Using a computer spreadsheet to characterize rock masses prior to subsidence prediction and numerical analysis.
O'Connor KM; Siekmeier JA; Powell LR
Minneapolis, MN: U.S. Department of the Interior, Bureau of Mines, RI 9581, 1996 Jan; :1-75
To characterize rock mass overlying high-extraction coal mines, the USBM utilizes a computer spreadsheet program and modified Rock Mass Rating (RMR) system. The spreadsheet calculates an RMR based on a bed's engineering properties determined from core logs and laboratory tests. An in situ deformation modulus and a bending stiffness are computed for each bed. Stiffness-versus-depth plots identify groups of beds with similar stiffness. Large variations in stiffness between adjacent beds are considered significant horizontal discontinuities where slip is likely. Time domain reflectometry (TDR) is used to verify this hypothesis by measuring shear displacement along such discontinuities. A model of the overburden is built by assuming that a near-surface laminated beam exists above a transition zone in which large plastic slip occurs along horizontal discontinuities. Increasingly thicker groups of beds are modeled to determine the most probable beam thickness based on a comparison with measured deflection profiles.
Coal-mines; Computer-applications; Deflection; Deformation; Discontinuities; Geologic-strata; Geologic-structures; Ground-subsidence; Mechanical-properties; Numerical-analysis; Overburden; Rock-mechanics; Site-characterization; Stiffness; Time-domain; Underground-mining; Quantitative-analysis
Report of Investigations
NTIS Accession No.
Minneapolis, MN: U.S. Department of the Interior, Bureau of Mines, RI 9581