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Stability of underground openings: an old challenge, new problems (In French)
393A 926414 WIPP intermediate scale borehole test - a pretest analysis Arguello, J G Rock Mechanics as a Multidisciplinary Science: Proc 32nd US Symposium, Norman, 10-12 July 1991 P909-918. Publ Rotterdam: A A Balkema, 1991 A 0.91m diameter horizontal borehole will be drilled through an already creeping pillar in the WIPP, as part of a program to examine scale effects in closure in rock salt. A pretest calculation using the 3D finite element code JAC3D was carried out to identify any unexpected behaviour. The geomechanical model, geometry, and boundary and initial conditions are outlined. Pillar behaviour prior to and after drilling the borehole is described. Ovalisation of the bore, with greater convergence in the vertical direction than the horizontal, is predicted. High stress levels still remain around the bore even after a 2 year period. 926415 Stress induced anisotropy in rock and its influence on wellbore stability Wu, B; Hudson, J A Rock Mechanics as a Multidisciplinary Science: Proc 32nd US Symposium, Norman, 10-12 July 1991 P941-950. Publ Rotterdam. A A Balkema, 1991
Underground excavation failure mechanisms See also: 926095 926418 General (areal) subsidence above partial extraction mines Part 1 Cole, K; Statham, I Ground Engng V25, N2, March 1992, P45-55 Isolated examples of trough subsidence above partial extraction mines have been reported in the UK, crownhole subsidence being more common. General subsidence results from deterioration and ultimate collapse of ground at or above the working level. Categories of collapse condition for partial extraction mines are outlined. Mine pillar collapse mechanisms and the many contributing factors are examined. Pillar stress and strength calculations considering geological and geometric parameters are illustrated. 926419 General (areal) subsidence above partial extraction mines Part 2 Cole, K; Statham, I Ground Engng V25, N3, April 1992, P36-40
Rocks around underground excavations are in an extremely non-hydrostatic stress state. Originally isotropic materials may develop stress-induced anisotropy. This phenomenon was studied in triaxial tests on Springwell sandstone. A hydrostatic stress was first applied, then a deviatoric stress well below peak strength. The hydrostatic stress was varied while the deviatoric stress remained constant. The anisotropy developed is discussed. A closed form solution for hollow cylinders is presented to demonstrate the implications of stress induced anisotropy for wellbore stability.
In an earlier paper, general subsidence over partial extraction mines, controlling factors, and collapse mechanisms were explained. From this base, failure processes in coal mines are further examined, with results of tests on coal pillars summarised, comparisons made between strengths of coal and overburden pillars, and failure of overburden pillars in coal mines considered. Effects of quality of overburden rock, mine flooding, uneven pillar loading, and mine layout and mining procedures are discussed. Finally, remedial grouting and assessment of collapse potential are described.
926416 3D stress effects in elastoplastic wellbore failure models Ewy, R T Rock Mechanics as a Multidisciplinary Science: Proc 32nd US Symposium, Norman, 10-12 July 1991 P951-960. Publ Rotterdam: A A Balkema, 1991
926420 Stability of underground openings: an old challenge, new problems (In French) Maury, V lndustrie Minerale V73, Not, 1991, P53-56
Analysis of underground structures can be with 2D or 3D stress analysis, and in the latter case a 2D or 3D strength criterion may be used. Analytical and numerical results for failure of a borehole are presented for all these options, considering both nonaxisymmetric and axisymmetric cases. Linear elastic and elastic-perfectly plastic analyses show that accounting for all three stresses has significant effect on results, even if a 2D strength criterion is employed. If a 3D criterion is used, the differences are even more pronounced. 926417 Evaluation of mud weight in soft shale levels Charlez, P; Heugas, O Rock Mechanics as a Multidisciplinary Science: Proc 32nd US Symposium, Norman, 10-12 July 1991 P1005-1014. Publ Rotterdam: A A Balkema, 1991 A method based on finite element modelling of a Cam clay material with a hydraulic diffusivity equation to describe fluid coupling is presented for determination of mud density needed to prevent mechanical instability of deep boreholes in soft clays or shales. The theoretical formulation is presented and parameter determination described. Application to wellbore stability analysis is discussed considering boundary conditions and simulation of the drilling process. Strong dependence of stability on wellbore deviation and a time effect due to consolidation are seen.
Stability of underground structures is an age-old problem. As today's structures are becoming bigger, or deeper, or are in more hostile conditions, understanding of failure mechanisms becomes even more important. Failure modes of rock around underground openings are illustrated: shear, tensile, and extensile failures. Effects of in situ stress, discontinuities, and temperature on stability are considered. Mathematical modelling of underground failures and future developments are briefly examined. 926421 Cost function in roof-support selection Fraher, R; Haycocks, C Proc 8th Annual Workshop Generic Mineral Technology Center Mine Systems Design and Ground Control, Reno, 5-6 November 1990 P109-115. Publ Blacksburg: Virginia Polytechnic Institute and State University, 1990 Design of openings in room and pillar mines generally relies on interpolation of data from sparsely located boreholes. The main aim is to be able to predict nature and location of potential roof falls. Probabilistic simulations allow testing of different layouts against roof conditions. Economic implications of roof falls can be evaluated and layout optimised. Support type, geology, location in the mine, and elapsed time since mining should all be taken into account. A roof rating system (RRS) is proposed for use in the work.
© 1992 Pergamon Press Ltd. Reproduction not permitted
Underground excavation failure mechanisms See also: 926095 926418 General (areal) subsidence above partial extraction mines Part 1 Cole, K; Statham, I Ground Engng V25, N2, March 1992, P45-55 Isolated examples of trough subsidence above partial extraction mines have been reported in the UK, crownhole subsidence being more common. General subsidence results from deterioration and ultimate collapse of ground at or above the working level. Categories of collapse condition for partial extraction mines are outlined. Mine pillar collapse mechanisms and the many contributing factors are examined. Pillar stress and strength calculations considering geological and geometric parameters are illustrated. 926419 General (areal) subsidence above partial extraction mines Part 2 Cole, K; Statham, I Ground Engng V25, N3, April 1992, P36-40
Rocks around underground excavations are in an extremely non-hydrostatic stress state. Originally isotropic materials may develop stress-induced anisotropy. This phenomenon was studied in triaxial tests on Springwell sandstone. A hydrostatic stress was first applied, then a deviatoric stress well below peak strength. The hydrostatic stress was varied while the deviatoric stress remained constant. The anisotropy developed is discussed. A closed form solution for hollow cylinders is presented to demonstrate the implications of stress induced anisotropy for wellbore stability.
In an earlier paper, general subsidence over partial extraction mines, controlling factors, and collapse mechanisms were explained. From this base, failure processes in coal mines are further examined, with results of tests on coal pillars summarised, comparisons made between strengths of coal and overburden pillars, and failure of overburden pillars in coal mines considered. Effects of quality of overburden rock, mine flooding, uneven pillar loading, and mine layout and mining procedures are discussed. Finally, remedial grouting and assessment of collapse potential are described.
926416 3D stress effects in elastoplastic wellbore failure models Ewy, R T Rock Mechanics as a Multidisciplinary Science: Proc 32nd US Symposium, Norman, 10-12 July 1991 P951-960. Publ Rotterdam: A A Balkema, 1991
926420 Stability of underground openings: an old challenge, new problems (In French) Maury, V lndustrie Minerale V73, Not, 1991, P53-56
Analysis of underground structures can be with 2D or 3D stress analysis, and in the latter case a 2D or 3D strength criterion may be used. Analytical and numerical results for failure of a borehole are presented for all these options, considering both nonaxisymmetric and axisymmetric cases. Linear elastic and elastic-perfectly plastic analyses show that accounting for all three stresses has significant effect on results, even if a 2D strength criterion is employed. If a 3D criterion is used, the differences are even more pronounced. 926417 Evaluation of mud weight in soft shale levels Charlez, P; Heugas, O Rock Mechanics as a Multidisciplinary Science: Proc 32nd US Symposium, Norman, 10-12 July 1991 P1005-1014. Publ Rotterdam: A A Balkema, 1991 A method based on finite element modelling of a Cam clay material with a hydraulic diffusivity equation to describe fluid coupling is presented for determination of mud density needed to prevent mechanical instability of deep boreholes in soft clays or shales. The theoretical formulation is presented and parameter determination described. Application to wellbore stability analysis is discussed considering boundary conditions and simulation of the drilling process. Strong dependence of stability on wellbore deviation and a time effect due to consolidation are seen.
Stability of underground structures is an age-old problem. As today's structures are becoming bigger, or deeper, or are in more hostile conditions, understanding of failure mechanisms becomes even more important. Failure modes of rock around underground openings are illustrated: shear, tensile, and extensile failures. Effects of in situ stress, discontinuities, and temperature on stability are considered. Mathematical modelling of underground failures and future developments are briefly examined. 926421 Cost function in roof-support selection Fraher, R; Haycocks, C Proc 8th Annual Workshop Generic Mineral Technology Center Mine Systems Design and Ground Control, Reno, 5-6 November 1990 P109-115. Publ Blacksburg: Virginia Polytechnic Institute and State University, 1990 Design of openings in room and pillar mines generally relies on interpolation of data from sparsely located boreholes. The main aim is to be able to predict nature and location of potential roof falls. Probabilistic simulations allow testing of different layouts against roof conditions. Economic implications of roof falls can be evaluated and layout optimised. Support type, geology, location in the mine, and elapsed time since mining should all be taken into account. A roof rating system (RRS) is proposed for use in the work.
© 1992 Pergamon Press Ltd. Reproduction not permitted