Evolution Characteristics of Land Subsidence in Beijing Section of Beijing-Tianjin Intercity Railway Before and After the South-to-North Water Diversion Project

Objectives The Beijing section of Beijing-Tianjin Intercity Railway is 50 km long. The railway line crosses the subsidence area from Dongbalizhuang to Dajiaoting in Beijing. The uneven subsidence along the line poses a certain threat to the safe operation of high-speed railway. The South-to-North Water Diversion Project has brought new water sources to Beijing, the exploitation of groundwater in the plain area has decreased, and the development trend of land subsidence has slowed down.

Methods Taking the Beijing section of Beijing-Tianjin Intercity Railway as the research area, we select Radarsat-2(2011—2015) and Sentinel-1(2016—2019)satellite images, and use permanent scatterer InSAR (PS-InSAR) technology to obtain the time-series subsidence information along and near the railway. The difference of subsidence evolution along the railway before and after the South-to-North Water Diversion in the study area is analyzed. On this basis, combined with the geological data and groundwater dynamic monitoring data along the railway, the response relationship between compressible layer thickness difference, groundwater level change and land subsidence is analyzed.

Results Before the South-to-North Water Diversion (2011—2014), the average length of the area with annual subsidence greater than 30 mm along the railway is 13.25 km, accounting for about 26.50% of the total length of Beijing section. After the South-to-North Water Diversion (2015—2019), it has been reduced to about 8.87 km, accounting for about 17.74% of the total length of Beijing section. Similarly, the mean value of the annual subsidence extreme value along the railway decreases from 105 mm to 78 mm, and the extreme value position moves eastward obviously from DK17 to near DK20.

Conclusions The subsidence along the railway is consistent with the development trend of regional subsidence funnel, which is mainly affected by the decline of groundwater level caused by long-term over exploitation of groundwater and the thickness of compressible layer. After the South-to-North Water Diversion Project, the subsidence along the railway has slowed down significantly. There is no obvious interaction between the normal operation of Beijing-Tianjin Intercity Railway and the subsidence along the railway.