南宁在建地铁沿线地表沉降监测

南宁作为北部湾经济区的核心城市及中国-东盟博览会的永久举办地,正处于城市地铁修建及工程建设的高峰期。南宁位于复杂地质水文条件的南宁盆地中西部,地铁施工及运行有可能引发地表沉降等潜在风险,但关于南宁地铁修建区的沉降规律系统的认识仍十分有限。利用永久性散射体雷达干涉测量技术（Permanent Scatterers InSAR,PS-InSAR）处理54景Sentinel-1A影像,监测了2017年4月-2018年12月南宁市区地表沉降信息。结果表明,监测期内南宁地表形变速率为-23.8~9.0 mm/a,研究区大部分区域稳定,沉降点分布零星;4个重点沉降区位于蒲庙镇、九曲湾农场、江南地铁站及北湖-万秀村-虎丘一带;重点沉降区形变曲线总体上随时间变化呈现出不均匀下降;沉降成因可能与膨胀土膨胀特性、弃土滑坡、施工作业、列车流量过大及地下水位下降有关。5条地铁沉降值均属于安全范围。研究表明,南宁雨季降水丰富,地铁修建区表土以松散的第四系覆盖层为主,下伏基岩以工程力学性质存在一定不稳定性的第三系膨胀土为主,建议利用PS-InSAR技术对沉降重点区域及地铁沿线开展长期监测。

Surface Subsidence Monitoring during the Construction of Nanning Subways

Nanning is the core city of the Beibu Gulf Economic Zone and the permanent venue of the China-ASEAN Expo, which is undergoing the construction peak of urban subways. Nanning is located in the central and western part of the Nanning Basin, where the geological and hydrological conditions are complicated. The construction and operation of subways may cause potential risks such as surface subsidence. However, it remains understudied regarding the surface subsidence along Nanning subways. In this paper, 54 Sentinel-1A images of Nanning city from April 2017 to December 2018 were processed by Permanent Scatterers Interferometric Synthetic Aperture Radar （PS-InSAR）, and then the surface subsidence information was extracted. Results showed that the surface deformation rate was -23.8~9.0 mm/a during the monitoring period, and most of the study area was stable, and the settlement point distribution was sporadic. There were four key subsidence areas , including Pumiao Town, Jiuquwan Farm, Jiangnan Subway Station, and Beihu- Wanxiu Village- Huqiu. The deformation curve of key settlement areas showed an uneven decline trend with time; the reason causing settlement may be attributed to the expansion characteristics of expansive soil, spoil landslide, construction operation, excessive train flow, and drop in the groundwater level. The sedimentation value of the five subways were all within the safe range. The rainy season precipitation of Nanning is rich, and the topsoil of the subway construction area is mainly composed of loose Quaternary overburden, where the underlying bedrock is mainly composed of Tertiary expansive soil with certain instability of engineering mechanics. Therefore, our findings suggest that the PS-InSAR technology should be used for long-term monitoring of key settlement areas and subways of Nanning for safe metro operation.