Land subsidence investigation of the steeply dipping coal seams in the Urumqi coalfield, China, using MT-InSAR technology based on the deformation model analysis

The Urumqi coalfield is representative of the steeply dipping coal seams found in China. Geological hazards caused by mining such coal seams are mainly collapse pits and ground fissures, which are characterized by rapid-speed, non-linear, and long-lasting land subsidence. The feasibility of using MT-InSAR technology to monitor surface deformation in mining areas has been demonstrated in previous studies. However, the choice of deformation model needs to be considered when monitoring inclined ore-body with complex subsidence patterns. In this study, we firstly analyzed the applicability of the deformation models based on the SBAS-InSAR technology for monitoring mining-induced subsidence. Two-dimensional deformations were then retrieved from Sentinel-1 ascending and descending orbital images between 2019 and 2021 based on the selected model. Cross-validation between two InSAR-based results and external validation between leveling and MT-InSAR measurements were used to assess deformation accuracy. Opposite measurements from ascending and descending orbits indicated that there was significant horizontal displacement in the study area. Wavelet coherency analysis revealed that extreme weather conditions had an impact on the surface deformation in the reconstructed Liudaowan old goaf. Land subsidence on the northwest side of the Weihuliang mine was mitigated by landfill and compaction in 2020. It is noteworthy that landslides were likely to occur on unprotected slopes, as evidenced by subsidence funnels and surrounding bead-shaped collapse pits distributed in the landfill slopes. The analysis of the B1 + 2 and B3 + 6 coal seams in the Wudong mine shows that the horizontal displacement was mainly influenced by strong in-situ stress. This study provides significant references for further studying the subsidence mechanism of the steeply dipping coal seams, preventing geological disasters and conducting ecological restoration in the Urumqi coalfield.