Optical Fiber Sensing Technology To Monitor Steel Soil Cement Mixing Wall

This paper presents a new method to measure the core material's (H-pile) deformation of soil mixed wall by the BOTDA distributed optic fiber sensing technology. The fiber optic laying on the surface of H-pile can get the strain and horizontal displacement of H-pile which can guide the construction in the excavation process. With laboratory tests, field tests and finite element analysis, this paper achieves the following results and conclusions about the method of application and H-pile deformation mechanism:1 Designing the packaging process of distributed optical fiber on the H-pile. The optical fiber forms U-shaped loop on the H-pile surface and is combined with the H-pile with structural adhesive to work closely both, then this paper gets the data about deformation of H-pile with the strain of fiber. The construction method not only solves the corrosion of steel that makes it not easy to bond with the fiber optic, but also solve the problem of fiber that shear fracture easily, then this paper achieves a good package about distributed sensing fiber on a large steel structure.2 By the laboratory tests of H-pile and comparing the measured data of the fiber optic and strain gauge, the result between the two is consistent. The difference is that optical fiber measurements have large data and the curve is smooth, but strain gauge is point-measurement, and it has few data and is large dispersion. By comparing the strain of fiber optic laid on different position, the deformation in the angle at the flange and the web is more stable than in the flange, so the angle at the flange and the web is fit as the place where fiber optic sensor lays on. The consistency is found about value of enhanced optical fiber and normal optical fiber, indicating that the two kinds of fiber in the measurements can achieve good results;3 The real-time data, remote and all-weather monitoring are achieved with computer control program in the Guangzhou JFE Steel factory's fourth pit. The calculation, which is not need to determine the location of the neutral surface, about H-pile horizontal displacement is proposed and the temperature self-compensation is achieved. By the data acquisition and processing, the strain and horizontal displacement of H-pile were get to do safety warning of the excavation process;4 The soil pit uplift, horizontal displacement and H-pile vertical displacement, horizontal displacement law is analysis through the ABAQUS finite element model which simulates the excavation process. The simulate value and measuring value of strain and horizontal displacement is consistent by analysis, indicating that BOTDA distributed optical fiber sensing technology can be applied to monitor the excavation works, and it has good prospects in civil engineering measurement.