DFOS Technology On Land Subsidence And Ground Fissures

With the acceleration of urbanization and use of groundwater resource, land subsidence and ground fissures hazard has become increasingly worse, which has made a threat to local people's lives and property safety, and restricted the sustainable development of cities. The monitoring of land subsidence and ground fissures play an extremely important role in the prevention and control of the hazard. Therefore, it is important to explore an effective monitoring technology of land subsidence and ground fissures by the geological workers. In this thesis, based on the developmental mechanism and deformation characteristics, the laboratory and filed tests were carried out, the feasibility of distributed monitoring technology on land subsidence and ground fissures were studied. This technology has been verified in the field monitoring of land subsidence in Suzhou City and ground fissures in Jiangyin City. The distributed monitoring technology provided a new and effective method for the monitoring and control of the hazards of land subsidence and ground fissures. The results are presented as follows:(1) The actuality and deficiency of the monitoring techniques of land subsidence and ground fissures were discussed. The sensing principle, the main technical performance indicators? technical characteristics, application range of BOTDR, BOTDA and FBG optical fiber sensing technology were introduced.(2) According to the deformation characteristics of land subsidence and ground fissures, the feasibility of distributed monitoring technology on land subsidence and ground fissures were analyzed from the sensing fiber (cable) selection and packaging, laying of optical fiber, coupling of sensing optic cable and soil deformation, monitoring of large deformation of sensing optic cable, temperature compensation of sensing fiber optic and data transmission.(3) Three types of distributed fiber sensors used to the distributed monitoring of land subsidence and ground fissures have been developed, which were the fixed-point distributed optical fiber sensor, FBG-based static water level and the metal-based distributed sensing cable. The measuring principle, technical characteristics and the range of application were analyzed and their technical points were obtained.(4) The simulation tests of distributed optical fiber monitoring of land subsidence and ground fissures were carried out, the balloon deflation method was used to simulate the occurring process of land subsidence and ground fissures, the positing property of distributed optical fiber was analyzed, the construction technology of distributed optical fiber monitoring was mastered, and the technical base was provide for the distributed monitoring of land subsidence and ground fissures.(5) The field test of distributed optical fiber monitoring of land subsidence in Shengze town, Suzhou City, was carried out, the feasibility of the sensing fiber optic cable and FBG displacement used to the land subsidence deformation monitoring were verified.(6) The field test of distributed optical fiber monitoring of ground fissures in Jiangyin City, was carried out. The monitoring method with direct burying in horizontal direction was used and the occurrence of ground fissures was targeted effectively. The feasibility of the fixed-point distributed optical fiber monitoring technology used to the land subsidence deformation monitoring was verified.