苏州地面沉降区土层微观结构和宏观力学性质分析

地面沉降是苏州地区主要的地质灾害之一,由于长期开采地下水,该地区地面沉降不断加剧,制约了经济发展。结合土体微观结构定量分析和宏观力学性质试验,探索地面沉降问题的微宏观机制。以苏州地面沉降区200m的钻孔土样为研究对象,开展了快速固结、液塑限测定等一系列土工试验。采用冷冻干燥法获取各土层的SEM图像,使用PCAS分析软件对土样进行微观结构分析并在钻孔中布设FBG光缆进行持续性土层应变监测。结合液、塑限试验,快速固结实验数据,微观结构定量分析结果与光纤监测数据,得出以下结论:沉积土层的含水率,液性指数,压缩系数随深度递减;随着深度的增加,土层的定向性由差变好;第二承压含水层土层孔隙大且数量多,压缩潜力强于第三承压含水层,稳定性较差,有必要开展进一步监测研究。

The Analysis of the Microstructure and the Mechanical Properties of Land Subsidence Area in Suzhou

The land subsidence is one of the main geological disaster in Suzhou, China. Owing to long-term extraction of groundwater, the land subsidence area has continuously extended which hinders the development of local economy. A series of experiments have been carried out in this study. In order to study the mechanism of land subsidence, the experiment combines the quantitative analysis of soil microstructure with the macroscopic mechanical test, and the soil samples were taken from a 200m borehole in Shengze, Suzhou. A larger number of SEM images were obtained after using the method of vacuum freeze-drying. The imaging analysis software PCAS was used to acquire the parameters of soil microstructure and the fiber Bragg grating (FBG) techniques were used to monitor the soil layers in the borehole. The data in liquid and plastic limit tests, quick consolidated tests, the quantitative analysis of microscopic structure and the data of distributed fiber optic sensing indicate that the moisture content, the liquid index and the compression coefficient get smaller and the microstructure orientation become more obvious with the depth of strata increasing. There is a large number of microscopic pore structures in the water-bearing sand layer of the second confined and the volume is big enough, which causes a great potential of subsidence in the future and this remains to be investigated.