Determination of characteristic height with Janssen formula of storage material and its variation law in silo with flat bottom

Because Janssen formula is derived under certain assumptions, there is a certain deviation between the theoretical value and the real value of the storage material pressure in silo. The characteristic height of storage material in silo is an important parameter in Janssen formula, which affects the accuracy of calculation. Therefore, the experimental study on the characteristic height of storage material in silo was carried out in this study. The vertical pressure at the bottom of the storage material pile and the total friction force on the silo wall were measured by using the comprehensive test device for measuring the storage material pressure in silo, when wheat was used as storage material. And the value of the characteristic height was calculated according to the relationship between the vertical pressure at the bottom of the storage material pile and the characteristic height and the relationship between the total friction force on the wall and the characteristic height. The relationship between the characteristic height of the whole storage material pile and the filling height was studied. The relationship between the characteristic height in the storage material pile and the filling height, and the distribution law of the characteristic height in the storage material pile were discussed. The conclusions are as follows: 1) The test value of characteristic height of storage material pile in silo is greater than theoretical value of Janssen formula. 2) The measured value of vertical pressure at the bottom of the storage pile is greater than theoretical value of Janssen formula, and the measured value of total friction force on the silo wall is less than theoretical value of Janssen formula. When the ratio of height to diameter H/D less than 1.5, the measured value of vertical pressure at the bottom of the storage pile and the total friction force on the silo wall are close to theoretical value of Janssen formula, and the relative difference (the absolute difference between the measured value and the theoretical value divided by the measured value) is within 6%. When the ratio of height to diameter was H/D greater than or equal to 1.5, the relative difference between the tested value and theoretical value of Janssen formula is more than 6%. 3) For the characteristic height λ of the entire storage pile in silo (that is, the solid cylinder with the largest radius), when the ratio of height to diameter H/D less than 0.9, it gradually decreases as the filling height of the storage increases; When H/D greater than or equal to 0.9, the characteristic height λ remains nearly constant, and this stage is the stable stage of the characteristic height. 4) For the characteristic height of solid cylinder with different radiuses in storage material pile, when the filling height less than 0.44 m, they all decrease with the increase of filling height of storage material; when the filling height greater than or equal to 0.44 m, with the increase of filling height of storage material, the value of the cylinder with the largest diameter (the whole storage material pile) remains almost unchanged, and the values of the remaining cylinders decrease nonlinearly at different rates and tend to be equal. 5) The characteristic height of the solid cylinder with different radiuses in the storage material pile basically decrease with the increase of the cylinder radius. This study provides a method for the determination of the characteristic height of storage material in Janssen's formulas, which enables Janssen's formulas to be used for the accurate calculation of the pressure of storage material in silo.