Over the past centuary many experiments on pressures in silos have been conducted, many of these have led to huge amounts of information being gathered. As a result of this, the researchers were faced with the challenge of choosing what data should be analysed and reported. For the most part, only the highest pressure recorded at any location was reported. Unfortunately the worst event for most silos is not one of high pressure, but the condition of greatest asymmetry of pressures. As part of thesis we are going to look more carefully at these pressures.

Edinburgh Laboratory Pilot Scale Tests

When trying to understand the pressures that are present within a silo, it is very helpful to carry out a test on an experimental scale silo. We had the opportunity to carry out one of these tests with Dr. Zhong and found this to be a most rewarding experience. The test material used for this experiment was rice, however many tests have been carried out using solids such as sand and barley. The experimental silo set up at the university originally had a rough wall interior, but before our test the silo had been stripped and the interal walls are now smooth. The picture on the left shows the experimental silo along with the storage silo for the rice. Pressure gauges are placed at 8 levels, 4 gauges at each level, within the silo. These record the pressures within the silo during the test. The data can then be transfered to excel for analysis.

The test itself if very straight forward. The filling process starts by preparing the top of the silo with a an inverted cone to ensure the symmetric filling. This generally takes approximately 25 minutes. The photographs on the left and bottom left show the rice being poured into the silo. Also in this picture it is possible to see the pressure cells on the silo walls. These ae the grey squares which can be seen at different levels throughout.

Once the silo is completely filled the material is allowed to settle. This is done to recreate real life conditions. For this experiment, the material is left for 25 minutes. The picture below shows the settled solid.

After this time the shoot at the bottom of the silo is opened and the material is allowed to discharge. It discharges at a rate of approximately 100mm per minute and takes a total of 32 minutes and 45 seconds to completely empty. 

Results and Analysis

Most of the data recorded from this experiment will take many days to analysis and interpret. However there are some initial observations that can be noted. Firstly the flow pattern of the material during discharge. To the right is a line diagram showing the changes in the material. Initally the rice is pyramid shape, but over time it becomes flat before finally taking an inverted cone shape. The material flatens out at a height of 3.2m from the bottom after approximately 6 minutes. After 6.5 minutes the flow is starting to form an inverted cone and this is fully formed after 9 minutes and at a height of 3m from the bottom of the silo. The two pictures below show the rice as it is forming an inverted cone shape during discharge.

It is also possible to calculate how much solid remains in the silo after discharge is completed and the angle at which it remains. 


On the right there is picture which shows the location of the pressure cell level from which the following results were gathered.

The graph below shows the pressures recorded at all pressure cells on one level within the silo. It is not a match to the experiment that we undertook, however it does give an idea of what is expected from the results of the recorded silo pressure measurements.

Back to Top