Performance of earth pressure cell as grain pressure transducer in a model silo
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Institute of Agrophysics, Polish Academy of Sciences, Doświadczalna 4, 20-290 Lublin 27, Poland
Biosystems and Agricultural Engineering Department, University of Kentucky, Lexington, KY, USA
Int. Agrophys. 2007, 21(1): 73–79
Numerous methods have been proposed for determining the pressure exerted by grain at discrete locations in a storage structure, but few satisfactory solutions have been found. Earth pressure cells were tested as potential measurement devices for grain bins. Earth pressure cells are commercial transducers designed for geotechnical applications. Calibration of the earth pressure cell was performed in a pressurized chamber filled with wheat under normal load as well as shear load. The cell was tested in a model grain silo 1.83 m in diameter d with a height hc of 5.75 m. Vertical floor pressures and horizontal wall pressures were measured at different points in the model bin. The vertical floor pressure pvi was measured at two different radial locations and horizontal wall pressure ph was measured at four different wall heights. The vertical floor pressure obtained using the earth pressure cell was in good agreement with the mean floor pressure pv calculated using load cells that supported the entire floor or the bin. Considerable variation in the vertical floor pressure along the silo floor radius was observed. The variation of the lateral-to-vertical pressure ratio, K, was monitored during each fill-unload cycle of the model silo. In the case of the maximum h/d ratio of 2, K increased during filling and stabilized after reaching a grain h/d ratio of 1.3. At the onset of discharge, the pressure ratio immediately increased up to value of approximately 0.7, and remained stable during unloading down to a h/d ratio of approximately 0.65 when K decreased rapidly.