Correlation of Mobility Cone Index with Fundamental Engineering Properties of Soil
Final rept. Oct 1980-Jan 1981
ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS STRUCTURES LAB
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Cone index CI has been used successfully by the U.S. Army Engineer Waterways Experiment Station WES as a descriptor of soil strength in establishing empirical soil-vehicle relations for predicting the performance of ground-crawling vehicles. CI is a measure of the resistance of the soil to the penetration of a right-circular cone. CI is measured in pounds per square inch, but it is considered an undimensioned index for obvious reasons. Recent developments in analytical modeling of vehicle performance require that the soil be described in terms of its fundamental properties such as angle of internal friction, cohesion, stiffness, density, etc. In order to utilize the larger CI data base and establish correspondence between the empirical studies and theoretical mobility models, it was necessary to correlate CI with the engineering properties of soil. This paper describes the development of a mathematical model that treats the cone penetration process as expansion of a series of spherical cavities, simulating the geometry of the cone, in an elastic-plastic isotropic medium. The stresses required to expand these cavities are integrated over the surface area of the cone in order to determine the forces resisting the penetration of the cone, in terms of the fundamental engineering properties of soil. Analytical predictions are made for the standard WES cone penetrometer, which is a 30-degree, right-circular cone of 0.5 sq in. base area, and the results are compared with experimental data for various types of soil. The results achieved indicate good agreement between CI and basic engineering soil properties.
- Soil Mechanics