Viscous properties of soil

Abstract

Dynamic problems connected with the wave propagation in soils not saturated with water and with wave interaction with obstacles and structural elements at the present time are solved on the basis of models in which plastic but not viscous soil properties are taken into account [1–5]. An analysis of experimental data and their comparison with the calculated results [4, 5] confirms that it is permissible to apply the model of an elasticplastic medium to soils in problems concerning the interaction of waves and structures. At the same time plane-wave damping in soils takes place more intensively than would follow from calculations carried out on the basis of models of an elastic-plastic medium. For example, if in a section of a poured sandy soil, taken as the initial section, the maximum stress in the wave is σm=ll kgf/cm2 and its duration is 6=8 msec, then at a distance of 25 cm the calculations give σm=9.5 kgf/cm2, while the experiment gives σm= 5 kgf/cm2. If in the initial section σm= 20 kgf/cm2 and θ=6 msec, then at a distance of 35 cm the calculation gives αm= l7 kgf/cm2, while the experiment gives σm= 9 kgf/cm2. In the calculations it was assumed that unloading takes place with a constant strain. This deviation of the calculated results from the experiment can be explained, in the first place, by the dependence of the α(ɛ) on the strain rate $$\mathop \varepsilon \limits^ \circ $$ , which is not taken into account in the model of an elastic-plastic medium. The viscous properties cause additional energy losses and a more intensive damping of the waves. Experimentally the dependence of the σ (ɛ) curves on the strain rate has been investigated for many soils [5–8]. The dynamic load on the test sample was produced by a body falling from a height or being accelerated by some method. Below we present test results of viscous soil properties when the test sample is compressed by an air shock wave. Compression curves and approximate numerical values of the coefficient of viscosity are obtained.