Pre- and Postcollapse Ground Deformation Revealed by SAR Interferometry: A Case Study of Foshan (China)‎ Ground Collapse

Abstract EN

On the evening of 7 February 2018, a deadly collapse of a metro tunnel under construction in the Southern China city of Foshan caused 11 deaths, 8 injuries, and 1 missing person.

For disaster prevention and mitigation, the spatiotemporal ground deformations before and after the collapse event were derived from 55 Sentinel-1A synthetic aperture radar (SAR) images spanning from March 2017 to January 2019.

The results showed that prominent ground subsidence in the shape of a funnel with a maximum rate of 42 mm/year was observed in the vicinity of the collapse area before the accident.

After the accident, the area and magnitude of subsidence decreased compared with precollapse subsidence.

This decrease is related to the progress of tunnel excavation and groundwater changes.

In the temporal domain, continuous subsidence was observed over a year before and after the accident, and accelerated subsidence appeared one month before the collapse accident.

Soft soil consolidation and tunnel-induced soil losses were the main reasons for the subsidence over the study area.

The leakage of groundwater accounted for the collapse event.

The leaked groundwater eroded the soil, resulting in the formation of an arched hole.

The connection between the arched hole and the tunnel reduced the bearing capacity of the soil layer above the arched hole, triggering the collapse event.

The findings provide scientific evidence for future collapse monitoring and early warning due to tunnel excavation.