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Potash Miners Get Ahead of Their Geotechnical Risk

 Potash Miner Gets Ahead of Their Geotechnical Risk

A SkyGeo Case Study

10 times more data and 25 times more updates gives dike safety engineer new insights into dike stability and sinkhole detection to get ahead of geotechnical risk.

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.

Sinkhole detection along the dike over a width of 400m. Green indicates relatively stable areas, red indicates areas with displacement of over 250 mm/year.

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 displacement troughs, with diameters of 10s to 100s of meters and depths up to a few centimeters superposed on the uneven regional displacement pattern.

Cracks and slides are also widespread, which makes detection difficult so sinkholes in between stations are easily overlooked.

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 displacement troughs with a diameter of 10-100m, which show up in the Sinkhole Scanner.

Much more data

With InSAR Monitoring, the dike safety manager suddenly has much more displacement data, over a larger area and monthly updates.

Assessment of sinkhole formation can be done with much higher confidence than before.

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.

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 displacement 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.

Since displacement measurements are constantly updated, growth patterns and acceleration over time of displacement deviations become visible.

Subsidence profile along the crest, evolving over 12 months. Sinkhole precursors are indicated of local accelerations of displacement as well as strong local deviations from expected regional displacement trends.

Regional context

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.