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TBM performance prediction using rock fracture parameters. Technical note
140A 855009 TBM performance prediction using rock fracture parameters. Technical note Nelson, P P; Ingraffea, A R; O'Rourke, T D lnt J Rock Mech Min Sci V22, N3, June 1985, P189-192
855013 True triaxial cell for low and high pressure experiments. Technical note Michelis, P Int J Rock Mech Min Sci ~ 2 , N3, June 1985, Pt83-188
Data from case histories of six tunnels were used to investigate the relationship between TBM performance and rock properties related to fracture propagation. The critical energy release rate, a criterion which includes the effect of rock strength and stiffness, can be correlated with optimum TBM performance for massive, brittle rock. Correlation between field penetration index and critical energy release rate is consistent with formation of rock chips by a fracture process. Data from four sedimentary units indicated a relationship between total hardness and critical energy release rate. This may provide a mechanistic basis for the previously observed correlation between TBM performance and total hardness.
A triaxial cell for testing prismatic specimens is describer. Axial load is applied via a stiff testing machine and the intermediate and minor stresses are generated by PVC bags filled with and pressurized by hydraulic oil, The intermediate stress is applied to the specimen surface via two sets o f metal prisms. Friction is minimised by interposing a lubricated copper membrane between the prisms and the specimen surface. Strain ma) be measured at any part of the sample by dial gauges or LVDTs. The cell has provided satisfactory performance for a varlet? of three dimensional stress paths.
Strength characteristics 855010 Effects of freeze-thaw and softening on a natural day at low stresses Graham, J; Au, V C S Can Geotech J V22. N1, Feb 1985. P69-78 Load-controlled drained tests and stress-controlled undrained tests at low stresses on samples of natural plastic clay show that freeze-thaw cycling produces higher pore-water pressure at failure, lower consolidation stiffness, higher relative stiffness and lower strengths when compared with undisturbed samples. Softening produces similar results, but less marked changes, depending on stress levels. Yielding is seen along steeply rising stress paths in these samples and occurs at shear stresses below those for rupture. Freeze-thaw cycling produces a strongly defined fissure structure in the clay. These findings are significant for design of structures in areas with cold winter climates. 855011 Free-fall penetrometer: Impact and penetration in reconstituted clays (In French) Levacher, D Can Geotech J V22, N1, Feb 1985. P129-135 The usefulness of the free-fall penetrometer for the determination of in situ mechanical properties of reconstituted clays is demonstrated. Laboratory tests indicate that shear strength may be computed directly as a function of depth. 855012 Critical assessment of methods of correcting for drift from the yield surface in elasto-plastic finite dement analysis Potts, D M; Gens, A Int J Nam Anal Meth Geomech V9. N2, March-April 1985. P149-t59 Many discretizations are required in finite element analysis of elasto-plasto boundary value problems. This leads to yield surface drift - ie the stress state predicted after incremental loading does not lie on the current yield surface. Five methods accounting for this drift are examined. They correct by projecting the total strain increment and accumulative effective stress direction back along the plastic flow. One, the 'correct' method, additionally accounts for the changes in elastic strain which accompany stress correction. When applied to the analysis of stress changes adjacent to a single pile in uniform soil. only the "correct' method gave accurate predictions.
855014 Cyclic behavior of pavement base materials McVay, M; Taesiri. Y J Geotech Engng Div ASCE V l l l NI. Jan I985. Pl-17 Florida sand was subjected to cyclic loading in a conventional triaxial apparatus with cyclic varying compressive loads and cyclic compressive-tensile loads being applied° Cyclic compressive-tensile loading led to material anisotropy and greater cyclic strain build up than compressive only loading. The influence of stress path decreased with increasing initial confining pressure. To model the behaviour of the sand. improved constitutive relationships were developed using the bounding surface plasticity model. 855015 Temperature effects on volume measurements. Technical note Stewart, W; Wong, C K J Geotech Engng Div ASCE VIII NI. Jan 1985. P140-144 Measurement of volume change during triaxiat testing can be important in determining sample compressibility and shear strength parameters. The effect of ambient temperature change on two automatic volume change logging machines is examined and found to be significant, especially for small sample volume changes. Equations which compensate for apparatus-induced volume changes are outlined. 855016 Experimental behavionr of rocks under triaxial strains and stresses (In French) Gaziev. E; Morozov. A: Chaganian, V Rev Fr Geoteeh N29. 1984, P43-48 An experimental technique is presented to examine the strength and deformability of rocks under triaxial stress conditions with lateral strain control. A mathematical analysis of the limit state of materials is compared with experimental results and work of other authors. 855017 Mathematical modelfing of cyclic behaviour of soils Nova, R Proc of the Symposium on Geotechnical Aspects of Coastal and Offshore Structures, Bangkok, 14-18 Dec 1981 P47-59. Publ Rotterdam: A. A. Balkema. t983 Model presented that allows a better understanding of the decay of undrained cohesion of a normally consolidated clay, and the effects of the type of test, the number of preshearing cycles and the intensity of cyclic loading, The predictions concerning the variation of pore pressures and shear moduli with number of cycles are discussed. The prediction of the behaviour of sand under cyclic loading at constant stram or stress amplitude and the number of cycles necessary to cause liquefaction is possible using the model.
855013 True triaxial cell for low and high pressure experiments. Technical note Michelis, P Int J Rock Mech Min Sci ~ 2 , N3, June 1985, Pt83-188
Data from case histories of six tunnels were used to investigate the relationship between TBM performance and rock properties related to fracture propagation. The critical energy release rate, a criterion which includes the effect of rock strength and stiffness, can be correlated with optimum TBM performance for massive, brittle rock. Correlation between field penetration index and critical energy release rate is consistent with formation of rock chips by a fracture process. Data from four sedimentary units indicated a relationship between total hardness and critical energy release rate. This may provide a mechanistic basis for the previously observed correlation between TBM performance and total hardness.
A triaxial cell for testing prismatic specimens is describer. Axial load is applied via a stiff testing machine and the intermediate and minor stresses are generated by PVC bags filled with and pressurized by hydraulic oil, The intermediate stress is applied to the specimen surface via two sets o f metal prisms. Friction is minimised by interposing a lubricated copper membrane between the prisms and the specimen surface. Strain ma) be measured at any part of the sample by dial gauges or LVDTs. The cell has provided satisfactory performance for a varlet? of three dimensional stress paths.
Strength characteristics 855010 Effects of freeze-thaw and softening on a natural day at low stresses Graham, J; Au, V C S Can Geotech J V22. N1, Feb 1985. P69-78 Load-controlled drained tests and stress-controlled undrained tests at low stresses on samples of natural plastic clay show that freeze-thaw cycling produces higher pore-water pressure at failure, lower consolidation stiffness, higher relative stiffness and lower strengths when compared with undisturbed samples. Softening produces similar results, but less marked changes, depending on stress levels. Yielding is seen along steeply rising stress paths in these samples and occurs at shear stresses below those for rupture. Freeze-thaw cycling produces a strongly defined fissure structure in the clay. These findings are significant for design of structures in areas with cold winter climates. 855011 Free-fall penetrometer: Impact and penetration in reconstituted clays (In French) Levacher, D Can Geotech J V22, N1, Feb 1985. P129-135 The usefulness of the free-fall penetrometer for the determination of in situ mechanical properties of reconstituted clays is demonstrated. Laboratory tests indicate that shear strength may be computed directly as a function of depth. 855012 Critical assessment of methods of correcting for drift from the yield surface in elasto-plastic finite dement analysis Potts, D M; Gens, A Int J Nam Anal Meth Geomech V9. N2, March-April 1985. P149-t59 Many discretizations are required in finite element analysis of elasto-plasto boundary value problems. This leads to yield surface drift - ie the stress state predicted after incremental loading does not lie on the current yield surface. Five methods accounting for this drift are examined. They correct by projecting the total strain increment and accumulative effective stress direction back along the plastic flow. One, the 'correct' method, additionally accounts for the changes in elastic strain which accompany stress correction. When applied to the analysis of stress changes adjacent to a single pile in uniform soil. only the "correct' method gave accurate predictions.
855014 Cyclic behavior of pavement base materials McVay, M; Taesiri. Y J Geotech Engng Div ASCE V l l l NI. Jan I985. Pl-17 Florida sand was subjected to cyclic loading in a conventional triaxial apparatus with cyclic varying compressive loads and cyclic compressive-tensile loads being applied° Cyclic compressive-tensile loading led to material anisotropy and greater cyclic strain build up than compressive only loading. The influence of stress path decreased with increasing initial confining pressure. To model the behaviour of the sand. improved constitutive relationships were developed using the bounding surface plasticity model. 855015 Temperature effects on volume measurements. Technical note Stewart, W; Wong, C K J Geotech Engng Div ASCE VIII NI. Jan 1985. P140-144 Measurement of volume change during triaxiat testing can be important in determining sample compressibility and shear strength parameters. The effect of ambient temperature change on two automatic volume change logging machines is examined and found to be significant, especially for small sample volume changes. Equations which compensate for apparatus-induced volume changes are outlined. 855016 Experimental behavionr of rocks under triaxial strains and stresses (In French) Gaziev. E; Morozov. A: Chaganian, V Rev Fr Geoteeh N29. 1984, P43-48 An experimental technique is presented to examine the strength and deformability of rocks under triaxial stress conditions with lateral strain control. A mathematical analysis of the limit state of materials is compared with experimental results and work of other authors. 855017 Mathematical modelfing of cyclic behaviour of soils Nova, R Proc of the Symposium on Geotechnical Aspects of Coastal and Offshore Structures, Bangkok, 14-18 Dec 1981 P47-59. Publ Rotterdam: A. A. Balkema. t983 Model presented that allows a better understanding of the decay of undrained cohesion of a normally consolidated clay, and the effects of the type of test, the number of preshearing cycles and the intensity of cyclic loading, The predictions concerning the variation of pore pressures and shear moduli with number of cycles are discussed. The prediction of the behaviour of sand under cyclic loading at constant stram or stress amplitude and the number of cycles necessary to cause liquefaction is possible using the model.