Problem statement
Silos consist of massive concrete cylinders, often assembled in silo complexes, which store large quantities of material – in this case grain. The height is 45-55 m and the diameter 7-9 m. The thickness of the walls varies from about 350 mm at the bottom down to about 200 mm at the top. Traditional inspection of these types of structures requires scaffolding or rope climbing and involves both safety risks and downtime. The project aimed to carry out a detailed remote inspection of four silos using drones and photogrammetry to identify cracking, delamination and other damage, and to assess the accuracy and cost-effectiveness of the method.
Results
The results from each silo can be summarized as follows:
- First silo: Limited cracks, mainly on the northern façade. Crack width <1 mm. Generally good condition.
- Second silo: Vertical cracks with lengths of several meters and crack widths up to 4.8 mm. The damage was concentrated on the south-eastern façade. Recommended for further investigation and repair.
- Third silo: combination of horizontal and vertical cracks, with lengths up to 24 m and crack widths up to 3 mm. The damage is extensive and may indicate ongoing movements in the structure.
- Fourth silo: Vertical cracks along large parts of the perimeter, lengths up to 14,5 m and crack widths between 2-3,5 mm. Considered to be in need of repair in the near future.
All silos were documented in high-resolution 3D models with millimeter precision, confirming the reliability of the method. The remote inspection provided a comprehensive picture without having to interrupt operations.
Solution
The inspection program was implemented in stages:
- Data collection: Drone flights around each silo at a distance of 4-6 m from the façade, about 2000-4000 images per silo.
- 3D modeling: Processing of imagery in Agisoft Metashape to create photorealistic 3D models.
- Damage inventory: Cracks and damages were marked and measured in the model (length, width, orientation). This is done with a proprietary algorithm.
- Analysis: Assessment of damage severity per silo and comparison between the four sites.
The methodology enabled a safe, cost-effective and time-saving damage inventory and demonstrated the potential of remote inspection as a future standard method for structures that are difficult to access without scaffolding or climbing personnel.
Equipment
- DJI Matrice 300 RTK with H20 Triple-Sensor (zoom, wide angle, laser rangefinder)
- DJI Mavic 2 Pro with 20 MP Hasselblad camera
- Agisoft Metashape (photogrammetry and 3D modeling)
- Software for image analysis and fracture measurement
Standards
- EN 1990: Eurocodes – Basic rules
- EN 1991-1-1: Eurocode 1 – Loads on structures
- EN 1992-1-1: Eurocode 2 – Concrete structures
- ISO 16311 series – Condition assessment of concrete structures
- Guidelines for drone-based photogrammetry and remote sensing
