Vertical stresses within granular materials in silos

Abstract

Cylindrical silos are used to store granular materials, such as grain, sugar, flour and pharmaceutical items. They undergo different types of loadings during their operational lifetime. There are several techniques used by the design engineers to evaluate the vertical stresses within these silos. This paper summarises the numerical analysis of vertical normal stresses within the granular material stored in the silos, and validation of simulations through model tests in the laboratory. Analytical methods were developed in the past to quantify the vertical stresses in silos. Due to arching, the vertical stresses within the granular material contained within the silos are significantly less than that expected from the overburden weight. The dependence of arching on material properties and the geometry of the silo is studied through several laboratory trials. Sand, placed at 30% relative density, was used in the laboratory model tests. Numerical simulations were carried out using FLAC, a commercially available finite difference software, and the vertical stress variation with depth was compared with test results, then the implications were discussed. Although an aspect ratio of six (height/diameter) was used in the laboratory study, extrapolation for higher aspect ratios is discussed using the FLAC simulations.