Double Sliding Phenomena and Seismic Response of Earth Structures

Strong earthquake excitation usually induces large shear strains to earth structures resulting to the generation of low shear-strength surfaces, and subsequently, to sliding along these surfaces. The generation of permanent deformations is a phenomenon commonly examined through the well-known procedure of sliding block proposed by Newmark. Nevertheless, many types of earth structures include pre-existing potentially-sliding surfaces, like base liners on waste landfills or geosynthetic layers on soil embankments. These structures when subjected to dynamic loading may develop two sliding surfaces, a phenomenon that can be referred as double sliding. Finally, in some cases sliding phenomena are even desired in the seismic design, as they are considered to act like isolators that could alter the induced acceleration levels, protecting thus the earth structure. In the current study, a series of finite-element analyses of a typical landfill/embankment is conducted. Initially, the effect of base sliding on the dynamic response is evaluated, and since that response is proven to be considerable, a simple analytical model (based on the principles of the sliding block approach) is developed. The characteristics of double sliding are investigated and the main aspects related to this phenomenon are determined. Parameters such as the properties of interface, the angle of sliding plane, and the mass of sliding blocks are examined. The effect of the aforementioned parameters on the permanent deformations is evaluated. The results of this investigation present a clear indication of the complicated role of double sliding on the response of earth structures, and consequently, the necessity of incorporating properly this phenomenon on the seismic design of such structures.