*Article* **Monitoring Roadbed Stability in Permafrost Area of Qinghai–Tibet Railway by MT-InSAR Technology**

**Hui Liu 1,2, Songbo Huang 1,2, Chou Xie 3,4,\*, Bangsen Tian 3,4,\*, Mi Chen 1,2 and Zhanqiang Chang 1,2**

<sup>1</sup> College of Resources Environment and Tourism, Capital Normal University, Beijing 100048, China


<sup>4</sup> University of Chinese Academy of Sciences, Beijing 100049, China

**\*** Correspondence: xiechou@aircas.ac.cn (C.X.); tianbs@aircas.ac.cn (B.T.)

**Abstract:** Permafrost areas pose a threat to the safe operation of linear projects such as the Qinghai–Tibet railway due to the repeated alternating effects of frost heaving and thawing settlement of frozen soil in permafrost area. Time series InSAR technology can effectively obtain ground deformation information with an accuracy of up to millimeters. Therefore, it is of great significance to use time series InSAR technology to monitor the deformation of the permafrost section of the Qinghai–Tibet railway. This study uses multi-time InSAR (MT-InSAR) technology to monitor the deformation of the whole section of the Qinghai–Tibet railway, detect the uneven settlement of the railway roadbed in space, and detect the seasonal changes in the roadbed in the time domain. At the same time, the local deformation sections over the years are compared and discussed. The time series deformation monitoring results of the permafrost section Sentinel-1 data in 2020 show that the length of the railway roadbed from Tanggula station to Za'gya Zangbo station (TZ) section is approximately 620 m, the deformation of the east and west sides is uneven, and the average annual deformation difference is 60.68 mm/a. The impact of frozen soil in WangKun station to Budongquan station (WB) section on railway roadbed shows the distribution characteristics of high in the middle and low at both ends, and the maximum annual average settlement can reach −158.46 mm/a. This study shows that the deformation of permafrost varies with different ground layers. The impact of human activities on frozen soil deformation is less than that of topography and hydrothermal conditions. At the same time, the study determined that compared with other sections, the roadbed deformation of TZ and WB sections is more obvious.

**Keywords:** MT-InSAR; frozen soil deformation; Qinghai–Tibet corridor; roadbed deformation; climate response
