Why have continuum theories previously failed to describe sandpile formation?

Granular piling may or may not induce a counterintuitive phenomenon of pressure dip at the center of a pile base. Understanding the behavior is a long-standing challenge in granular dynamics modeling. Here we show that the experimental observations of dip or nondip piles can be satisfactorily reproduced by the classic elastoplastic models. Our results demonstrate that (i) dynamic history is a critical factor in the successful description of a piling process and (ii) the dip phenomena are complicated, involving numerous variables associated not only with piling operation but also material properties. Our findings can explain why previous attempts failed to describe piling processes and may open up a new direction to describe granular materials in nature and many industrial processes.