Systematic and random features of measured pressures on full-scale silo walls

It is well known that the pressures exerted by bulk solids on silo walls vary between filling and discharge. It is less frequently observed that these pressures vary all over the silo wall both in space and in time during discharge. The pressure at any point may be understood as having two components: one systematic and the other random. The systematic component relates to the stored solid, the silo geometry, geometric imperfections in the silo wall, the eccentricity of filling and discharge, and the flow pattern. It can be attributed to causal phenomena. The random component leads to pressure variations with time at any point on the wall which are not related to each other and which are normally ignored in design. In this paper, careful measurements of pressures on the walls of a prototype silo subject to both concentric and eccentric flow are studied to extract the systematic and random components of pressure. The form of the systematic pressure distribution and the magnitudes of the random variations are related to Janssen pressures. The results lead to pressure distributions which can be used as a more rigorous basis for future silo design codes.