TDR monitoring of overburden deformation to verify modeled behavior: Fid-Bau Portal

TDR monitoring of overburden deformation to verify modeled behavior

O'Connor, K.M. / Siekmeier, J.A.

This paper presents a comprehensive procedure for sampling, monitoring, modeling, and numerical simulation of rock mass behavior. Motivated by research into high extraction mining within bedded strata, this procedure has proven to be effective in a variety of mining and geotechnical applications. It begins by systematically estimating a rock mass rating for every stratum identified in drill-core logs and computing an empirical bending stiffness for each stratum. Then significant horizontal discontinuities are identified where adjacent strata have a large contrast in stiffness, and displacements along these discontinuities are monitored by placing a coaxial cable in each drill hole and anchoring it to the rock with expansive grout. As mining occurs and shear stresses are redistributed, displacements along the rock mass discontinuities cause deformation of the embedded cables which is monitored using time domain reflectometry (TDR). Measurements have verified modeled behavior of horizontally bedded sedimentary rock along the centerline of a coal mine longwall panel. The locations and magnitudes of simulated displacements are consistent with those measured using TDR. The importance of incorporating variations in rock stiffness and plastic sliding along 'stiffness discontinuities' into any numerical model that is intended to accurately simulate rock mass behavior has been confirmed by experience with TDR monitoring on many projects.