The concept of measuring the friction between a bulk solid and a wall material is very simple. However, experience together with previous wall friction measurement research suggest that variables that influence wall friction values are difficult to quantify and, so far, are proving unreliable to predict with any degree of confidence. In this paper some preliminary test results are presented for different bulk solids on different wall plates where variables examined include particle size distribution, moisture content, test cell size and shear speed. The outcomes presented confirm the authors' belief that with the present state of knowledge about wall friction it is dangerous to estimate appropriate wall friction values to use in design without undertaking measurements designed to duplicate field conditions as closely as possible. The results also emphasize the necessity for further in-depth research on this challenging topic!
Halford, W., Lawler, C., Grima, A. P. & Arnold, P. C. (2013). Some influences on wall friction measurements - a preliminary investigation. 11th International Congress on Bulk Materials Storage, Handling and Transportation (pp. 1-10). Australia: University of Newcastle.