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Does scale influence in situ stress measurements? -some findings at the Underground Research Laboratory
289A near zero to about 0.6%. Porosity closure at laboratory confining pressures up to maximum in situ str& is inter@r&ed’ih terms of microcrack porosity resulting from stress relief on drilling, with in situ values of porosity around 0.05%. Foliation controls microcrack orientations, which precludes their use for estimating principal stress directions.
915192 Sbe& nidasu~hts in the Sioux Falls quart&e and the state of stress in the Midcontinent Haimson, B C Rock Mechanics Contributions and Challenges: Proc 3lsr US Symposium, Coldcn, 18-20 June 1990 P397-404. Pub1 Rotterdam: A A Balkema, 1990
915189 Fracture-induced stress heterogeneity: examples from the Cajon Pass scientific drillbole near the San Andreas Fault, California Shamir, G, Zoback, M D; Comet, F H Proc international Symposium on Rock Joints, Loen, 4-6 June 1990 P719-724. Pub1 Rotter&m: A A Balkema. 1990
Nine hydraulic fracturing tests were conducted in Dakota, USA, in a continuing effort to determine the state of stress in the midcontinent. Although it has long been perceived that the state of stress in this region is compressive, with relatively high horizontal stresses, the results show the contrary. Reasons for this discrepancy, considering the relative closeness of bounding faults of the Midcontinent Rift, are discussed. More data are necessary to improve confidence in suggested stress provinces.
Wellbore breakouts to depth 3Skm in the Cajon Pass borehole show depth dependent changes in orientation, which occur at wavelengths varying from hundreds of metres to a few centimetres, as well as discontinuity across fractures. This indicates the ambient stress field is locally perturbed by faults and fractures, the effect being amplified by wellbore induced stress concentration. Analysis shows azimuth of the borehole wall stress concentration depends on geometry of the faults and the slip vector. Principal stresses are inclined to the borehole axis and the stress field is heterogeneous on a variety of scales. 915190 Scale effects influencing hydraulic fracture and overcuring stress measurements
Enever, J R; Walton, J R; Wold, M B hoc 1st Zn~ernational Workshop on Scak E&cts in Rock Masses, Loen, 7-8 June 1990 P317-326. Pub1 Rotterdam: A A Balkema, 1990 Results of numerous surface and subsurface stress measurements by hydraulic fracturing and overcoring methods are presented and examined considering geological conditions. Stress and structural interaction at scales from regional to mine-wide and local are illustrated, and scale effects, such as locked-in stress effects, acting at the dimension of the measuring device are discussed.
915193 Does scale influence in situ stress measurements? -some
findings at tke Underground Research Laboratory Martin, C D; Read, R S; Chandler, N A Proc 1st inrernational Workshop on Scale Effects in Rock Masses, Loen, 7-g June 1990 P307-316. Pub1 Rotterdam: A A Balkema. 1990 In situ stress measurements at the URL site in the Lac du Bonnet granite batholith have been made using the overcoring, hydraulic fracturing, under-excavation, and convergence techniques. Tests in volumes varying by five orders of magnitude indicate average stress magnitude is little influenced by scale, but scatter is significantly affected. Stress measurements by hydraulic fracturing were consistent with those from overcoring as long as the hydraulic fractures remained coaxial with the borehole.
Site Investigation and Field Observatioti See: 915296, 915407
Measurement of in situ stress Remote sensing and photographic techniques
See also: 915068, 915447
See also: 915008, 915024 915191 Overcoring in highly stressed granite - the influence of microcracking Martin, C D; Christiansson, R Inr J Rock Mech Min Sci V28, NI, Jan 1991, P53-70 Data from 81 overcoring tests using the continuously monitored CSIR triaxial cell are analysed. The tests were carried out at level 240 in the URL, in 13 boreholes in a relatively uniform, massive granite rock mass in an area about 60m square. Stress induced microcracking was greatest for overcored samples from boreholes perpendicular to the major principal stress direction. It situ stresses calculated from tests in these holes did not agree with the general in situ stress state at the 240 level. Anisotropy caused by stress-induced microcracking is considered the cause of this discrepancy. Stresses calculated using an anisotropic solution are in better agreement. Implications of this work for overcoring stress measurement are discussed. 0
915194 Important be&b of geologic interpretation of air photos for the development of a hydroelectric power project in the occidental Andes of Peru suyo, E hoc 6th b&rnational congress International Association of Engineering Geology, Amsterdam, 6-10 August 1990 V2, P863-869. Pub1 Rotterdam: A A Balkema, 1990 Feasibility studies for a hydroelectric plant on the Canete river on the Pacific slopes of the Andes have recently been completed. Airborne photographic studies formed a major part of the work. Geological features of areas suitable for reservoir impoundment were examined and 8 sites selected for further detailed investigation. Siting of the powerhouse structure was decided upon after identifying regions of high active seasonal debris flows.
1991 Pergamon Press plc. Reproduction
not permitted
915192 Sbe& nidasu~hts in the Sioux Falls quart&e and the state of stress in the Midcontinent Haimson, B C Rock Mechanics Contributions and Challenges: Proc 3lsr US Symposium, Coldcn, 18-20 June 1990 P397-404. Pub1 Rotterdam: A A Balkema, 1990
915189 Fracture-induced stress heterogeneity: examples from the Cajon Pass scientific drillbole near the San Andreas Fault, California Shamir, G, Zoback, M D; Comet, F H Proc international Symposium on Rock Joints, Loen, 4-6 June 1990 P719-724. Pub1 Rotter&m: A A Balkema. 1990
Nine hydraulic fracturing tests were conducted in Dakota, USA, in a continuing effort to determine the state of stress in the midcontinent. Although it has long been perceived that the state of stress in this region is compressive, with relatively high horizontal stresses, the results show the contrary. Reasons for this discrepancy, considering the relative closeness of bounding faults of the Midcontinent Rift, are discussed. More data are necessary to improve confidence in suggested stress provinces.
Wellbore breakouts to depth 3Skm in the Cajon Pass borehole show depth dependent changes in orientation, which occur at wavelengths varying from hundreds of metres to a few centimetres, as well as discontinuity across fractures. This indicates the ambient stress field is locally perturbed by faults and fractures, the effect being amplified by wellbore induced stress concentration. Analysis shows azimuth of the borehole wall stress concentration depends on geometry of the faults and the slip vector. Principal stresses are inclined to the borehole axis and the stress field is heterogeneous on a variety of scales. 915190 Scale effects influencing hydraulic fracture and overcuring stress measurements
Enever, J R; Walton, J R; Wold, M B hoc 1st Zn~ernational Workshop on Scak E&cts in Rock Masses, Loen, 7-8 June 1990 P317-326. Pub1 Rotterdam: A A Balkema, 1990 Results of numerous surface and subsurface stress measurements by hydraulic fracturing and overcoring methods are presented and examined considering geological conditions. Stress and structural interaction at scales from regional to mine-wide and local are illustrated, and scale effects, such as locked-in stress effects, acting at the dimension of the measuring device are discussed.
915193 Does scale influence in situ stress measurements? -some
findings at tke Underground Research Laboratory Martin, C D; Read, R S; Chandler, N A Proc 1st inrernational Workshop on Scale Effects in Rock Masses, Loen, 7-g June 1990 P307-316. Pub1 Rotterdam: A A Balkema. 1990 In situ stress measurements at the URL site in the Lac du Bonnet granite batholith have been made using the overcoring, hydraulic fracturing, under-excavation, and convergence techniques. Tests in volumes varying by five orders of magnitude indicate average stress magnitude is little influenced by scale, but scatter is significantly affected. Stress measurements by hydraulic fracturing were consistent with those from overcoring as long as the hydraulic fractures remained coaxial with the borehole.
Site Investigation and Field Observatioti See: 915296, 915407
Measurement of in situ stress Remote sensing and photographic techniques
See also: 915068, 915447
See also: 915008, 915024 915191 Overcoring in highly stressed granite - the influence of microcracking Martin, C D; Christiansson, R Inr J Rock Mech Min Sci V28, NI, Jan 1991, P53-70 Data from 81 overcoring tests using the continuously monitored CSIR triaxial cell are analysed. The tests were carried out at level 240 in the URL, in 13 boreholes in a relatively uniform, massive granite rock mass in an area about 60m square. Stress induced microcracking was greatest for overcored samples from boreholes perpendicular to the major principal stress direction. It situ stresses calculated from tests in these holes did not agree with the general in situ stress state at the 240 level. Anisotropy caused by stress-induced microcracking is considered the cause of this discrepancy. Stresses calculated using an anisotropic solution are in better agreement. Implications of this work for overcoring stress measurement are discussed. 0
915194 Important be&b of geologic interpretation of air photos for the development of a hydroelectric power project in the occidental Andes of Peru suyo, E hoc 6th b&rnational congress International Association of Engineering Geology, Amsterdam, 6-10 August 1990 V2, P863-869. Pub1 Rotterdam: A A Balkema, 1990 Feasibility studies for a hydroelectric plant on the Canete river on the Pacific slopes of the Andes have recently been completed. Airborne photographic studies formed a major part of the work. Geological features of areas suitable for reservoir impoundment were examined and 8 sites selected for further detailed investigation. Siting of the powerhouse structure was decided upon after identifying regions of high active seasonal debris flows.
1991 Pergamon Press plc. Reproduction
not permitted