‘Pre and post’ mine geotechnical conditions for surface mines, developed from the comprehensive exploration program

Abstract

The “best coal deposit in the world” may not make the “best coal mine in the world” because the physical characteristics of the mine site are unfavorable for the economic removal of the overburden, recovery of the coal, and post-mined reclamation. A comprehensive coal exploration program can provide the basic data for geotechnical interpretations. The exploration program entails detailed stratigraphic interpretations, based on coring and geophysical logging, which concentrate on determining the environment of deposition of the units at the site. This determination allows the geologist to predict the extent, thickness, and variability of the units. These predictions are directly incorporated into geotechnical interpretations. The geotechnical interpretations, however, must be calibrated before they can be utilized by the engineer in mine design. Sonic logs, obtained during the coal quality/geotechnical drilling phase, provide an aerially extensive and inexpensive interpretation of physical rock properties of each stratigraphic unit of interest. Results of the sonic logging study are used to guide future geotechnical drilling in order to evaluate the entire range of physical properties that exist at a site. Post-mined problems are anticipated through the use of an engineering geologic analysis of the site stratigraphy. Classification of mine spoil and measurement of the physical spoil properties allow estimation of spoil pile stability, spoil swell, and settlement conditions. Thus, the use of “worst and best conditions models” defines the expected range in the physical properties of the overburden and underburden within the mine site. Potentially unstable sites, ground-water seepage areas, and other adverse geotechnical conditions can be avoided during mine planning or special investigations can be made to evaluate these conditions. The mine planner, designer, and operator is provided information about the geotechnical conditions to be expected at the site, so that a successful mine can be opened.