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Soft soil performance of a four-wheel-drive log skidder
ABSTRACTS
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obtained from "sector curves" which relate the influence factor to the stress or displacement at or beneath the apex of the sector to the relative size of the sector, and can be obtained by integration of the point load values over a uniformly loaded sector of small angle. Some examples pf sector curves for the case of vertical loading of a semi-infinite mass are given in the paper. (J. Soil Mech. Fndns Div., Sept. 1969.) 22.
E. S. Rush. Soft soil performance of a four-wheel-drive log skidder. Trans. ASAE, 4, 546 (1969). A means for evaluating vehicle performance in soft soils is necessary for efficient use of ground machines in military and civilian off-road operations. The results of soil trafficability studies conducted by the U.S. Army Engineer Waterways Experiment Station (WES) have demonstrated that soil strength can be related to vehicle performance. The methods and techniques of measuring the trafficability of soft, fine-grained soils have been summarized in numerous WES reports. These reports contain formulas for determining the minimum soil strength requirements for military vehicles to complete a prescribed number of passes; they also contain curves relating soil strength to towing capabilities.
23.
A. L. Russell. Amphibious Vehicles. Proc. lnstn Mech. Engrs, Auto Div., 183 (5), 99-111 (19681969). Although the motor vehicle has now been with us for rather more than half a century, there has not been significant progress in the evolution of amphibious vehicles until the last two or three decades. Probably the largest obstacle in this field has been the conflict of requirements between land and water conveyance, which tends to make an amphibious vehicle more expensive than the boat and road vehicle of similar capacity which it replaces. The additional expense involved in uniting these functions is always heavy and is often prohibitive, and it is only in certain specialist applications that the true amphibian can be a satisfactory solution, principally either where separate vehicle and vessel are highly inconvenient or completely impractical, or where exceptional versatility is required.
24.
D. A. Sangrey, D. J. Henkel and M. I. Esrig. The effective stress response of a saturated clay soil to repeated loading. Can. Geotechnical J., 6, 241 (Aug. 1969). The results of a series of tests designed to examine the behavior of saturated clay soil under repeated loading are reported. Triaxial tests, under conditions of axial symmetry, were used and the rates of deformation were chosen so as to permit the accurate measurement of pore water pressure at all stages of the tests. It was found that, for any particular consolidation history, a critical level of repeated stress existed. Below this critical level, a state of nonfailure equilibrium was reached in which the stressstrain curves followed closed hysteresis loops. Above the critical level of repeated stress, effective stress failure occurred; and each cycle of loading produced cumulative increases in deformation. An interesting feature of the test results was that a linear relationship between the magnitude of the applied repeated stress and the increase in pore water pressure was found for stress levels below the critical value. (Authors' summary.)
25.
E. Schultze. Friction of cohesionless soils. Der bauingenieur, 43 (9), 313-320 (Sept. 1968). The relationship between angle of internal friction (p) and porosity (~,) can be approximately described by a formula of Caquot and Kerisel, cot p - 0 / C ) c, The coefficient C in practical cases has to be determined by at least one laboratory test. The effect of intermediate principal stress in plane strain tests causes angles of internal friction which are about 10~o higher than those obtained under triaxial compression. Since small changes in the friction coefficient considerably increase the magnitude of earth pressure, neglect this fact leads to designs of retaining walls which are too conservative. Increasing the normal stress on the shear surface, reveals a decrease of the angle of internal friction, since the Mohr envelope is curved even for very low normal pressures. This factor at present stage however only qualitatively can be considered in practical cases. (J. Soil Mech. Fndns Div., Sept. 1969.)
26.
D. Sehuring. Theory of the cross-country wheel. Forsch. Ingenieurwesen, 34 (6), 165-176 (1968). Author presents a critical review of the existing literature on the problem of the driven wheel on soft ground. The literature has proliferated of late, probably as a consequence of the American Moon program. Author attempts to unify many of the different approaches made, particularly to the problem of rolling resistance coefficient. The wheel/soil displacements are discussed, and the stress distribution along the contact surface are considered, making use of several variations of the shearing/compressing soil model. Finally, the problems are indicated which remain to be
83
obtained from "sector curves" which relate the influence factor to the stress or displacement at or beneath the apex of the sector to the relative size of the sector, and can be obtained by integration of the point load values over a uniformly loaded sector of small angle. Some examples pf sector curves for the case of vertical loading of a semi-infinite mass are given in the paper. (J. Soil Mech. Fndns Div., Sept. 1969.) 22.
E. S. Rush. Soft soil performance of a four-wheel-drive log skidder. Trans. ASAE, 4, 546 (1969). A means for evaluating vehicle performance in soft soils is necessary for efficient use of ground machines in military and civilian off-road operations. The results of soil trafficability studies conducted by the U.S. Army Engineer Waterways Experiment Station (WES) have demonstrated that soil strength can be related to vehicle performance. The methods and techniques of measuring the trafficability of soft, fine-grained soils have been summarized in numerous WES reports. These reports contain formulas for determining the minimum soil strength requirements for military vehicles to complete a prescribed number of passes; they also contain curves relating soil strength to towing capabilities.
23.
A. L. Russell. Amphibious Vehicles. Proc. lnstn Mech. Engrs, Auto Div., 183 (5), 99-111 (19681969). Although the motor vehicle has now been with us for rather more than half a century, there has not been significant progress in the evolution of amphibious vehicles until the last two or three decades. Probably the largest obstacle in this field has been the conflict of requirements between land and water conveyance, which tends to make an amphibious vehicle more expensive than the boat and road vehicle of similar capacity which it replaces. The additional expense involved in uniting these functions is always heavy and is often prohibitive, and it is only in certain specialist applications that the true amphibian can be a satisfactory solution, principally either where separate vehicle and vessel are highly inconvenient or completely impractical, or where exceptional versatility is required.
24.
D. A. Sangrey, D. J. Henkel and M. I. Esrig. The effective stress response of a saturated clay soil to repeated loading. Can. Geotechnical J., 6, 241 (Aug. 1969). The results of a series of tests designed to examine the behavior of saturated clay soil under repeated loading are reported. Triaxial tests, under conditions of axial symmetry, were used and the rates of deformation were chosen so as to permit the accurate measurement of pore water pressure at all stages of the tests. It was found that, for any particular consolidation history, a critical level of repeated stress existed. Below this critical level, a state of nonfailure equilibrium was reached in which the stressstrain curves followed closed hysteresis loops. Above the critical level of repeated stress, effective stress failure occurred; and each cycle of loading produced cumulative increases in deformation. An interesting feature of the test results was that a linear relationship between the magnitude of the applied repeated stress and the increase in pore water pressure was found for stress levels below the critical value. (Authors' summary.)
25.
E. Schultze. Friction of cohesionless soils. Der bauingenieur, 43 (9), 313-320 (Sept. 1968). The relationship between angle of internal friction (p) and porosity (~,) can be approximately described by a formula of Caquot and Kerisel, cot p - 0 / C ) c, The coefficient C in practical cases has to be determined by at least one laboratory test. The effect of intermediate principal stress in plane strain tests causes angles of internal friction which are about 10~o higher than those obtained under triaxial compression. Since small changes in the friction coefficient considerably increase the magnitude of earth pressure, neglect this fact leads to designs of retaining walls which are too conservative. Increasing the normal stress on the shear surface, reveals a decrease of the angle of internal friction, since the Mohr envelope is curved even for very low normal pressures. This factor at present stage however only qualitatively can be considered in practical cases. (J. Soil Mech. Fndns Div., Sept. 1969.)
26.
D. Sehuring. Theory of the cross-country wheel. Forsch. Ingenieurwesen, 34 (6), 165-176 (1968). Author presents a critical review of the existing literature on the problem of the driven wheel on soft ground. The literature has proliferated of late, probably as a consequence of the American Moon program. Author attempts to unify many of the different approaches made, particularly to the problem of rolling resistance coefficient. The wheel/soil displacements are discussed, and the stress distribution along the contact surface are considered, making use of several variations of the shearing/compressing soil model. Finally, the problems are indicated which remain to be