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By Frank A. Stephens

The process of converting iron ore (principally Fe,03 or Fe30,) into iron carbide (Fe,C) to be used as feedstock for steel-making yields complex mixtures of several Fe-containing compounds as a function of processing conditions. In addition to the above compounds (hematite, magnetite and cementite), the mixtures typically contain wustite (FeO) and metallic iron(Fe). Mossbauer spectroscopy has been developed into aquantitative analytical method for monitoring the degree of conversion to carbide from samples periodically extracted from a fluidized bed reactor type of pilot plant. Calibration of absolute quantities of the above five compounds is based on standards prepared from known mixtures of the high purity individual phases. The PC-based spectrometer allows fitting of the well-known spectral components of each of the five phases, the resulting spectral areas then being compared with the calibration curves via PC software to yield the weight fraction of each. Emphasis has been placed on standardizing and simplifying the analysis procedure for routine use in an industrial environment.

Jan 1, 1993

By D Ray, D Brett

A clay-capping trial was established in 1996 on Magazine Dump at the Mt Lyell Copper Mine. The trial was initially constructed under the Mount Lyell Remediation Research and Demonstration Program, a co-operative venture between the State and Federal governments. The detailed engineering design for the clay cover included the following features; reshaping and compaction of dump batters, 5 m vertical bench interval, overall side-slopes of 2.5:1, emplacement of clay in four 150 mm lifts, compaction by a 10 t vibrating roller or ætrack rollingÆ on batters with density testing for quality control. A small section at the base of the dump ( The trial also generated certain unexpected findings. Field permeability tests on the cover yielded uncertain results and oxygen remains available throughout the dump. The flow data indicate that, while total outflow has decreased as a result of storm shedding, inputs from groundwater and batter infiltration are still significant. Outflow during the driest weeks of the year may have risen following capping. Detailed assessment of the data is hampered by insufficient pre-capping information; however, there is a possibility that conductivity flux emitted when flows in the receiving environment are at their annual minimum is unchanged or worse post-capping.

Jan 1, 2003

By M. Tomono

Harima Works is operating as the zinc and lead simultaneous smelter utilizing the imperial Smelting Process. The smelter commenced its operation in 1966 with designed capacities of 3500 t/M of zinc and 1500 t/M of lead. After that, owing to the results of progressive developments and improvements in operating efficiency and equipments, it has doubled its production figure. This report reviews our recent developments carried out from 1983 to 1985. Firstly, the furnace bottom design was modified for the purpose of reducing carbon consumption ratio. As a result, shaft operating condition has been satisfactory and carbon consumption ratio was improved by 2%, in addition, furnace zinc production was increased by about 8%. Secondly, the oxygen enriched operation at sintering machine was tested from July 1984 to June 1985, in order to increase the sinter productivity, and to solve the capacity imbalance between sinter plant and ISF. As the test result, it was found out that sulfur elimination rate was increased by approx 10% with the oxygen enrichment of 500 Nm3/hr.

Jan 1, 1986

By Suthan Pooranampillai

This paper presents a case study of the use of single axis cement deep soil mixing (CDSM) to deal with static settlement and seismic stability of the foundation soils under a reinforced soil slope (RSS) embankment up to 50 feet high. As part of the widening of Interstate 5 (I-5) to allow High Occupancy Vehicle (HOV) lanes in Tacoma, Washington, a new approach and span over the Puyallup River will be constructed. During the soils investigation and design phase of the project, low plasticity silts (ML) inter-bedded with silty sand layers and organic silt where identified as being potentially liquefiable. CDSM was selected to address the embankment foundation concerns and allow for future trenchless installation of utility lines beneath the embankment. The presence of a confined, artesian aquifer within the design depth of the CDSM led to the installation of a depressurization system to avoid an upward gradient through the wet soil-cement. In addition to addressing the design approach, the paper discusses the challenges associated with quality assurance of CDSM within the time constraints of an ongoing project. The limited recovery rate of conventional triple tube coring in the soil-cement and double tube wet sampling led to the use of sonic coring to provide a near continuous core of the soil-cement.

By Martin N. Kelley

The Great Belt Link is a $3.5 billion fixed link across an 18 km (12 mile) wide body of water that separates the island of Zealand, on which Copenhagen is situated, and the main land mass of Denmark, Jutland, which is part of the European continent. The project consists of three main contracts. The first contract is an 8 km (5 mile) long, two-bore railway tunnel for the eastern half, the second contract is a 6.6 km (4 mile) combination railroad and highway bridge for the western half, and the third contract is a 6.7 km (4 mile) long high-level highway bridge for the eastern half. This paper will discuss the Eastern Railway Tunnel Project and the methods of construction that the joint venture consortium plans to use, along with its equipment selection. The ground conditions to be encountered begin with glacial tills, which are a mixture of clay, silt, sand, gravel, cobbles, and granitic boulders. The boulders can be up to 1-3 m (3-10 ft) in diameter. Underlying the till is a marl which is sometimes highly fractured with hydrostatic pressures of up to 8 bar. About 40% of the tunnel is in till and 40% in marl, with the remaining 20% being a mixed face of the two formations.

Jan 1, 1991

MODELLING FOR DESIGN AND CONTROL AT KALGOORLIE NICKEL SMELTER Modelling at KNS has been driven by a need to have better tools to answer questions about control, design and optimisation of the plant. This paper describes a number of modelling tools developed for use at KNS and how the development of modelling tools fits with a design and control strategy. In the area of control, a thermodynamic model has been developed to allow process parameters to be calculated. The model allows for the automatic selection of data from a laboratory data base, desired operating set points are input and the operating parameters are calculated. The model has the ability to adjust the burner efficiency and the furnace heat loss depending upon conditions. To assist with the testing of proposed furnace design changes, various mathematical models of the burner and shaft have been created using PHOENICS. These models are particularly well suited to combustion heat transfer and flow aspects of both the burners and shaft. Validation of these models have been based on novel sampling and measuring techniques in the shaft and also by using scale and cold models. Overall plant energy and cost structures can be analysed using a flowsheet simulation, developed to evaluate potential alterations to the plant flowsheet. This model system allows the global evaluation of process changes.

Jan 1, 1993

By R. M. Brick, J. T. Richards

Tests have been conducted to determine the mechanical properties of several beryllium copper alloys down to liquid air temperatures. The materials investigated include beryllium copper, beryl-lium-cobalt-copper, and beryllium-zinc-copper in the wrought and cast conditions. As a means of evaluation, the influence of cold work and age hardening treatment upon subzero behavior has been observed. The effects of temperature upon both elastic and plastic deformation are also considered. THE low temperature mechanical properties of beryllium copper are of current interest in view of the increasing number of subzero applications. At extremely low temperatures, beryllium copper components are employed in temperature control and gas liquefaction equipment. At more moderate temperatures, such as those encountered in arctic regions, these alloys find use in a wide range of civilian and military applications. Although several previous subzero investigations have included beryllium copper,'-' none have been complete with respect to test temperatures or materials employed. As indicated in Table I, the alloy: used by Colbeck and MacGillivray,1 Walle,2 and Kostenets' were nonstandard and were not representative of present commercial practice. In addition, Kostenets4 did not test age hardened specimens, while the temperature in the other investigations", "-' were not carried below —100°F. These tests, however, indicate that beryllium copper offers interesting possibilities in subzero atmospheres, since the increase in strength with decreasing temperature is not accompanied by a reduction in ductility or impact resistance. As a means of checking and extending this earlier work at subzero temperatures, an investigation was undertaken at the University of Pennsylvania. In addition to testing the standard 2 pct beryllium copper, other alloys were also considered in wrought and cast forms. Charpy impact and tension tests were included with particular emphasis on the elastic characteristics, since beryllium copper is frequently selected for its spring qualities. Nominal test temperatures were +80°, —75", —200°, and —300°F. Test Materials Wrought beryllium copper, beryllium-cobalt-copper, and beryllium-zinc-copper specimens were machined from 0.560 in. diameter rod. These alloys were tested in the solution treated, cold drawn, or age hardened conditions. In the case of solution treated beryllium copper, some specimens were aged (3 hr at 600°F) for maximum hardness and others were overaged (1 1/2 hr at 750°F) to determine the effect of heat treatment. The compositions and average room temperature properties of these wrought alloys are presented in Table 11. The casting alloy versions of beryllium copper and beryllium-cobalt-copper were prepared as sand-cast cylinders, roughly 3/4 in. diameter x 6 in. long. Test specimens were machined from these cylinders. Conditions tested included as cast as well as solution treated and age hardened. Table 111 lists compositional and room temperature property data for the cast alloys. Test Methods Tension tests were conducted on specimens having a 0.25 in. diameter reduced section over a 1 in. gage length. To insure axiality, specimens were loaded by means of hardened chains. The yield strength at 0.2 pct offset was obtained from autographically recorded stress-strain curves resulting from a spe-

Jan 1, 1955

By Xiaofei Guan, Adam C. Powell, Uday B. Pal, Srikanth Gopalan

This paper reports a solid oxide membrane (SOM) electrolysis experiment using an LSM– Inconel inert anode current collector for production of Mg and O2 at 1423K. The electrochemical performance of the SOM cell was evaluated by using various electrochemical techniques including electrochemical impedance spectroscopy, potentiodynamic scans, and potentiostatic electrolysis. The effects of Mg solubility in the flux on the current efficiency and the YSZ membrane stability during SOM electrolysis were discussed and examined through experiment and modeling. The electronic transference number of the flux were measured to assess the Mg dissolution in the flux during SOM electrolysis. A negative correlation between the electronic transference number of the flux and the current efficiency of the SOM electrolysis was observed.

Jan 1, 2014

By M. Younis, E. Comis

"The success of a tunnel project relies on many factors, but one of the most important is also the most overlooked: coordination by all parties involved during the design stages. This is particularly true of segment design and TBM design. Tunnel lining with segmental rings is usually designed according to the standards of reinforced concrete construction based on a given GBR. However, for TBM tunneling, the determination of loads during ring erection, advance of the TBM, earth pressure, and bedding of the articulated ring are all part of the tunnel lining design as well. TBM design can be heavily affected by the segment arrangement, dimension, and weight, but these are usually given as a fixed input to the TBM manufacturer—a process that can cause unnecessary complications. The authors propose that the industry evaluate the process as it stands. In order to find the optimum balance between lining design and TBM cost and operational workflow, both designs should be finalized concurrently. This requires coordination between the TBM manufacturer and segment designer from the early stages. The aim of this paper is to evaluate the influence of the segment lining design on TBM cost and performance, and to provide commentary on existing design guidelines to optimize lining and TBM procurement. INTRODUCTION The conventional project setup for tunnel lining design and the design and manufacture of the tunnel boring machine (TBM) should be coordinated in a timelier manner. It is widely acknowledged that the design of segments must consider the forces exerted by TBM rams during tunnel construction, but other inputs are most frequently provided to the TBM manufacturer as fixed parameters to design around. This paper describes other important factors in TBM design that impact not only the interaction with the segments, but also the construction of the tunnel in terms of overall production and even safety. For example, the segment width and tapering have direct influence on shield body length and thrust cylinder size. Furthermore, TBM geometry can also affect the backup (trailing gear) layout and length."

Jan 1, 2016

By A. Davis

Pit lake chemistry depends on the lithology and hydrologic characteristics of the ultimate pit surface, the availability of buffering capacity in the wall rock versus oxidizable sulfide content, and the alkalinity of recharging ground water. In this paper, we assess the geochemistry of 11 existing pit lakes, ranging from the acidic Red Hill and Berkeley pit lakes (pH 2.6 to 2.8) to the alkaline Yerington Pit lake (pH 8.45). Predicted pit lake chemistry is similar to that in existing pits with the long-term pit lake chemistry lying on a geochemical continuum between end members consisting of influent calcium bicarbonate ground water, and naturally occurring sulfate-rich evaporite playa lakes.

Jan 1, 1996

By S F. Rogers, P W. Booth

Digital photogrammetry is revolutionising the task of geotechnical mapping of jointed rock masses and has greatly increased in popularity and sophistication in recent years. Modern commercially available digital photogrammetry software systems can provide geotechnical practitioners with a user friendly tool for rapid data acquisition. The data can be acquired remotely from large exposure areas, some of which may be otherwise out of reach due to restrictions on time, access or safety.Photogrammetry is a complimentary technology to discrete fracture network (DFN) modelling because it can provide the large, statistically significant, spatially located geotechnical data sets required to produce the most robust results. It also provides the flexibility to selectively map structures at a range of scales, depending on the focus of the DFN modelling.Integration of the interpreted rock structure data derived from photogrammetry with modern DFN modelling methods really advances the rock engineering process. The ability to generate 3D fracture models driven by the statistical structural data and conditioned to the features observed by the photogrammetry yields a synthetic rock mass on which improved design methods can be applied. The generation of multiple equi-probable conditioned DFN models allows the use of probabilistic methods for assessing kinematic stability, rock block size distribution as well as a range of other applications.CITATION:Rogers, S F and Booth, P W, 2014. Integrated photogrammetry and discrete fracture network modelling for improved rock mass characterisation and engineering design, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 203–208 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By Earl T. Hayes

For several years the Northwest Electrodevelopment Laboratory of the Bureau of Mines, in cooperation with the Air Materiel Command, U. S. Air Force, has been studying zirconium alloys. A preliminary survey of these alloys has been completed and reported as a Bureau of Mines Report of Investigations. 4/ Originally the purpose was to determine the suitability of zirconium alloys in medium-temperature applications. However, data also were obtained on other properties of these alloys, and later the scope was broadened to include amore detailed investigation of a selected group. The zirconium-titanium system was one of those chosen. The Bureau of Mines has been instrumental in the commercial development of both of these metals and has constructed pilot plants for the production of titanium at Boulder City, Nev., and for zirconium at Albany, Oreg. Both elements are in subgroup A, fourth series of the periodic table, and therefore have many properties in common. Since both have similar atomic structures and lattice dimensions the possibility of extended mutual solubility seemed likely. Inc transition-point diagram of Fast indicated that the two metals are completely miscible in all proportions in both the alpha and beta forms.

Jan 1, 1951

By Z. T. Yuan, S. L. Qi, Q. Y. Meng, G. X. Zou, L. X. Li, J. W. Lu

"The selective separation of pentlandite from serpentine was investigated using the magnetic coating-magnetic separation by conditioning slurry pH value, stirring speed, magnetic field intensity and controlling dosages of sodium hexametaphosphate (SHMP) and sodium oleate (SO). The optimal conditions were obtained as follows: the natural pH of 6.8-7.2, stirring speed of 2300 rpm, magnetic field intensity of 200 kA m-1, SHMP of 60 mg L-1, and SO of 400 mg L-1. Results showed that the Ni grade was 21.4% with the Ni recovery of 81.4% and MgO content of 3.8%. FTIR indicated that coagulant of SO preferentially adsorbed onto pentlandite and magnetite particles while hardly adsorbing onto serpentine particles when dispersant of SHMP was used. Thus, the selective magnetic coating of magnetite on pentlandite surfaces could be formed due to the formation of hydrophobic surfaces on pentlandite and magnetite particles. Calculations of DLVO (Derjaguin-Landau-Verwey-Overbeek) confirmed that interactions between magnetite and pentlandite particles were much stronger than that between magnetite and serpentine due to the existence of hydrophobic interactions with the addition of SO. Consequently, the pentlandite was successfully separated from serpentine. Therefore, this study exhibits the potential to separate pentlandite from serpentine minerals for practical applications and thus deserves further study.INTRODUCTION It has been well known that the separation of pentlandite from serpentine is a worldwide challenging issue in the processing of sulphide nickel-copper ores. Because the serpentine mainly causes the high pulp viscosity and slime coating on the pentlandite, which interferes with the flotation process of pentlandite (Cao et al., 2016; Feng et al., 2012). The fibrous mineral of serpentine preferentially attaches to the air bubble, forming bubble-macrofibers aggregates, which are easily floated into the nickel concentrates, resulting in the decline of Ni grade (Alvarez-Silva et al., 2016; Kusuma et al., 2014). In addition, the serpentine adheres to the pentlandite as hetero-aggregation or slime coating via the electrical interaction between a positively charged serpentine and a negatively charged pentlandite, which decreases the hydrophobicity of pentlandite and reduces the collector adsorption (Feng et al., 2013). In other words, the presence of serpentine or the occurrence of aggregates (including slime coating and bubble-macrofibers aggregates) seriously affects the flotation process and deteriorates the flotation of pentlandite. Therefore, we propose magnetic separation to recover pentlandite from serpentine with the magnetic coating technology, which is different from forth flotation."

Jan 1, 2018

When the Organic Act of 1910 established the Bureau of Mines within the Department of the Interior, the Bureau's programs involved only health and safety research and, education, and fuels testing. As the Federal Government's primary agency for research in minerals, the Bureau has expanded its scientific and technological investigations to mining, processing mineral substances, eliminating occupational health and safety hazards in the mineral industries, economic development, and resource conservation. Today, Bureau activities cover a broad spectrum of programs for meeting the diverse (and sometimes conflicting) needs of mineral industries, government, and the public. In the 1960's, the Bureau initiated programs to resolve environmental problems associated with past mining and mineral processing. In the 1970's, the energy crisis raised the national consciousness concerning our limited supplies of domestic mineral and fuel resources. Dependence on foreign sources of raw materials critical to our national economy and competition from other countries for these world supplies stimulated the need to conserve and use with intelligence the Nation's minerals, metals, and fuels.1

Jan 1, 1977

By Vijay Kumar, Serhat Baycan, Karsten Beckhans

For the deep foundation of podium and tower of the Kuala Lumpur City Centre, BAUER (MALAYSIA) SDN. BHD. constructed 225 bored piles with diameter range of 2.0 to 2.5 m. In order to comply with the depth requirement of the design, for planning purposes and preparation for site, the drilling equipment was required to achieve a maximum drilling depth of 150 m. Actual piles constructed on site were deeper than 120 m. These dimensions caused superlative challenges which included but were not limited to; controlling the open hole stability over time with polymer, installing 70-ton heavy steel cages, pouring up to 550 m³ concrete continuously, in conjunction with installation of kingposts into workable, fresh concrete. The piling works were executed with a BG 72, the biggest drilling rig globally available, and the stringent verticality of the pile bore holes which required approval prior to cage installation. For verification of verticality, Bauer’s patented Drilling Inclination System was successfully used.

Nov 1, 2022

By K. A. Natarajan, Abha Kumari

"The effect of applied DC potentials on the bioleaching of a chalcopyrite concentrate in the presence of Acidithiobacillus ferrooxidans is discussed. Copper dissolution was the highest at an applied potential of +600mV (SCE), while all the dissolved copper got cathodically deposited at a negative potential of -600mV (SCE). Electrobioleaching at an applied potential of +600mV (SCE) was established at different pulp densities as a function of time. The effect of applied potentials and electrolytic currents on the activity and growth of bacterial cells was assessed. Preadaptation of bacterial cells to the concentrate slurry and electrolytic growth conditions significantly enhanced copper dissolution. Electrochemical and biochemical mechanisms involved in electrobioleaching are illustrated with respect to oxidative dissolution and biocatalysis of anodic oxidation. IntroductionIn recent years, the bioleaching of low-grade chalcopyrite ores as well as their flotation concentrates has been receiving increased attention. Use of mesophilic bacteria such as Acidithiobacillus ferrooxidans in the bioleaching of chalcopyrite does not yield desirable copper extraction rates due to its easy passivation.Bioleaching of chalcopyrite using A. ferrooxidans has been reported to be very inefficient, and use of thermophilic bacteria at higher temperatures is recommended to improve its bioleaching rates. Bioleaching under imposed applied DC potentials or currents has been shown to enhance not only bioleaching kinetics but also to confer selectivity in mineral dissolution (Abhakumari, 1996; Chirpa Selvi and Natarajan, 1998; Natarajan, 1992a, b,c). Electrochemical principles governing electrobioleaching have been earlier illustrated (Jyothi et.al, 1989). The role of applied potentials on the activity and growth of A. ferrooxidans has also been studied (Natarajan, 1992b). Also, the electrochemical aspects of bioleaching of several sulfide minerals when present alone or in binary and ternary combinations have been reported (Jyothi et al., 1989). The electroleaching of copper-nickel concentrate (Natarajan et al., 1985) and electrobioleaching of sphalerite concentrates have already been studied (Selvi et al.,1998). However, it is possible to enhance the bioleaching rate of chalcopyrite in the presence of A. ferrooxidans under galvanic conditions in the presence of nobler minerals such as pyrite (Jyothi et al.,1989). Also, dissolution of chalcopyrite can be significantly enhanced under applied potential conditions. Ali Ahmadi and his coworkers recently studied the electrochemical bioleaching of chalcopyrite concentrates using moderate thermophiles (Ahmadi et al., 2010, 2011)."

Jan 1, 2015

By Moritz Schleeh, Christian Moormann

Temporary working platforms are generally required in order to ensure that heavy construction machinery such as drilling and trench wall units, pile drivers, vehicle and crawler cranes can be set up safely at the site of operation. Considering all possible operating and loading conditions, especially on ground of low shear strength and stiffness, the design and construction of temporary mobile working platforms needs to be considered more as a serious engineering task than as a second order structure of minor relevance. Working platforms reinforced with one or several geosynthetic layers have proven to be especially effective with regard to stability, serviceability and durability but their design requests even more sophisticated approaches. Existing design models are often based on simplified assumptions and do not consider the complex interaction between construction machinery, working platform and subgrade. Non-monotonic loading as well as elastoplastic and time-variant deformation of cohesive subsoil can adversely affect the base layer system and the serviceability and stability of the construction machinery operating on it. In this context, there is a need for improvement of design approaches and their optimisation considering that there are no generally accepted design approaches or technical codes of practice available for the design of temporary working platforms. The present paper deals with the multifaceted and non-trivial interaction effects of working platforms investigated by model tests, field measurements and numerical simulations to develop a design approach that ensures a safe installation and operation of heavy plants on unstable ground.

May 1, 2022

By D. Brabec

One of the analytical problems in exploration geochemistry is the choice of a method of sample attack which would be rapid, simple and reliable in terms of precision and discrimination between different concentration levels of elements sought. The wet sample attacks currently used in analysis of silicate rocks vary from total decomposition to leaching by weak extractants. The total decomposition of such materials is usually achieved either by alkaline fusion or hydrofluoric acid attack. The first method requires the use of platinum vessels which is both expensive and slow for batch operation. The second type of attack is more widely applied in rock geochemistry1, but it is still relatively slow for exploration purposes and requires extra care (especially when hydrofluoric acid is used in mixture with perchloric acid). Considerable improvement in speed can be achieved by using the sample attacks which release only part of the metal present in a rock.2,4 One of such attacks is the leaching of pulverized rocks by hot aqua regia.3 Another technique widely used in geochemical prospecting involves fusion of the samples with potassium pyrosulfate (or bisulfate) followed by an acid leach of the malt .5 One of the advantages of these techniques is the use of glassware in decomposition stage which considerably increases the analytical productivity. It should be noted that partial chemical attacks tend to extract from a rock mainly the non-silicate metal which may give results more significant for exploration purposes than the analysis for total metal.

Jan 1, 1970

By Lewis L. Oriard

The authors outline the development and application of blasting methods put into use 11 years ago at the Berkeley Open-Pit Mine, Butte, Montana. The blast design uses a very short delay (5 milliseconds) between detonation of explosives charges, a feature challenged several times in principle despite its success for Anaconda. Concern is expressed over the categorical rejection of very short delay blasting which can make the difference between success and failure of major mining operations. There is ample evidence to show that the method can be used successfully and not violate the concerns of the public.

Jan 1, 1980

By X. G. Zhao, M. Cai, L. K. Ma, P. F. Li

"Crack initiation stress is one of the characteristic stress thresholds in the rock deformation process under compression. By analyzing AE responses of brittle rocks in uniaxial compression, a new method which is called cumulative AE hit (CAEH) method is proposed for determining the crack initiation stress. An advantage of the CAEH method is that the method removes the user's subjective judgment. To verify the CAEH method, uniaxial compression tests with AE measurement using 77 crystalline rock specimens were conducted. The test specimens cover eight rock classes with different mineral grain distributions. Crack initiation stresses of these specimens were determined by the proposed CAEH method and the LSR method, and the resulting mean crack initiation stresses determined using the two methods were comparable. In addition, taking one rock class with 20 specimens for example, the mean crack initiation stresses determined using the CAEH method and those from several established strain-based and AE-based methods were similar. Hence, the CAEH method can be used as an alternative method for crack initiation stress determination.INTRODUCTIONExperimental observations indicate that the failure process of brittle rocks is associated with crack initiation, crack propagation, crack damage and final strain localization (Brace et al., 1966; Bieniawski, 1967; Lockner, 1993; Wawersik & Fairhurst, 1970). Compression tests on cylindrical specimen are often used to characterize the crack development process. The crack initiation stress (sci), crack damage stress (scd), and peak stress (sc) represent important stress thresholds during the failure process of brittle rocks. Among the three characteristic stress magnitudes, sci is difficult to be determined objectively, directly from examining the stress–strain curves. Some researchers argued that sci obtained from laboratory compression tests is an important parameter for estimating the spalling failure observed in brittle rocks around underground excavations (Andersson et al., 2009; Diederichs, 2007; Martin, 1997). sci can also be used to estimate rock tensile strength and Hoek-Brown failure criterion parameter mi (Cai, 2010). Over the last 40 years, various strain-based methods have been proposed to determine the crack initiation stress in compression tests (Brace et al., 1966; Diederichs, 2007; Eberhardt et al., 1998; Lajtai, 1974; Martin & Chandler, 1994; Stacey, 1981). Nicksiar and Martin (2012) proposed a Lateral Strain Response (LSR) method for establishing sci for low-porosity rocks. Meanwhile, they also used different strain-based methods to evaluate sci of Äspö diorite, and the results showed that all strain-based methods gave acceptable crack initiation stress values. Subsequently, they utilized the LSR method to further investigate the crack initiation stresses in igneous, metamorphic, and sedimentary rocks in compression tests (Nicksiar & Martin, 2013). Compared with previously proposed strain-based methods, an advantage of the LSR method is that it removes the user judgment when interpreting sci. However, the use of the LSR method relies on accurate determination of scd and on having a polynomial fitting equation to find the maximum LSR value."

Jan 1, 2015