Jenike & Johanson project engineer Aleef Rahman explains how silo failures can be prevented through an understanding of material flow, operational scenarios and routine maintenance.
Across Australia, several notable silo failures in recent times highlight the ongoing risks that arise when bulk loads and material behaviour are underestimated.
In October 2024, two large grain silos facility collapsed, spilling thousands of tonnes of wheat and prompting emergency response and regulatory investigations. Other incidents include a five-metre transportable farm silo overturning in Goondiwindi, Queensland (2020), a man buried in a silo in Arcturus, Central Queensland (2024), and a worker hospitalised in Victoria (2021) after being trapped beneath two tonnes of grain released from a small silo following a blockage and unsafe operating practices.
These events, ranging from structural collapses to internal grain surges, highlight that silo failures are not isolated cases but part of a broader pattern of hazards across Australia’s bulk handling sector.
Such failures often result from an inadequate consideration of material-induced loads that silo/bins are subjected to under actual operating conditions. These incidents highlight the importance of understanding bin loads, including wall pressures, flow-induced stresses, and asymmetric loading, as well as identifying material flow patterns within silos. Phenomena such as powder flooding or rathole collapse can occur when flow behaviour is not properly assessed, creating serious operational risks.
While the Victoria grain surge incident was not a structural failure, it illustrates how inadequate flow analysis can lead to uncontrolled discharge. Proper evaluation of flow behaviour at the design stage supports safer operating procedures and reduces risk to personnel.
Silos are dynamic systems where material properties change, flow patterns evolve, and operating conditions vary throughout a structure’s service life, which should be considered in the design to ensure structural strength and ensure right safety measures/protocol are developed to follow during operating conditions.
The following sections present failure scenarios, and common assumptions made across three stages: Design, construction and operation.
Design stage
Assuming material properties remain constant over time, or that changes in wall friction (such as polishing of the liner) do not alter flow patterns, is a common mistake that can lead to unexpected bin loads and structural failure.
Prior to designing storage silos for handling bulk materials, it is essential to understand their material flow properties. These properties form the basis of design when determining silo geometry, depending on the selected flow regime.
Key parameters include particle size distribution, bulk density, cohesive strength, angle of repose, and drawdown angle.
It is also important to recognise that these properties can evolve over time due to changes in composition, moisture content, particle size, and other factors. Such variations not only influence the flow pattern during discharge but also directly affect wall pressures and internal load distributions.
Once the material is well characterised, both the expected flow behaviour and associated bin loads can be assessed, providing a more reliable basis for safe and robust silo design.
There are three distinct flow patterns that are likely to be developed in your silo, as shown in the figure below.
Designers sometimes assume that material will flow perfectly, but in reality, ratholes, eccentric discharge, and uneven fill can produce asymmetrical loads that exceed design assumptions.
Silo failures often happen when bin wall loads are underestimated, especially during eccentric discharge.
In practice, flow is rarely perfectly symmetric. Ratholes, partial emptying, or discharge near one side of the walls can produce uneven pressures that can exceed what the silo was designed for. If the resulting flow channel intersects the silo wall, non-uniform pressures will develop around the circumference of the silo, leading to circumferential bending and axial compression on the cylinder shell.
Therefore, designs should not only consider water-level and uneven fill during filling and discharge, but also asymmetric bin loads resulting from off-centre flow.
The flow pattern inside a silo/bin is also influenced by the feeders. A mass flow bin may fail to operate under the mass flow condition if the feeder is improperly designed, allowing flow channels to develop, and causing loads to concentrate in certain areas.
Designs need to account for these situations to keep silos safe and structurally sound.
Designers sometimes assume that environmental conditions won’t affect the silo, but in reality, humidity changes or temperature fluctuations can cause changes in material properties, leading to flow issues such as caking and bridging, or silo wall deformations (periodic contractive behaviour), leading to increased wall pressures that were not accounted for in the design.
It is important to recognise that these effects can occur gradually over time or rapidly under certain conditions, such as wet weather or seasonal temperature fluctuations. Ignoring temperature and moisture influences during design can compromise silo integrity. Proper assessment of these factors is essential to ensure safe and reliable silo performance.
Construction stage
Designers sometimes assume silos will be built to exact specifications, but even small deviations or poor workmanship can compromise structural performance and increase the risk of failure.
Small alterations during construction, such as incorrect panel assembly, insufficient welding, or unapproved modifications, can compromise the structural integrity of the silo. These deviations can result in uneven load distribution, reduced resistance to wall pressures, and increased risk of local buckling or collapse.
Ensuring that the silo is built exactly to the approved design and maintaining high-quality workmanship throughout construction is essential. Careful oversight, adherence to specifications, and proper inspection during assembly help prevent structural weaknesses that could otherwise lead to operational failures.
Operation stage
Operators often assume silos will function safely under any conditions, but improper use or delayed maintenance can create loads and stresses not accounted for in the design, leading to failure.
Overfilling, rapid discharge, ignoring blockages, or bypassing safety procedures can generate unexpected loads and stresses. Coupled with delayed or inadequate maintenance, these factors can weaken structural components, increasing the risk of wall buckling, panel failure, or collapse.
Clear operational procedures and proper personnel training are essential. Routine inspection and maintenance help identify wear, damage, or flow issues early. Monitoring material flow and adhering to engineer-approved guidelines ensures that silos operate within their design limits, protecting both personnel and assets while maintaining safe, reliable performance.
Summary
Silo failures in Australia often arise from underestimated loads, changing material properties, temperature and moisture fluctuations, poor workmanship, deviations from approved designs, and improper operation or maintenance. Preventing these failures requires an understanding of material flow, careful consideration of operational scenarios, adherence to design specifications, and routine inspection and maintenance. Applying these principles helps ensure silos operate safely and reliably, protecting personnel and assets, and maintaining the continuity of bulk handling processes.