THE DESIGN OF COAL MINE ROOF SUPPORT AND YIELDING PILLARS FOR LONGWALL MINING IN THE APPALACHIAN COALFIELD (ROCK MASS CLASSIFICATION, STRESS, FAILURE)

In this thesis, the existing Geomechanics Classification (Bieniawski, 1979) was modified for use in underground coal mines through the introduction of adjustment modifiers for strata weathering, horizontal stress, and roof support. Sixty-two roof case histories were collected from two mines exploiting the Pittsburgh and Lower Kittanning coal seams. Geologic and material property variables were examined with respect to supported stand-up time, while survival and regression analyses were used in deriving the adjustment multipliers. Guidelines for roofspan selection and roof support design were an integral facet of the modified classification scheme.;The main contributions of the research lies in: (i) modifications introduced to the Geomechanics Classification (RMR System), (ii) the correlation between changes in pillar stress and the extent of the yield zone surrounding a longwall chain pillar, and (iii) the proposal of design procedures involving coal mine roof support and chain pillars. Numerical examples obtained from mine case histories are provided to illustrate the use of the design procedures.;Tentative design guidelines for chain pillars are provided on the basis of a field investigation and numerical modeling of longwall chain pillar behavior. A longwall chain pillar was instrumented with vibrating wire stressmeters to quantify the change in stress distribution as longwall mining proceeded outby the pillar. A sonic probe, supplied by the U. S. Bureau of Mines, Denver Research Center, was used to conduct a velocity profile across the pillar before and after mining to delineate the failed and stable regions of the pillar. Velocity profiles across the pillar were supplemented by an examination of changes in the dynamic modulus and the shear wave frequency.