Buoyancy Reduction Coefficients for Underground Silos in Sand and Clay

To elucidate the anti-floating problem of underground cylindrical grain silos, the water buoyancy effect and groundwater buoyancy reduction were evaluated for underground cylindrical silos in sand and clay. For testing, three silos of different diameters were installed in testing tanks with sand or clay, which were subsequently saturated with water. The buoyancy models were first verified using silos submerged in pure water. Using these models in the underground silo tests, factors favorable to anti-floating design, such as the effects of friction between the silo wall and soil and the negative pressure at the bottom of the granary, were considered. In dense well-graded saturated coarse sand, the comprehensive buoyancy reduction coefficient was in a range of 0.40-0.45 and the buoyancy reduction coefficient was 0.95. In saturated clay, the comprehensive buoyancy reduction coefficient was in a range of 0.50-0.53 and the buoyancy reduction coefficient was 0.79. These results demonstrate the requirement for considering the buoyancy reduction of different soils for the anti-floating design of underground silos.