TY - JOUR
T1 - Characterization of an unstable rock mass based on borehole logs and diverse borehole radar data
AU - Spillmann, Thomas
AU - Maurer, Hansruedi
AU - Willenberg, Heike
AU - Evans, Keith F.
AU - Heincke, Björn
AU - Green, Alan G.
N1 - Funding Information:
We thank Simon Loew and Erik Eberhardt for their cooperation in this interdisciplinary project and appreciate the very helpful suggestions provided by Heinrich Horstmeyer. The comments by two journal reviewers are greatly appreciated. The optical televiewer logs and the inclinometer surveys were performed by Terratec GmbH (Germany) and Stump Foratec AG (Switzerland), respectively. We are grateful to Jean Daniel-Rouiller from CREALP (Research Centre on Alpine Environment, Switzerland) for providing the digital terrain model and geodetic survey data, and to the local authorities of Randa for providing logistical support. This project was funded by the Swiss National Science Foundation (Project No. 2000-066877).
PY - 2007/1
Y1 - 2007/1
N2 - Unstable rocky slopes are major hazards to the growing number of people that live and travel though mountainous regions. To construct effective barriers to falling rock, it is necessary to know the positions, dimensions and shapes of structures along which failure may occur. To investigate an unstable mountain slope distinguished by numerous open fracture zones, we have taken advantage of three moderately deep (51.0-120.8 m) boreholes to acquire geophysical logs and record single-hole radar, vertical radar profiling (VRP) and crosshole radar data. We observed spallation zones, displacements and borehole radar velocity and amplitude anomalies at 16 of the 46 discontinuities identified in the borehole optical televiewer images. The results of the VRP and crosshole experiments were disappointing at our study site; the source of only one VRP reflection was determined and the crosshole velocity and amplitude tomograms were remarkably featureless. In contrast, much useful structural information was provided by the single-hole radar experiments. Radar reflections were recorded from many surface and borehole fracture zones, demonstrating that the strong electrical property contrasts of these features extended some distance into the adjacent rock mass. The single-hole radar data suggested possible connections between 6 surface and 4 borehole fractures and led to the discovery of 5 additional near-surface fracture zones. Of particular importance, they supplied key details on the subsurface geometries and minimum subsurface lengths of 8 of the 10 previously known surface fracture zones and all of the newly discovered ones. The vast majority of surface fracture zones extended at least 40-60 m into the subsurface, demonstrating that their depth and surface dimensions are comparable.
AB - Unstable rocky slopes are major hazards to the growing number of people that live and travel though mountainous regions. To construct effective barriers to falling rock, it is necessary to know the positions, dimensions and shapes of structures along which failure may occur. To investigate an unstable mountain slope distinguished by numerous open fracture zones, we have taken advantage of three moderately deep (51.0-120.8 m) boreholes to acquire geophysical logs and record single-hole radar, vertical radar profiling (VRP) and crosshole radar data. We observed spallation zones, displacements and borehole radar velocity and amplitude anomalies at 16 of the 46 discontinuities identified in the borehole optical televiewer images. The results of the VRP and crosshole experiments were disappointing at our study site; the source of only one VRP reflection was determined and the crosshole velocity and amplitude tomograms were remarkably featureless. In contrast, much useful structural information was provided by the single-hole radar experiments. Radar reflections were recorded from many surface and borehole fracture zones, demonstrating that the strong electrical property contrasts of these features extended some distance into the adjacent rock mass. The single-hole radar data suggested possible connections between 6 surface and 4 borehole fractures and led to the discovery of 5 additional near-surface fracture zones. Of particular importance, they supplied key details on the subsurface geometries and minimum subsurface lengths of 8 of the 10 previously known surface fracture zones and all of the newly discovered ones. The vast majority of surface fracture zones extended at least 40-60 m into the subsurface, demonstrating that their depth and surface dimensions are comparable.
KW - Borehole geophysics
KW - Crosshole radar
KW - Fracture mapping
KW - Single-hole radar
KW - Vertical radar profiling (VRP)
UR - http://www.scopus.com/inward/record.url?scp=33751077274&partnerID=8YFLogxK
U2 - 10.1016/j.jappgeo.2006.04.006
DO - 10.1016/j.jappgeo.2006.04.006
M3 - Article
AN - SCOPUS:33751077274
VL - 61
SP - 16
EP - 38
JO - Journal of Applied Geophysics
JF - Journal of Applied Geophysics
SN - 0926-9851
IS - 1
ER -