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The structural safety of farm tower silos for whole-plant silage, and other cylindrical containers of wet materials that can become saturated in the lower part, necessitate a thorough knowledge of the liquid pressures that the silo wall has to withstand. The Canadian Farm Building Code has provisions for hydrostatic pressures in a farm tower silo, but the provisions are empirical and incomplete. This paper presents the results of a first attempt at using a finite element consolidation analysis of the fiber stresses and pore water pressures in the saturated zone of a body of silage. Each finite element analysis is preceded by a laminar analysis to determine the height of the saturated zone. The effects of the moisture content of the silage, its coefficient of permeability, the silo diameter and height and the bottom drain position were investigated in a parametric study. It was concluded that the excess hydrostatic pore water pressures were relatively small, and thus the normal hydrostatic pore water pressure is the most important component of liquid pressure at depth. An accurate determination of the height of the saturated zone, therefore, is essential. It could also be concluded that bottom drains should be placed near the wall. Finally, it was concluded that the finite element method can be a powerful research tool in solving this problem once the basic material properties are better known.
silage pressures at saturation in a tower silo
Lau, A. and J.C. Jofriet 1988. SILAGE PRESSURES AT SATURATION IN A TOWER SILO. Canadian Agricultural Engineering 30(1):83-92.
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