Understanding Historic Data Gives Asset Managers Unique Insights
A SkyGeo Case Study
The capability to analyse uplift data since 1992 gives asset managers unique insights.
Many tunnels connect the roads and waterways of the city of Antwerp, supporting high volumes of traffic. Building deep foundations and underground structures is challenging there due to the presence of a subsoil layer called the “Boom Clay”.
This clay is prone to slow, long-term swelling behavior that puts the stability of the infrastructure at risk. In order to evaluate the long-term effects of this swelling clay, the Belgian Department of Public Works tasked SkyGeo with assessing the exact actual displacement on three tunnels to prevent uncontrolled release of road segments at the entrance of the tunnel.
Aggregate time-series of a single segment between 1993 and 2018 at the entrance to the Kennedytunnel.
Unambiguous results
Three tunnels were investigated using InSAR data: Liefkenshoektunnel, Kennedytunnel and Beverentunnel.
We combined image stacks from multiple satellites and aggregated uplift per segment along the highway. The data showed a clear correlation between uplift rate and the distance to the tunnel entrances.
Local geotechnical inspection then confirmed the uplift is caused by swelling of the Boom Clay. The added insight is, that this uplift is occurring at a steady rate over decades and is still ongoing.
Historical data Obtaining tunnel displacement data since 1992 allowed the asset manager to extract the subtle long-term displacement patterns. Uplift of only 1 – 1.5 millimeter per year affects the tunnel entrances.
By measuring with a single, uniform method over decades, an accurate picture of stability trends emerges.
Aggregated data of 120,000 measurement points over 20 years shows distribution of uplift rates along the highway. This indicates stress accumulating slowly, getting worse towards tunnel entrances for the Kennedytunnel.
Visual interpretation of patterns: tunnel stability
In this project, plots of aggregated displacement rates versus the distance to the tunnel entrance proved useful and are configurable by the user.
The numerical results of our satellite analysis are accessible via our online platform for direct reference or for download.
Next steps: risk audits on tunnels
Using satellite radar interferometry, bridges and tunnels located anywhere on earth can be monitored for millimeter-level displacements with a revisit time of a few days. Displacements can be decomposed into horizontal and vertical displacement.
After interpretation and correlation with performance – or even incidents – the tunnels can be ranked based on displacement’s impact on functional health. The asset manager gets city-wide insights into the necessity for inspection and remediation.