Abstract: Excessive levels of horizontal stresses cause ground-fall hazards in underground mines in the Appalachian Basin. At an underground stone mine in Pennsylvania, a modified stress-control mine layout is reducing the hazardous conditions associated with excessive horizontal stresses. A microseismic monitoring system is in place to measure levels of rock stability and provide information on the effectiveness of the design technique. The microseismic data is supplemented with frequent and extensive mapping of roof falls and roof rock damage. Findings to date show that the stress-control layout provides more stable conditions, resulting in a safer environment for the mine workers. Introduction The U.S. National Institute for Occupational Safety and Health (NIOSH) continues to study the impact of different mine layouts to control the damaging effect' and resultant hazardous conditions of horizontal stress in underground stone mines, Successful stable mine designs need to be identified and communicated to the underground stone industry, so that safer working conditions for miners can be achieved. As underground stone production increases, so will the need to develop and use safe mine layouts to minimize hazardous ground conditions. Excessive levels of horizontal stress are present in many parts of the earth’s crust and have often been produced by tectonic plates pushing towards one another. Residual stresses from these events have been retained in rock, even at low overburden (Bickel, 1993). The study was conducted at an underground stone mine in southwestern Pennsylvania. There, excessive levels of horizontal stress were known to exist and such stresses have been observed to cause roof falls. At this mine site a traditional room-and-pillar and a new stress-control layout were in use. The ability of these two mine layouts to control ground was accomplished by mapping roof falls and roof damage areas and by monitoring seismic activity with a 12-channel microseismic system. How can horizontal stress affect roof stability? At the mine, the measured N60°E horizontal stress field (Iannacchione et al., 1998) matched reasonably well with the regional east-northeast stress field found in other mines within this region (Fig. 1). Additionally, maximum values of horizontal stresses ranged from about 10 to 35 MPa (1,400 to 5,000 psi), with an average of about 25 MPa (3,600 psi). This range in values of horizontal stress is 10 times greater than the stress produced from the overburden weight in this part of the mine. The effects of excessive levels of horizontal stress on roof rock stability have been discussed by several researchers (Emery 1964; Parker, 1966; Parker, 1973; Gale 1986; Mark and Mucho, 1994; Mucho and Mark, 1994; Iannacchione et al., 1998). Mining perpendicular to the orientation of the maximum levels of horizontal stress can concentrate that stress in the immediate roof rock. When stress levels exceed the strength of the roof rock, beams within the roof can buckle and fail in shear (Fig. 2). Traces of failure planes often appear as low-angle shears approximately 15 0 from horizontal and oriented perpendicular to the direction of the maximum levels of horizontal stress. In some mining situations, the shear planes can occur with enough frequency to coalesce, forming a semilinear trend tens-to-hundreds of meters in length across a mining section. Major shear zones can result in large roof falls that are often oval in shape, with the long axis perpendicular to the orientation of the maximum levels of horizontal stress (Fig. 3). Typically, these falls show stress concentrations along the axial ends of the oval, oriented perpendicular to the maximum stress direction (Fig. 3). Elevated stress levels are also found in the solid rock above the caved area. It is not uncommon for this oval-shaped type of fall to grow vertically and horizontally over the course of days, weeks and even years, depending on conditions.

Abstract: Neural networks were used to calibrate an online ash analyzer at the Usibelli Coal Mine, Healy, Alaska, by relating the Americium and Cesium counts to the ash content. A total of 104 samples were collected from the mine, with 47 being from screened coal, and the rest being from unscreened coal. Each sample corresponded to 20 seconds of coal on the running conveyor belt. Neural network modeling used the quick stop training procedure. Therefore, the samples were split into training, calibration and prediction subsets. Special techniques, using genetic algorithms, were developed to representatively split the sample into the three subsets. Two separate approaches were tried. In one approach, the screened and unscreened coal was modeled separately. In another, a single model was developed for the entire dataset. No advantage was seen from modeling the two subsets separately. The neural network method performed very well on average but not individually, i.e. though each prediction was unreliable, the average of a few predictions was close to the true average. Thus, the method demonstrated that the analyzers were accurate at 2-3 minutes intervals (average of 6-9 samples), but not at 20 seconds (each prediction).

Abstract: In 1999, 1 Gt (1.1 billion st) of coal was produced in the United States. Of this total, 37% was produced in Wyoming, Montana and North Dakota. Coals of Tertiary age from these states typically have low ash contents. Most of these coals have sulfur contents that are in compliance with Clean Air Act standards and most have low concentrations of the trace elements that are of environmental concern. The U.S. Geological Survey (USGS) National Coal Resource Assessment for these states includes geologic, stratigraphic, palynologic and geochemical studies and resource calculations for major Tertiary coal zones in the Powder River, Williston, Greater Green River, Hanna and Carbon Basins. Calculated resources are 595 Gt (655 billion st). Results of the study are available in a USGS Professional Paper and a USGS OpenFile Report, both in CD-ROM format. FIGURE 1 Major coal basins in the contiguous United States (modified from Fort Union Coal Assessment Team, 1999; Chapter ES, Fig. ES-1). nichols p. 33-38 copy 12/30/02, 2:34 PM 33 34 JANUARY 2003 ■ MINING ENGINEERING The objectives of the NCRA were to compile all pertinent information on the selected coal beds or coal zones, to identify compliant coal in the region, to compile a publicly available digital database and to publish spatial digital products in a variety of interpretative and interactive forms. The coal assessment in Wyoming, Montana and North Dakota focused on ten producing coal zones designated as priority “assessment units” in five coal basins (Fig. 2). The assessment included local and regional geologic, stratigraphic, palynological and coal-geochemical studies, in addition to resource calculations. Final products for the assessment in the Northern Rocky Mountains and Great Plains region include publications in CD-ROM format (Flores et al., 1999; Fort Union Coal Assessment Team, 1999) that present the results of the study in a variety of formats. These CDROM’s contain software for viewing, printing, querying and downloading text, graphics, spatial layers and raw data. Coal assessed Coal assessment units the Northern Rocky Mountains and Great Plains region included the WyodakAnderson, Anderson-Canyon, Rosebud-Robinson and Knobloch coal zones in the Powder River Basin of Wyoming and Montana; the Harmon, Hansen, Beulah-Zap and Hagel coal zones in the Williston Basin in North Dakota; the Deadman coal zone in the Greater Green River Basin in Wyoming; selected coal beds in the Ferris and Hanna Formations in the Hanna Basin in Wyoming; and the Johnson-107 coal zones in the Carbon Basin in Wyoming (Table 2; Fig. 2). Coals in the Bighorn, Bull Mountain, Denver, North Park, Raton and Wind River basins (Fig. 2) were not assessed in detail for this study because they have lower potentials for development. These basins are summarized in the final report by the Fort Union Coal Assessment Team (1999). Geology and age Coal assessed in Wyoming, Montana and North Dakota is present in basins of early Tertiary (Paleocene) age. The coal formed from peat that accumulated in swamps adjacent to fluvial drainages within tectonically subsiding basins bordered by low mountain ranges or, in the case of the Williston Basin, the coastal plain of an inland seaway. The thickness of the peat deposits varied according to local conditions in the depositional environments, including subsidence rate, rainfall and the susceptibility of the peat swamp to flooding. In the Powder River Basin, peat deposits of exceptional thickness, but with limited lateral extent, accumulated. The coal beds that developed from the peat deposits tend to be lenticular in form, and they tend to be discontinuous and variable in thickness. Coal of Paleocene age is present from the surface down to a depth of about 1,800 m (6,000 ft) in the Powder River, Williston and Greater Great River Basins and from the surface to a depth of 3,600 m (12,000 ft) in the Hanna Basin. The geological age of the coal was determined using palynology (the branch of science concerned with the study of pollens and spores) (Figs. 3 and 4). Palynological biozones were identified on the basis of fossil pollen that is found only in certain intervals in Paleocene rocks (for example, Nichols, 1999). The palynological biozones were used to establish the age of individual coal zones FIGURE 2 Coal basins in the Northern Rocky Mountains and Great Plains region. Basins indicated in bold type contain coal beds or coal zones studied in detail for the USGS coal assessment (modified from Fort Union Coal Assessment Team, 1999, Chapter IN, Fig. IN-1).

Abstract: The Chromite mining and chromimum-iron alloy production in 2001～2002 year in the world and the trend of development are introduced.

Abstract: The experience of assembly(3 components)and shift of semi-mobile crushing plant in Qidashan Iron Ore Mine can be taken for reference in the case that new technology and new equipment of intermittent-continuous haulage system are adopted for achieving high economic profits

Abstract: The experimental application of bottom-hole detonation technology in Chengchao Iron Ore Mine and the problems occurred in the experiment are described.Besides,the latest progresses achieved by Chinese research institutes or mining enterprises in study of the technology,the three advantages and bright future of the technology are explained.

Abstract: By means of mechanics model about wallrock deformation and break,the feature and mechanism of deformation or break of weak rock under textural stress and the mode of stress transfer are theoretically analysed and calculated.The results of analysis and calculation are the basis for determining the principle of propping the tunnel surrounded by weak wallrock.

Abstract: The study trace and achievement of BGRIMM emulsion explosive technology are presented in this paper and the development of linked technology is forecasted.

Abstract: In order to overcome shortage of model for predicting size performance of block blasted,a new approach of gray correlation analysis of blasting parameters(such as burden of hole,concentration coefficient of holes,unit consumption of explosive)influencing size performance of block blasted is introduced based on a series of blasting tests.The correlation sequence of these blasting parameters is obtained that can be taken as reference for reasonable selection of blasting parameters.

Abstract: Waste tailings contain a remarkable bit of useful minerals.To extract these minerals,the properties of tailings and some issues about extraction should be paid special attentions.

Abstract: According to the serious status of china's iron ore resource,measures are recommended to stabilize and enlarge home-produced iron ore supply capability and to establish ensured and reliable iron ore supply system in foreign countries.