Simplified theoretical analysis of the seismic response of artificially compacted gravels

Despite extensive use of gravely materials for the construction of big earthworks, theoretical prediction of their seismic response is often based on very simple schemes, unable to reproduce most of the important features observed at sample scales. Theoretical models capable of simulating the effects of artificial compaction on the stress-strain response of these soils under complex static and dynamic loading conditions would be particularly useful for designing more cost effective solutions in the construction of large embankments. This paper is aimed to fill this gap by reporting the results of a simplified theoretical study on the seismic response of an artificial deposit of gravels compacted at different densities. A previously defined critical state multiple yielding elasto-plastic constitutive model, validated with the results of a large variety of triaxial tests on gravels (measurement from small to large strains, samples compacted at different initial soil densities, monotonic and cyclic loading conducted at largely different stress levels), is here adopted to calculate the shear stiffness and the damping an equivalent visco-elastic model. These results form the input of a finite differences one dimensional analysis implemented to study the propagation of shear waves into horizontally layered gravel deposits subjected to variable motion of their underlying bedrock. Analyses are performed in the frequency and time domains by varying the maximum amplitude of the base acceleration to evaluate the filtering and amplification effects of the deposit. The results of this study are parametrically reported in terms of free surface accelerations and amplification ratios, to show how artificial compaction affects the response of gravel.