The relation of geology to stress changes caused by underground excavation in crystalline rocks at Idaho Springs, Colorado

Abstract

6 diameters ahead of the crosscut, 2 diameters ahead of the face in acrylic, 1.25 diameters in concrete, and 1 diameter in granite. These subsidiary stress peaks are not explained by available theory. Such rock-mass behavior, if not anticipated, might result, especially in a complex (multiple-opening) underground operation, in damage of support systems owing to overloading. Laboratory and field data suggest that the stress field may have both residual (locked-in) and tectonic or gravity components. The release of residual strain energy is principally brought about by excavation through excavation-induced fault movements. Disturbances of the stress field caused by the intermittent excavation in the mine in part were time dependent, with stabilization requiring weeks to months.

Estimating in situ Stresses

“…9.9). Other cases of alignment of in situ stresses with faults and joint sets have been reported by Preston (1968), Lee, Nichols and Abel (1969), Eisbacher and Bielenstein (1971), Hast (1972), Lee, Abel and Nichols (1976), Kim and Smith (1980), Gay and Van Der Heever (1982), Leijon (1986), Enever, Walton and Windsor (1990) and Wong (1993). The alignment of in situ principal stresses with rock fabric was also reported by Carlsson and Olsson (1982) regarding the state of stress at the site of the Forsmark power plant in Sweden.…”

Technology Transfer at Edgar Mine: Phase 1; October 2016

“…The USGS (Lee 1976) concluded that there were multiple factors contributing to the observed variation between individual stress measurements, including localized faulting, differences in rock type, and a complex tectonic history at the Edgar Mine. This may explain some of the differences between the USGS consensus stress state and the 2015 measurement, including the nearly double magnitude of the 2015 horizontal stress components.…”

“…In situ stresses were measured historically by the United States Geological Survey (USGS) and others at the Edgar Experimental Mine using the United States Bureau of Mines Borehole Deformation Gauge (USBM BDG) and other techniques (Lee et al 1976). These Agapito Associates, Inc.…”