Monitoring and Analysis of Land Subsidence Along Beijing-Tianjin Inter-City Railway

Land subsidence, as a slow and persistent geological disaster, threatens the safety of urban constructions and linear structures. Beijing-Tianjin intercity railway was built across some of the severe subsidence funnels. By combining with the hydrogeology condition and the InSAR (Interferometric Synthetic Aperture Radar) monitoring result, the corresponding analysis was conducted to reveal the situation and variational rule of the railway subsidence. Several indicators such as gradient, profiles and time-series analysis were used for describing the the land settlement along and across the railway. The result shows that areas with thick compressible layers, frequent over-exploitation and great decline of groundwater has larger subsidence rate. The middle confined groundwater level has much closer trend with subsidence than shallow groundwater. The railway is threatened by the subsidence along it, despite massive efforts are done to avoid crossing the subsidence cones in the railway route selection. The gradient, which is used to describe the uneven subsidence, shows some extrema at the edge area of the subsidence bowl. The maximal gradient value which means the most serious non-uniform settlement of the railway happens at a distance of 14200 m from the beginning. The profiles of the three lines have relatively larger vertical velocity in the middle where the railway goes through. With time goes by, the cumulative non-uniform deformation along the railway should be paid enough attention.