Multi-channel Rayleigh wave data were acquired across a 1m diameter spillway tunnel along three parallel traverses with surface to tunnel separations of 0.90 m, 2.15 m, and 3.13 m, respectively. The data were acquired by placing a 24-channel array across the tunnel (perpendicular to the center-line of the spillway tunnel) and walking the sledge hammer source through the array starting with a far-offset of 10 m. The 4.5 Hz geophone array spacing was at 0.5 m intervals. Single shot data were analyzed to visually locate and to highlight attenuation effects associated with the tunnel. The field records were then velocity filtered in order to enhance back-scattered Rayleigh wave energy thereby allowing for visual identification of the tunnel location. The same single shot data were analyzed using the Attenuation Analysis of Rayleigh Waves (AARW) method. The intent was to demonstrate the utility of these approaches to tunnel delineation at a site where the geometry of the target and the nature of the encompassing soil was known. Electrical resistivity data was also acquired along the traverses for comparison purposes.
Fracture detection and delineation is very important for salt mines operation because fracturing significantly increases the probability of failure of supporting pillars and overlaying water protective beds.Results of forward modeling studies confirmed the feasibility of georadar with a 400 MHz antenna to reliably detect the millimetric scale fracture.3-D GPR data were acquired in the potash mine near the city of Solikamsk, Russia to evaluate the effectiveness of imaging technology to detect and delineate the fractures in heterogeneous salt rock. Continuous common-offset data were obtained at seven parallel profiles across the fracture exposed in the wall of a mine pillar. The pillar was 4.5 m thick and comprised of interbedded layers of salt rock and clay. The open millimetric scale subvertical fracture crosscuts the pillar at angle of 25°.Data were collected using commercial OKO georadar system (Logis, Russia) with a 400 MHz shielded antenna. ReflexW and OpendTect software were used for processing and interpretation of the 2-D radargrams and combined 3-D data set.The 3-D migration allowed generating a true image of subsurface structures and creating a spatial model of fractures. Using the image of known fracture as interpretation template, fracture having no surface evidence was detected.
SAGEEP 2010Keystone, Colorado
Electrical Resistivity Tomography (ERT) data were acquired on the ground surface across an underground limestone mine access tunnel in an effort to characterize the roof rock. This investigation was conducted because simultaneous localized failure occurred on the ceiling of the access tunnel and elsewhere in the mine along a previously unknown northwest trending lineament.The interpretation of the ERT data indicates the limestone roof rock above the tunnel is dissected by several prominent clay-bearing near-vertical solution-widened fractures (joints or faults) that are not visually exposed on the ceiling of the tunnel. Roof rock failure in the mine access tunnel occurred at the intersection of projected lineament and one of the more prominent interpreted solution-widened fractures. 865 Downloaded 06/14/16 to 128.111.121.42. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/ SAGEEP 2010 Keystone, Colorado
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