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Support for tunnels subjected to changing rock loads: a comparison of design methods
245A 924311 Development of a prototype hard rock excavating machine Handewith, H J; Coski, W D; Thimons, E D Proc 1989 Rapid Excavation and Tunnelling Conference, Los Angeles, 11-14 June 1989 P769-787. Publ Littleton: SME, 1989 The RAMEX excavation system is presented. It combines low velocity, high energy impact with kerr cutting. Used with a boom mining machine, it can cut almost any shape in hard rock. It is non-explosive, flexible, continuous, and produces little vibration or damage to remnant rock. The test program used in its development is described. Comparisons are made on the basis of total, capital, and individual component costs and on time with excavation by drill and blast, TBM, and roadheader.
Rock and Soil Reinforcement and Support See: 924439
924314 Development, testing and application of a non-steel tendon for artificial ground support Howarth, D F; Renwick, M T Proc 6tk Australia-New Zealand Conference on Geomechaalcs, Christclu~cli, 3-7 Febcuary 1992 P90-95. Publ New Zealand: New Zealand Geomechanics Society, 1992 Retreat Iongwall mining often requires the coal seam to be reinforced with bolts to control rib deformation and minimise spaUing. Timber and fibreglass bolts have been unsuccessful, whilst steel bolts damage pit machinery as the seam is mined. To overcome this, the highly oriented polyethylene (HOPE) bar has been developed. It is made from die drawn polyethylene, which has improved mechanical characteristics. Laboratory short term, cyclic load, and creep tests on resin grouted HOPE bars are described. Field tests in longwalling and in an open pit in an aggressive environment demonstrate the HOPE bar applicability. 924315 Fully grouted anchors under shock loading Hagendorn, H Rock Mechanics as a Multia~sciplinary Science: Proc 32nd US Symposium, Norman, 10-12 July 1991 P501-509. Publ Rotterdam: A A Balkema, 1991 Rod and tube anchors of fibre reinforced epoxy and polyester resins, respectively, were mounted in concrete blocks and subject to shock loading by impact on the block. Instrumentation was installed to allow assessment of dynamic loading and slip of the anchors. Subsequent to dynamic testing, the anchors were overcored and the cores cut into lengths for pushout testing. From these results it is possible to specify bond length so that failure under given dynamic loading is avoided.
Bolts and anchors See also: 924392
924312 Five-year monitoring of load losses on prestressed cementgrouted rock anchors Benmokrane, B; Ballivy, G Can Geotech J 1/28, N5, Oct 1991, P668-677 Results are presented from a site where nine anchors were grouted to various lengths in a sound greywacke rock mass. Tension was applied to the anchors which were blocked off at about 80% of failure load. Load variation occurs in two phases, rapid loss for about 6 months, then a much slower, uniform decrease. Instantaneous loss of load at lock-off was also measured. Variation in grouted length had practically no influence on observed load loss or its evolution with time.
924313 Support for tunnels subjected to changing rock loads: a comparison of design methods Speers, C R Tunnlg Underground Space Technol V7, NI, 1992, P25-32 A number of cases can be found where field stresses or rock loads change subsequent to tunnel development. Two empirical methods (Q, RMR) and an analytical method using finite element or finite difference approaches are examined for their ability to design support under these conditions. Bolt length, bolt spacing, support pressure, and displacement and convergence of the tunnel should be predicted at each stage of the applied loading. The empirical methods generally lead to underdesign, particularly with regard to bolt capacity. Best results are obtained from the analytic approach, but this becomes very complex if real conditions differ greatly from the simplified conditions assumed here.
Direct rock support methods See also: 924443 924316 Geotextiles for backfilling of deep level mines Dickson, M G; Strydom, C S Proc 4th International Conference on Geotextiles, Geomembranes and Related Products, The Hague, 28 May-I June 1990 I/2, P849-852. Publ Rotterdam: A A Balkema, 1990 Backfilling is increasingly used to support mined out stopes in South African mines. Deslimed mine railings are a preferred fill material on the grounds of ease of handling and relatively free draining properties. Geotextiles are used to support the fill during drainage before it becomes self-supporting. The layouts used to instal fills are illustrated: geotextile bag system, geotextile grout pack, paddock system,and pressure cushion. Geotextile standards and requirements for these operations are discussed.
Grouting 924317 Individual groutability of rocks Ewert, F K int Water Power Dam Constr V44, NI, Jan 1992, P23-30 Installation of a grout curtain at a damsite is expensive and should only be carried out where essential. The decision to grout or not is generally made on the basis of results of water pressure tests, with a limit value of water absorption rate. The characteristics of water conducting voids and the ambiguity of
© 1992 Pergamon Press Ltd. Reproduction not permitted
Rock and Soil Reinforcement and Support See: 924439
924314 Development, testing and application of a non-steel tendon for artificial ground support Howarth, D F; Renwick, M T Proc 6tk Australia-New Zealand Conference on Geomechaalcs, Christclu~cli, 3-7 Febcuary 1992 P90-95. Publ New Zealand: New Zealand Geomechanics Society, 1992 Retreat Iongwall mining often requires the coal seam to be reinforced with bolts to control rib deformation and minimise spaUing. Timber and fibreglass bolts have been unsuccessful, whilst steel bolts damage pit machinery as the seam is mined. To overcome this, the highly oriented polyethylene (HOPE) bar has been developed. It is made from die drawn polyethylene, which has improved mechanical characteristics. Laboratory short term, cyclic load, and creep tests on resin grouted HOPE bars are described. Field tests in longwalling and in an open pit in an aggressive environment demonstrate the HOPE bar applicability. 924315 Fully grouted anchors under shock loading Hagendorn, H Rock Mechanics as a Multia~sciplinary Science: Proc 32nd US Symposium, Norman, 10-12 July 1991 P501-509. Publ Rotterdam: A A Balkema, 1991 Rod and tube anchors of fibre reinforced epoxy and polyester resins, respectively, were mounted in concrete blocks and subject to shock loading by impact on the block. Instrumentation was installed to allow assessment of dynamic loading and slip of the anchors. Subsequent to dynamic testing, the anchors were overcored and the cores cut into lengths for pushout testing. From these results it is possible to specify bond length so that failure under given dynamic loading is avoided.
Bolts and anchors See also: 924392
924312 Five-year monitoring of load losses on prestressed cementgrouted rock anchors Benmokrane, B; Ballivy, G Can Geotech J 1/28, N5, Oct 1991, P668-677 Results are presented from a site where nine anchors were grouted to various lengths in a sound greywacke rock mass. Tension was applied to the anchors which were blocked off at about 80% of failure load. Load variation occurs in two phases, rapid loss for about 6 months, then a much slower, uniform decrease. Instantaneous loss of load at lock-off was also measured. Variation in grouted length had practically no influence on observed load loss or its evolution with time.
924313 Support for tunnels subjected to changing rock loads: a comparison of design methods Speers, C R Tunnlg Underground Space Technol V7, NI, 1992, P25-32 A number of cases can be found where field stresses or rock loads change subsequent to tunnel development. Two empirical methods (Q, RMR) and an analytical method using finite element or finite difference approaches are examined for their ability to design support under these conditions. Bolt length, bolt spacing, support pressure, and displacement and convergence of the tunnel should be predicted at each stage of the applied loading. The empirical methods generally lead to underdesign, particularly with regard to bolt capacity. Best results are obtained from the analytic approach, but this becomes very complex if real conditions differ greatly from the simplified conditions assumed here.
Direct rock support methods See also: 924443 924316 Geotextiles for backfilling of deep level mines Dickson, M G; Strydom, C S Proc 4th International Conference on Geotextiles, Geomembranes and Related Products, The Hague, 28 May-I June 1990 I/2, P849-852. Publ Rotterdam: A A Balkema, 1990 Backfilling is increasingly used to support mined out stopes in South African mines. Deslimed mine railings are a preferred fill material on the grounds of ease of handling and relatively free draining properties. Geotextiles are used to support the fill during drainage before it becomes self-supporting. The layouts used to instal fills are illustrated: geotextile bag system, geotextile grout pack, paddock system,and pressure cushion. Geotextile standards and requirements for these operations are discussed.
Grouting 924317 Individual groutability of rocks Ewert, F K int Water Power Dam Constr V44, NI, Jan 1992, P23-30 Installation of a grout curtain at a damsite is expensive and should only be carried out where essential. The decision to grout or not is generally made on the basis of results of water pressure tests, with a limit value of water absorption rate. The characteristics of water conducting voids and the ambiguity of
© 1992 Pergamon Press Ltd. Reproduction not permitted