CASE-STUDY OF MONITORING CHANGES IN ROOF STABILITY

The U. S. Bureau of Mines implemented an integrated static and geophys ical monitoring program in a southern Wyoming mine to study changes in seismic wave propagation properties in roof strata. The purpose was t o develop techniques to assess roof stability problems. Monitoring con sisted of recording deformation and stress histones and calculating se ismic velocity profiles. In addition, the geology and roof conditions were mapped, and cores were tested at the beginning and end of monitor ing to assess structural damage. The instruments were initially instal led at the development face, and monitoring continued until the mechan ized retreat face approached the instruments. Results were analyzed us ing standard history plots, velocity tomographs, and numerical modelin g techniques. Changes in velocity, frequency, amplitude, dynamic Young modulus, and dynamic Poisson's ratio were related to roof deformation , fracturing, and support requirements. Calculated dynamic deformation properties showed the most sensitivity to changes in ground condition s. A reduction in seismic velocity of 17% occurred after 60 mm of roof deformation following installation of supplementary support Inelastic deformation occurred first in the mine floor and spread to the pillar and the mine roof.