| Foundation settlement is called the ground subsidence, which is point to occur water level lowering in a certain surface area in the ground. The building load, the rise and fall of groundwater, Soil wet or swell-shrink, construction influence, vibration and so on all affect the settlement of soft soil foundation. Foundation settlement will lead to the destruction of buildings and production facilities, therefore, in order to ensure the safety of the project operation, Supervise the construction quality, prevent engineering accident, we need to monitor the settlement of high-rise building. Settlement instrument is a kind of calculating the surface settlement equipment which is accord to the measuring deformation elevation changes. This kind of equipment can be used for the dam, highway, railway, soft foundation reinforcement and so on.Traditional instrument of foundation settlement has a lot of kinds, such as pipe type settlement instrument, vibrating string type settlement instrument, hydraulic settlement instrument, layered settlement instrument and so on, in signal collected, all these traditional settlement instruments have one thing in common, namely make the settlement changes into electromagnetic signal, and then through test electric signal to measure the size of the settlement. Due to the traditional settlement instruments are poor in electromagnetic impact resistance, and are vulnerable to interference under specific conditions, Therefore, it is very important to develop settlement instrument which can real-time online monitoring of foundation settlement and have the ability of electromagnetic interference resistance. In recent years, sensing technology of fiber Bragg grating is developing rapidly. It can measure the drift small changes in the quantities of the outside world by reflection wavelength of grid, and with repeatability, high linear degree effects. So the technology can realize the high precision and distributed online measurement of stress and strain; And fiber Bragg grating sensor also has a lot of merits, such as the electromagnetic interference ability, good insulation, small volume, simple operation, long-distance transmission, easy to serial reuse and collect sensing and transmission one, etc. Therefore, FBG technology will have wide application prospects in the foundation settlement measurements. This paper designs a cup type optical fiber Bragg grating settlement instrument on measuring foundation settlement, and makes the theory analysis and experimental research of foundation settlement monitoring. This settlement instrument combine optical fiber Bragg grating pressure sensor and communicating vessels to measure foundation settlement, according to the measurement range of settlement and SL60-94"earth and rock dam safety monitoring technical specifications" and JTGF10-2006"highway sub grade construction technology standard" regulation, the settlement monitoring device meet the safety requirements. The main research contents are as follows:1. Based on the diaphragm elastic theory and strength of the cantilever beam strain characteristics established mathematical model of settlement instrument, and designed the real-time online monitoring of cup type optical fiber Bragg grating settlement instrument.2. According to the design of cup type optical fiber Bragg grating settlement instrument, select3161stainless steel as processing materials of the strength cantilever beam and corrugated diaphragm, select45#steel as processing materials of cylinder shell, the pressure rod, shell cover gasket, mineral water bottle choice for top cylinder container, coil use the hose of good toughness. According to the material and theoretical calculation, the size of each part is identified.3. According to the material and the size, calculate the cup type optical fiber Bragg grating settlement instrument theory sensitivity, theoretical sensitivity is18.85pm/cm; theoretical resolution is0.53mm.4. By the manual ascending and descending spherical vessel, the testing experiment of settlement instrument is got. The experimental results show that nonlinear error of the settlement instrument is1.73%FS, sensitivity isl5.24pm/cm. |
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