Analysis of dynamical effects in the formation of compaction bands

Compaction Bands (CBs) cause significant permeability alterations in geomaterials, hence understanding their formation conditions appears of key importance to all engineering applications involving fluid extraction/injection from/into the ground. In this work, the dynamical effects induced by CB formation are analyzed by means of a Finite Element formulation at finite strains. The propagation of longitudinal elastic waves caused by the occurrence of a first CB is associated with a decrease of both total stress and of pore pressure. On the other hand, reflected waves at the interface with a softer material or a recently formed CB cause a local increase of effective stress. Depending upon the considered geometry, the aforementioned effective stress increase could bring about, at the locations where two reflected elastic waves collide, the formation of further CBs in a cascade fashion. The spatial distribution of the subsequently formed CBs is found to follow a regular geometric pattern.