Procedures for Prediction of Ground Shock Phenomena Based on One-Dimensional Shock Propagation Considerations. Report 2. Experimental Study of Loading-Unloading Stress Wave Interactions in a Soil Shock Tube

摘要

The report describes a definitive experimental study in which shock-induced square-wave pulses in soil were observed to give way to decaying pulse shapes, as in a gas shock tube, and rapid attenuation of peak stress occurred thereafter due to nonlinear propagation in the rarefaction. In the study three different duration pulses were applied to an 8-ft vertical column of granular material confined under boundary conditions leading to a stress-strain (Sigma - Epsilon) behavior described by d to the 2nd power Sigma/d Epsilon to the 2nd power > 0, i.e., a strain-hardening type of response. Applied stresses ranged from 50 to 500 psi. The report describes a simple modification to be applied to the prediction procedure described in the first report of this series in order to take into account, to a first approximation, the nonlinear propagation of unloading waves that occurs in real media because of nonlinear stress-strain behavior in the unloading branch. The procedure which predicts stress and motion histories based on the conservation laws, a measured constitutive relationship, and the applied pressure-time profile, is demonstrated by predicting the entire sequence of an experimentally observed square-wave pulse transformation into a decaying pulse. (Author)