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Undrained deep penetration, II: pore pressures
89A 873032 Undrained deep penetration, II: pore pressures Baligh, M N
sand displacements (corresponding to lmm of cone displacement) ranged from lmm to 0.01ram. The accuracy of the displacement measured was about 10%. Auth.
Geotechnique V36, N4, Dec 1986, P487-501 Undrained deep penetration causes significant excess pore pressures that dominate other soil stresses and hold the key to understanding of penetration mechanisms. On the basis of the stress path method, important factors affecting penetration pore pressures in clays are identified and are incorporated in comprehensive prediction methods. Results are required to establish the necessary framework for the interpretation of existing penetration test data, the development of new in situ tests and the analysis of pile installation effects in a systematic and rational manner. Auth. 873033 Strength of undulating shear surfaces in rock Davis, R O; Salt, G A Geotechnique V36, N4, Dec 1986, 1)503-509 Slip on rough shear surfaces in rock is conventionally represented by one of two kinematic mechanisms. A third mechanism is proposed, applicable to undulating shear surfaces. Elastic flattening is suggested as a possible kinematic mechanism for slip at large normal stresses. The work required to flatten the shear surface elastically is calculated and is then used in a Griffith-type crack growth analysis. It is found that flattening is a viable failure mechanism, but it is not clear whether flattening or basal fracture may be the preferred mechanism for failure of an undulating joint. 873034 Effects of stress relief on some overeonsolidated clays Kirkpatrick, W M; Khan, A J; Mirza, A A Geotecimique V36, N4, Dec 1986, 1)511-525 Experiments into the effects of stress relief in some overconsolidated clays in which sample and in situ conditions are simulated in the laboratory are described. Samples are prepared by unloading the soil from in situ stress to atmospheric stress under undrained conditions with the minimum physical disturbance. Tests on LOC kaolins and illites, as well as HOC illites, are described. Results are similar to those for normally consolidated clays in that there is a significant loss of residual pore pressure and undrained strength on unloaded samples compared with in situ soil. The most significant variable governing the amount of the losses is the extent of the stress change needed to unload the soil from its in situ stresses to zero or atmospheric pressure. Results indicated that stress relief effects will not be important if the mean effective stress level from which the clays are unloaded to atmospheric pressure is less than about 100kPa. It is concluded that the in situ undrained stress strain behaviour can be predicted with reasonable accuracy by the consolidated undrained test on samples provided that the samples are reconsolidated by the effective stresses of the in situ soil. 873035 Method for measuring the deformations of a sand surface. Technical note de Pater, C J; Nieuwenhuis, J D Geotechnique V36, N4, Dec 1986, 1)581-585 A method is described to determine the deformations of a sand bed behind a glass window. For this measurement double-exposure photographs are made on high resolution film. The sand displacements between exposures are determined with the aid of the interference pattern that is formed by directing a laser beam through the negative. The technique is illustrated with a measurement of the displacement field around a half-cone pressed against the window. Detectable
873036 New device for measuring local axial strains on triaxial specimens. Technical note Clayton, C R I; Khatrush, S A Geotechnique V36, N4, Dec 1986, P593-597 The design for an accurate, temperature and voltage stabilized, robust, small, light, cheap DC device for the measurement of local strains on triaxial specimens is presented. It makes use of the Hall effect, and should find applications not only in research laboratories but also in commercial soil mechanics environment. 873037 Complex behaviour of a coal sample in a large scale in situ compression test Cyrul, T lnt J Min Geol Engng V4, N4, Dec 1986, P257-271 A large scale in situ compression test of a laminated coal cube is described. Various data obtained from the test are presented in the form of graphs. A method of strain measurement was described which provides extensive data from one test. This study demonstrated the complex behaviour of laminated and heterogeneous samples under uniform uniaxial loading. It includes local strain fluctuations, regional and global bending, as well as regional and global torsion. These ideas can contribute in providing more realistic criteria for the determination of coal pillar stability. 873038 Pillar strength approaches based on a new failure criterion for coal seams Sheorey, P R; Das, M N; Bordia, S K; Singh, B
Int J Min Geoi Engng V4, N4, Dec 1986, P273-290 Two new pillar strength approaches based on a tentative empirical failure criterion for coal seams are proposed. The first, progressive failure type approach, gives incorrect estimates of pillar strength for low width-height ratios. The second pillar strength approach performs satisfactorily for both slender and fiat pillars, and can consequently be used in a variety of situations like chain pillars and shaft pillar areas (provided pillar load is estimated properly), besides regular pillar arrays. The performance of these new equations has been compared with some of the more popular strength formulae as tested against 16 failed and 27 stable pillar case studies. A nomogram is presented for pillar design based on the second approach developed. 873039 Shear failure of rock joints: appropriate constraints for empirical relations Gerrard, C Int J Rock Mech Min Sci V23, N6, Dec 1986, P421-429 The effect of normal stress on the shear strength and dilatant characteristics of a joint is examined in terms of related physical constraints that are assumed to apply for extreme values of the normal stress. Three forms of empirical relations are examined with regard to their ability to incorporate the required physical constraints. Two are considered for further development. The resultant expressions for the shear strength and dilatancy of rock joints, as functions of the normal stress, are compared with previous theories. They are shown to have advantages in terms of their compliance with the required physical constraints as well as improved consistency and versatility.
© 1987 Pergamon Journals Ltd. Reproduction not permitted
sand displacements (corresponding to lmm of cone displacement) ranged from lmm to 0.01ram. The accuracy of the displacement measured was about 10%. Auth.
Geotechnique V36, N4, Dec 1986, P487-501 Undrained deep penetration causes significant excess pore pressures that dominate other soil stresses and hold the key to understanding of penetration mechanisms. On the basis of the stress path method, important factors affecting penetration pore pressures in clays are identified and are incorporated in comprehensive prediction methods. Results are required to establish the necessary framework for the interpretation of existing penetration test data, the development of new in situ tests and the analysis of pile installation effects in a systematic and rational manner. Auth. 873033 Strength of undulating shear surfaces in rock Davis, R O; Salt, G A Geotechnique V36, N4, Dec 1986, 1)503-509 Slip on rough shear surfaces in rock is conventionally represented by one of two kinematic mechanisms. A third mechanism is proposed, applicable to undulating shear surfaces. Elastic flattening is suggested as a possible kinematic mechanism for slip at large normal stresses. The work required to flatten the shear surface elastically is calculated and is then used in a Griffith-type crack growth analysis. It is found that flattening is a viable failure mechanism, but it is not clear whether flattening or basal fracture may be the preferred mechanism for failure of an undulating joint. 873034 Effects of stress relief on some overeonsolidated clays Kirkpatrick, W M; Khan, A J; Mirza, A A Geotecimique V36, N4, Dec 1986, 1)511-525 Experiments into the effects of stress relief in some overconsolidated clays in which sample and in situ conditions are simulated in the laboratory are described. Samples are prepared by unloading the soil from in situ stress to atmospheric stress under undrained conditions with the minimum physical disturbance. Tests on LOC kaolins and illites, as well as HOC illites, are described. Results are similar to those for normally consolidated clays in that there is a significant loss of residual pore pressure and undrained strength on unloaded samples compared with in situ soil. The most significant variable governing the amount of the losses is the extent of the stress change needed to unload the soil from its in situ stresses to zero or atmospheric pressure. Results indicated that stress relief effects will not be important if the mean effective stress level from which the clays are unloaded to atmospheric pressure is less than about 100kPa. It is concluded that the in situ undrained stress strain behaviour can be predicted with reasonable accuracy by the consolidated undrained test on samples provided that the samples are reconsolidated by the effective stresses of the in situ soil. 873035 Method for measuring the deformations of a sand surface. Technical note de Pater, C J; Nieuwenhuis, J D Geotechnique V36, N4, Dec 1986, 1)581-585 A method is described to determine the deformations of a sand bed behind a glass window. For this measurement double-exposure photographs are made on high resolution film. The sand displacements between exposures are determined with the aid of the interference pattern that is formed by directing a laser beam through the negative. The technique is illustrated with a measurement of the displacement field around a half-cone pressed against the window. Detectable
873036 New device for measuring local axial strains on triaxial specimens. Technical note Clayton, C R I; Khatrush, S A Geotechnique V36, N4, Dec 1986, P593-597 The design for an accurate, temperature and voltage stabilized, robust, small, light, cheap DC device for the measurement of local strains on triaxial specimens is presented. It makes use of the Hall effect, and should find applications not only in research laboratories but also in commercial soil mechanics environment. 873037 Complex behaviour of a coal sample in a large scale in situ compression test Cyrul, T lnt J Min Geol Engng V4, N4, Dec 1986, P257-271 A large scale in situ compression test of a laminated coal cube is described. Various data obtained from the test are presented in the form of graphs. A method of strain measurement was described which provides extensive data from one test. This study demonstrated the complex behaviour of laminated and heterogeneous samples under uniform uniaxial loading. It includes local strain fluctuations, regional and global bending, as well as regional and global torsion. These ideas can contribute in providing more realistic criteria for the determination of coal pillar stability. 873038 Pillar strength approaches based on a new failure criterion for coal seams Sheorey, P R; Das, M N; Bordia, S K; Singh, B
Int J Min Geoi Engng V4, N4, Dec 1986, P273-290 Two new pillar strength approaches based on a tentative empirical failure criterion for coal seams are proposed. The first, progressive failure type approach, gives incorrect estimates of pillar strength for low width-height ratios. The second pillar strength approach performs satisfactorily for both slender and fiat pillars, and can consequently be used in a variety of situations like chain pillars and shaft pillar areas (provided pillar load is estimated properly), besides regular pillar arrays. The performance of these new equations has been compared with some of the more popular strength formulae as tested against 16 failed and 27 stable pillar case studies. A nomogram is presented for pillar design based on the second approach developed. 873039 Shear failure of rock joints: appropriate constraints for empirical relations Gerrard, C Int J Rock Mech Min Sci V23, N6, Dec 1986, P421-429 The effect of normal stress on the shear strength and dilatant characteristics of a joint is examined in terms of related physical constraints that are assumed to apply for extreme values of the normal stress. Three forms of empirical relations are examined with regard to their ability to incorporate the required physical constraints. Two are considered for further development. The resultant expressions for the shear strength and dilatancy of rock joints, as functions of the normal stress, are compared with previous theories. They are shown to have advantages in terms of their compliance with the required physical constraints as well as improved consistency and versatility.
© 1987 Pergamon Journals Ltd. Reproduction not permitted