## 5 Conclusion  
A case study based on SBAS-InSAR technology and TerraSAR X imaginary is presented to investigate the long-term deformation for highways built on soft clay subgrade after the road construction over a 13-month period from October 2014 to November 2015. A comparative study of the linear model and seasonal model were conducted. The deformation parameters and corresponding time series deformation were estimated for both models on the two highways, respectively.  
After our comparative analysis, similar spatial distribution of subsidence and temporal seasonal fluctuation can be found in both models. The main difference between the two groups of measurements generated by the two models is that the maximum subsidence occurred in August 2015 through the linear model, whereas, in June 2015, through the seasonal model. According to the seasonal model measurements, the most obvious subsidence was up to \(-65\) mm, whereas the subsidence recovery effect in November 2015, with magnitude, accumulated to 23 mm. The reasons suggested for this seasonal effect are related to the hydrogeological conditions and external climatic factors, including temperature and precipitation. We also conducted concrete deformation monitoring and analysis over typical ground features.  
To assess the accuracy for the two groups of case study measurements, residual phase and ground leveling deformation are utilized to evaluate the modeling and external accuracy, respectively. Compared to the linear model, the RMS of residual phase for the seasonal model was improved with 14% and 20% for Lungui Highway and G1501 Highway, respectively. The external accuracy evaluated by leveling measurements was improved from \(\pm 4\) mm to \(\pm 3\) mm for Lungui Highway. Consequently, seasonal model is more highly recommended in our case study.  
The major deficiency of this case is that only limited leveling measurements are available. The two models utilized in this experiment are pure mathematical empirical models, without specific physical parameters. Future study will focus on time series deformation modelling, considering concrete inner and external coefficients, such as temperature, humidity, and rheological parameters.  
[PERSON] designed the experiment. [PERSON] carried out the experiment. [PERSON] and [PERSON] analyzed the experimental results. [PERSON], [PERSON] and [PERSON] participated in the discussion of the experimental conclusion. [PERSON] wrote the manuscript of the paper. All the authors contributed to the revision of the manuscript, reviewed and approved the manuscript.  
This work was supported by the National Natural Science Foundation (No: 41701536, 61701047, 41674040) of China, Natural Science Foundation of Hunan Province (No. 2017J3322, 2019)50639), Key Project of Education Department of Hunan Province (No. 18A148), the Key Laboratory of Special Environment Road Engineering of Hunan Province (No. kiji30405), and the Open Fund of Key Laboratory of Road Structure and Material of Ministry of Transport (No. kij090209).  
The TerraSAR-X satellite images used in this paper are provided by the German Space Center (DLR) (Data Order Program Project: MTH3393). Thanks for Professor [PERSON] of Transportation Engineering  
Figure 19: Time series deformation results compared with leveling measurements on K4 (the location is shown in Figure 9).  
College for providing the leveling deformation data of Lungui Highway, which provides available validation data for this paper.  
The authors declare no conflict of interest.