Research On Monitor Of Subgrade Deformation Subjected To Vehicle Loads Based On FBG Technology In Seasonal Frozen Region

In this article,the self-developed embedded-beam detectors which based on the fiber Bragg gratings were used to monitor the deformation of subgrade in the flood protecting embankment.The site is located at the north bank of Songhua River in Harbin.The SM130 interrogator made by MOI in America was chosen to realize the works of data acquisition,analysis and storage.The detector's deflection was solved according to the deformation equation of cantilever beam in material mechanics.A two-year in-situ monitoring was conducted,and the deformation characteristics of subgrade under different periods,different vehicle load and velocities were analyzed.The main works and results are as follows:(1)First,the basic structure and working principle of FBG sensors were introduced.Then,considering the subgrade's differences in cover depth,section form and vehicle load,two kinds of layout methods,namely the shallow-setting semi-flexible probe for short distance and the deep-setting semi-rigid probe for long distance were designed.At the same time,the fixed ends were embedded in field by precast pile and on-site concrete,respectively.By comparing,the SM130 interrogator was used in the data acquisition,analysis and storage.(2)Based on the mechanical mechanism,the design principle of the FBG embedded-beam was described.And the methods of calculation and calibration were also given in this work.(3)The deformation of subgrade is great affected by the freeze-thaw cycles.When the subgrade is in the situation of thawing,its deformation is notably larger than that when it had melted completely even under the same load.Although it has experienced two cycles of feeze-thawing,its deformation is still not stable.Under the vehicle load,the deformation is still obvious.(4)The maximum residual deformation of subgrade developed nearly exponentially with the increase of vehicle load.When the total weight of the vehicle rises to 9.5 times,the maximum residual deformation can rised to 215 times.When the vehicle's speed increases,the subgrade's deformation is tend to decrease,however,the specific relation and more exact conclusions will not obtained until more detailed research was conducted.(5)The freeze-thaw and heavy vehicles are the two most key factors to the stablility of subgrade.If the two combined,there is likely to magnify the deformation of subgrade,that is to say,the combination will enlarge the disaster.So,it is worthy of more attention in the engineering.