- Email: [email protected]
52. Soils and model tests
78
ABSTRACTS necessary correction to the dynamic-factor formula is taken into account with the use in calculations of the rolling radius obtaining for a driven wheel. However, there is also a simultaneous correction made to the concept of an overall-road resistance coefficient, from which the additional losses connected with tyre tangential elasticity should be excluded. ( M I R A 67)
52.
K. H, Roscoe. Soils and model tests. J. Strain Analysis, 3 (1) (1968). Two main uses of model testing in soil mechanics are considered. The first is to examine, usually on only a qualitative basis, at a reduced scale the assumptions that have been made in theoretical analyses of prototype problems, the object being to develop analysis and models side by side with a view to improvement of the former. A n outline is then given of current methods of analysis based only on failure conditions and of the use of new methods developed at Cambridge of investigating the behaviour of soils in models at all stress levels. Thereafter attention is confined to the second use of models in which attempts are made to satisfy the conditions of similarity so that prototype behaviour can be predicted from model data. These conditions are derived. Simulation of soils by other media is discussed but is not considered to be a rewarding procedure. It is then shown how the Cambridge approach to the mechanical behaviour of soils has enabled the formulation of a useful law in model testing for work-hardening soils, and similar granular media, at all working loads. This law states the conditions under which the same soil may be used in model and prototype. Finally the potentialities of centrifugal model testing are discussed; they provide a n opportunity of satisfying simultaneously this law and the conditions of similitude. (Author's Summary)
53.
S. S. Saakyan. Slip of a driven wheel on a plastic media. National Tillage Machinery Lab., Auburn, Ala. 21st Jan. 1967, 8 p. Trans of Mekhanizatsiya i Elektrifikatsiya Sotsialisticheskogo Selskogo Khozyaistva (USSR), 4, 35-39 (1953). The roiling of powered transport wheels on a plastic media is accompanied by slipping. The magnitude of the slip is found to depend on the depth of rut, diameter of wheel, the initial soil compaction and the coefficient of friction of the soil. Slip may increase to 10 per cent in deep ruts on tilled soil and this is significantly reflected in the rolling resistance of the wheel. The relationship of the degree of slip of driven wheels to depth of rut and angle of subtended by the rim on the soil can be expressed by a parabolic equating e p s i l o n = p h i to the n power, with an exponent greater than one. Consequently a small rut and the use of larger diameter wheels provided the main conditions for decreased slip. In addition this slip was accompanied by harmful conditions in that there was a somewhat lower productivity of the soil and an increased rolling resistance. (U.S. Gov. Res. Dev. Rep., 10.1.68, PB-176437T)
54.
John L. B. Selwood. Standard tests for engineering testing of amphibious land vehicles (Tracked). Selwood Research inc Kensington Md. 30th June, 44 p. Rept. no. 105-1-004 (1967). The test h a n d b o o k provides very brief descriptions of the tests that might be required in the engineering testing of amphibious landing vehicles, tracked (LVT). The purpose is to provide simple and standard methods for issuing test directives. It consists of three sections covering an introduction dealing with definitions, procedures and policy instructions, etc.; a section on land tests; a section on water tests. (U.S. Gov. Res. Dev. Rep.. 10.9.67, AD-654747)
55.
A. Singh and J. K. Mitchell. General stress-strain-time function for soils. J. Soil Mec. Fndns. Div., ASCE, 94, SM1, Proc. Paper 5728, January, pp. 21-46 (1968). The stress-strain-time behavior of soils m a y assume a variety of forms, depending on such factors as soil type, soil structure, stress history, drainage conditions, and type of loading. Generalizations concerning creep in soils suggested by various investigators are sometimes contradictory. However, test results show that there exist linear relationships between logarithm of strain rate and logarithm of time for a given stress and between logarithm of strain rate and stress at any given time, provided the creep stress level is between the practical limits of about 30 per cent to 90 per cent of the initial soil strength. These findings lead to a simple three-parameter general stress-strain-rate-time relationship. Integration of this relationship yields creep curves which are observed to agree in form with the experimental results. (Author's Summary)
ABSTRACTS necessary correction to the dynamic-factor formula is taken into account with the use in calculations of the rolling radius obtaining for a driven wheel. However, there is also a simultaneous correction made to the concept of an overall-road resistance coefficient, from which the additional losses connected with tyre tangential elasticity should be excluded. ( M I R A 67)
52.
K. H, Roscoe. Soils and model tests. J. Strain Analysis, 3 (1) (1968). Two main uses of model testing in soil mechanics are considered. The first is to examine, usually on only a qualitative basis, at a reduced scale the assumptions that have been made in theoretical analyses of prototype problems, the object being to develop analysis and models side by side with a view to improvement of the former. A n outline is then given of current methods of analysis based only on failure conditions and of the use of new methods developed at Cambridge of investigating the behaviour of soils in models at all stress levels. Thereafter attention is confined to the second use of models in which attempts are made to satisfy the conditions of similarity so that prototype behaviour can be predicted from model data. These conditions are derived. Simulation of soils by other media is discussed but is not considered to be a rewarding procedure. It is then shown how the Cambridge approach to the mechanical behaviour of soils has enabled the formulation of a useful law in model testing for work-hardening soils, and similar granular media, at all working loads. This law states the conditions under which the same soil may be used in model and prototype. Finally the potentialities of centrifugal model testing are discussed; they provide a n opportunity of satisfying simultaneously this law and the conditions of similitude. (Author's Summary)
53.
S. S. Saakyan. Slip of a driven wheel on a plastic media. National Tillage Machinery Lab., Auburn, Ala. 21st Jan. 1967, 8 p. Trans of Mekhanizatsiya i Elektrifikatsiya Sotsialisticheskogo Selskogo Khozyaistva (USSR), 4, 35-39 (1953). The roiling of powered transport wheels on a plastic media is accompanied by slipping. The magnitude of the slip is found to depend on the depth of rut, diameter of wheel, the initial soil compaction and the coefficient of friction of the soil. Slip may increase to 10 per cent in deep ruts on tilled soil and this is significantly reflected in the rolling resistance of the wheel. The relationship of the degree of slip of driven wheels to depth of rut and angle of subtended by the rim on the soil can be expressed by a parabolic equating e p s i l o n = p h i to the n power, with an exponent greater than one. Consequently a small rut and the use of larger diameter wheels provided the main conditions for decreased slip. In addition this slip was accompanied by harmful conditions in that there was a somewhat lower productivity of the soil and an increased rolling resistance. (U.S. Gov. Res. Dev. Rep., 10.1.68, PB-176437T)
54.
John L. B. Selwood. Standard tests for engineering testing of amphibious land vehicles (Tracked). Selwood Research inc Kensington Md. 30th June, 44 p. Rept. no. 105-1-004 (1967). The test h a n d b o o k provides very brief descriptions of the tests that might be required in the engineering testing of amphibious landing vehicles, tracked (LVT). The purpose is to provide simple and standard methods for issuing test directives. It consists of three sections covering an introduction dealing with definitions, procedures and policy instructions, etc.; a section on land tests; a section on water tests. (U.S. Gov. Res. Dev. Rep.. 10.9.67, AD-654747)
55.
A. Singh and J. K. Mitchell. General stress-strain-time function for soils. J. Soil Mec. Fndns. Div., ASCE, 94, SM1, Proc. Paper 5728, January, pp. 21-46 (1968). The stress-strain-time behavior of soils m a y assume a variety of forms, depending on such factors as soil type, soil structure, stress history, drainage conditions, and type of loading. Generalizations concerning creep in soils suggested by various investigators are sometimes contradictory. However, test results show that there exist linear relationships between logarithm of strain rate and logarithm of time for a given stress and between logarithm of strain rate and stress at any given time, provided the creep stress level is between the practical limits of about 30 per cent to 90 per cent of the initial soil strength. These findings lead to a simple three-parameter general stress-strain-rate-time relationship. Integration of this relationship yields creep curves which are observed to agree in form with the experimental results. (Author's Summary)