Abstract
This work explores, for the first time, the application of a Terrestrial Laser Scanner (TLS) and a comparison of point clouds in the 4D monitoring of active sinkholes. The approach is tested in three highly-active sinkholes related to the dissolution of salt-bearing evaporites overlain by unconsolidated alluvium. The sinkholes are located in urbanized areas and have caused severe damage to critical infrastructure (flood-control dike, a major highway). The 3D displacement models derived from the comparison of point clouds with exceptionally high spatial resolution allow complex spatial and temporal subsidence patterns within one of the sinkholes to be resolved. Detected changes in the subsidence activity (e.g., sinkhole expansion, translation of the maximum subsidence zone, development of incipient secondary collapses) are related to potential controlling factors such as floods, water table changes or remedial measures. In contrast, with detailed mapping and high-precision leveling, the displacement models, covering a relatively short time span of around 6 months, do not capture the subtle subsidence (<0.6–1 cm) that affects the marginal zones of the sinkholes, precluding precise mapping of the edges of the subsidence areas. However, the performance of TLS can be adversely affected by some methodological limitations and local conditions: (1) limited accuracy in large investigation areas that require the acquisition of a high number of scans, increasing the registration error; (2) surface changes unrelated to sinkhole activity (e.g., vegetation, loose material); (3) traffic-related vibrations and wind blast that affect the stability of the scanner.
Highlights
Bibliometric data show that investigations dealing with sinkholes have increased dramatically over the last two decades, concordant with a rapid rise in sinkhole-related damage on a global scale
The comparison of 3D point clouds allowed the accurate measurement of the deformation with a high spatial resolution in the portion of the sinkhole affected by greater subsidence
Terrestrial Laser Scanner (TLS) surveying and point cloud comparison is a suitable technique for the 4D monitoring of specific active sinkholes characterized by rapid subsidence
Summary
Bibliometric data show that investigations dealing with sinkholes have increased dramatically over the last two decades, concordant with a rapid rise in sinkhole-related damage on a global scale. Evidence suggests there is need to explore and develop approaches aimed at monitoring sinkhole-related subsidence, which tends to be very localised and may have variable behaviour, ranging from long-sustained gradual settlement to instantaneous catastrophic collapse. The latter may result in the loss of human life. Subsidence monitoring in sinkhole-prone areas may allow the implementation of early warning systems through detection, with sufficient anticipation of precursory slow subsidence preceding sudden collapse as well as other signs of instability, like fissures or scarplets, indicative of the development of an incipient sinkhole This latter, challenging task has been one of the main objectives underlying a significant proportion of the sinkhole monitoring investigations carried out over the last decade, frequently using recently developed technology
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