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49. An analysis of the triaxial test for cohesionless soils
ABSTRACTS
77
48.
R. E. Olson and L. M. Campbell. Bushing friction in triaxial shear testing. Matls. Res. Stand., 7 (2), 45-52 (1967). For economic reasons, the force in the loading piston of the triaxial shear apparatus is usually measured outside the cell. Frictional losses in the bushing-seals assembly then introduce errors into the interpretation of the shear data. We measured these frictional losses for both stat'onary and rotating solid and ball bushings as a function of lateral load and lever arm of the lateral load. For ball bushings, additional variables included type of seal, diametral compression of seal, cell pressure, deformation rate, efficacy of special lubricants, and the set-up time. The experiments demonstrated that the stationary ball bushing with an X-ring seal of 4 per cent diametral compression is the most satisfactory solution to the bushing problem for most triaxial shear tests. Lateral load and its lever arm should be minimized. Rotating bushings gave less total friction than did the ball bushings but the net friction was essentially the same. Further, rotating solid or ball bushings applied undesirable reciprocating lateral motions to the soil specimens. (Author's Summary)
49.
Paul R. Paslay and Jay B. Weidler. An analysis of the triaxial test for cohesionless soils. Brown Univ., Providence R. I., Div. of Engineering. May. 32 p. (1967). Several implications of an earlier analytical formulation for cohesionless soils are deduced for the triaxial test (a compression test in the presence of a hydrostatic pressure). A specific form for the loading surface is adopted in order to illustrate certain difficulties associated with uniqueness and stability. In certain important respects the limited analytical and numerical results appear to agree with experience in soil mechanics testing. (US Gov. Res. Dev. Rep., 25.11.67, AD-653858)
50.
Peter W. I-Ialey. Mobility environmental research study one-pass program. Army TankAutomotive Center, Warran, Mich. Land Locomotion Lab. Jan., 66 p. ATAC-TR-8785 (1965). The overall purpose of this program was to develop a quick, accurate, predict!on for onepass performance of a vehicle operating in fine-grained soft soil conditions and a slippery soil layer over a hard-pan. The specific objective was to predict performance using existing analytical Land Locomotion Mechanics expressions as a datum for new relationships. Performance curves of drawbar-pull vs. slip were constructed from measured vehicle tests and on the basis of measured Land Locomotion Mechanics Soil Values. Coefficient of friction values were obtained for the slippery soil layer condition in the same manner. Predicted performance for the vehicles tested was within the accuracy level of 25 per cent (that is expected from Land Locomotion Mechanics prediction techniques) for 55 per cent of the tests conducted. The remaining 45 per cent of the test results indicated the need, in some instances, for more realistic test techniques with regard to the vehicle test and soil data collection. A quick-data reduction procedure for predicting performance cannot be readily obtained. (U.S. Gov. Res. Dev. Rep., 10.8.67, D-467165)
51.
V. A. Petrushov. On the vehicle dynamic factor taking into account tyre-equipment properties. A v t o m . Prom., May, 5, 14-17 (in Russian) (1967). No translation of the original article is known to exist. In the design and comparative evaluation of vehicles, E. A. Chudakov's non-dimensional dynamic factor D is utilised, the formula for which is as follows : D-=
G ,,
=
~
where P°a is the full, overall peripheral force at the vehicle driving wheels, M a the torque applied to the driving wheels, rl~ the driving-wheel rolling radius, Pw the aerodynamic drag, and G a the vehicle weight. Although the rolling-radius value entering into this formula is accepted as being constant, this is not so in fact, since, as the applied torque increases, the rolling radius of the vehicle driving wheels decreases the more the higher the coefficient of tyre tangential elasticity. With the variation in rolling radius through the application of a rising torque taken into account, the dynamic factor is 8-15 per cent higher during operation in the lower gears than without it taken into account. In the higher gears, the difference in the dynamic factor with the variation in rolling radius taken into account is slight. Analysis of the vehicle dynamic factor taking into account the internal properties of the tyre equipment, these being linked with tyre tangential elasticity through the n u m b e r of driving wheels and the type of drive, shows that the
77
48.
R. E. Olson and L. M. Campbell. Bushing friction in triaxial shear testing. Matls. Res. Stand., 7 (2), 45-52 (1967). For economic reasons, the force in the loading piston of the triaxial shear apparatus is usually measured outside the cell. Frictional losses in the bushing-seals assembly then introduce errors into the interpretation of the shear data. We measured these frictional losses for both stat'onary and rotating solid and ball bushings as a function of lateral load and lever arm of the lateral load. For ball bushings, additional variables included type of seal, diametral compression of seal, cell pressure, deformation rate, efficacy of special lubricants, and the set-up time. The experiments demonstrated that the stationary ball bushing with an X-ring seal of 4 per cent diametral compression is the most satisfactory solution to the bushing problem for most triaxial shear tests. Lateral load and its lever arm should be minimized. Rotating bushings gave less total friction than did the ball bushings but the net friction was essentially the same. Further, rotating solid or ball bushings applied undesirable reciprocating lateral motions to the soil specimens. (Author's Summary)
49.
Paul R. Paslay and Jay B. Weidler. An analysis of the triaxial test for cohesionless soils. Brown Univ., Providence R. I., Div. of Engineering. May. 32 p. (1967). Several implications of an earlier analytical formulation for cohesionless soils are deduced for the triaxial test (a compression test in the presence of a hydrostatic pressure). A specific form for the loading surface is adopted in order to illustrate certain difficulties associated with uniqueness and stability. In certain important respects the limited analytical and numerical results appear to agree with experience in soil mechanics testing. (US Gov. Res. Dev. Rep., 25.11.67, AD-653858)
50.
Peter W. I-Ialey. Mobility environmental research study one-pass program. Army TankAutomotive Center, Warran, Mich. Land Locomotion Lab. Jan., 66 p. ATAC-TR-8785 (1965). The overall purpose of this program was to develop a quick, accurate, predict!on for onepass performance of a vehicle operating in fine-grained soft soil conditions and a slippery soil layer over a hard-pan. The specific objective was to predict performance using existing analytical Land Locomotion Mechanics expressions as a datum for new relationships. Performance curves of drawbar-pull vs. slip were constructed from measured vehicle tests and on the basis of measured Land Locomotion Mechanics Soil Values. Coefficient of friction values were obtained for the slippery soil layer condition in the same manner. Predicted performance for the vehicles tested was within the accuracy level of 25 per cent (that is expected from Land Locomotion Mechanics prediction techniques) for 55 per cent of the tests conducted. The remaining 45 per cent of the test results indicated the need, in some instances, for more realistic test techniques with regard to the vehicle test and soil data collection. A quick-data reduction procedure for predicting performance cannot be readily obtained. (U.S. Gov. Res. Dev. Rep., 10.8.67, D-467165)
51.
V. A. Petrushov. On the vehicle dynamic factor taking into account tyre-equipment properties. A v t o m . Prom., May, 5, 14-17 (in Russian) (1967). No translation of the original article is known to exist. In the design and comparative evaluation of vehicles, E. A. Chudakov's non-dimensional dynamic factor D is utilised, the formula for which is as follows : D-=
G ,,
=
~
where P°a is the full, overall peripheral force at the vehicle driving wheels, M a the torque applied to the driving wheels, rl~ the driving-wheel rolling radius, Pw the aerodynamic drag, and G a the vehicle weight. Although the rolling-radius value entering into this formula is accepted as being constant, this is not so in fact, since, as the applied torque increases, the rolling radius of the vehicle driving wheels decreases the more the higher the coefficient of tyre tangential elasticity. With the variation in rolling radius through the application of a rising torque taken into account, the dynamic factor is 8-15 per cent higher during operation in the lower gears than without it taken into account. In the higher gears, the difference in the dynamic factor with the variation in rolling radius taken into account is slight. Analysis of the vehicle dynamic factor taking into account the internal properties of the tyre equipment, these being linked with tyre tangential elasticity through the n u m b e r of driving wheels and the type of drive, shows that the