Published: Jan 1954
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The paper is subdivided into four parts: (I) Density and Compaction; (II) Propagation Velocity and Dynamic Moduli of Elasticity; (III) Viscosity, Damping, and Shear; and (IV) Response Curves and Critical Frequencies. In Part I the behavior of small particles under various types of loads is studied. Many of the statements are well known. It was felt, however, that a collection of theoretical and physical considerations would clarify some of the phenomena governing compaction procedures. The rather controversial question of maximum desirable or obtainable compaction is discussed. Some suggestions are made to grade subsoil components in such a form as to obtain optimum compaction. In Part II the determination of the dynamic moduli of elasticity of soils by means of propagation waves is discussed. The time difference between arrival of compression wave fronts at various points was used to calculate the wave velocity. Seismographs on the soil surface and pressure cells buried below the surface recorded the transmitted waves produced by impact blows. Comparison between static and dynamic moduli of elasticity are made and suggestions for further studies are advanced. In Part III a method for determining damping, viscosity, and shear modulus of soils is presented. An attempt was made to concentrate the shear effect on a small soil mass, that is, to a specimen as thin as possible. It is shown that the . vibrating system is nonlinear with respect to damping and elasticity. In other words, the familiar solutions for a linear system with viscous damping yielded erroneous results. A mathematical model taking into account slipping of the soil particles is suggested. Typical response curves for such a system are derived and compared with experimental values. In Part IV, experimental and theoretical investigations referring to a study on the vibrating soil-mass system are covered. Experimental data from several sources are compared with analytical data based on a theory advanced by E. Reissner. This investigation indicated that a simplified soil-mass system, when reduced to a finite soil mass with linear elastic and damping characteristics, will not suffice, whereas the assumption of an isotropic semi-infinite space, including the dispersion effect of propagation waves, seems to present the best approach toward a general solution.
Bernhard, R. K.
Professor of Engineering Mechanics, Rutgers University, New Brunswick, N.J.
Associate Research Engineer, Stevens Institute of TechnologyRutgers University, Hoboken, N. J.