10x more data and 25x more updates gives dike safety engineer new insights in dike stability and sinkhole detection.
Sinkholes, a looming disaster
In the vicinity of the Dead Sea, a client operates salt ponds surrounded by a system of dikes. A progressive salt karst system is associated with the sudden occurrence of sinkholes. One of these unnoticed sinkholes created a large breach in a dike, draining the entire basin and causing $38M in damages. Thanks to InSAR Monitoring, the client now identifies sinkholes as early as possible and minimizes the probability of a collapse causing dike failure.
Traditional levelling method falls short
Previously, height change detection was done with Lidar + levelling campaigns every 6 months. With monuments installed every 500m and in high suspect zones every 200m.
The whole region sinks rapidly and unevenly. Sinkhole precursors present themselves as local round subsidence troughs, with diameters of 10s to 100s of meters and depths up to a few centimeters superposed on the uneven regional subsidence pattern. Cracks and slides are also widespread, which makes detection difficult so sinkholes in between stations are easily overlooked.
Much more data
With InSAR Monitoring, the dike safety manager suddenly has much more deformation data, over a larger area and monthly updates. Assessment of sinkhole formation can be done with much higher confidence than before.
High accuracy identification
With over 20,000 measurements per km2 on and around the dike, there are no gaps larger than a sinkhole diameter in between measurement points. The regional subsidence rates vary between 0 – 30 cm per year. To visualize precursors on the crest of the dike, time series are aggregated over cells 100m across, and 20m along the dike.
Understand failure modes
Since deformation measurements are constantly updated, growth patterns and acceleration over time of subsidence deviations become visible
By measuring regional geology and active faults, local sinkhole patterns can be isolated and understood better than ever.
Since the mining company started using Sinkhole Scanner, it has avoided sinkhole damage to their dikes altogether. In one case a likely precursor turned out to form a sinkhole near the foreshore about a year after identification. Sinkhole Scanner remains in use to observe the dikes. In case a high-risk precursor pattern shows up, in-situ geophysical assessment can be done. Then, where needed, preventive maintenance is done.
Deformation profile along the crest, evolving over 12 months. Sinkhole precursors are indicated of local accelerations of subsidence as well as strong local deviations from expected regional subsidence trends.
SkyGeo identified a precursor at the toe of the dike. This sinkhole formed within 12 months of identification. Based on the location and severity of the precursor, the dike safety manager decided not to reinforce the dike locally.
Geological cross section of the situation. Prior to the collapse of a sinkhole, the ground surface is subsiding above the developing cavities. This shows up as localized subsidence troughs with a diameter of 10-100m, which show up in the Sinkhole Scanner.
Sinkhole detection along the dike over a width of 400m. Green indicates relatively stable areas, red indicates areas with subsidence of over 250 mm/year.