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15. Stress-strain relations for clays: an energy theory
ABSTRACTS
65
The percentage distribution according to the volume of each particle instead of to sieve size seems more rational, because in this manner the shape of the particles is better taken into account. This distribution of the three phases by size fractions would give more complete indications on gas and liquid permeability changes as a function of relative saturation. Plasticity characteristics are advantageously interpreted in the triangular diagram according to the percentage by weight of: fine particles (less than 2 microns), coarse particles, and water. The same diagram proves to be suitable also for representing contact stresses between adjacent particles. (App. Mech. Rev., 1968.) 12.
R. Lundgren, J. K. Mitchell and J. H. Wilson. Effects of loading method on triaxial test results. J. soil Mech. Fndns Div ASCE 94 (2), 407-419 (Mar. 1968). Existing loading methods, namely strain-controlled and stress-controlled techniques, are discussed and their relative merits noted. In particular, the stress-control technique permits complete pore-pressure equalization (or drainage, depending on test type) at each stage of test, while often avoiding the long testing times involved in strain-rate controlled testing; but failure may be abrupt, making it impossible to obtain stress-strain relationship beyond peak stress. Authors describe an original apparatus and technique which combines desirable features of each type. Testing begins as stress-controlled, and then, as peak stress is approached, a changeover to strain-control is made. A smooth changeover is required, and authors suggest that observed strain-rate immediately prior to changeover should be used thereafter. The results using all three testing techniques are compared for undrained and drained tests, and the importance of permeability in determining load increment duration in stress-controlled tests is indicated (App. Mech. Rev., 1968.)
13.
J. D. Nelson and E. Vey. Relative cleanliness as a measure of lunar soil strength. J. geophys. Res. 73, 3747-3764 (1968). In general, lunar soil strength increases in ultra-high vacuum, owing to the desorption of gas from the particle surfaces. Most results are only qualitative because of lack of quantitative information about the cleanliness of the particle surfaces at the time of measurement. Cleanliness of the particle surfaces affects soil strength markedly because of an increase in interparticle forces after the desorption of gas. These forces are predominantly van der Waals forces; bridging and, at high values of relative cleanliness, chemical bonding would probably be significant. (Soil and Fertilizer, 1968.)
14.
H. P. Oza. Standard dynamic penetration test and bearing capacity of soils. Soil Mech. and Fndn Engng 6 (3), 283-296 (July 1967). Standard (dynamic) penetration tests is an inexpensive and quick method of subsurface exploration for foundation engineering. Several such tests were carried out for different projects. Simultaneously, plate-loading tests were conducted in the nearby pits at the same depths. These results, together with the laboratory work of index properties, are presented in the paper. A discussion of the factors influencing the SPT values is given, along with a brief literature survey. Later, a suggested correlation of allowable bearing capacity versus SPT values is presented. It is also suggested that this relationship could be used for all except highly plastic soils. (App. Mech. Rev., 1968.)
15.
A. C. Palmer. Stress-strain relations for clays: an energy theory. Geotechnique 17, 348-358 (1967). A theory for the internal energy of clay/water systems is derived. In this theory the observed critical state property is central. Only when the relation between mean compressive stress and void ratio is the same as that in the critical state is there a balance between interparticle forces and external forces. This concept leads to a description of internal energy changes in triaxial tests; if this is combined with a description of plastic dissipation, an energy balance can be written. Comparison with experiments on kaolin shows a simple pattern in the behaviour of the parameter describing dissipation. A stress-strain relation for any triaxial stress path can now be derived. A final section of the Paper explores the consequences of linking this with the normality concept of plasticity theory. (Authors' summary.)
16.
W. Prager. Model of plastic behaviour. Proc. 5th U.S. National Congress of App. Meehs., June 14-17, ASME, 435-450 (1966). This is a nice survey article in which the theoretical laws of plastic behavior of solid materials have been represented by mechanical models with the aid of mechanical components such as springs, dashpots, moving wheels, sliding pins, etc. After an introduction in Sec. 1, basic concepts of plasticity are reviewed in Sec. 2. In Sec. 3, one-dimensional elastic, perfectly plastic
65
The percentage distribution according to the volume of each particle instead of to sieve size seems more rational, because in this manner the shape of the particles is better taken into account. This distribution of the three phases by size fractions would give more complete indications on gas and liquid permeability changes as a function of relative saturation. Plasticity characteristics are advantageously interpreted in the triangular diagram according to the percentage by weight of: fine particles (less than 2 microns), coarse particles, and water. The same diagram proves to be suitable also for representing contact stresses between adjacent particles. (App. Mech. Rev., 1968.) 12.
R. Lundgren, J. K. Mitchell and J. H. Wilson. Effects of loading method on triaxial test results. J. soil Mech. Fndns Div ASCE 94 (2), 407-419 (Mar. 1968). Existing loading methods, namely strain-controlled and stress-controlled techniques, are discussed and their relative merits noted. In particular, the stress-control technique permits complete pore-pressure equalization (or drainage, depending on test type) at each stage of test, while often avoiding the long testing times involved in strain-rate controlled testing; but failure may be abrupt, making it impossible to obtain stress-strain relationship beyond peak stress. Authors describe an original apparatus and technique which combines desirable features of each type. Testing begins as stress-controlled, and then, as peak stress is approached, a changeover to strain-control is made. A smooth changeover is required, and authors suggest that observed strain-rate immediately prior to changeover should be used thereafter. The results using all three testing techniques are compared for undrained and drained tests, and the importance of permeability in determining load increment duration in stress-controlled tests is indicated (App. Mech. Rev., 1968.)
13.
J. D. Nelson and E. Vey. Relative cleanliness as a measure of lunar soil strength. J. geophys. Res. 73, 3747-3764 (1968). In general, lunar soil strength increases in ultra-high vacuum, owing to the desorption of gas from the particle surfaces. Most results are only qualitative because of lack of quantitative information about the cleanliness of the particle surfaces at the time of measurement. Cleanliness of the particle surfaces affects soil strength markedly because of an increase in interparticle forces after the desorption of gas. These forces are predominantly van der Waals forces; bridging and, at high values of relative cleanliness, chemical bonding would probably be significant. (Soil and Fertilizer, 1968.)
14.
H. P. Oza. Standard dynamic penetration test and bearing capacity of soils. Soil Mech. and Fndn Engng 6 (3), 283-296 (July 1967). Standard (dynamic) penetration tests is an inexpensive and quick method of subsurface exploration for foundation engineering. Several such tests were carried out for different projects. Simultaneously, plate-loading tests were conducted in the nearby pits at the same depths. These results, together with the laboratory work of index properties, are presented in the paper. A discussion of the factors influencing the SPT values is given, along with a brief literature survey. Later, a suggested correlation of allowable bearing capacity versus SPT values is presented. It is also suggested that this relationship could be used for all except highly plastic soils. (App. Mech. Rev., 1968.)
15.
A. C. Palmer. Stress-strain relations for clays: an energy theory. Geotechnique 17, 348-358 (1967). A theory for the internal energy of clay/water systems is derived. In this theory the observed critical state property is central. Only when the relation between mean compressive stress and void ratio is the same as that in the critical state is there a balance between interparticle forces and external forces. This concept leads to a description of internal energy changes in triaxial tests; if this is combined with a description of plastic dissipation, an energy balance can be written. Comparison with experiments on kaolin shows a simple pattern in the behaviour of the parameter describing dissipation. A stress-strain relation for any triaxial stress path can now be derived. A final section of the Paper explores the consequences of linking this with the normality concept of plasticity theory. (Authors' summary.)
16.
W. Prager. Model of plastic behaviour. Proc. 5th U.S. National Congress of App. Meehs., June 14-17, ASME, 435-450 (1966). This is a nice survey article in which the theoretical laws of plastic behavior of solid materials have been represented by mechanical models with the aid of mechanical components such as springs, dashpots, moving wheels, sliding pins, etc. After an introduction in Sec. 1, basic concepts of plasticity are reviewed in Sec. 2. In Sec. 3, one-dimensional elastic, perfectly plastic