Digitial Inspection of Retaining Structures on Large Scale

Tunnels, bridges and retaining walls are the backbone of Austria’s infrastructure in the Alpine area. While increased traffic loads, extreme weather events stress the aging infrastructure, their safe operation is of great social-economic importance.  An early detection of structural deficiencies is crucial to minimize costs for rehabilitation measures and to guarantee public safety.

Due to the large number of more than 100 000 retaining structures along public road and railways, the maintenance poses a great challenge to structural operators: communities, counties, the highway agency (ASFiNAG) and federal railways (ÖBB). Ever since the tragic failure of a cantilever wall on the Brenner highway in 2012, novel, objective methods for safety assessment are in high demand. Up to date, traditional surveying methods constitute the state-of-the art in monitoring structural performance of retaining walls in an objective way. However, this method is time costly and requires closure of driving lanes. Therefore, it is unfeasible to monitor a large number of structures with the current state of the art methodology.

The IGMS provides a service for tilt monitoring of retaining walls with mobile mapping. We cooperate with other industry partners to perform data acquisition while travelling with up to 100 km/h. In such way, we can guarantee route availability and do not constrain the free-flowing traffic. Along with data acquisition, we process the big data in a highly automatic manner, so that costs reduce to a minimum when a large number of objects are monitored in one go.

Operators receive a digital representation of the structure, including geo-referenced point clouds with tenths of millions points (click here to access a dataset in a 3D viewer) and images for inspection tasks. More importantly, the processed point cloud data indicates whether deformations or tilt changes occurred between the times of measurements. Lateral displacements larger than 3.5 mm can be identified with 95% confidence. The IGMS method contributes to a fast preselection of malfunctioning structures. In a second step, operators can then initiate more detailed inspection and investigations.

Mobile Mapping is used for map generation and infrastructure inventory primarily. The IGMS approach is unique and there are no comparable studies in terms of deformation analysis with mobile mapping data. However, large scale inspection tasks will have a significant impact in the future, as onerous environmental influences will affect pavement, tunnels, bridges and retaining walls all around the world. Currently, the IGMS service is in operation in Styria and Lower Austria, monitoring 13 retaining walls of different types, shapes and ages. The acceptance of the IGMS service is growing and has the potential to become appied across Austria and beyond its borders.