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The analysis of problems in soil dynamics is complicated by many factors, principal of which is the particulate nature of the soil. During several years of association with the investigations of R. K. Bernhard, the author has had opportunities to examine many records of oscillations obtained under a great variety of conditions, and it has appeared to him that no mathematical model so far proposed is adequate to represent the induced motion of the soil except over severely limited force amplitude and frequency ranges. It is certain that any tractable mathematical model will be limited in its application, but the author believes that the range of similarity in behavior between a model and its oscillator-soil prototype can be made usefully wide when certain soil-dynamic types are isolated and their contributing effects formulated individually. A possible formulation of this type is considered here. When the surface of the earth is subjected to motion, such as that imparted to it by a mechanical oscillator, there result three general dynamical states of the medium that must be recognized explicitly. Limiting attention to a small volume of the soil subjected to a periodic oscillation, it will be convenient to consider it to be in one of three cases of excitation: 1. A high energy state in which the medium changes its statistical chararacteristics, such as bulk density, porosity, and permeability; 2. A medium energy state in which the particulate configuration of the soil undergoes irreversible local changes without resulting in significant changes in the statistical characteristics of the soil; and 3. A low energy state in which the changes in the particulate configuration are cyclic.
Slade, J. J.
Rutgers University, New Brunswick, N. J.