Abstract: In the evening of February 7,2018,a deadly ground collapse of a metro tunnel under construction occurred in Foshan,Guangdong Province,China. The accident caused 11 deaths,8 injuries,1 missing person,and direct economic loss of more than 53 million yuan. In order to understand the mechanism of this collapse,it is necessary to examine the deformation characteristics of the ground before and after the event. Compared with the ground-based observation techniques,the synthetic aperture radar (SAR) interferometry technique has demonstrated its potential for monitoring the collapse sinkholes due to the advantages of covering large areas,mapping of high-density spatial and historical ground deformation. Therefore,using the 56 Sentinel-1A spanning from 2017-03 to 2019-01,we obtain the spatial-temporal deformation information of the study area by using Small Baseline Subset SAR Interferometry(SBAS-InSAR) techniques. It is found that continuous ground subsidence occurred in the collapse area and its adjacent areas,and the deformation rate reached more than 30·a^-1,while areas far away from the sinkhole was mostly stable. In order to further verify the reliability of the deformation and analyze the connection between the land subsidence and the collapse,we carry out a field survey and a detailed analysis of the deformation characteristics near the collapse area,and find uneven ground subsidence in the sinkhole and its adjacent areas. The maximum subsidence at the collapse site was nearly 37 mm over the past year of collapse accident. What's more,accelerated subsidence appeared one month before the collapse accident,which was related to the metro construction disturbance. Meanwhile,based on the local geological data and accident investigation report,it is considered that the collapse accident was caused by the water supply pipeline damage and the poor engineering geological environment at the accident site. In the end,we reasonably deduce the mechanism of collapse formation: due to the uneven settlement of the mucky soil under the water supply pipeline,the distribution of bearing capacity of mucky soil to the water supply pipeline was also uneven. The water leakage in the pipeline saturated the stratum,weakened the mechanical properties of the mucky soil layer,and the Metro construction disturbance increased the deformation of the saturated soil layer and pipeline leakage,and the water penetrated down to the fine sand layer below the shield machine tail. With the increase of water content,the bearing capacity of the fine sand layer was reduced,which led to the subsidence of the shield machine tail and the cracks in the pipe segments that had not reached the freezing point,and the shield machine tail was permeable with water and sand. But the builders failed to plug the leak,and the flooding became more severe. The sand layer under the shield machine quickly drained away,resulting in the downward displacement and deformation of the shield machine. After the tunnel structure was damaged,a huge amount of sediment suddenly poured into the tunnel,and caused a rapid impact of air waves in the limited space of the tunnel,which eventually led to the tunnel and the ground collapse. The results can provide theoretical basis for the collapse monitoring and early warning of shield tunneling in the future.