联合InSAR和SSA的膨胀土边坡形变特征分析——以南水北调工程为例

膨胀土边坡具有吸水剧烈膨胀、失水剧烈收缩及反复胀缩形变的特性,工程中与外界接触极易引发膨胀土滑坡。南水北调中线工程是一项缓解我国华北平原水资源短缺、优化水资源配置的国家重大战略工程。中线总干渠约有1/3段穿越膨胀土区域,增加了南水北调工程沿线边坡失稳的可能性,亟须开展膨胀土边坡形变监测和特征分析。基于此,本文收集了112景Sentinel-1A升轨SAR数据,采用时间序列InSAR技术获取了中线某渠道沿线2017年3月12日—2021年4月8日的时间序列形变,并基于奇异谱分析(SSA)对时间序列形变进行分解提取膨胀土边坡形变特征。研究结果表明:干渠挖方膨胀土边坡由于卸荷回弹作用表现为抬升形变,最大年抬升速率约为18 mm/a;填充膨胀土边坡由于土体固结作用表现为下沉形变,最大年下沉速率约为15 mm/a;膨胀土形变量大小与填挖深度正相关,挖方越深抬升形变越大,填充越高下沉形变越大;降雨和温度是影响干渠膨胀土边坡形变的主要外部因素,其造成的形变会时滞2~3个月。本文研究将为南水北调工程膨胀土边坡稳定性评估提供科学依据。

Deformation characteristics analysis of the expansive soil slope by integrating of InSAR and SSA techniques: a case study of the South-to-North Water Diversion Project

Expansive soil can damage the civil engineering structures due to the swelling-shrinking characteristic when they are exposed to the water. Middle Route Project of the South-to-North Water Diversion is an important project for alleviating water shortages and optimizing water resource allocation in the North China Plain. One third of water channel in the Middle Route passes through the expansive soil region, threatening the safety of the South-to-North Water Diversion Project. It is urgent to monitor the ground deformation of expansive soil slope so that better understanding its engineering stability. In this context, 112 Sentinel-1A synthetic aperture radar (SAR) images with ascending orbit were processed by multi-temporal interferometric SAR (InSAR) technique to observe the time series deformation along the South-to-North Water Diversion Project. Meanwhile, the singular spectrum analysis (SSA) technique was used to decompose the time series deformation to analyze the deformation characteristics. The uplift deformation was observed in the excavating expansive soil slope, where the maximum deformation rate was 18 mm/a. This uplift deformation was mainly due to the soil unloading and rebound. In the filling region, the subsidence was observed due to the soil consolidation and the maximum subsiding rate was 15 mm/a. The magnitude of ground deformation was correlated with the excavating and filling thickness:the deeper excavation means the greater uplift, and the higher filling means the greater subsidence. The precipitation and temperature, which can cause the deformation temporal delay of 2~3 months, are two main external contributor to the expansive soil slope. This study will provide the evidence to the stability assessment of expansive soil slope along the South-to-North Water Diversion Project.