筒仓静态储粮的边界压力及仓壁摩擦力试验研究

    Experimental study on boundary pressure and wall friction under static grain storage in silo

    • 摘要: 为了研究筒仓散装粮堆的边界压力和仓壁摩擦力的分布规律,研制了模型筒仓试验装置,基于仓体的微缝分离设计,实现各分离仓体受力的独立测量。以小麦为例,通过实测,发现不同装粮高度下,粮堆底部压力沿径向呈现不均匀分布特征,其不均匀分布程度随装粮高度逐渐增加;当装粮高度大于筒仓直径后,仓壁侧压力开始逐渐小于Janssen公式计算结果;而仓壁摩擦力在整个粮堆深度范围内均小于Janssen公式计算结果。试验表明,仓壁实测摩擦力与侧压力之比小于小麦与仓壁的摩擦系数,且随粮堆深度的增加不断变化,表明静态储粮下储料与仓壁边界之间尚未达到极限平衡状态;侧压力系数接近主动态,且小于主动土压力系数。研究结果可为散体物料压力理论提供参考。

       

      Abstract: The authors participated in the design of the silo model test facility, which can be used to measure the storage force of the grain heap, such as the bottom pressure, the side wall pressure and the friction force of the bulk grain heap. The self-designed silo model was 480 mm in diameter and 2 102 mm high. The silo wall, constructed of organic glass, was composed of 3 separate parts. There is a 1-mm thick gap between each part of the walls to prevent the outflow of grain. The 3 parts of the wall were named Top Wall (l 000 mm high, fixed on the steel frame), Middle Wall (100 mm high) and Upper Wall (1 000 mm high). The silo bottom, which can be raised and lowered, was divided into 4 parts (1 concentric circle and 3 concentric rings). The Top Wall, the Middle Wall and each parts of silo bottom were supported on three force sensors to measure the wall friction as well as the vertical pressure on the floor. Three earth pressure cells were embedded in the middle line of the Middle Wall to measure the wall lateral pressure. Two experimental schemes were carried out. No.1 scheme is that: Fill the silo model with wheat to a height of 100 mm at each time until the height of the wheat reached 1 000 mm. Record the data obtained from each of the force sensors supported under each part of the silo bottom as well as the force sensors supported under the Upper Wall of each grain height. This scheme is designed to measure the radial distribution of bottom pressure under different grain heights. The No.2 scheme is that: Fill the silo model with wheat to a height of 1 000 mm and then raise the flat bottom to the lower edge of the Middle Wall. Drop the bottom by 50 mm at each time. Meanwhile, record the data obtained from the earth pressure cells embedded in the Middle Wall and the data obtained from the force sensors supported under the Middle Wall at difficult depths of wheat. The distribution of the storage force at the boundary was measured in the experiment. The rationality of the model test data is verified by compared with the classic theory. Combined with the experimental data, it is found that the bottom pressure of silo grain heap presents the uneven distribution characteristics of “large in middle and small on sides”, and the uneven distribution degree is gradually obvious with the increase of grain loading height. The lateral pressure of silo wall is slightly larger than that of Janssen formula when the depth is more than 0.5 m. The friction of the side wall is larger than that of Janssen formula along the whole depth of wheat. And the value of the friction coefficient between the grain and the silo wall is smaller than external friction coefficient measured by directly sheared tests along the whole depth of wheat. It proved that the value of wall friction calculated by Janssen formula is larger than what it really is and the state between the wheat and silo wall haven’t reach the limit equilibrium. The lateral pressure coefficient measured by experiment is closed to Rankine's main dynamic and is less than active earth pressure coefficient. The experiment results show that the model silo test device has good repeatability, and it can provide a simple and feasible technical support for the theory of storage pressure.

       

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