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By D. S. Choi, H. D. Dahl, D. L. McCain

The paper examines current room and pillar mining practice in the U.S.A. from the standpoint of rock mechanics. Consideration is given to the deformation characteristics of the roof formation and the coal seam as determined in the laboratory as well as in the field. The results can be utilized by the practicing mining engineer to improve current mine design practice.

Jan 1, 1982

By B. R. Pothini, H. von Schonfeldt

In underground coal mining many excavated openings have a relatively short projected life span. To ensure safety for men and materials at a minimum cost over the projected operating life, only pillars for overburden support and roof bolts for support of the openings are used extensively. Mining activity constantly changes the geometry of the mine producing load changes on the structural support members of the openings that often induce unstable deformations which can lead to roof falls or pillar failures. The paper describes how simple deformation measurements can be used to design primary and supplementary roof supports and to predict roof falls and possibly pillar bumps. Specifically, bed separations in the roof measured directly with the help of borescopes and calculated from differential convergence data are used to optimize bolt links or support requirements for chemical stabilization of mine roofs. Roof falls are predicted on the basis of admissible values for cumulative convergence between roof and floor, convergence rate, and the change of the rate of convergence. The pillar extraction operations convergence anomalies detected from contouring identify bump prone pillars, while convergence and pillar dilation determine the yield zone in a pillar to verify pillar softening and de-stressing. Manuscript not received in time for publication.

Jan 1, 1983

By Jose F. Agapito

This paper describes part of a geotechnical program which was instrumental in obtaining information for the design of large oil shale pillars. The work was carried out during 1971 and 1972 in the experimental mine of the Colony Development Operation. Colony is an oil shale venture formed between Atlantic Richfield Company, Operator; The Oil Shale Corporation, Cleveland-Cliffs Iron Company, and Sohio Petroleum Company to conduct research and development in mining and retorting of oil shale. The property is located in the southern edge of the Piceance Creek Basin in northwestern Colorado, approximately 250 miles west of Denver. Mining was conducted by the room-and-pillar method in a 60-ft high portion of the Green River formation at a depth of 600 to 850 ft. Pillar dimensions are approximately 60 ft by 60 ft. The mine site is in the eastern face of the canyon containing the Middle Fork of Parachute Creek. The distance from the mine to the side of the mountain varies from 500 to 1200 ft, and its height above the stream floor is approximately 700 ft.

Jan 5, 1974

By Jose F. T. Agapito

The mining engineer must be able to predict the structural behavior of the rock around underground openings so that he can answer questions relating to safety and economics. With the present status of rock mechanics knowledge, exact predictions cannot be attained and approximate idealizations are made. As a first approximation, structural design makes use of theory, laboratory testing of rock properties, and available experience from excavations in similar rock formations. However, realistic design can usually be obtained only after in-situ observations and measurements are made. After all the information is collected, judgement and experience play a most important role in the final formulation of the design. This paper describes part of a geotechnical program which was instrumental in obtaining information for the design of large oil shale pillars. The work was carried out during 1971 and 1972 in the experimental mine of the Colony Development Operation. Colony is an oil shale venture formed between Atlantic Richfield Company, Operator, The Oil Shale Corporation, Cleveland-Cliffs Iron Company, and Sohio Petroleum Company to conduct research and development in mining and retorting of oil shale, The property is located in the southern edge of the Piceance Creek Basin in northwestern Colorado, approximately 250 miles west of Denver (Figure 1) . Mining was conducted by the room-and-pillar method in a 60-ft high portion of the Green River Formation at a depth of 600 to 850 ft, Pillar dimensions are approximately 60 ft by 60 ft. The mine site is in the eastern face of the canyon containing the Middle Fork of Parachute Creek, The distance from the mine to the side of the mountain varies from 500 to 1,200 ft, and its height above the stream floor is approximately 700 ft.

Jan 1, 1974

By K. G. Davies, M. J. Royea

"A major program of pillar recovery at the Sullivan mine has been assisted for the past several years by a concerted series of rock mechanics investigations. The object of these investigations is to measure the parameters of rock behaviour which influence pillar mining. This quantitative information is then used in the design of mining methods appropriate for various conditions.Instrumentation to measure absolute rock stress, changes in rock stress and the gross deformation of rock masses has been developed. Various instruments are described, as are instrument evaluation procedures and typical test results. The data from underground measurement projects have been used to modify pillar extraction sequences along re-treat fronts. Rock mechanics information from individual pillars has been incorporated into the design of mining methods to suit particular circumstances."

Jan 1, 1968

By P. P. Andrieux

The recovery of the Zone G crown pillar, located between the bottom of the open pit and the top of the underground workings at the Raglan Katinniq Mine in Nunavik, started in the summer of 2008 and should be completed by the end of 2009. This article describes the rock mechanics-based approach implemented to design the recovery of this valuable block of ore. The stereophotography-based ShapeMetriX3D technique was first used to provide a comprehensive assessment of the various joint sets that comprised the pillar. Then, the statistical distributions obtained for the dip, dip direction, spacing and persistence of these sets were used in conjunction with the geometry of the large-scale faults present in the area to build and run a series of explicit rigid numerical models. Each of these models had a slightly different jointing geometry, randomly constructed from these statistical distributions. Incorporating in a properly formulated numerical model the variability of some of the input parameters has allowed the engineering team to assess in a rational and reliable manner the likelihood of success of the proposed mining method and sequence.

May 1, 2009

The Sto Tomas II orebody of Philex Mining Corporation is a porphyry copper deposit located at Padcal, Tuba, Benguet, Philippines. It was mined through open pit method for the first two years starting 1958 and subsequently through underground method using the Block Cave System. The slusher type of draw was employed at the upper levels of the orebody from mid-year of 1959 up to 1994 and then shifted to LHD as the ore became more competent at the lower levels. Application of rock mechanics played a vital role during the conceptualisation of the LHD method of draw, the first of its kind in the Philippines. Rock mechanics is a combined responsibility of the geology and the mine engineering staffs, with the geology providing the vital information to the mine engineering to include in the mine planning the following:the general geology of the orebody; the ground characterisation through rockmass classification; determination of the cavability of the ore column (this includes our experience on airblasts which occurred during the early stage of our last slusher blocks); undercutting sequence; fragmentation of the rockmass in the ore column; drawzone spacing; proper draw control procedure; lay-out of openings; and the design of ground supports based on the rockmass condition. For the proper interpretation of the rockmass that would cater to the diverse mining situations, Philex adopted the modified geomechanics rockmass classification (Mining Rockmass Rating, MRMR) as this system is recognised and used by most of the block cave mine worldwide. This paper aims to discuss and present the role of rock mechanics in the analysis and determination of geomechanical issues encountered in Philex mechanised block cave operation.

Jan 1, 2000

By Paul Hughes

This paper summarizes current underhand paste backfill mining as applied to Goldcorp Inc?s Red Lake Mine, Newcrest Mining Ltd?s Kencana Mine and the Lanfranchi Nickel Mine as well as ongoing research at the University of British Columbia?s Norman B. Keevil Institute of Mining Engineering. The Red Lake Mine utilises a 6 m wide undercut with a 2 MPa unconfined strength paste in order to selectively mine its high grade, high-stress orebody. Kencana?s orebody is located in a poor rock mass environment. An 8 m wide, 2 MPa unconfined strength paste sill allows a safe working condition for its high grade orebody. The Lanfranchi Nickel Mine utilises a cable-supported, 2 MPa paste, with 12 m span sills, to optimize the mining of the squeezing rock mass. This paper details the rock mechanic hazards, ground support techniques, paste practices and unique conditions for each mine. Further, an update of ongoing research at the University of British Columbia, focussing on the optimization of safe mining in underhand cut-and-fill mining in high-stress/weak rock masses, is presented.

May 1, 2011

By Caner Zanbak

Deformational behavior of a rock mass can be modeled with a constitutive law based on theories of elasticity, and plastic and viscous deformation. For most rock types, such constitutive models may be used with confidence because there is no geochemical interaction between the rock-forming minerals and water. However, if volume changes in the rock due to geochemical phase transitions are predicted, then these volume changes must be converted into mechanical parameters and must be included into the constitutive laws. In this paper, geochemical phase transitions between anhydrite (CaS04) and gypsum (CaS04-2H20) will be brought to the attention of researchers in rock mechanics. Hydration of anhydrite to gypsum may yield volume increases up to 62.6 percent and dehydration of gypsum to anhydrite may cause volume decreases up to 38.5 percent. If one were to convert the volume increases in hydrating anhydrite into strains and calculates the required stresses to restrict the expansions, the magnitude of stresses will be found at GPa levels. Such stresses on swelling anhydrite layers cannot be provided by geologic media. Therefore, the host rocks will deform under these high stresses. On the other hand, under increasing stresses, geochemical transition of anhydrite to gypsum may stop after some hydration of anhydrite, and anhydrite and gypsum systems may become stable. Changes in temperature and solution compositions in the anhydritel gypsum system also control the stability of the geochemical system, and therefore, the extent of volume changes. A similar conceptual model can be drawn for volume decreases due to dehydration of gypsum to anhydrite. In this case, stress reduction on the gypsum layer may cause extensive fracturing and changes in the state of stress in the host rock mass.

Jan 1, 1984

By David E. Fogelson, James J. Olson

Rock mechanics as a guide to a safe underground operation is gaining importance as more is under- stood of rock behavior under stress and of the competency of rock after blasting. The U. S. Bureau of Mines' Twin Cities Mining Research Center and White Pine Copper Co. personnel undertook a joint research program recently to define how the rock adjacent to a newly opened underground working could be left as undisturbed as possible. The goal was to leave a competent structure which would tend to limit rock falls and thus decrease the incidence of fatalities from this greatest of all underground hazards. High-amplitude stress waves and borehole gases create a crushed zone in the rock, the thickness of which is about equal to the borehole radius. Beyond the crushed zone, additional structural damage occurs to the rock from the microstructural level up to visible fractures that may extend several feet. This type of rock damage near the final excavation lines reduces rock strength and increases the possibility of failure of the openings from subsequent vibrations or stresses.

Jan 9, 1969

By B. Rao Pothini, Julio H. Thaler, W. L. Finlay

The White Pine room-and-pillar mine started in 1955 from a suboutcrop, down gentle dips, and with a competent sandstone roof. As mining depths increased, extraction decreased 1% every 35 feet. Moreover, roofs became shaly and less competent, and regions of high fault and joint densities, sometimes with and some- times without high lateral stresses, increased the tendencies towards roof falls. Instinctive reactions towards narrower openings did not alleviate the problem. Careful consideration of rock mechanics principles culminated in the development of two variants to the conventional room-and-pillar mining system based on the concept of stress relief through load deflection. The two systems-EquiAdvance Cave, and PressureArch Panel Mining-are complementary. The objective of the former system is to provide relief from lateral stresses through advance caving and in the process also to achieve higher extraction at depth. Where surface subsidence cannot be allowed, the alternative PressureArch Panel concept is utilized to provide stress relief and moderately high extraction ratio. Both systems have been under trial for over three years and, together, produced over three million tons of copper ore. These two systems, and their production test results to date, are described.

Jan 1, 1977

By John D. Smith

This paper describes how a knowledge of inherent rock characteristics can aid the mining engineer in his design of a mining method for a massive domelike structure. The paper shows how the pertinent rock characteristics were measured and analyzed and how the data obtained was used for design purposes. This analysis was conducted in 1964 in a producing salt dome, since that time, mine management has tried certain of the recommendations for mine design changes. The results of such changes are presented.

Jan 1, 1968

By K McNabb, M H. Turner, P A. Jenkin

Mining of the Agnew nickel deposit commenced in 1970 using a variety of underground mining methods, though with mixed success due to the difficult ground conditions. WMC Resources Ltd acquired the operation in 1989, and commenced nickel production with an open pit. In 1995 all production reverted to the rejuvenated underground mine, using exclusively SLC (sublevel caving) methods. Currently the mine produces 1.4 Mt per annum, at an average grade of 1.74 per cent Ni. Underground mining of the Perseverance orebody has always presented significant challenges due to the difficult ground conditions in the weak and altered ultramafic rocks. The range of problems include areas of swelling minerals, intense and extremely weak shear zones, relatively high in situ stress, and in other areas very brittle rocks. Under these conditions rock mechanics input has been and remains a critical element of the mining strategy. Severe ground behaviour difficulties down to a depth of 500 m below surface prompted a review of the mining strategy for the large disseminated nickel orebody, including evaluation of alternative mining methods. However, sublevel caving was ultimately selected as the preferred method, and a re-design of the SLC cross-cut layout followed. A selection of rock mechanics investigations of interest are described, including complex virgin stress measurements, detailed ground behaviour monitoring, and the use of non-linear stress analyses to re-design the mine layout. Subsequent ground behaviour, support design and production scheduling are also described.

Jan 1, 2000

By J. F. Cuderman

A technique using propellants has been developed for producing multiple fractures about a wellbore. The use of propellants having a range of burn rates permits precise control of combustion gas release and thereby of borehole pressurization. The pressure rise- time is the key variable governing fracture behavior. The peak pressure attained is of secondary importance and appears to be a function of in situ stress and loading rate. The fracture geometry is governed by the in situ stresses and pressure risetimes. The major fractures occur along the principal planes of stress and along apparent planes of maximum shear stress.

Jan 1, 1984

By H. A. von Schonfeldt, H. Douglas Dahl

INTRODUCTION During the past decade, significant pro¬gress has been made in applying rock mechanics principles to mine design problems by a great number of researchers. Some of these new techniques have found their way into the engineering and planning offices of the operating mine. In spite of these advances, however, the application of rock mechanics in the day-to-day mine planning and design of our domestic coal mines is rela¬tively rare. There are a number of reasons responsi¬ble for this relatively slow progress, not the least of which is the question of how to measure the success or cost effectiveness of a sizable rock mechanics effort in an opera¬ting mine. Firstly, the properties of geologic materials generally vary over a wide range and it is, therefore, difficult to assess whether an improvement in the mining conditions is due to a design change or due to a change in the geologic conditions. A second reason for the slow acceptance of rock mechanics in engineering thinking is the fact that some of the concepts are quite difficult and that physical evidence of their validity to mine design is still rare. Thirdly, com¬munication between research, engineering and applications oriented people appears to function only intermittently. In our view, however, the most important impediment lies in the "state-of-the-art." Exactly how much can rock mechanics help the mine operator? The best that rock mechanics can do at present is determine whether one approach is better than another when weighed against some design objective (stress, strain, deformation). We cannot determine the abso¬lute best ground control design -- only what is better. If ground control is lost, the statement that "it's the best one we looked at" means very little to the harried operator. While the "state-of-the art" has advanced a great deal, it has certainly not been reduced to an engineering matter in that design hand¬books are available -- they are not. The success of a rock mechanics program, there¬fore, can be determined only over a long period of time of continuous effort.

Jan 1, 1977

By Francois E. Heuze

The mined geologic burial of high-level nuclear waste is how the favored option for disposal. The underground repositories must keep the waste away from the biosphere for very long times - several thousands to tens of thousands of years. Also, access must be maintained to the vaults for several tens of years, so that the waste can be retrieved, if necessary. Both the excavation of the underground chambers, and the radiogenic heating will disturb the rock mass. The overall rock mechanics problem is to understand and predict the processes associated with these perturbations, and their impact oh the isolation and containment of the waste (3)**. The specific rock. mechanics issues which have been identified for the three candidate hard rocks (basalt, granite, and tuff), are summarized in Table 1. The table also indicates the level of adequacy of our knowledge in the areas of the various issues. Such an evaluation is consistent with the general consensus of the rock mechanics profession, as explained in several key reports and publications (1 to 11). The main shortcomings of today's rock mechanics for waste repositories can be summarized as: ? lack of resolution for remote mapping of fractures in rock masses ? great difficulty in testing large volumes of rocks to determine their mechanical properties.

Jan 1, 1981

By K. F. Unrug

Eastern coalfields have been extensively strip mined. In the past, contour mining left vast areas of post-mining highwalls and benches. Thin seams, which cannot be feasibly mined with conventional methods, quite often contain substantial reserves of high quality coal. Unconventional secondary recovery methods may permit economical production of that coal, increased use of reserves, and provide resources for restoration of orphaned land. Technical and rock mechanics implications of secondary mining methods are discussed to determine their limitations and the objectives of required research.

Jan 1, 1986

By K. F. Unrug

An overview of the history of mining technology, both past and present, shows that some of the new concepts being successfully applied have changed the reserve categorization and are having an overall impact on production. Past coal mining operations in the eastern coal fields, and especially in Appalachia, extensively utilized stripping with the predominately applied contour method. As a result, vast mountainous areas have abandoned benches left behind by past mining operations. While thicker seams previously stripped were usually mined by underground or mountain top removal methods, thin seams beyond technical or economical limits were left intact after contour mining had reached the ultimate height of the wall. These thin seams quite often contain high BTU, low ash and sulfur coal that makes them attractive for a secondary recovery due to the market requirements. Secondary highwall recovery has obvious potential and is economically attractive; however, with the present state of industrial experience and lack of analysis of site data, a trial and error approach is used by operators.

Jan 1, 1983

By H. William Ahrenholz

Many technical meetings were attended by mining people during the past year in which rock mechanics was either the main subject for discussion or was a prominent part of the program. Several universities continued to offer short courses in the applications of rock mechanics for practicing mining engineers. At the beginning of the year, the AIME Committee on Rock Mechanics achieved standing-committee status. It is to assume responsibility for coordinating all AIME activities in this area. Eleven professional societies are now participating in a newly formed Intersociety Committee for Rock Mechanics. AIME and its constituent societies has three representatives. Delegates from the Intersociety Committee will serve on the U.S. National Committee for Rock Mechanics which is being formed by the national Academy of Sciences.

Jan 2, 1967

By Chas. L. Emery

"The laws of rock mechanics apply equally well to all rock structures, and open pits are not exceptions. The concepts and some arguments about the emphasis to be placed on various aspects of open-pit design are discussed in this article.RocksROCK can be described as a granular material consisting of grains and glue. The grains may be fragments of other rocks or polycrystalline aggregates. The glue may be ferruginous, calcareous, argillaceous, siliceous or other material connecting the grains. In a crystal intergrowth, the outer layers of the crystals in contact with each other may be considered to act as a glue. Water may be a glue in clay or a grain in a crystal structure. Air and other fluids or gases are grains if they occupy spaces in a granular mass. Such grains are functional either chemically or mechanically or both."

Jan 1, 1966