Principles of soil-tool interaction

Abstract

The paper analyses the process of borehole forming in soil through penetration by a conical tool under periodically repeated load impulses. Tests were carried out in the laboratory and in the field, on disturbed and undisturbed soil respectively, under quasi-static and dynamic loading. These tests yielded relationships between the frontal resistance force of the soil and the toll displacement, and also between the cone resistance on the one hand and the cross-sectional area of the tool and its velocity of penetration on the other. It was found that as the frontal resistance force increases in the loading stage, both recoverable and nonrecoverable deformations are produced; moreover, the tool displacement in the loading stage considerably exceeds its counterpart in the unloading stage, as the restoring force of the soil decreases. Results indicate that the variation pattern of the frontal resistance force is practically unaffected by the cyclic character of the process, and that the soils studied fall under the category of cyclically ideal materials. Analysis and generalization of the results of the present study, and of others, yielded a set of mechanical characteristics representing the actual properties of the soil. These characteristics in turn yielded a piecewise-linear relationship between the frontal resistance force and the tool displacement—an approximation which can serve as a basis for minimization of the energy consumption of the cyclic borehole forming process, and eventually for mathematical description of the soil-tool interaction in general.