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Destress slot concept for bulk mining at depth
323A 935425 Back analysis of stope stability at Aasil mine using instrumentation data and numerical modelling Hutchinson, D J; Grabinsky, M W Proc International Symposium on Rock Support, Sudbury, 1619 June 1992 P167-176. Publ Rotterdam." A A Balkema, 1992 Instrumentation was installed in the Ansil mine to monitor the interaction between rock mass and cable bolt support over a series of stopes in the upper horizon of the complex shaped orebody. Three dimensional (I-DEAS/ABAQUS, EXAMINE) and two dimensional (PHASES, EXAMINE) numerical modelling was used to back-analyse mining-induced stresses. Comparison of field observations and numerical results produces a consistent picture of hangingwall behaviour. The reasons for instability of some stopes whilst others adjacent remain stable are examined. An approach for forward analysis of stope stability will be developed from this work. 935426 Destress slot concept for bulk mining at depth Landriault, D; Oliver, P Proc International Symposium on Rock Support, Sudbury, 1619 June 1992 P211.217. Publ Rotterdam: A A Balkema, 1992 As hard rock mines go to greater depths, increased field stresses lead to greater potential for rockburst. The destress slot concept to minimise these effects has been used in bulk vertical retreat mining at the lower part (5000 to 7200 level) of the Creighton Mine in Ontario. Results of a 4 year monitoring study are reviewed. Success is assessed from data collected and by numerical analysis. Refinements to this destress method have been indicated from further numerical studies, and initial results from their implementation are presented.
Underground excavation failure mechanisms 935427 Displacement discontinuities and stress changes between roof strata and their influence on longwall mining under aquifers Lin, S lnt J Geotech Geoi Engng Vll, N1, March 1993, P37-50 Water inflow is one problem when using the longwall caving method beneath aquifers. Physical model tests were carried out to examine the development of bed separation at the two stages of roof layer movement over a longwall face. Relations between roof displacement and stress concentration/relief were investigated. Further work used an analytical model based on assumption of laminated rock beams to identify potential discontinuities which could form water conduits to the mine. The promise of this combined physical/analytical approach is discussed.
935429 Consequences of the downfall during construction of the Karawanken Tunnel (In German and English) Maidl, B; Handke, D Tmmel N1, 1993, P14-20 The Karawanken Tunnel between Yugoslavia and Austria suffered a major face collapse when crossing clayey dolomite. The tunnel has 90 sq m section and was driven as crown and bench with shotcrete initial support. Groundwater inflows were expected and drainage measures taken to reduce high pressures which might occur. The face collapse occurred in a water-filled fault zone, where clay interlayers were present in the rock. The fault zone had not been detected by geological survey, but was identified by advance drilling. The preventive measures taken were, however, inadequate. 935430 Influence of in situ stress field on the stability of mine tunnels Whittaker, B N; Smith, S F; Gexin Sun; Hui Chen Proe ISRM Symposium: Euroek'92, Chester, 14-17 September 1992 P227-232. Publ London: Thomas Telford, 1992 The influence of various stress field combinations on the stability of mine tunnels has been studied using small scale physical model tests. Homogeneous and stratified rock masses were simulated using plaster/sand/water mixtures. A biaxial test rig was used to impose hydrostatic stress and stress fields with horizontal to vertical stress ratios of 3:1 and 1:3. Circular, arched, and rectangular tunnels have been tested. Results are discussed with reference to mine tunnel design and support specification. 935431 Stress and time-dependent fracture around cavities in physical models of potash salt rock Carter, B J; Lajtai, E Z Proc ISRM Symposium: Eurock'92, Chester, 14-17 September 1992 P269-274. Pub! London." Thomas Telford, 1992 Fractures in the Saskatchewan potash mines occur often and are potential conduits for water inflow. Physical model tests, using blocks under uniaxial compression, have been carried out to study initiation and evolution of primary, remote, and sidewall fractures. The blocks were made from layers of potash, rock salt, and limestone representing mine strata and contained single or multiple circular or rectangular cavities, Discrete fractures are stable, but lead to additional offset cracks, and crack length increases with increasing stress. Above a threshold level (about 50% UCS), rate of total crack length growth increases exponentially with time.
935428 Fracture energy release and size effect in borehole breakout Bazant, Z P; Lin, F B; Lippmann, H Int J Num Anal Meth Geomech V17, N1, Jan 1993, P1-14
935432 Wahleach power tunnel monitoring Baker, D G Proc 3rd International Symposium on Field Measurements in Geomechanics, Oslo, 9-11 September 1991 V2, P467-479. Publ Rotterdam: A A Baikema, 1991
A simple analytical solution is presented of the remote stresses which cause collapse of a circular cylindrical cavity in an infinite elastic half space. The simplifying assumptions are formulated and fracture mechanics concepts applied to provide a solution for borehole collapse which reveals the size effect. Plasticity aspects of failure are neglected to make this solution feasible. Reality may lie between the solutions of plasticity and fracture mechanics, but is probably closer to the latter in most cases.
The steel liner of the pressure tunnel at the Wahleach hydroelectric plant failed in tension at one location in January 1989. Subsequent investigation revealed 8 zones of compression buckling. All these deformations were attributed to movements in the rock slope. Temporary repair was carried out and a comprehensive instrumentation and remote data acquisition system installed to monitor the lining and the slope prior to permanent relining. Details of the instrumentation and repair are presented.
© 1993 Pergamon Press Ltd. Reproduction not permitted RMMS 30/~-K
Underground excavation failure mechanisms 935427 Displacement discontinuities and stress changes between roof strata and their influence on longwall mining under aquifers Lin, S lnt J Geotech Geoi Engng Vll, N1, March 1993, P37-50 Water inflow is one problem when using the longwall caving method beneath aquifers. Physical model tests were carried out to examine the development of bed separation at the two stages of roof layer movement over a longwall face. Relations between roof displacement and stress concentration/relief were investigated. Further work used an analytical model based on assumption of laminated rock beams to identify potential discontinuities which could form water conduits to the mine. The promise of this combined physical/analytical approach is discussed.
935429 Consequences of the downfall during construction of the Karawanken Tunnel (In German and English) Maidl, B; Handke, D Tmmel N1, 1993, P14-20 The Karawanken Tunnel between Yugoslavia and Austria suffered a major face collapse when crossing clayey dolomite. The tunnel has 90 sq m section and was driven as crown and bench with shotcrete initial support. Groundwater inflows were expected and drainage measures taken to reduce high pressures which might occur. The face collapse occurred in a water-filled fault zone, where clay interlayers were present in the rock. The fault zone had not been detected by geological survey, but was identified by advance drilling. The preventive measures taken were, however, inadequate. 935430 Influence of in situ stress field on the stability of mine tunnels Whittaker, B N; Smith, S F; Gexin Sun; Hui Chen Proe ISRM Symposium: Euroek'92, Chester, 14-17 September 1992 P227-232. Publ London: Thomas Telford, 1992 The influence of various stress field combinations on the stability of mine tunnels has been studied using small scale physical model tests. Homogeneous and stratified rock masses were simulated using plaster/sand/water mixtures. A biaxial test rig was used to impose hydrostatic stress and stress fields with horizontal to vertical stress ratios of 3:1 and 1:3. Circular, arched, and rectangular tunnels have been tested. Results are discussed with reference to mine tunnel design and support specification. 935431 Stress and time-dependent fracture around cavities in physical models of potash salt rock Carter, B J; Lajtai, E Z Proc ISRM Symposium: Eurock'92, Chester, 14-17 September 1992 P269-274. Pub! London." Thomas Telford, 1992 Fractures in the Saskatchewan potash mines occur often and are potential conduits for water inflow. Physical model tests, using blocks under uniaxial compression, have been carried out to study initiation and evolution of primary, remote, and sidewall fractures. The blocks were made from layers of potash, rock salt, and limestone representing mine strata and contained single or multiple circular or rectangular cavities, Discrete fractures are stable, but lead to additional offset cracks, and crack length increases with increasing stress. Above a threshold level (about 50% UCS), rate of total crack length growth increases exponentially with time.
935428 Fracture energy release and size effect in borehole breakout Bazant, Z P; Lin, F B; Lippmann, H Int J Num Anal Meth Geomech V17, N1, Jan 1993, P1-14
935432 Wahleach power tunnel monitoring Baker, D G Proc 3rd International Symposium on Field Measurements in Geomechanics, Oslo, 9-11 September 1991 V2, P467-479. Publ Rotterdam: A A Baikema, 1991
A simple analytical solution is presented of the remote stresses which cause collapse of a circular cylindrical cavity in an infinite elastic half space. The simplifying assumptions are formulated and fracture mechanics concepts applied to provide a solution for borehole collapse which reveals the size effect. Plasticity aspects of failure are neglected to make this solution feasible. Reality may lie between the solutions of plasticity and fracture mechanics, but is probably closer to the latter in most cases.
The steel liner of the pressure tunnel at the Wahleach hydroelectric plant failed in tension at one location in January 1989. Subsequent investigation revealed 8 zones of compression buckling. All these deformations were attributed to movements in the rock slope. Temporary repair was carried out and a comprehensive instrumentation and remote data acquisition system installed to monitor the lining and the slope prior to permanent relining. Details of the instrumentation and repair are presented.
© 1993 Pergamon Press Ltd. Reproduction not permitted RMMS 30/~-K