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Contribution by G. Narsimhan It was with much pleasure that I went through D.F. Malan's excellent paper. The following explanatory and critical note has been the result of my deep study of the paper. Although by qualifications and experience I have been a chemical engineer, involved over four decades with problems in the modeling and simulation of transport-limited (heat and mass) chemical reactions in multi-phase systems, I have of and on interested myself in challenging problems in extractive metallurgy. This is the first time I have veered of to continuum mechanics, at the age of 71! Author's reply. I thank Professor Narsimhan for his extensive contribution to the paper. It provided me with the stimulus to derive an extended model. However, there are some inaccuracies in his arguments that need further discussion. Professor Narsimhan's main concern is that there is not a good enough fit between the derived viscoelastic Kelvin model and the experimental data supplied by Güler1 (see Figure l1 on page 218 of my paper). I will therefore explain the choice of a viscoelastic model in more detail and also make specific comments on the arguments given in his contribution.

Jan 1, 1996

Contribution by J.S. Kuijpers* Kirsten's paper discusses the potential for seismic activity on faults in relation to depth, span, stope support, and discontinuity strength, and puts forward some explicit conclusions. Quoting from the author, the main conclusions are as follows, together with my comments. Author's reply The author gratefully acknowledges the contribution to his paper. It provides further elucidation to the very complex problem of quantifying the effects of mining-induced seismicity. The mechanical behaviour of rock under seismic excitation has been sadly neglected over the past twenty years, during which attention was almost exclusively focused on the study of the spatial location of seismic events. It is to be lamented that, on the eve of South Africa's movement to significantly greater depths of mining, so little quantities information is known about the mechanical effects of seismicity. It is a challenge at this stage to make up for this lapse in knowledge in the shortest possible time.

Jan 1, 1994

Contribution by F.S.A. de Frey The authors are to be congratulated on a job well done by making, in their paper, such a pool of information available to mining engineers. I would like to comment on the following statement: 'As an alternative to the commonly used deep-level mining methods, consideration should also be given to pillar mining at great depths as a logical extension of the current methods. For example, a 75 per cent extraction Or Ryder's discussion The moderate levels if average pillar stress (APS) (320 MPa) are consistent with pillar stability. Squat 10:1 pillars should never 'fail' in themselves, and foundation strengths are also not exceeded (the stresses are well below the 2 ½ x UCS rule-of-thumb provided the foundations comprise normal strong 200 MPa quartzites). Authors' reply We thank Dr de Frey for his contribution to our paper on shallow hard-rock pillar systems. To considerable extent, we share his enthusiasm the potential role of squat pillars in deep-level mining, although we harbour reservations concerning strata control, mining economics, other issues. We agree wholeheartedly that further research, together with carefully planned field trials, is warranted in pursuit of this potentially highly rewarding concept. .

Jan 1, 1995

Contribution by W.D. Ortlepp? The authors are to be commended for publishing their interesting view of an aspect of deep-level mining technology that is becoming increasingly topical and vitally important. This is the second paper in the journal within four months to deal with the crucial needs of highly stressed tunnel construction, the other being the paper on the design and testing of rockburst support in the February 1994 issue. Both papers re-examine important innovative ideas that are more than a quarter of a century old, but that have not yet been implemented by the industry. It is to be hoped that they will now, taken together, serve as a new starting point for a definitive examination of what constitutes proper tunnel-support design. There can be no question that the need to develop a design approach that will solve the problems of tunnelling at depths of 4000 m or more has now become crucial. Contribution by A.M.J. Vervoort* Although the overall paper is very interesting and the future research (comparison between numerical simulations and underground measurements) will be very challenging, I would like to make some remarks regarding the set-up of the numerical model and the interpretation of the elastic results.

Jan 1, 1995

Contribution by W. Assibey-Bonsu I congratulate Mr N.O. Lotter on his paper. There are two main aspects of the paper on which I would like to comment. One aspect is his review of P. Gy's sampling theory under the heading 'Sampling the mill feed' (p. 153). The other aspect relates to his reference to one of our papers1 that was published in the Journal (p. 152). My comments on the former will be given elsewhere'. Authors' reply: Dr Assibey-Bonsu's contribution to the subject is appreciated.

Jan 1, 1996

By G. F. Balderson

In response to the written contribution made by G. J. C. Young to the above paper, I would like to make the following points. Paragraph 1 The build-up of oxidized coatings on cone surfaces has not been a problem in other applications similar to that at President Steyn. The following companies have commented.

Jan 1, 1982

Contribution by W.D. Ortlepp In the Journal of May 1994, the authors first presented the concept and analysis that formed the basis for a design approach for deep tunnels, now expressed more explicitly in the present paper (March/April 1996). In a contribution in the Journal of March/April 1995, I expressed a certain disquiet about the validity of their original approach. The authors responded to these criticisms in the same issue. It is apparent to me now that both the contribution and its rebuttals were written, probably for different reasons, in such an obscure and pedantic way as to further confuse the reader rather than provide enlightenment. My concern still persists. But in order to avoid further confusion I will attempt to pose my uncertainties and difficulties in a much more direct way. On page 98 (top of 2nd column) in the earlier paper, an important statement concluded as follows: '. . . the horizontal ellipse requires 140 per cent less force for equivalent stability'.

Jan 1, 1996

By N. B. Strydom

I have read with interest all the papers dealing with heat transfer and the setting of heat stress limits that have appeared during the past two decades. Scientifically speaking, most of them can be rated as being of a high standard, and some of them have been acclaimed internationally as masterpieces of logical and calculated reasoning. Weathering of ore minerals A short course on 'The Weathering of Ore Minerals and the Textural Evaluation of Base Metal Gossans' is to be given by Dr I.M. Reynolds in Grahamstown from 4th to 6th October, 1982.

Jan 1, 1982

The authors and Iscor's management are to be congratulated on an interesting and detailed paper that discloses Iscor's philosophy, strategy, and action concerning what can also be termed productivity improvement. Aside from the pioneering work of Beeforth and Dicks regarding Dynamic Profitability Analysis at Vaal Reefs, there appears to be a shortage of papers on this topic from the mining groups.

Jan 1, 1990

By M. B. Algeo

Discussion of the above paper M. B. ALGEO The management and staff of Buffelsfontein Gold Mining Company Limited are to be congratulated on the excellent performances described in the paper presented by Mr Christos. In this day and age, with the current economic and labour situation, the mining industry is being constantly pressed to increase the productivity of ever-diminishing quanta of resources. Stress in rock The ISRM Symposium, 1976 is to be held in Sydney from 9th to 13th August, 1976. It is being organized by The Australian Geo. mechanics Society as a regional symposium of the International Society for Rock Mechanics. Thermal analysis The First European Symposium on Thermal Analysis will be held at the University of Salford on 20th to 24th September, 1976.

Jan 12, 1975

Discussion of the previous paper E. N. H. MOLLOY The first 22-foot-diameter Aerofall mill was installed at Mangula in 1957. This was fitted with cast-iron trunnion'! located to the mill shell with 2-inch-diameter mild-steel bolts. O.F .S. Branch Minutes of the General Meeting held at the Welkom Club on Wednesday, 2nd June, 1976, at 4.00 p.m. Mr G. J. C. Young (Chairman of the O.F.S. Branch) was in the Chair. Also present were:

Jan 9, 1976

By M. G. Spengler

Mr More O'Ferrall must be complimented on a paper that will be a useful reference for the re-working of previously abandoned workings. His paper so closely mirrors experiences at East Rand Proprietary Mines, Limited, that it could well have been based on occurrences in that mine. Corrosion The Scientific Society of Mechanical Engineers is organizing the 115th event of the European Federation for Corrosion in Budapest, from 18th to 22nd October 1982.

Jan 1, 1981

The validity of a steady state assumption made by Adams and Nicol (1986) in the modelling of the elution of gold from activated carbon was investigated. It is shown that the accuracy of the steady state approximation is dependent, not only on the magnitudes of the solution flow rate and reactor volume, but also on the lumped elution rate constant. Under the experimental conditions used by Adams and Nicol (1986) the steady state assumption was inaccurate. This could be circumvented in this instance by applying a rigorous general model which accounts for unsteady state behaviour in the solution and in the activated carbon to the experimental data.

Jan 1, 1997

By S. L. Crouch

A. C. Dieringt The procedure described by Professor Crouch for the modelling of mining in faulted ground allows the elastic and inelastic deformation to occur simultaneously, that is, fault slip occurs while an element is being mined. The energy release rates (ERR) shown in Crouch's Fig. 10 are apparently calculated from his equation 9 using the i total deformation Din (see the upper load line of Fig. I) Refractories The institute of 'Gesteinsh iittenkunde' of the technical university at Aachen, the Refractories Research Institute at Bonn, and the Verein Deutscher Eisenshiittenleute (VDEh) at Diisseldorf are to hold the XXII International Refractory Colloquium on 27th and 28th September, 1979, at Aachen.

Jan 1, 1979

By J. Meintjes

by I. J. BARKER and A. B. STEWART J. MEINTJES I read the above paper with considerable interest. I would like to point out, however, that it is fallacious to conclude that the adverse effects of a high inductive reactance on furnace operation can be cancelled by connecting capacitors in series - or for that matter, in shunt - with the power supply.

Jan 1, 1980

By F. L. D. Cloete

he above article by E. Barnea, which appeared in the January 1978 issue of the Journal (vol. 78, no. 6, pp. 143-145), calls for comment in view of the author's claims for the novelty of his proof. He states in his article that its main purpose is to give a mathematically acceptable proof by induction of the 'recently proposed' equation

Jan 1, 1978

The above paper is an important contribution to the field of physicochemical studies in ferromanganese production. The authors are to be congratulated on the well planned and competently executed experimental work and on the interpretation of the data. Although the paper is essentially descriptive, the results lend themselves to thermodynamic interpretation (but in such a complex system as that studied this cannot be done rigorously), as well as to an examination of the probable reduction mechanisms that operate at various stages.

Jan 1, 1979

By F. L. D. Cloete

The following discussion relates to the paper by G. S. Hansford, C. D. Levy, and J. W. de Kock that appeared in the March 1976 issue of the Journal (vol. 76, no. 8, pp. 363-369) Competition for student members Each year the South African Institute of Mining and Metallurgy offers a prize (or prizes should the entries warrant it) of up to RI00 for the best paper or dissertation on a topic appropriate to the interests of the Institute. Engineering in South West Africa The SW A Engineering Profession Steering Committee was established on 4th April, 1977, its purpose being to formulate an Act covering the engineering profession in South West Africa.

Jan 1, 1978

The following contributions were received to the paper entitled 'Safety in South African mines: An analysis of accident statistics', by H.S. Eisner and J.P. Leger, which appeared in the J. S. Afr. Inst. Min. Metal., vol. 88, no. 1, Jan. 1988, pp. 1-7. Contribution by H. WAGNER* The paper by Dr H.S. Eisner and Mr J.P. Leger is critical of the safety situation on South African mines and portrays the industry as having little concern for the health and safety of its workers. Moreover, the casual reader gains the impression of deliberate misinformation by the industry to the public concerning safety maters. Furthermore, certain socio-economic reasons are advanced for the apparent differences between the fatality and injury rates reported for coal mines in South Africa and those for the United Kingdom. Contribution by S.A. WATTS. Authors Eisner and Leger are to be commended on their paper, which highlights, according to their interpretation, various shortcomings of both the Chamber of Mines accident statistics and those published by the Department of Mineral and Energy Affairs. Authors' Reply We gratefully acknowledge Dr Wagner's contribution to the discussion on our paper. For convenience, we shal use his sequence of comments in our reply. Before doing so, however, it may be useful to explain how our paper came to be written. After the explosion at Hlobane Colliery in 1983, one of us (HSE), in February 1984, was retained by the lawyers acting for some of the dependants of the victims to advise on technical maters relating to the explosion. Contribution by Ms S.A. Wats Some of the points made by Ms Wats have already been answered in our comments on Dr Wagner's contribution. We are fully aware that the number of accidents leading to absences of less than 4 days would be much greater than shown in our bar chart, and are grateful to Ms Wats for drawing attention to the specific exceptions that can make a 1-3 day accident compensable and that are clearly responsible for the relatively low count in that category of the chart.

Jan 1, 1988

It is perhaps somewhat unusual for a contributor to comment on the authors' reply to his critique. However, I should like to return to a specific comment made by the authors. Award to Bob Laburn The Federation of Societies of Professional Engineers (FSPE) is pleased to announce that the 1984 FSPE Award for Services to the Engineering Profession was presented to Dr R. J. (Bob) Laburn at a function held on 14th February, 1984.

Jan 1, 1984