Study on stress dips in granite residual soil based on experiments and DEM

The stress dip, a local minimum in the vertical stress distribution beneath granular piles, has captured the interest of many researchers. Studying stress dips in granite residual soil is of critical importance due to its relevance to engineering projects, soil mechanics, and particle behaviors. The purpose of this study is to confirm the existence of the stress dip in granite residual soil and explore its evolution during accumulation. In this work, granite residual soil conical piles were formed by the localized source piling method in experiments. During the experiment, Teflon film was placed below the piles to hinder the formation of stress dips, while the vertical stress distribution beneath each pile at varying heights was measured to monitor the evolution of stress dips. Besides, DEM simulations were employed to analyze the formation and evolution mechanism of the stress dips. The experimental and simulation results showed that stress dips can be formed in granite residual soil piles, occurring both in the center and locally. Stress dips evolve gradually through accumulation rather than being intrinsic properties of the piles. From a spatial perspective, no clear pattern is observed in the location of the stress dips. Quantitatively, as pile size increases, stress dips become more prevalent throughout the entire scope, although individual dips may dissipate. The normalized analysis of the central stress dip suggests that the normalized stress distribution pattern of the central stress dip is independent of pile size. The formation and evolution of stress dips are influenced by the force chain network, which consists of arch and ring force chains that are promoted by the supporting effect of the base plate and the particle squeezing effect.