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By Christopher Mark

Horizontal stresses are caused by global plate tectonic forces. During 1995 alone, they were largely responsible for closing two U.S. longwall mines. This paper presents six case histories from Pennsylvania, West Virginia, Kentucky, and Alabama. In each case history, a mine encountered roof falls or difficult ground conditions in the headgate, caused by horizontal stress concentrations. The problems are detailed, and the control measures adopted are described. In most cases, nearby longwall panels without stress concentrations were trouble-free. The paper also discusses detailed measurements made at two adjacent Pennsylvania longwalls. One headgate was oriented to avoid a horizontal stress concentration, and the other was not. Eliminating the stress concentration dramatically reduced roof support loads and roof deformation. The paper concludes that proper panel orientation and sequence is the key to maintaining headgate ground control. The optimum orientation is not parallel with the maximum horizontal stress, as previously thought, but rather 20° in the stress shadow of the gob. Other stress control techniques, including artificial support, are briefly discussed.

Jan 1, 1997

By D. Dolinar, T. P. Mucho

Horizontal stresses are caused by global platetectonic forces. During 1995 alone they were largely responsible for the closing of two longwall mines in the United States. This paper presents six case histories from Pennsylvania, West Virginia, Kentucky and Alabama. In each case, a mine encountered roof falls or difficult ground conditions at the headgate caused by horizontal-stress concentrations. The problems are detailed, and the control measures adopted are described. In most cases, nearby longwall panels without stress concentrations were trouble free. The paper also discusses detailed measurements that were made at two adjacent Pennsylvania longwalls. One headgate was oriented to avoid a horizontal-stress concentration, and the other was not. Eliminating the stress concentration dramatically reduced roof support loads and roof deformation. The paper concludes that proper panel orientation and sequence is the key to maintaining headgate ground control. The optimum orientation is not parallel to the maximum horizontal stress, as previously thought, but rather it is 20o in the stress shadow of the gob. Other stress-control techniques, including artificial support, are briefly discussed

Jan 1, 1999

By Thomas P. Mucho, Dennis Dolinar, Christopher Mark

Horizontal stresses are caused by global plate tectonic forces. During 1995 alone, they were largely responsible for closing two U.S. longwall mines. This paper presents six case histories from Pennsylvania. West Virginia, Kentucky and Alabama. In each case history, a mine encountered roof falls or difficult ground conditions in the headgate, caused by horizontal stress concentrations. The problems are detailed and the control measures adopted are described. In most cases, nearby longwall panels without stress concentrations were trouble-free. The paper also discusses detailed measurements made at two adjacent Pennsylvania longwalls. One headgate was oriented to avoid a horizontal stress concentration, and the other was not. Eliminating the stress concentration dramatically reduced roof support loads and roof deformation. The paper concludes that proper panel orientation and sequence is the key to maintaining headgate ground control. The optimum orientation is not parallel with the maximum horizontal stress, as previously thought but rather 200 in the stress shadow of the gob. Other stress control techniques, including artificial support, are briefly discussed.

Feb 24, 1997

By Nemcik JA, Gale W. J

The magnitude and orientation of the in situ stressfield has been determined as a key factor in controlling the stability of openings for both coal mine development and extraction. Monitoring of roadway and pillar behaviour in conjunction with numerical analysis has identified specific stress control measures that have been successfully applied to improve productivity in underground coal mining operations. The influence of the major horizontal stressfield on the stability of openings has been identified at a wide range of sites including mines in Australia, Britain, the USA, New Zealand and Japan. Stress mapping, stress measurement and stress monitoring techniques have been applied to define the in situ stress regime and, together with the correlation of measurements of rock deformation and rock reinforcement behaviour, has enabled appropriate stress control measures to be developed. Stress control measures for development headings have required the selection of roadway orientation, roadway sequencing, reinforcement density and pillar size. The monitoring of behaviour at a range of trial sites has confirmed significant improvements in development stability. Stress control measures for longwall extraction have required rational selection of longwall orientation and extraction direction. Where a mine layout design incorporating the optimum longwall layout design has not been possible, the use of sacrificial roadways has been successfully applied to protect key roadways from stress concentration effects. Comprehensive in situ

Jan 1, 1992

By S. M. Matthews

The magnitude and orientation of the in situ stressfield has been determined as a key factor in controlling the stability of openings for both coal mine development and extraction. Monitoring of roadway and pillar behaviour in conjunction with numerical analysis has identified specific stress control measures that have been successfully applied to improve productivity in underground coal mining operations. The influence of the major horizontal stressfield on the stability of openings has been identified at a wide range of sites including mines in Australia, Britain, the USA, New Zealand and Japan. Stress mapping, stress measurement and stress monitoring techniques have been applied to define the in situ stress regime and, together with the correlation of measurements of rock deformation and rock reinforcement behaviour, has enabled appropriate stress control measures to be developed. Stress control measures for development headings have required the selection of roadway orientation, roadway sequencing, reinforcement density and pillar size. The monitoring of behaviour at a range of trial sites has confirmed significant improvements in development stability. Stress control measures for longwall extraction have required rational selection of longwall orientation and extraction direction. Where a mine layout design incorporating the optimum longwall layout design has not been possible, the use of sacrificial roadways has been successfully applied to protect key roadways from stress concentration effects. Comprehensive in situ monitoring of behaviour has been carried out to confirm the mechanisms involved.

Jan 1, 1992

By J. Nielen van der Merwe

The effects of horizontal stress in coal mine roofs in South Africa did not receive the attention it deserved for several years, but now there is a danger that it may be over emphasized. A number of phenomena that are ascribed to elevated levels of horizontal stress, are shown to he explained by fundamental considerations. The stress concentration caused by the creation of an opening in rock and the beam effects in a stratified roof are briefly reviewed It is shown that guttering can be present without high horizontal stress, depending on the nature of the roof material. Three examples from practice are presented where horizontal stress was initially erroneously believed to be responsible for roof collapses A comprehensive program of roof displacement monitoring in South Africa yielded results that are compatible with gravity loading on roof beams without the assistance of horizontal stress. It is also shown that one of the diagrams that are used to explain guttering as a result of horizontal stress is misleading The over emphasis on horizontal stress may obscure the real causes of roof instability, resulting in ineffective remedial action to be taken by mine operators.

Jan 1, 2000

By J. B. Lizak

This paper is not available for inclusion in the Proceedings at the time of printing, but it will be included as an insert.

Jan 1, 1984

By J. F. T. Agapito, L. J. Gilbride

High horizontal stresses were recognized to impact roof stability more than 60 years ago. Since then, numerous measurements associated high horizontal stresses with difficult ground conditions. This paper presents case histories illustrating the practical usage of roof stress determinations for helping assess stability, not only in the case of high horizontal stresses but also of low stresses. Examples are given of high stresses associated with faults, mine design changes, quantification of stress shadow effect, and anistrophy. The paper concludes with a comparative evaluation on the effect of various stress fields on ground support requirements.

Jan 1, 2002

By A. P. Squelch

The question of what stress condition exists in the hangingwall of tabular stopes remains topical and largely unanswered. Limited field data exist to quantify the situation and provide calibration for investigative computer modelling exercises. Work conducted in1989 and 1990 under a Chamber of Mines Research Organization (now the CSIR: Division of Mining Technology) programme of research into the behaviour and benefits of backfill may assist with this situation. The original work was motivated by the premise that the improved hangingwall stability in backfilled panels (identified by rockfall accident analyses) is due to a change in the hangingwall stress regime. Current, largely theoretical, studies into mechanisms of stope hangingwall behaviour and support interaction could benefit from considering these data. Keywords: Backfill, horizontal stress, stope hangingwall, hangingwall stability, support interaction.

Jan 1, 2002

By Thomas E. Bruner

Today many small diameter tunnels are being constructed in Metropolitan areas and towns as transmission holes for utilities such as water, electricity, natural gas and sewage, to name a few. These tunnels function as utilities beneath the streets, highways, railways, and other structures where open-cut techniques are impractical for any one of a number of reasons. Many such bores range in diameter from 15 to 72 inches and in lengths from 100 to 500 feet. Auger drills with auger type heads have long been used to bore these "road crossings" as they are usually termed; however, many such crossings must be bored in rock with rock-boring heads. Rock with a compressive strength of 15,000 p.s.i. and higher seems to present the greatest challenge for the contractor. These rocks include most igneous and metamorphic rocks and some sedimentary rocks. In general, this grasps most granites, basalts, gneisses, slates, schists, quartzites, limestones, and cherts. In the past ten years boring machines have been developed and used to excavate road crossings through hard rock. Many crossings have been successfully excavated using these machines, and the degree of success has increased substantially in the last few years. A variety of machines have been built and manufactured to bore most rock in a range of diameters up to 72 inches. The machines vary in capabilities, size ranges, and designs but all perform the same basic task and function of boring horizontally. Incidently, here the term horizontal implies horizontal or within five degrees of horizontal. In addition, there is a wide variety of designs, sizes, and types of drill stems, joints, and pipe to meet the various conditions and

Jan 1, 1974

By A. Noble

Linear circuit analysis (LCA) is a fundamental tool which has been used to evaluate mineral separation circuits during the preliminary design phase. Traditionally, the LCA methodology uses the analytic circuit solution to determine the relative slope of the circuit?s partition curve. This value is then used as an indicative performance measure suitable for the comparison and ranking of alternative circuit configurations. Unfortunately, the partition curve slope only reflects the separation potential of middling material. In most mineral systems, this material represents a small portion of the initial feed (due to liberation) as well as a small portion of the revenue potential (due to the incremental value). Respecting these limitations, the authors have developed new separation performance indicators which may be derived from the analytical circuit solution and used in LCA problems. These indicators inherently reflect the separation potential of pure material, providing a better indication of lost revenue due to misplaced material. The complete methodology has been integrated with prior software to produce the Heuristic Optimizer for Resource Separation Economics (HORSE).

Feb 23, 2014

By Paul Staples, Paul Messenger, Greg Lane

"Every project is different. While “conventional” SAG and ball mill circuits will suit many projects, for others there are alternatives, which may produce improved outcomes. This paper examines particular examples of recent front end designs which either went against conventional thinking or which employed “out of the box” thinking to realize the desired results.One such example is the design strategy employed for a small capacity gold plant in Victoria, Australia. The selection of HPGR technology for small capacity projects is not generally favoured, given the relatively high cost of small HPGR machines. However, the unusual size distribution of the gold and its liberation characteristics were expected to lead to improved gold recovery offsetting the higher capital cost.Another example is the first large scale application of milling in acid for copper recovery, at a project in south east Asia. The stainless steel, single stage SAG mill using ceramic grinding media was more expensive than a mill constructed of conventional materials. However, the steps of scrubbing, slurrying, grinding and leaching could all be achieved in a single unit operation and the need for thickening and repulping with acid after milling was eliminated.Rod mills were selected for both primary and secondary milling duties for another south east Asian project despite their somewhat outdated reputation. A review of previous industry experience confirmed that rod mills could outperform conventional rod/ball or SAG/ball circuits in cases where the size distribution of the ground product is critical to downstream recovery.These examples are discussed with particular focus on the key drivers in each case."

Jan 1, 2008

By Karen Talbot, Noah Maier, Rob Jameson, Giuseppe Gaspari

A storage and drainage tunnel advancing below I-75 in Detroit, Michigan experienced sudden subsidence. The Tunnel Boring Machine (TBM) was damaged to the extent that its shield, cutting head and extensive interior components needed to be extracted and replaced along with several completed tunnel segments. The tunnel was 16 feet (4.9m) in diameter with crown over 79 feet (24m) deep at the time. The tunneling contractor immediately engaged their designers and specialty subcontractors to develop a scheme to access the machine and repair the tunnel. They required a shaft 99 feet (30m) deep, with unobstructed plan dimension of 50 feet (15m) to accommodate the large components that needed to be removed and replaced. This precluded the application of an internally braced excavation and instead earth support solutions focused on use of a compression ring. Since the completed tunnel section behind the TBM obstructed closure of the compression ring below its invert, this paper describes the innovative access shaft solution employed. A conventional compression ring was constructed using 5 feet (1.5m) diameter drilled shafts down to the tunnel crown. In front of, and to the sides of the tunnel heading, the secant shafts were extended to over 150 feet (46m) depth, creating a horseshoe of support extending 50 feet (15m) below the planned excavation invert. Larger diameter "King Pile" shafts were drilled immediately to either side of the tunnel, overlapped into each end of the secant "horseshoe". The king pile shafts, together with a heavily reinforced ring beam above the crown elevation, acted as a door frame to transfer hoop loads from the incomplete secant arc into reaction supports above and below the tunnel. These oversize king pile shafts were extended and socketed into rock over 70 feet (21m) below tunnel invert. Very tight installation tolerances were necessary to maintain secant shaft alignment to depths exceeding 150 feet (46m). The project operational, geotechnical, and quality data was managed and visualized using a custom GIS interface. This paper will present the design approach employed and review the construction and quality program selected to repair the tunnel.

Oct 1, 2022

By Hoeve. J.

"In the unconformity-type uranium deposit at Midwest Lake, mineralization is associated with extensive host rock alteration, which affects the metamorphic basement as well as the overlying Athabasca Group sandstones. Host rock alteration is manifested by (I) transformation of clay minerals [kaolinite into illite and chlorite (sudoile)]; (2) bleaching due to removal of hematite from the lateritic paleoweathering profile and the overlying red bed, Athabasca Group sandstones; (3) loss of coherence of the sandstone resulting from corrosion of quartz cement; and (4) in the immediate vicinity of high-grade ore, development of a clay envelope due to residual enrichment of clay minerals caused by massive dissolution of quartz. Clay mineral transformation and bleaching are the most prominent and the most widespread alteration effects, forming haloes that extend for several kilometres along the strike of the mineralized structure and also constitute distinct alteration pipes that rise f or several hundred metres above the unconformity to be truncated at the present top of the bedrock.Although the two haloes are largely congruent features, cross-culling relationship s indicate that clay mineral alteration represents an earlier phase in the history of the deposit than the large-scale bleaching that gave rise to the superimposed bleaching halo.Because clay mineral alteration and bleaching are intimately tied to the mineralization and extend well beyond the limits of the actual orebodies, host rock alteration may be used as an ore guide in exploration and drill-hole evaluation. In this application a third hydrothermal discharge centre was identified, as yet untested for are, which is located between the hydrothermal centres associated with the two known orebodies of the deposit.It is estimated that host rock alteration may enlarge a potential drill-target by a factor 10 - 20X. Information on the configuration of bleaching haloes can be obtained from systematic core logging, whereas diagnostic clay mineral alteration is readily identified by means of automated, quantitative XRD techniques."

Jan 1, 1984

By J. S. Fox

Major-element data for unaltered, unmineralized felsic host rocks from a number of stratigraphically simple, massive volcanogenic Zn-Cu(-Pb) sulphide deposits of low metamorphic grade have been compiled. The petrochemical affinities of these host rocks have been determined (by standard means and by discriminant analysis) and compared. This comparison indicates that volcanogenic deposits in felsic terrains are not restricted to the classical calc-alkaline rock association as previously thought, but can actually be hosted by rocks showing a range of iron content. There is a positive correlation between differentiation trend and are tenor. Zn-Cu ores usually have iron-rich felsic hosts (most Canadian Shield deposits); Pb-Zn -Cu ores have iron-poor felsic hosts (Japanese, Iberian and Tasmanian deposits). This parallels the antipathetic relationship between iron content and background lead levels evident in young, unmineralized, island arcs as well as in many older belts. Correlations between differentiation trend on one hand and massive ore mineralogy and the relative proportions of various rock type (including rhyolite, quartz-porphyry and coarse pyroclastic rocks) on the other are also evident. It is concluded that the recognition of a calc-alkaline differentiation trend cannot be used as a prospecting guide, as has previously been proposed. However, in view of the above correlations, the recognition of a given trend may aid in the formulation of an effective exploration philosophy.

Jan 1, 1979

By Kyle T. Chomyn

Multi-disciplinary engineering analysis and advanced modeling techniques were used to identify and develop low cost design modifications to improve a blast furnace hot blast air distribution main that experienced frequent refractory failures. Piping flexibility analysis helped identify the root causes of refractory damage and determine the need for new expansion joints. Finite element analysis was used to optimize a custom-designed elbow-to-elbow tie-rod system, which ensures thermal expansion loads are not placed on connecting piping. Heat transfer coefficients through the elbows were estimated using computational fluid dynamics (CFD) flow modeling. The cast refractory design was changed to a more reliable brick refractory design. Excessive draft was occurring during furnace back-drafting, so the system was assessed using CFD, and a passive flow-reduction spool was designed. This firstprinciples engineering design approach allowed for optimization and verification, ensuring that the new design addressed the root cause of the previous deficiencies.

Aug 17, 2017

By Bart de Graaff, Victor van Straaten, Edo Engel

The hot blast system is key ancillary plant equipment with respect to safe and stable operations during a long blast furnace campaign. Hot blast stove designs have been optimized to such an extent that in some cases, their lifetimes have surpassed the campaign lengths of the associated blast furnaces by a substantial margin, with the exception of the burner and a few critical areas. This article presents recent developments with respect to designing, building new and operating existing hot blast systems for a long lifetime and at optimized performance. These developments include fundamental improvements such as dome combustion designs as well as increasingly comprehensive packages for inspection, assessment and maintenance techniques. Examples of such techniques are burner replacement with the hot blast system at operating temperature, improved double shell approaches and TOFD measurement applications.

Oct 1, 2019

By R. M. Smailer

Detailed description of the development of the FIOR process1 and, subsequently, other technical papers relating to the operation and start up of the FIOR plant2,3 are available in the technical literature. The Fluidized Iron Ore Reduction (FIOR) process plant constructed in the Matanzas region of Venezuela represents the first commercial application of this technology. The FIOR process was developed by Exxon Company during the 1950's and 1960's; and the facility in Venezuela was designed and constructed by Davy McKee with the plant start up in 1976. While there is a minority government ownership in the company, FIOR de Venezuela operates as a private sector company with the majority of the ownership being private capital.

Jan 1, 1981

By Albert F. Duzy

Recently there have been some problems associated with hot coal in shipments from the USA to overseas markets. This paper will serve several functions. First, a brief review is presented, together with a selective bibliography. Second, a thorough discussion of coal oxidation is covered. Third, potential effects of storage are presented and, lastly, methods are suggested for the safe storage and bulk transfer of coal. The scope includes coal storage for power plants.

Jan 1, 1983

By D. Zhao

High temperature deformation characteristics of austenitic 304L, and martensitic 410 and 416 stainless steels were investigated by conducting compression tests over a wide range of temperatures and strain rates (950-1250 C and 0.001-20 s-1). Flow behaviors of the three alloys were characterized. Optical metallography was performed to determine the as-deformed microstructures. The flow behaviors were related to microstructural phenomena during high temperature deformation. Dynamic recrystallization was responsible for the flow softening. Both dynamic and static recrystallization were operating, and the recrystallized grain size increased with increasing temperature and decreasing strain rate. Strain rate sensitivity was found to increased with increasing temperature and decreasing strain rate. No defects such as cracking and shear bands were observed at those test conditions. Preferred processing conditions can be selected by considering as-deformed microstructure and strain rate sensitivity.

Jan 1, 1994