achievement of planned production rate has been the chief cause. Minerals processing projects are by no means the only kind of plant to suffer from startup delays, as some authors cited in this paper considered inorganic chemical plants and other types of facilities. Furthermore, mines are not without fault and there have been many that were closed after years of disappointing performance. However, our interests as a group are most sharply focused on mineral processing and our database for such projects is relatively extensive. It is sufficient to say that the conclusions made or repeated in the following text can be readily extended to most types of projects.

Jan 1, 2004

By Faruk Oksuz, Clay Haynes, David Egger

The United States Army Corps of Engineers (USACE) has committed to solve a major drainage problem in the suburban Chicago community of Griffith, Indiana. The Cady Marsh Ditch is currently undersized and on occasion spills its banks causing flooding and economic setbacks to the community. Preliminary studies have identified both tunnel and surface solutions as being attractive and viable. The USACE has decided that this project is an opportunity to use the design-build contracting approach to maximize ingenuity in project approach and to allow the market to dictate whether a surface or subsurface solution is most attractive. The tunnel would be over one-mile in length through sands, gravels and clay. Water control will be an issue during tunneling. The paper will explore the contracting approach to the project and the adaptation of Underground Technology Research Council (UTRC) guidelines for underground contracting to a design build project. The roles of Owner, Owner’s consultant, and design-build contractor will be defined as interpreted by the USACE and key contract provisions will be described and contrasted with a traditional design-bid-build approach to tunnel construction.

Jan 1, 2003

By Murray D. Lester

The relationship between bauxite and energy has two distinct aspects. On the one hand, since virtually all of the bauxite that is mined winds up as aluminum metal, the economic health and future of the bauxite industry and of the bauxite-producing countries depend on the continuing vigour and competitiveness of aluminum against alternative metals and materials. The price of aluminum is, in turn, particularly dependent on the price of energy. Hence, the need for bauxite is ultimately affected by the price of energy. The second aspect relates to location of the bauxite industry. There is no shortage of bauxite resources in the world. For various reasons, as we shall see, there is a growing tendency toward the integration of bauxite mining, bauxite refining and aluminum smelting in those countries that have the resources both of bauxite and of energy necessary to support the entire production chain. Thus, the availability of attractive energy supplies will increasingly favour development of bauxite mining: the traditional export of bauxite as a simple raw material is likely to diminish in relative terms. In short, both the amount of bauxite mined and where this mining will take place are related to energy considerations. Let us first have a brief look at the four basic activities that are involved in our integrated operations: A. The bauxite is mined and moved to an ore plant. This step does not require more than relatively modest amounts of energy normally associated with excavation, loading and shipping of any bulk material. We need about four or five tonnes of bauxite for every tonne of metal produced.

Jan 1, 1984

By C. L. Schneider, R. P. King

The ability to predict the liberation spectra that will be produced by a closed-continuous grinding circuit is of fundamental importance for the design, optimization and control of most operations in an ore dressing plant. The only known approach through which such a calculation can be performed is the population-balance-model equation. The latest, and certainly most significant, advance made in this area is the solution proposed by King (1990), which requires one textural parameter measured directly from the ore being studied. The main advantage of King's solution is that, unlike the conventional solutions, it does not require the estimation of hundreds of arbitrary parameters that cannot be independently measured. However, King's solution relies heavily on a knowledge of the detailed internal structure of the Andrews-Mika diagram (Andrews and Mika, 1975), which has never been measured for any ore. The characterization of the internal structure if the Andrews-Mika diagram requires the measurement of the liberation spectra at several progeny sizes produced by the breakage of monosize-monograde particles at several different grades. In this paper, a procedure based on magnetic fluid fractionation for generating seven narrow-size, narrow-grade samples is presented. Each of these samples was then broken into six progeny size classes in an ultrasonic mill. The one- dimensional liberation spectra of each of the 42 progeny and seven parent particle samples were then measured by image analysis. The measured linear-grade distributions are presented in this paper. The calculation of the correspondent volumetric-grade distributions is discussed.

Jan 1, 1995

By D. J. Kennedy, A. W. Stokes, W. G. Klinowski

Sulphur hexafluoride (SF6) has become an accepted standard in the field of mine ventilation tracer gas studies. It has a wide variety of uses for defining mine ventilation flows that cannot be adequately described using conventional instruments such as anemometers and smoke tubes. The Cape Breton Coal Research Laboratory (CBCRL), Energy, Mines and Resources Canada, has been using SF for the past 4 years and has developed numerous release and sampling systems to increase its versatility. The CBCRL has also completed a successful field trial of an automated rapid sequential SF6 analyzer (which gives a pseudo real-time readout) that can be used underground. In doing this work, the authors recognised the potential of being able to use more than one tracer gas simultaneously in an underground study. Two alternative tracer gases (Freon-13B1 and Freon-12) have already been used by CBCRL in some of their underground work. These gases can be measured by gas chromatography utilising an electron capture detector in a similar manner to SF6. A description of these gases, the methods for 6' their handling, release and sampling are given in this paper together with a brief outline of the analytical system used to measure them. Their suitability to mining applications is compared with SF6. A study in which these three gases were used together is discussed and the results and conclusions given. Some of the additional uses for multiple tracer gases to assist the mine ventilation engineer in resolving problems and improving his day-to-day monitoring are discussed. Finally, a brief analysis of developments which can be expected in the near future is outlined.

Jan 1, 1987

By J. Peck, M. J. Scoble, C. Hendricks

This paper is based on field studies in North American surface mines. The work involved the adaptation of microprocessor-based instrumentation to monitor various operating parameters on-board rotary blasthole drills and mining shovels. Following a review of instrumentation and monitoring methodology - drawing on experience gained under field conditions-the paper will focus on the application of monitoring technology within the framework of an Integrated Equipment Monitoring System. Such a system will permit real-time performance evaluation of key equipment involved in surface mine production. Drill performance monitoring has been demonstrated through work to date, to provide significant input into blast design, reserve estimation, mine planning and production control processes, through an improved facility for ground characterization. Monitoring excavation equipment has been proven valuable in assessing how effectively the input from drill monitored data has been used in the evolution of blast designs. This specifically refers to assessing blast efficiency through measuring associated levels of excavator performance in relation to muckpile characteristics. The medium-term goal of equipment instrumentation and monitoring has been to assist mines in optimizing the overall rock breakage and handling process. Based on the reported results, this has been accomplished. Long-term efforts now concern using a greater understanding of equipment performance and response to varying operating conditions as a foundation for the implementation of mining automation.

Jan 1, 1993

By D. C. Rotherham

The Kidston gold discoveries were originally made about 1907, and by 1934, 1.76 Mg (62,000 oz) of gold had been produced from placer and lode mining of higher grade, most¬ly oxidized gold ore. As mining in the lode ore penetrated deeper, costs increased and the world gold price stagnated. The lode or underground production averaged close to 6.9 g/t (0.2 oz per ton) Au for the 201 kt mined. No mining or development took place from 1934 until 1965. Kidston's high grade ores were exhausted by 1934. From 1965 to 1976, exploration had developed 3 Mt of about 3 g/t (0.88 oz per ton) Au. Placer Pacific acquired rights to the property in 1976 and began a geologic and engineering study of the district. It was clear that the deposit had the potential for becom¬ing a large-tonnage, low-grade producer. However, explora¬tion had to discover the tonnage and grade and engineering needed to solve the obstacles of production costs. Bulk material handling problems were addressed by Placer's wide experience in open pit mining, and the increase in work index accompanying deeper ores was handled by Placer's metallurgists. The matter of power for the operation was solved by engineering studies. These showed that power could be generated and brought in economically. The price of gold also increased after 1976, and this helped in the economic analysis. The Kidston discovery since 1976 is really a combination of good exploration geology and careful engineering plan¬ning that overcame the obstacles presented by ore characteris¬tics and the location of the deposit. The attached paper by Harry Mustard is an extract of his honors thesis and explains the deposit geology.

Jan 1, 1990

By Naj Aziz

Both bolt profile shape and spacing (rib spacing) have been found to influence the bonding capacity of the grouted rock bolt. The bolt surface profile configuration has greater importance to rock bolting in strata reinforcement in mining than the steel rebar used in civil engineering construction. This is because a rock bolt in mining usually is subjected to greater dynamic loading than the steel rebar in civil engineering construction. The increased bonding capacity of a bolt is important when supported ground is either heavily fractured, faulted or the supported ground is of soft formation, typically that of coal measure rocks. Past laboratory studies have identified the bolt profile spacing as of significant relevance to bolt resin rock bonding increase, however, no attempt has been made to determine the optimum spacing between the bolt profiles spacing. Accordingly, a series of laboratory tests were carried out on 22 mm core diameter bolts, commonly used in Australian mines, installed in cylindrical steel sleeve. The study was carried out using both push and pull testing methods. The push test was carried out in 150 mm long sleeves while the pull testing was conducted in 115 mm long sleeves. Profile spacing tested include, 12.5, 25.0, 37.5, and 50 mm lengths. Additional studies undertaken include modelling the profile of the load-displacement data of pull testing. Bolts with a profile spacing of 37.5 mm were found to provide optimum load bearing capacity as compared to other tested profile spacings.

Jan 1, 2009