In recent years, Beijing is ongoing a tremendous urban constructions. Many Skyscraper and densely distributed subway lines, city rails have been constructed in this populated city with more than 20 million inhabitants. With subsidence velocity more than 100 to 150 mm yr⁻¹, land subsidence has become a common geological hazard in Beijing. Compared with uniform land subsidence owning to overexploitation of groundwater, the non-uniform subsidence caused by large-scale construction projects may cause more significant damages to buildings, municipal pipelines, bridges and infrastructures. Meanwhile, subsidence caused by subway tunneling excavation and operation makes possible damages to the upper buildings and bridges. By the end of 2018, a total of 21 metro lines with a total length of 636 km are operational covering 12 municipal districts in Beijing. In order to study the ground subsidence caused by large-scale engineering construction in Beijing, we obtained surface deformation information from February 2010 to December 2018 (Fig. 1).

PS-InSAR is an effective tool for monitoring land subsidence especially useful for urban areas because many man-made targets maintain stable scattering characteristics. It is possible to accurate description to the ground targets due to the high resolution.

Figure 2Land subsidence rate map and additional stress derived from building loads at different depths in the Central Business District.

The CBD located in Chaoyang District covers an area of 2.4×2.5 km². From 2000 to 2010, many high buildings were built in the area. According to the data provided by relevant departments, there are 21 buildings that are higher than 100 m. The impact of additional stress derived from building load on the land subsidence is expected to increase. The groundwater level has little variation due to the lowest water was extracted in this area during the period between 2003 and 2018. As a typical piedmont alluvial diluvial plain, Quaternary sediments are widely distributed in Beijing (Luo et al., 2019). Ranging from 100 to 110 m, the thickness of the compressible layer in CBD is relatively uniform. Thus, uneven land subsidence is not likely caused by the geological environment in the study area.

Figure 3(a) Additional stress derived from building loads at different depths of Group 1 characteristic points. (b) Additional stress derived from building loads at different depths of Group 2 characteristic points.

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Figure 4Average subsidence rete perpendicular to Beijing subway line 7 during 13 April 2010 to 10 December 2018. Subsidence rate profile AA' at Ciqikou station (a). Time series of coherent target above Ciqikou station (b).

Based on building information from 1702 buildings in CBD, additional stress derived from building loads provided by the Beijing Municipal Commission of Planning and Natural Resources was calculated using the method proposed by Boussinesq (Eq. 1).

where σ is the additional stress derived from the building loads of the grid point, n is the number of buildings, and P_i is the gravity of building i. X, Y is the projection coordinate of a point in the grid along the longitude, latitude with dimensions in World Geodetic System 1984 (WGS84), respectively. And Z is the depth of the point in the grid. X_i, Y_i is the projection coordinate of building i along the longitude, latitude with dimensions in WGS84, respectively, and Z_i is the foundation depth of building i. Additional stress maps of the whole study area can be obtained by using the kriging interpolation tool provided by ArcGIS. We found that the maximum value of additional stress derived from building loads is 246.54 kPa, and the pressure derived from the gravity of soil above the depth is 1491.12 kPa when the depth reaches 80 m underground. This result indicates that the depth of influence of additional stresses induced by building loads is 80 m in the CBD area. We also found that spatial distribution of land subsidence was generally consistent with that of additional stress. Figure 2 shows that the deformation rate varies from −5.9 to 2 mm yr⁻¹ in the west part of the study area, where the buildings generally have less than 4 floors and the value of additional stress is low, while the land subsidence rate varies from −47.9 to −0.5 mm yr⁻¹ in the middle and south of the study area, where many skyscrapers have been built and the value of additional stress is relatively high. To further explore the relationship between additional stress derived from building loads and land subsidence rate, two groups of characteristic points were selected. Figure 3 shows additional stresses at different depths of the characteristic points. To some extent, we can conclude that a characteristic point with a higher additional stress has a greater deformation rate.

In order to relieve traffic pressure in Beijing, 13 subway lines have been constructed between 2010 and 2018. The velocity map described the extent and magnitude of surface deformation perpendicular to the metro lines due to the ground excavation. Figure 4 shown the subsidence perpendicular to Beijing subway line No. 7. By analyzing the subsidence rate profile AA', we find that the influence range of ground subsidence caused by metro construction is 200 m perpendicular to the Metro line and that the maximum land subsidence rate is 23.2 mm yr⁻¹. The subsidence extent is distinguished by the load of ground buildings. Under the same construction conditions, the subsidence over the built up area where has larger volume ratio is more significant than the general area.

Time series analysis of PS around Ciqikou station shows that the land subsidence rate has undergone a significant change during the construction and operation periods. The cumulative land subsidence caused by excavation activities reached 65 mm during the construction of Metro Line 7. The land subsidence rate decreases after Dec of 2014 and the cumulative settlement is 21 mm during the subway operation period.

All data required to reproduce these findings cannot be shared at this time as the code also forms part of an ongoing study.

FL performed the experiments, analyzed the data and wrote the paper. HG and BC provided crucial guidance and support through the research. MG and CZ made important suggestions on data processing.

The authors declare that they have no conflict of interest.

This article is part of the special issue “TISOLS: the Tenth International Symposium On Land Subsidence – living with subsidence”. It is a result of the Tenth International Symposium on Land Subsidence, Delft, the Netherlands, 17–21 May 2021.

This research has been supported by the National Natural Science Foundation of China (grant no. 41771455/D010702) and the National “Double-Class” Construction of University Projects (Beijing Youth Top Talent Project (grant no. BJJWZYJH01201910028032)).