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Scale effects in the determination of mechanical properties of jointed rock masses
276A 935055 Nor-Sand: a simple critical state model for sand Jefferies, M G Geotechnique V43, N1, March 1993, P91-103 A Cambridge-type constitutive model for dilatant materials has been developed from the fundamental axioms of critical state theory. An infinity of normal consolidation loci forces the separation of state from overconsolidation and prevents direct coupling of yield surface size to void ratio. Consequently, Axiom 2 of critical state theory is used as the basis of an incremental hardening rule with state parameter psi as a rate variable. A range of models can be developed within the general scheme. The simple generalised model, Nor-Sand, reproduces many constitutive features of natural sands.
935056 Voids and granulometry: effects on shear modulus of unsaturated sands Qian, X; Gray, D H; Woods, R D
J Geotech Engng Div ASCE Vl19, N2, Feb 1993, P295-314 Effects of capillarity on the small strain shear modulus of partially saturated sands have been examined in resonant column tests. Influences of void ratio, confining pressure, grain shape, and grain size distribution were studied. Capillary stresses significantly increase shear modulus, the effects being more pronounced at low void ratio and confining pressure. Optimum degree of saturation and its relation with the other variables is discussed.
935057 Strength of laboratory-sized coal specimens vs. underground coal pillars Peng, S S Min Engng V45, N2, Feb 1993, P157-158 Reduction factors for predicting coal pillar strength from laboratory test data range from one one sixth to one half, depending on the formula selected. Recent case studies indicate that the reduction factor is not always justifiable. Assumptions, particularly those concerning cleating when extrapolating the laboratory results, are critically examined. Laboratory data are presented which demonstrate that strength values depend very much on how the sample was retrieved from the mine and how the laboratory specimen was prepared.
935058 Mathematical modelling of scale effects in rock joints Muralha, J; Pinto de Cunha, A Proc ISRM Symposium: Eurock '92, Chester, 14-17 September 1992 P287-292. Publ London: Thomas Telford,
935059 Deficiencies in rock test data Farmer, I W; Kemeny, J M
Proc I S R M Symposium: Eurock'92, Chester, 14-17 September 1992 P298-303. Publ London: Thomas Telford, 1992 Rocks and rock masses are inherently heterogeneous and generally poorly characterised. Spatial variability and measurement sources of errors in acquisition of discontinuity data and measurement of in situ stress, hydraulic properties, and geomechanical properties are discussed. The effect of scale of measurement in the field and the laboratory on the parameter values obtained is also examined. Current design methods, often based on empirical or observational approaches, are unsuitable for structures such as waste repositories. For these, even designs based on large scale in situ tests may be inadequate, and a totally new approach may be required. 935060 Elasto-plastic stiffness matrix of rock mass element with soft clay strata and its application Li Zhenzi; Sun Zongqi Proc Conference on Fractured and Jointed Rock Masses, Lake Tahoe, 3-5 June 1992 P420-422. Publ California."
Lawrence Berkeley Laboratory, 1992 The elastoplastic stiffness matrix of a rock mass containing soft clay layers is formulated using a fault element to describe the clay strata. The elastoplastic stiffness matrix of the fault element is formulated using the constitutive relation between plastic increment stress and strain. A numerical example illustrates this procedure used in analysis of a tunnel between two parallel clay layers. Results agree well with those from the boundary element method. 935061 Scale effects in the determination of mechanical properties of jointed rock masses Pinto da Cunha, A; Muralha, J Proc Conference on Fractured and Jointed Rock Masses', Lake Tahoe, 3-5 June 1992 P497-504. Publ California:
Lawrence Berkeley Laboratory, 1992 Results from measurements of scale effects on deformability and strength of joint sets have been collected from several major engineering projects. A linear Coulomb envelope has been used to model shear strength for single joints and joint sets. This criterion gives excellent fit in the normal stress range 0.3-2MPa, but care should be taken if results are extrapolated to very low values of normal stress. 935062 Case history evaluating field vane correction factors Herlache, W A; Hall, C A; Vahdani, S; Taylor, H T Proc Conference Stability and Performance of Slopes and
1992
Embankments !i, Berkeley, 29 June-1 July 1992 I/1, P737755. Publ New York: ASCE, 1992 (,4SCE Special Geotechnical Publication No 31)
Published data from several groups of shear tests are examined and relations describing trend of mean shear strength of systematic joint sets or groups of joints from a given rock mass as the tested discontinuity size increases from laboratory to in situ scale are studied. A new shear strength model for joint sets is proposed which takes into account their area. This is used in probabilistic analysis of rock slopes and the importance of this scale effect is discussed.
A temporary slope failed in an embankment under construction on soft clay (San Francisco Bay Mud). Both field vane and laboratory test data were available for estimation of the undrained shear strength of the clay. Values inferred from field vane tests are seen to require correction (reduction) for this case. Two suitable correction factors are suggested. Stability analysis was carried out. Creep deformation in the soft clay foundation is considered to have initiated the failure.
© 1993 Pergamon Press Ltd. Reproduction not permitted
935056 Voids and granulometry: effects on shear modulus of unsaturated sands Qian, X; Gray, D H; Woods, R D
J Geotech Engng Div ASCE Vl19, N2, Feb 1993, P295-314 Effects of capillarity on the small strain shear modulus of partially saturated sands have been examined in resonant column tests. Influences of void ratio, confining pressure, grain shape, and grain size distribution were studied. Capillary stresses significantly increase shear modulus, the effects being more pronounced at low void ratio and confining pressure. Optimum degree of saturation and its relation with the other variables is discussed.
935057 Strength of laboratory-sized coal specimens vs. underground coal pillars Peng, S S Min Engng V45, N2, Feb 1993, P157-158 Reduction factors for predicting coal pillar strength from laboratory test data range from one one sixth to one half, depending on the formula selected. Recent case studies indicate that the reduction factor is not always justifiable. Assumptions, particularly those concerning cleating when extrapolating the laboratory results, are critically examined. Laboratory data are presented which demonstrate that strength values depend very much on how the sample was retrieved from the mine and how the laboratory specimen was prepared.
935058 Mathematical modelling of scale effects in rock joints Muralha, J; Pinto de Cunha, A Proc ISRM Symposium: Eurock '92, Chester, 14-17 September 1992 P287-292. Publ London: Thomas Telford,
935059 Deficiencies in rock test data Farmer, I W; Kemeny, J M
Proc I S R M Symposium: Eurock'92, Chester, 14-17 September 1992 P298-303. Publ London: Thomas Telford, 1992 Rocks and rock masses are inherently heterogeneous and generally poorly characterised. Spatial variability and measurement sources of errors in acquisition of discontinuity data and measurement of in situ stress, hydraulic properties, and geomechanical properties are discussed. The effect of scale of measurement in the field and the laboratory on the parameter values obtained is also examined. Current design methods, often based on empirical or observational approaches, are unsuitable for structures such as waste repositories. For these, even designs based on large scale in situ tests may be inadequate, and a totally new approach may be required. 935060 Elasto-plastic stiffness matrix of rock mass element with soft clay strata and its application Li Zhenzi; Sun Zongqi Proc Conference on Fractured and Jointed Rock Masses, Lake Tahoe, 3-5 June 1992 P420-422. Publ California."
Lawrence Berkeley Laboratory, 1992 The elastoplastic stiffness matrix of a rock mass containing soft clay layers is formulated using a fault element to describe the clay strata. The elastoplastic stiffness matrix of the fault element is formulated using the constitutive relation between plastic increment stress and strain. A numerical example illustrates this procedure used in analysis of a tunnel between two parallel clay layers. Results agree well with those from the boundary element method. 935061 Scale effects in the determination of mechanical properties of jointed rock masses Pinto da Cunha, A; Muralha, J Proc Conference on Fractured and Jointed Rock Masses', Lake Tahoe, 3-5 June 1992 P497-504. Publ California:
Lawrence Berkeley Laboratory, 1992 Results from measurements of scale effects on deformability and strength of joint sets have been collected from several major engineering projects. A linear Coulomb envelope has been used to model shear strength for single joints and joint sets. This criterion gives excellent fit in the normal stress range 0.3-2MPa, but care should be taken if results are extrapolated to very low values of normal stress. 935062 Case history evaluating field vane correction factors Herlache, W A; Hall, C A; Vahdani, S; Taylor, H T Proc Conference Stability and Performance of Slopes and
1992
Embankments !i, Berkeley, 29 June-1 July 1992 I/1, P737755. Publ New York: ASCE, 1992 (,4SCE Special Geotechnical Publication No 31)
Published data from several groups of shear tests are examined and relations describing trend of mean shear strength of systematic joint sets or groups of joints from a given rock mass as the tested discontinuity size increases from laboratory to in situ scale are studied. A new shear strength model for joint sets is proposed which takes into account their area. This is used in probabilistic analysis of rock slopes and the importance of this scale effect is discussed.
A temporary slope failed in an embankment under construction on soft clay (San Francisco Bay Mud). Both field vane and laboratory test data were available for estimation of the undrained shear strength of the clay. Values inferred from field vane tests are seen to require correction (reduction) for this case. Two suitable correction factors are suggested. Stability analysis was carried out. Creep deformation in the soft clay foundation is considered to have initiated the failure.
© 1993 Pergamon Press Ltd. Reproduction not permitted