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Mapping subsurface fractures by radio-frequency holography: a simulation
102A Possible influences of thermal and elastic anisotropy and paleostress, and whether the whole core or merely the outer region is involved in expansion are discussed.
Geophysical techniques
922231 Comparison of the USBM gage and the CSIRO cell in various rock conditions Cai, M; Thomas, L J Rock Mechanics as a Muitidisciplinary Science: Proc 32nd US Symposium, Norman, 10-12 July 1991 P129-138. Publ Rotterdam." A A Balkema. 1991
922234 Curing cave-ins Steed, P M Can Alin J VII_'..V6 Jul.v Au.~, J~,91, P50-53
Performance of the two gauges was compared in the laboratory under known biaxial stresses simulating field conditions. In isotropic, homogeneous, continuous rocks, errors are less than 10%, but neither performs well in thinly bedded or fractured rocks. In this case, the errors are, however, approximately equal and opposite in sense, so a combined reading is reasonably accurate. Reasons for these effects are discussed. The CSIRO gauge is more flexible in use but care must be taken in bonding and temperature compensation. The USBM gauge is simpler but cannot provide the complete stress strain state from one instrument.
Site Investigation and Field Observation See: 922468
Remote sensing and photographic techniques 922232 Some observations on a comparative aerial photography interpretation of a landslipped area Fookes, P G; Dale, S G; Land, J M Q J Engng Geol 1/24, N3, 1991, P249-265 The difficulties in interpretation of aerial photographs and the importance of studies at the site to confirm initial impressions are highlighted by reference to a slope in Papua New Guinea. A landslip complex in gently folded Tertiary sediments, overlain by young colluvium and covered by rainforest, is the case examined. Eight interpretations were made, three observers being aware of a new landslip, five being unaware. Differences within and between these two groups are discussed.
Structural and geotechnical mapping 922233 GIS techniques and statistical models in evaluating landslide hazard Carrara, A; Cardinali, M; Detti, R; Guzetti, F; Pasqui, V; Reichenbach, P Earth Surf Process Land I"16, N5, Aug 1991, P427-445 The use of a Geographical Information System and numerical cartography to assist in application of statistical models for assessing regional landslide hazards is described. The area examined is a small drainage basin in Umbria, Italy. Contour lines and geological data were taken from maps and slope cover data from remote sensing. These were analysed to delineate slope units according to 40 geological, geomorphological, and vegetative parameters. The statistical package SPSS (1988) was used to assess stability. Potential improvements to the procedure are suggested.
See also. 9222/_" ,25426
Unrecorded underg=ound worki'~.gs exist in many areas, and their collapse m:~ cause sinkholes at the surface. This was seen around Cobalt. Ontario, and a remedial program instigated. G P R proved the most efficient cavity location technique in the hard rock overburden. Gross geometry of the openings was determined by diamond core and percussive probe drilling. Ultrasonic distance measuring instruments and videocameras lowered into the hole provided additional information, including that on rock competence and failure modes. Pneumatic or hydraulic fill is then used for void stabilisation. 922235 Methods to identify and reduce potential surface stream water losses into abandoned underground mines Ackman, T E; Jones, J R Environ Geol Water Sci VI7, N3, May-June 1991. P227-232 Restricting mine water inflow decreases the volume of acid mine drainage produced. Stream loss zones to underground workings are not apparent from surface visual observations and may be some distance from the workings. Along the Staub Run, Maryland. electromagnetic streambed conductivity surveys were used to identify zones of increased relative water saturation to depths less than 15m. These generally correlated with gauged stream flow losses. Shallow (lm) grouting with expandable polyurethane grout of the alluvial streambed significantly reduced flow losses. 922236 Application of electromagnetic techniques in survey of contaminated groundwater at an abandoned mine complex in southwestern Indiana, U.S.A. Brooks, G A; Olyphant, G A: Harper, D Environ Geol Water Sci V18, NI, July-Aug 1991, P39-47 r
Electromagnetic geophysical surveys plus data from cores and monitoring wells were used to map the range of groundwater pollution around a large abandoned mine complex and identify contaminant travel paths. Resistivity surveys around a surface pyritic spoil dump indicate a widespread contaminant plume has not developed in the 40 years since the dump was created. Most acid drainage is in the form of surface runoff, concentrated around stream channels. A conductive layer at depth correlates to a thick alluvial deposit which forms a connection with a flooded underground mine. 922237 Mapping subsurface fractures by radio-frequency holography: a simulation Lorrain, P Geophys J V106. N2, Aug 1991, P333-339 A simulation of radio-frequency holographic mapping of fractures in an otherwise fairly homogeneous low conductivity rock mass or salt is presented. Noisy synthetic data were used to simulate holograms recorded in a single borehole and Fourier optics used to reconstruct images. Fractures were resolved at distances 150-200m. Applications are discussed. This method of imaging fractures is particularly useful as electric current flows easily through fractures, even when hydraulic conductivity is too low to be measured.
© 1992 Pergamon Press Ltd. Reproduction not permitted
Geophysical techniques
922231 Comparison of the USBM gage and the CSIRO cell in various rock conditions Cai, M; Thomas, L J Rock Mechanics as a Muitidisciplinary Science: Proc 32nd US Symposium, Norman, 10-12 July 1991 P129-138. Publ Rotterdam." A A Balkema. 1991
922234 Curing cave-ins Steed, P M Can Alin J VII_'..V6 Jul.v Au.~, J~,91, P50-53
Performance of the two gauges was compared in the laboratory under known biaxial stresses simulating field conditions. In isotropic, homogeneous, continuous rocks, errors are less than 10%, but neither performs well in thinly bedded or fractured rocks. In this case, the errors are, however, approximately equal and opposite in sense, so a combined reading is reasonably accurate. Reasons for these effects are discussed. The CSIRO gauge is more flexible in use but care must be taken in bonding and temperature compensation. The USBM gauge is simpler but cannot provide the complete stress strain state from one instrument.
Site Investigation and Field Observation See: 922468
Remote sensing and photographic techniques 922232 Some observations on a comparative aerial photography interpretation of a landslipped area Fookes, P G; Dale, S G; Land, J M Q J Engng Geol 1/24, N3, 1991, P249-265 The difficulties in interpretation of aerial photographs and the importance of studies at the site to confirm initial impressions are highlighted by reference to a slope in Papua New Guinea. A landslip complex in gently folded Tertiary sediments, overlain by young colluvium and covered by rainforest, is the case examined. Eight interpretations were made, three observers being aware of a new landslip, five being unaware. Differences within and between these two groups are discussed.
Structural and geotechnical mapping 922233 GIS techniques and statistical models in evaluating landslide hazard Carrara, A; Cardinali, M; Detti, R; Guzetti, F; Pasqui, V; Reichenbach, P Earth Surf Process Land I"16, N5, Aug 1991, P427-445 The use of a Geographical Information System and numerical cartography to assist in application of statistical models for assessing regional landslide hazards is described. The area examined is a small drainage basin in Umbria, Italy. Contour lines and geological data were taken from maps and slope cover data from remote sensing. These were analysed to delineate slope units according to 40 geological, geomorphological, and vegetative parameters. The statistical package SPSS (1988) was used to assess stability. Potential improvements to the procedure are suggested.
See also. 9222/_" ,25426
Unrecorded underg=ound worki'~.gs exist in many areas, and their collapse m:~ cause sinkholes at the surface. This was seen around Cobalt. Ontario, and a remedial program instigated. G P R proved the most efficient cavity location technique in the hard rock overburden. Gross geometry of the openings was determined by diamond core and percussive probe drilling. Ultrasonic distance measuring instruments and videocameras lowered into the hole provided additional information, including that on rock competence and failure modes. Pneumatic or hydraulic fill is then used for void stabilisation. 922235 Methods to identify and reduce potential surface stream water losses into abandoned underground mines Ackman, T E; Jones, J R Environ Geol Water Sci VI7, N3, May-June 1991. P227-232 Restricting mine water inflow decreases the volume of acid mine drainage produced. Stream loss zones to underground workings are not apparent from surface visual observations and may be some distance from the workings. Along the Staub Run, Maryland. electromagnetic streambed conductivity surveys were used to identify zones of increased relative water saturation to depths less than 15m. These generally correlated with gauged stream flow losses. Shallow (lm) grouting with expandable polyurethane grout of the alluvial streambed significantly reduced flow losses. 922236 Application of electromagnetic techniques in survey of contaminated groundwater at an abandoned mine complex in southwestern Indiana, U.S.A. Brooks, G A; Olyphant, G A: Harper, D Environ Geol Water Sci V18, NI, July-Aug 1991, P39-47 r
Electromagnetic geophysical surveys plus data from cores and monitoring wells were used to map the range of groundwater pollution around a large abandoned mine complex and identify contaminant travel paths. Resistivity surveys around a surface pyritic spoil dump indicate a widespread contaminant plume has not developed in the 40 years since the dump was created. Most acid drainage is in the form of surface runoff, concentrated around stream channels. A conductive layer at depth correlates to a thick alluvial deposit which forms a connection with a flooded underground mine. 922237 Mapping subsurface fractures by radio-frequency holography: a simulation Lorrain, P Geophys J V106. N2, Aug 1991, P333-339 A simulation of radio-frequency holographic mapping of fractures in an otherwise fairly homogeneous low conductivity rock mass or salt is presented. Noisy synthetic data were used to simulate holograms recorded in a single borehole and Fourier optics used to reconstruct images. Fractures were resolved at distances 150-200m. Applications are discussed. This method of imaging fractures is particularly useful as electric current flows easily through fractures, even when hydraulic conductivity is too low to be measured.
© 1992 Pergamon Press Ltd. Reproduction not permitted