A coal mine bump is a sudden, violent failure of a coal pillar or groups of pillars which occurs primarily owing to excess stress buildups during pillar retreat operations and longwall mining. The intensity of bumps ranges from minor thumping of coal pillars to large quantities of coal being suddenly ejected into the mine workings where men and machinery are present. Some of the larger bumps have displaced entire coal pillars into mine entries. Others have sent shock waves throughout entire mining sections, some being felt hundreds of meters away on the surface. For a more complete definition of bumps, please consult Holland and Thomas (1054). According to the II.S. Department of Labor, Mine Safety and Health Administration (MSHA), coal mine bumps caused 44 accidents from 1078 to ]qFI4 and resulted in 14 fatalities from 19.50 to 10F14 in the Eastern States of Kentucky, West Virginia, Virginia, and Pennsylvania (Goode, et al., l984).
Several research tasks have been conducted to acquire fundamental knowledge for controlling this hazard in U.S. coal mines. These tasks follow: 1) Survey industrial practices and problems relative to the bump phenomena, 21 determine the geological and mechanical properties of coal strata that influence the occurrence of bumps, 3) measure the rate of pressure buildup and strata deformations during mining, 4) attain values of the ultimate strength of the coal pillars prone to bump, 5) investigate the influence of different mining methods, 6) evaluate the effectiveness of various control techniques, and 7) develop empirical and numerical models to analyze bump-prone mining panels. The collection of such information from different sites with various geological conditions, mining methods, and mining layouts will be helpful to the mining community in designing the most appropriate mining sequences, room and pillar geometries, and control techniques to reduce the potential of coal mine bumps.
Several coal mines where large bumps had resulted in fatalities were surveyed during 1084. Those bumps occurred under considerable overburdens (300 to 700 m), with the overlying strata comprised of very stiff, competent members of sandstones, siltstones, and shales. Some generalities for controlling bumps appeared evident during these field observations and lead to the following recommendations: 1) Roof spans projecting over the gob should be kept as short as possible, 2) complete splitting of barrier pillars should not be done when gob is located adjacent to barriers being split. 3) pillars should be approximately the same size and shape, 4) convergence of two gob lines should be avoided along active pillar lines, and 5) longwalls with specially designed gateroads may effectively replace conventional retreat mining in deep coal mines. The following data discuss preliminary findings at the first of several detailed field investigation sites.
GEOLOGICAL AND MECHANICAL CHARACTERISTICS
Underground geologic mapping and analysis of corehole data from the Olga Mine in McDowell County, West Virginia, indicate that the Pocahontas No. 4 Coalbed is overlain by a massive sandstone which has a widely spaced, unidirectional joint system. The No.4 Coalbed is underlain by a laterally discontinuous series of shales, siltstones, and sandstones.