Leslie L. Karafiath

Tire-soil interaction model for turning (steered) tires☆

Abstract A review of the experimental information on the development of lateral forces on tires traveling at an angle to their center plane is presented and the usefulness of the consideration of the lateral forces for the development of an analytical model is evaluated. Major components of the lateral force have been identified as the forces required to balance the tractive force and the drawbar pull vectorially. The lateral forces are generated by the shear stresses developing in the contact area and the horizontal component of the normal stresses acting on the in-ground portion of the curved side walls of the tire. The tire-soil interaction model for steady state straight travel has been expanded to include the necessary algorithms for the calculation of these lateral forces. The pattern of tractive force-slip and longitudinal-lateral force relationships is in general agreement with experiments.

General Yield Conditions in a Plasticity Analysis of Soil-Wheel Interaction

Abstract Plasticity theory and a general representation of the Mohr failure criterion are applied to the problem of soil-wheel interaction. Load, drawbar pull (or drag), and torque are computed for a rigid wheel being driven on Jones Beach sand. Analytical results obtained from solutions using a conventional Mohr-Coulomb linear failure envelope are compared to those obtained from a non-linear solution. Conclusions are drawn from the comparison that attest the importance of considering the nonlinearity of failure envelopes in certain cases for accuracy of soil-wheel interaction prediction. Preliminary experimental results show reasonable agreement with predicted values of wheel performance parameters.

Cone resistance in sand by incremental method

Abstract A new method has been developed for the determination of cone resistance under drained conditions. Numerical methods are used for the solution of the differential equations of plasticity theory for soils and for the determination of the stress states in the soil produced by the penetration of the cone. It is assumed that the stresses produced by the penetration of the cone remain ‘locked in’ the soil and constitute boundary conditions for further penetration. The computation starts with the cone base at the surface and is continued by successively incrementing the depth by a small amount. Charts are given for the computation of cone resistance in sands for various friction angles. The importance of the effect of the shear stresses generated at the surface of the cone and characterized by the interface friction angle, δ, is discussed in detail.

On the effect of base friction on bearing capacity

INTRODUCTION IN THE classic Prandtl solution for the bearing capacity of weightless soils, the bearing stresses are perpendicular to the loaded surface [1]. This implies that the base of the footing is perfectly smooth (8 = 0). Terzaghi [2] recognized the effect of base friction on bearing capacity and proposed that for perfectly rough (8 = q~) bases the angle a of the active zone be taken as equal to q~ instead of 45 + q0/2, as in the Prandtl solution. Meyerhof [3] proposed an approximate formula for the consideration of the roughness of the base of footing in bearing capacity calculations. Hu [4] and Assad Abdul-Baki and L. A. Beik [5] assumed ct to be variable and proposed to define the bearing capacity factors as minimum values for variable a; the latter authors related 8 at the edge of the footing to ~ by the appropriate equations of the theory of plasticity. Straight line boundaries of the active zones assumed by these authors suggest a uniform 8 across the base of the footing. The logarithmic spirals assumed in the radial zone are valid for weightless soil only; therefore, the proposed bearing capacity factors can be considered as only approximations. Negre and Stutz [6] obtained numerical solutions of the differential equations of plasticity for the case where 8 = q~ at the edge of the footing and decreases gradually toward the center. In this paper, the effect of base friction on the geometry of slip line fields and the distribution of bearing stresses is analyzed in both the two-dimensional and the axially symmetric case by theory of plasticity methods.