One-dimensional Stress Wave Propagation in Soils

Soil behavior during stress wave propagation was studied on a sand and two clays by making one-dimensional wave propagation tests on 5-meter long columns of the soils. Attempts were made to predict this behavior by determining soil properties in dynamic compression tests on small samples and by using these properties in a variety of mathematical models for soil. In all the wave propagation tests, stress and acceleration records were very similar, showing that the three soils differ in degree, not in kind. Peak stress and particle velocity attenuated to 20-40^ of the peak value in the length of the 5-meter column. The peak acceleration attenuated with the second power of arrival time. The rise time of the stress increased with depth. The wave velocity of the peak stress also increased with depth: average wave velocities ranged from 100 to 500 m/sec. Both time-dependent and time-independent dissipation was observed in all soils. Time-dependent dissipation was dominant in soft clay; timeindependent dissipation was more important in sand and stiff clay. Two theoretical soil models were analyzed: one to investigate the effect of combined time-dependent and time-independent dissipation, and one to study the effects of nonlinear stress-strain relations and geostatic stress. Comparison of the theoretical predictions from the first of those and two previously studied models (using properties obtained from compression tests on soil samples) with the wave propagation results showed 1. For clays the arrival time of the wave at the column base was within 10^ of that calculated from the tangent modulus, and for sand it was within 25$. 2. Attenuation of peak stress and particle velocity was predicted within ±50$ at the base of the column (5-meter length). One of the soils—a well-compacted kaolinite clay-exhibited an approximately linear loading relation during compression tests. Because of this linearity the model analyses were particularly applicable to the prediction of the behavior of this soil (all models used for predictions have linear loading relations). For this soil, attenuation was predicted within 10$ and wave velocity within 5$; thereby verifying the usefulness of the theoretical models used. In general, the earlier, simpler models are as suitable for predicting wave propagation behavior as the more complex models, but no single model can predict all properties reliably.